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Träfflista för sökning "WFRF:(Yao Huadong 1982) "

Sökning: WFRF:(Yao Huadong 1982)

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1.
  • Shao, Xinyuan, 1997, et al. (författare)
  • A comparison of two wave energy converters’ power performance and mooring fatigue characteristics – One WEC vs many WECs in a wave park with interaction effects
  • 2023
  • Ingår i: Journal of Ocean Engineering and Science. - 2468-0133. ; 8:4, s. 446-460
  • Tidskriftsartikel (refereegranskat)abstract
    • The production of renewable energy is key to satisfying the increasing demand for energy without further increasing pollution. Harnessing ocean energy from waves has attracted attention due to its high energy density. This study compares two generations of floating heaving point absorber WEC, WaveEL 3.0 and WaveEL 4.0, regarding their power performance and mooring line fatigue characteristics, which are essential in, e.g., LCoE calculations. The main differences between the two WECs are the principal dimensions and minor differences in their geometries. The DNV software SESAM was used for simulations and analyses of these WECs in terms of buoy heave motion resonances for maximising energy harvesting, motion characteristics, mooring line forces, fatigue of mooring lines, and hydrodynamic power production. The first part of the study presents results from simulations of unit WEC in the frequency domain and in the time domain for regular wave and irregular sea state conditions. A verification of the two WECs’ motion responses and axial mooring line forces is made against measurement data from a full-scale installation. In the second part of the study, the influence of interaction effects is investigated when the WECs are installed in wave parks. The wave park simulations used a fully-coupled non-linear method in SESAM that calculates the motions of the WECs and the mooring line forces simultaneously in the time domain. The amount of fatigue damage accumulated in the mooring lines was calculated using a relative tension-based fatigue analysis method and the rainflow counting method. Several factors that influence the power performance of the wave park and the accumulated fatigue damage of the mooring lines, for example, the WEC distance of the wave park, the sea state conditions, and the direction of incoming waves, are simulated and discussed. The study's main conclusion is that WaveEL 4.0, which has a longer tube than WaveEL 3.0, absorbs more hydrodynamic energy due to larger heave motions and more efficient power production. At the same time, the accumulated fatigue damage in the moorings is lower compared to WaveEL 3.0 if the distance between the WECs in the wave park is not too short. Its motions in the horizontal plane are larger, which may require a larger distance between the WEC units in a wave park to avoid losing efficiency due to hydrodynamic interaction effects.
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2.
  • Shao, Xinyuan, 1997, et al. (författare)
  • Performance analysis of two generations of heaving point absorber WECs in farms of hexagon-shaped array layouts
  • 2024
  • Ingår i: Ships and Offshore Structures. - : Taylor and Francis Ltd.. - 1754-212X .- 1744-5302. ; 19:6, s. 687-698
  • Tidskriftsartikel (refereegranskat)abstract
    • Numerical analyses are presented for two generations of a floating heaving point absorber wave energy converter (WEC) installed with different farm array layouts. The wave farm configurations are based on WECs developed by Waves4Power. The numerical models are developed in the DNV software package, Sesam. Parametric studies of the isolated WEC configurations and farm array layouts are conducted under typical environmental conditions and various incident wave directions to understand the hydrodynamic power performance and the levelised cost of energy (LCoE). Hexagonal layouts are proposed for deploying the WEC units and compared with a 10-unit layout termed StarBuoy, which has been reported in previous work. The results of the present study confirm that the interactions between arrayed units in a farm can have either positive or negative effects on the LCoE, which is dependent on the array layout and environmental conditions. The hexagonal array layouts lead to lower LCoE owing to constructive interaction effects.
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3.
  • Andersson, Josefin, 1994, et al. (författare)
  • Propulsion Installation Modelling for geared Ultra-high bypass ratio engine cycle design
  • 2020
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • About 3% of the greenhouse gas emissions in the EU are derived from aviation. By 2020, the global international aviation emissions are assumed to be approximately 70% higher than those in 2005 and a strong continued growth in travel demand is expected at least up until 2035. A radical reduction of emissions have to occur on multiple fronts ranging from incremental improvements of advanced propulsion systems to new fuels and electrification. The desire to get higher efficiencies has contributed to the movement from turbojet engines to today's high bypass ratio turbofan engines. The fuel consumption and propulsive efficiency of turbofan engines are highly dependent on the fan pressure ratio (FPR). Decreasing FPR gives an improved fuel and propulsive efficiency as long as installation losses do not exceed potential benefits. As part of the Clean Sky project IVANHOE, new types of nacelles will be developed to enable installation of propulsion systems with radically increased bypass ratio and reduced FPR. In this work the process of describing and selecting a suitable propulsion system is described. The cycle is defined by a multidisciplinary analysis considering nacelle drag, propulsion system weight and engine performance. Effects of variation in turbine cooling with cycle change and small size turbomachinery efficiency is considered defining the core size and pressure ratio. Variations in installed SFC with fan diameter choice is quantified along a suboptimal line of fan pressure ratio and bypass ratio for a specific optimal overall pressure ratio. The final cycle choice is presented.
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4.
  • Arabnejad Khanouki, Mohammad Hossein, 1988, et al. (författare)
  • Zero-emission propulsion system featuring, Flettner rotors, batteries and fuel cells, for a merchant ship
  • 2024
  • Ingår i: Ocean Engineering. - 0029-8018. ; 310
  • Tidskriftsartikel (refereegranskat)abstract
    • To meet the International Maritime Organization’s (IMO) goal of decarbonising the shipping sector by 2050, zero-emission ship propulsion systems should be developed to replace conventional fossil fuel-based ones. In this study, we propose a zero-emission hybrid hydrogen-wind-powered propulsion system to be retrofitted to a benchmark merchant ship with a conventional propulsion system. The ship and its propulsion systems are modelled using an in-house platform. We analyse power and energy requirements for the ship over a realistic route and one-year schedule, factoring in actual sea and weather conditions. Initially, we examine the battery-powered propulsion system, which proves impractical even with a reduction in the ship’s speed and the addition of a charging station. This retrofitted battery-powered propulsion system will occupy a significant portion of the existing ship’s deadweight due to its substantial weight, consequently reducing the ship’s cargo capacity. To address this, we evaluate integrating a hydrogen-powered fuel cell system with power equal to the non-propulsive constant load in the ship. We demonstrate that under these conditions, and with four Flettner rotors and the charging station positioned mid-port on the ship’s route, the size of the zero-emission propulsion system can be approximately 20% of the deadweight, rendering such a system feasible.
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6.
  • Chen, Zheng wei, et al. (författare)
  • Reducing the aerodynamic drag of high-speed trains by air blowing from the nose part: Effect of blowing speed
  • 2023
  • Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - 0167-6105. ; 238
  • Tidskriftsartikel (refereegranskat)abstract
    • To reduce the aerodynamic drag of high-speed trains, this work proposes an air blowing configuration on the head and tail cars of high-speed trains. The variation in the aerodynamic drag and slipstream velocity is analyzed under different blowing velocities, and the flow mechanism for train aerodynamic performance alteration is explained. The results show that under the blowing speeds of Ub = 0.05Ut, 0.10Ut, 0.15Ut, and 0.20Ut, where Ut is the train speed, the total drag coefficient (Cd) decreases by 5.81%, 10.78%, 13.70%, and 15.43% compared to the without-blowing case, respectively. However, with the increase in the blowing speed, the reduction trend of Cd tends to be smoother; namely, the decrement ratio compared to the previous blowing speed for the head car is 9.08%, 0.11%, 0.60%, and 1.14% for Ub = 0.05Ut, 0.10Ut, 0.15Ut, and 0.20Ut, respectively. The blowing measure generates an air gap between the coming flow and train surface, consequently causing a reduction in the viscous and pressure drag. In addition, the structure size and strength of the wake flow under different blowing cases show a decreasing trend from Ub = 0.00Ut to 0.10Ut and then an increasing trend from Ub = 0.10Ut to 0.20Ut. Thus, considering the blowing cost, efficiency, and flow structure evolution comprehensively, the case of Ub = 0.10Ut is recommended. Under this blowing speed, the reduction ratio of the aerodynamic drag is 9.18%, 12.77%, 10.90%, and 10.78% for the head, middle, tail car, and total train, respectively.
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7.
  • Chroneer, Zenitha, et al. (författare)
  • Prediktering av extern flödesakustiks påverkan på hyttbuller
  • 2019
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Vindljud är idag den största ljudkällan i lastbilar vid hastigheter på över 80 km/h. Det är viktigt för säkerheten att få ner ljudnivåerna eftersom denna typ av ljud kan orsaka trötthet och huvudvärk hos föraren. Andra ljudkällor som motorljud och vägljud har det jobbats ganska mycket med att få ner. I framtidens elektriska fordon där drivlineljuden nästan helt är borta kommer vindljuden bli alltmer framträdande. I detta projekt har vis studerat ljudet som bildas runt en a-stolpe och backspegel på en lastbil samt tittat på olika sätt att modellera detta virtuellt. För att korrelera detta mot verkligheten har mätningar gjorts på en specialbyggd lastbil där andra ljudkällor har minimerats. Genom att först studera en generisk geometri har en beräkningsmetodik tagits fram som inkluderar både strömningsfältet (CFD) och transporten av ljudet in i kupén (akustik). Denna metodik har sedan applicerats på en riktig geometri och resultaten har jämförts mot den uppmätta lastbilen. Beräkningarna överensstämmer väl med det som har uppmätts. Man får dock komma ihåg att mätningarna är gjorda utomhus med riktiga vindförhållanden medan beräkningarna är gjorda under perfekta förhållanden. Modellen fångar både det bredbandiga bedraget och i det fallet där vi ser en ton i mätningarna så ser vi även detta i beräkningarna. Slutsatser som kan dras av dessa beräkningar är att det är viktigt att ta med akustiska bidraget, antingen genom direkt modellering eller med analogier. För att fånga frekvensinnehållet krävs det tidsupplösta metoder medan enkla tidsmedelvärderade modeller kan rangordna olika koncept men saknar frekvensinnehållet.
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8.
  • Eliasson, P., et al. (författare)
  • Assessment of high-lift concepts for a regional aircraft in the ALONOCO project
  • 2012
  • Ingår i: 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Nashville, 9-12 January 2012. - Reston, Virigina : American Institute of Aeronautics and Astronautics. - 9781600869365
  • Konferensbidrag (refereegranskat)abstract
    • This work introduces the work conducted in the EU JTI project ANOLOCO, which has aimed at an assessment of aerodynamic and aeroacoustic performance of several high-lift configurations of a regional aircraft. The high-lift designs are for a laminar and slat-less wing, including configurations with a double slotted flap, single slotted flap, drooped nose and a Krueger flap. The aerodynamic performance is assessed from steady state RANS calculations up to maximum lift. The aeroacoustic performance is based on hybrid RANS-LES calculations for flow-induced noise generation, and using acoustic analogy methods for far-field noise propagation. Three different analogy methods are evaluated and compared. The assessment shows that the configuration with a Krueger flap gives the best performance. The maximum lift is close to 20% higher than for any other configuration and the noise levels are also reduced, up to 10 dB lower than the configuration with a double slotted flap.
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9.
  • Fares, Omar, 1992, et al. (författare)
  • Numerical Investigation of Narrow-Band Noise Generation by Automotive Cooling Fans
  • 2020
  • Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
  • Tidskriftsartikel (refereegranskat)abstract
    • Axial cooling fans are commonly used in electric vehicles to cool batteries with high heating load. One drawback of the cooling fans is the high aeroacoustic noise level resulting from the fan blades and the obstacles facing the airflow. To create a comfortable cabin environment in the vehicle, and to reduce exterior noise emission, a low-noise installation design of the axial fan is required. The purpose of the project is to develop an efficient computational aeroacoustics (CAA) simulation process to assist the cooling-fan installation design. This paper reports the current progress of the development, where the narrow-band components of the fan noise is focused on. Two methods are used to compute the noise source. In the first method the source is computed from the flow field obtained using the unsteady Reynolds-averaged Navier-Stokes equations (unsteady RANS, or URANS) model. In the second method, the azimuthal modes of the flow field obtained using the steady RANS with the moving reference frame model are treated as the sound source. While the first method is able to resolve any narrow-band noise source that is related to large-scale harmonic oscillations, the second method may only be able to estimate the sound source at the blade passing frequency and its harmonics. The acoustic field generated by the sound source is computed by solving the inhomogeneous Helmholtz equation. The simulation process based on both methods is applied to a benchmark case in the literature and the simulated results are compared with experimental data. Satisfactory agreement is observed from the comparison.
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11.
  • Guo, Chunyu, et al. (författare)
  • Influence of jet flow on hydrodynamic performance of a ducted propeller
  • 2023
  • Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35:12
  • Tidskriftsartikel (refereegranskat)abstract
    • This study introduces a concept that jet technology in the aeronautical field is used for active flow control to improve the hydrodynamic performance of a ducted propeller. Jet flow is added in front of the ducted propeller, and it produces a circumferential velocity that is opposite to the rotation direction of the rotor. An international standard ducted propeller was adopted to demonstrate this concept. The unsteady Reynolds-averaged Navier-Stokes method and the shear stress transport k − ω turbulence model were employed for the simulations. The open-source platform OpenFOAM was utilized. The overall efficiency η 0 of the ducted propeller first increases and then decreases with increasing the jet flow velocity R j f from 1 to 3 and the distance L to the rotation center from 0.2 D to 0.4 D . When the jet flow is at the optimal condition of R j f = 2 and L = 0.3 D , the maximum efficiency improvement of 3.1% is achieved for the ducted propeller. The reason is that the jet flow contributes to a pressure increase in the flow through the rotor. This effect is related to tip and hub vortices, which are disrupted by the jet flow and have relatively low vorticity magnitudes compared to the reference case without jet. The findings in this study have the potential to advance the development of active flow control technology for ships.
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12.
  • Guo, Chunyu, et al. (författare)
  • Numerical investigation of the scale effects of pump-jet propulsor with a pre-swirl stator
  • 2023
  • Ingår i: Physics of Fluids. - : AIP Publishing. - 1089-7666 .- 1070-6631. ; 35
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, the performance of a pump-jet propulsor (PJP) with pre-swirl stator in open water is numerically investigated. Both full-scale and model-scale configurations are considered. The Reynolds-averaged Navier–Stokes equations and shear stress transport ?−? turbulence model are used in the numerical calculation. The computational domain is discretized using structured grids, and a rotating grid is affixed to the rotor to deal with the relative motion between the rotor and stationary components. The mesh quality is determined based on a grid uncertainty analysis. The numerical method is validated using model-scale experimental data. The simulation results reveal the influences of the scale size on the hydrodynamic performance and the distributions of the velocity, pressure and vorticity under three advance coefficients. With the increase in the advance coefficients, the scale influences on the efficiency become more obvious, and the efficiency of the full-scale PJP is always higher than that of the model-scale PJP. The full-scale configuration is found with a more significant instability in the gap vortex development, because it presents larger interaction between tip leakage vortex (TLV) and the inner wall of the duct. As the main velocity increases, the TLV shedding is delayed. Finally, the development process of gap vortices is analyzed for the difference operation conditions.
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13.
  • Huang, Zhongjie, 1985, et al. (författare)
  • Aeroacoustic analysis of aerodynamically optimized joined-blade propeller for future electric aircraft at cruise and take-off
  • 2020
  • Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 107
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel propeller with the blade tips joined in pairs, named Boxprop, is designed and optimized for a conceptual electric aircraft using an efficient optimization platform. According to the thrust requirement of the electric aircraft at cruise, the Boxprop with optimal efficiency is down-selected from the Pareto front of thrust coefficient and propeller efficiency. Furthermore, the blade pitch angle is adjusted to meet the thrust requirement at take-off. It is found that the Boxprop is capable of suppressing tip vortices and inducing a wider wake behind blade tip in comparison to a conventional propeller usually shedding a concentrated tip vortex, which could potentially improve the propulsive efficiency. Afterwards, the aeroacoustic analysis performed by the hybrid integral method of Reynolds-Averaged Navier Stokes equations (RANS) and convected Ffowcs Williams and Hawkings (FW-H) equation shows that the tonal noise from the Boxprop with three joined blades operating at cruise is similar to a conventional three-bladed propeller, though being stronger than a conventional six-bladed propeller. Although the tip vortices have been suppressed by the joined-blade tips of the Boxprop, the corresponding tonal noise reduction is not prominent. Next, the Boxprop noise at take-off is studied. Unsteady RANS is used to resolve varying flow structures that become dominant under the take-off condition. Angle of attack (AOA) is found as an important factor influencing the noise generation. The radiated noise upstream and downstream of the propeller significantly intensifies due to increasing AOA. The AOA effects of the Boxprop follow a similar trend to a conventional propeller. The findings for the Boxprop aeroacoustics have enhanced the understanding of tip-vortex suppression techniques in connection with the tonal noise generation, which will be greatly helpful to the aeroacoustic design of Boxprop applied to electric aircraft in the future.
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14.
  • Huang, Zhongjie, 1985, et al. (författare)
  • Low-Noise Propeller Design for Quiet Electric Aircraft
  • 2020
  • Ingår i: AIAA AVIATION 2020 FORUM. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
  • Konferensbidrag (refereegranskat)abstract
    • Inspired by the tremendous success of electric cars, the electrification technology has recently attracted a great deal of attention in aviation industry. This leads to the advent of massive efforts on the development of electric aircraft. Electrification enables zero CO2 and NOx emissions for aircraft in the near future. However, the annoying noise radiated from electrified propulsion systems is still a great challenge. The major noise sources are propellers. In particular, short-haul electric aircraft are usually flying from small airports near communities, which would exaggerate the noise impacts on residents. This paper presents a study on the propeller noise for a hypothetical electric aircraft. First of all, the acoustic study focuses on the effects of blade number, blade diameter, and rotation speed for an isolated propeller. Then, an unique configuration of dual-rotating propeller is briefly investigated to explore its potential of low-noise generation. Lastly, multiple propellers installed on an aircraft with various distributive propulsion strategies are investigated. The overall noise emission of these distributive propulsion strategies are promising to reduce the total noise from electric aircraft. Nonetheless, the noise level is very sensitive to the installation location of every propeller. An interesting finding is that the acoustic-wave interaction among the propellers are limited to the near field, and is insignificant in the far field. The present results are expected to enhance the understanding of propeller noise generation mechanisms, which are beneficial to propose guidelines on the development of low-noise distributive propulsion systems for electric aircraft.
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15.
  • Jianfeng, Lin, 1994, et al. (författare)
  • Angle of attack impact on flow characteristics around finite-length rotating columns
  • 2024
  • Ingår i: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 36:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The finite-length rotating column has been extensively studied because of its importance in various fields, such as marine and aerospace. In this study, the hydrodynamic performance of a finite-length rotating column with two free ends at different angles of attack is investigated using a large eddy simulation method. The effects of various geometries (including an equal-section cylinder and a variable-section truncated cone), incoming flow velocities, column rotation speeds, and angles of attack on the lift and drag characteristics and wake field of the rotating column are analyzed. The results reveal that a free end creates a concentrated tip vortex, which shortens the effective length that can generate the Magnus effect. Across different geometries and computational conditions, a relatively consistent lift coefficient is found for angles of attack from 60° to 120°, with the cone design significantly reducing the drag by approximately 10% for angles of attack from 120° to 150°. These findings provide valuable insights into the practical application of finite-length rotating columns. Specific recommendations for optimizing the design of these columns are suggested, including choosing appropriate geometries and considering the effects of incoming flow velocities and column rotation speeds.
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16.
  • Jianfeng, Lin, 1994, et al. (författare)
  • Comprehensive Investigation of Flow Dynamics around Rotating Cylinders
  • 2024
  • Ingår i: 2024 EFDC1.
  • Konferensbidrag (refereegranskat)abstract
    • The study addresses the intricate dynamics of flow around rotating cylinders, a classic problem in fluid mechanics known for the Magnus effect. This research delves into unconventional yet compelling aspects of rotating cylinders, investigating the influence of rotational speed, incoming flow velocity, geometric shape, free surface, and angle of attack on lift-drag characteristics and wake flow fields. To begin with, fully parametric three-dimensional modelling of rotating cylinders was carried out using the Sobol design optimisation method coupled with computational fluid dynamics. The Sobol method efficiently explored the design space, focusing on critical parameters such as cylinder end diameters and lengths. The results revealed several local optimum values for lift and drag, showing the effect of the Magnus effect on vortex separation points and leading to significant variations in pressure and velocity distributions. Furthermore, the investigation was extended to the mode change of rotating cylinders in twophase flows through large eddy simulation. The findings showed that increasing the submergence depth generally improves lift generation, especially for rotations with higher speeds. At low submergence depths of less than one cylinder diameter, the pattern of vortices in the single-phase flow is altered under the same operating conditions. Surprisingly, the effectiveness of the Magnus effect diminishes at a depth of half the cylinder diameter. This study represents the first exploration of the mode change in rotating cylinders induced by two-phase flows. Additionally, the hydrodynamic performance of rotating cylinders at different angles of attack was investigated using an improved delayed detached eddy simulation method. The focus here is on the end effect of the rotating cylinder. The study identified an optimal spin ratio that maximised the lift-drag ratio while emphasising the profound influence of the angle of attack and spin ratio on the streamwise and crosswise vortex structures. In conclusion, this study not only sheds light on the intricate dynamics of flow around rotating cylinders and provides new insights into Magnus effect-induced phenomena, but also paves the way for future advances in engineering applications, such as optimising the performance of rotating structures in various fluid environments. Further exploration of these findings may contribute to the development of more efficient and robust engineering solutions in the fields of energy harvesting, aquatic robotics, and fluid transport systems.
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17.
  • Jianfeng, Lin, 1994, et al. (författare)
  • Hydrodynamic performance of a rim-driven thruster improved with gap geometry adjustment
  • 2023
  • Ingår i: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 17:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The hubless rim-driven thruster (RDT) has become increasingly interesting for ship propulsion. Gap flow has been proven as the main feature of RDT that cannot be simply neglected. In this study, based on a classical hubless RDT, the effects of the gap geometry are studied by adjusting its axial passage length, and inlet and outlet oblique angles. The hydrodynamic characteristics of the RDT were simulated with OpenFOAM based on the k – ω shear stress transport turbulence model. Due to the pressure increase after the main flow passes through the rotating blades, the flow inside gap is driven upstream, which is opposite to the main flow direction. It is found that the hydrodynamic efficiency is increased as the gap axial passage length is shortened, which is realized by increasing the oblique angle with the fixed inlet and outlet positions. Moving the inlet and outlet to further downstream and upstream positions has negligible effects on the hydrodynamic efficiency and leads to recirculating flow within the gap near its inlet. These findings shed light on the design of the gap geometry to improve the RDT hydrodynamic performance.
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18.
  • Jianfeng, Lin, 1994, et al. (författare)
  • Hydrodynamic response of swinging or slewing rotating cylinders subject to a ship's rolling motion
  • 2024
  • Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 36:6
  • Tidskriftsartikel (refereegranskat)abstract
    • In maritime engineering, ensuring vessel stability remains a paramount concern. This study investigates the hydrodynamic response of Magnus anti-rolling devices, modeled as swinging or slewing rotating cylinders, under a ship's rolling motion. Through numerical simulations using the overset mesh technique and large eddy simulation, we analyze various parameters, including rolling angles, rotating speeds, and swinging amplitudes. Our findings highlight the importance of considering the ship's degree of freedom as substantial ship rolling significantly affects hydrodynamic coefficients on the rotating cylinder. We observe interesting dynamics during slewing motion, with the cylinder forming a spiral tip vortex. Optimizing the cylinder's rotating speed enhances the lift-to-drag ratio, particularly for small rolling angles. Furthermore, the effective lift generated during swinging motion is lower than during slewing motion, emphasizing the need to optimize the swinging amplitude, which is recommended to be no less than 170°. These insights advance our understanding of Magnus anti-rolling devices and offer practical guidance for improving vessel stability in complex maritime environments.
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19.
  • Jianfeng, Lin, 1994, et al. (författare)
  • Modified Magnus effect and vortex modes of rotating cylinder due to interaction with free surface in two-phase flow
  • 2023
  • Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35
  • Tidskriftsartikel (refereegranskat)abstract
    • When employing rotating cylinders as ship anti-rolling devices based on the Magnus effect, the cylinders are near the free surface. However, most of the previous studies on rotating cylinders considered single-phase (SP) flows, where the interaction between the free surface and rotating cylinders was missing. In this study, we explore a rotating cylinder in a two-phase flow using large eddy simulation. Given low submergence depths of less than one cylinder diameter, the pattern of vortices classified as mode A in the SP flow under the same operation conditions is altered to mode E. As regards depths below 1.5 diameters, mode E is changed to mode F′. These modes mentioned above were defined by previous researchers to identify the different wake patterns of rotating cylinders. Increasing the submergence depth in general enhances the lift generation, and this effect is more significant for the rotation with a higher spin ratio of 4 as compared to another spin ratio of 0.5. Nevertheless, the Magnus effect fails when the higher spin ratio is set at a depth of half of the cylinder diameter. As the depth is increased, the drag from the lower spin ratio decays. In contrast, the higher ratio rises significantly up to the depth of two diameters and then drops. This study clarifies the importance of the free surface in affecting the Magus effect. It is also the first time that the mode change of rotating cylinders owing to two-phase flows has been found.
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20.
  • Jianfeng, Lin, 1994, et al. (författare)
  • Shape optimization and hydrodynamic simulation of a Magnus anti-rolling device based on fully parametric modeling
  • 2023
  • Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Ship anti-rolling devices are an essential component of modern vessels. The core component of the Magnus effect-based ship anti-rolling device is a rotating cylinder, hereinafter referred to as the Magnus cylinders. In this paper, fully parametric three-dimensional modeling of Magnus cylinders was performed, and the design space dimension was reduced using the Sobol design optimization method while still providing accurate and reliable results. The Sobol method generates quasi-random sequences that are more uniformly spaced in the search space and can more efficiently cover the entire solution space. The shape optimization study of the Magnus cylinder was carried out in conjunction with the computational fluid dynamics method to find the geometry of the Magnus cylinder with excellent hydrodynamic performance. Critical design parameters include the diameters of the cylinder ends and the length of the cylinder. The hydrodynamic and flow field characteristics of Magnus cylinders before and after the optimization were compared. The results show that there can be multiple local optimal values for lift and drag of Magnus cylinders within the design space to increase the lift and decrease the drag. The Magnus effect primarily influences the position of the vortex-shedding separation point at the surface of Magnus cylinders and deflects the wake to one side. For the optimized Magnus cylinder, the distribution of pressure and velocity in the flow field is significantly different. This research forms the basis for improving the practical application of Magnus anti-rolling devices.
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21.
  • Li, Bo, et al. (författare)
  • Wind tunnel test study on influence of open/close operation on aerodynamic noise characteristics of high-speed pantographs
  • 2024
  • Ingår i: Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology). - 1672-7207. ; 55:5, s. 1846-1854
  • Tidskriftsartikel (refereegranskat)abstract
    • Wind tunnel tests of aerodynamic noise at wind speeds from 160 km/h to 324 km/h were carried out for high speed pantograph developed by Beijing CRRC CED Co. Ltd. The effects of wind speed and open/close operation status on pantograph aerodynamic noise characteristics were analyzed, and the pantograph aerodynamic noise at higher speed was predicted. The results show that the aerodynamic noise of the pantograph and its propagation characteristics are closely related to the wind speed and operating status. The panhead and nearby areas are prone to single-tone noise due to the influence of shedding vortices. The total sound pressure energy of the far-field noise increases with the power of 5.6 − 6.0 of wind speed. The total sound pressure levels of the pantograph far-field noise in the open/closed state are predicted to be about 106.8 dB and 106.6 dB respectively at the wind speed of 400 km/h by data fitting.
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22.
  • Li, Peng, et al. (författare)
  • Improved efficiency with concave cavities on S3 surface of a rim-driven thruster
  • 2023
  • Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Rim-driven thrusters (RDT) are of great interest for the development of integrated electric motors for underwater vehicles. Gap flow is one of the most prominent flow characteristics and plays an important role in the hydrodynamic performance of RDT. In this study, the rim in a carefully designed RDT was modified with several concave cavities defined by four parameters, and their influence on hydrodynamics was carefully calculated and analyzed. The simulations were performed using the k-ω shear stress transport turbulence model by solving the unsteady Reynolds-averaged Navier–Stokes equations. The numerical method was verified using a popular combination. The numerical results showed that the concave cavities on the rim improve the propulsive efficiency of RDT by a maximum of 3.52%. The increase in the propulsive efficiency is directly associated with the parameters of the concave cavities. Nevertheless, the flow in the gap has a negligible effect on the main flow field through the RDT. According to the numerical analysis, the different pressure integrals at the front and back surfaces of the concave cavities are the main reason for the improvement of the propulsive efficiency. The modification of the rim is helpful and practical for the hydrodynamic optimization of the RDT.
  •  
23.
  • Li, Peng, et al. (författare)
  • The effects of domain division types on the performance prediction of a rim-driven thruster
  • 2023
  • Ingår i: Ocean Engineering. - 0029-8018. ; 287
  • Tidskriftsartikel (refereegranskat)abstract
    • The rim-driven thruster (RDT) is an innovative propulsion thruster. The rotating subdomain can contain different assemblies with different domain division types (DDT). This paper tried to figure out the effects of DDT on the performance of RDT. This paper uses the Delayed Detached Eddy Simulation (DDES) turbulence model to conduct the simulations. Three DDTs are carefully analyzed to understand their effects on predictive performance. The convergence analysis is performed by taking a typical method: Grid Convergence Index (GCI). Some theoretical results and the experimental hydrodynamics of a popular combination of Ka 4–70 and MARIN 19 A are used to validate the numerical method. The numerical results demonstrate that the computational efficiency is influenced by the cell number on the interfaces between two subdomains and an inherent characteristic of DDT. Moreover, the torques acting on rim surfaces are closely accounting for the gap flow. Moreover, regarding the morphology and variables of the vortex system, the third type of DDT enhances vortices presenting in the hub region and vortex-instability region. Although the present analysis is performed for an RDT, the findings should be generally applicable for other RDT designs with similar structures and operational conditions.
  •  
24.
  • Li, Xiaojian, 1991, et al. (författare)
  • A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles
  • 2020
  • Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
  • Tidskriftsartikel (refereegranskat)abstract
    • Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.
  •  
25.
  • Li, Xiaojian, 1991, et al. (författare)
  • A new method for performance map prediction of automotive turbocharger compressors with both vaneless and vaned diffusers
  • 2021
  • Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 235:6, s. 1734-1747
  • Tidskriftsartikel (refereegranskat)abstract
    • A new approach to predict the performance maps of automotive turbocharger compressors is presented. Firstly, a polynomial equation is applied to fit the experimental data of flow coefficient ratios for the centrifugal compressors with both vaneless and vaned diffusers. Based on this equation, the choke and surge flow coefficients under different machine Mach numbers can be quickly predicted. Secondly, a physically based piecewise elliptic equation is used to define compressors’ characteristic curves in terms of efficiency ratio. By introducing the flow coefficient ratio into the efficiency correlation, the empirical coefficients in the piecewise elliptic equation are uniquely calibrated by the experimental data, forming a unified algebraic equation to match the efficiency maps of the compressors with both vaneless and vaned diffusers. Then, a new universal equation, which connects the work coefficient, the impeller outlet flow coefficient and the non-dimensional equivalent impeller outlet width, is derived by using classical aerothermodynamic method. The off-design pressure ratio is predicted based on the equivalent impeller outlet width with less knowledge of the compressor geometry and no empirical coefficients. Finally, three state-of-the-art turbocharger compressors (one with vaneless diffuser, two with vaned diffusers) are chosen to validate the proposed method, and the results show a satisfactory accuracy for the performance map prediction. This method can be used for the preliminary design of turbocharger compressors with both vaneless and vaned diffusers, or to assess the design feasibility and challenges of the given design specifications.
  •  
26.
  • Li, Xiaojian, 1991, et al. (författare)
  • Installation effects on engine design
  • 2020
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Increasing the engine bypass ratio is one way to improve propulsive efficiency. However, an increase in the bypass ratio (BPR) has usually been associated with an increase in the fan diameter. Consequently, there can be a notable increase in the impact of the engine installation on the overall aircraft performance. In order to achieve a better balance between those factors, it requires novel nacelle and engine design concepts. This report mainly reviews installation effects on engine design. Firstly, the installation effects assessment methods are introduced. Then, the installation effects on engine cycle design, intake design and exhaust design are sequentially reviewed.
  •  
27.
  • Lin, Jianfeng, et al. (författare)
  • Experimental investigation and intelligent control of the magnus anti-rolling device for ship stability at zero speed
  • 2024
  • Ingår i: Ocean Engineering. - 0029-8018. ; 308
  • Tidskriftsartikel (refereegranskat)abstract
    • Under zero-speed conditions, ships are particularly susceptible to the effects of waves, which directly impact the safety of the vessel. A ship anti-rolling device based on the Magnus effect is designed to mitigate rolling motions across a full range of speeds, thereby enhancing the vessel's stability. This study presents an experimental investigation and intelligent control of Magnus anti-rolling devices aimed at enhancing ship stability at zero speed. The test setup, intelligent control algorithm, and experimental procedures specifically tailored for evaluating the Magnus anti-rolling device were designed. Following this, a comprehensive analysis was conducted to assess the effects of different cylinder geometries, swinging speeds, initial roll angles, and control methods on the anti-rolling characteristics of the device. Results demonstrate that the intelligent control method achieves an average anti-rolling efficiency of 89%. Additionally, the optimised geometric model of the Magnus anti-rolling device exhibits improved anti-rolling efficiency relative to the original model. The study confirms the stability and robustness of the intelligent Magnus anti-rolling device and suggests future research directions for practical applications aboard full-scale vessels in complex marine environments.
  •  
28.
  • Lv, Dazhou, et al. (författare)
  • Numerical study on transient aerodynamic characteristics of high-speed trains during the opening of braking plates based on dynamic-overset-grid technology
  • 2023
  • Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 233
  • Tidskriftsartikel (refereegranskat)abstract
    • The safety of high-speed trains is considerably compromised by increasing speed trends. Thus, braking plate technology has been applied to high-speed trains. The purpose of this study is to clarify the evolution law of the flow field of the vehicle during the opening of the braking plate and analyze the influence of the plate movement on the aerodynamic performance of the train. In this study, the flow field was computed using incompressible Navier–Stokes equations and the shear-stress transport (SST) k–ω turbulence model, and the unsteady flow over the opening brake plates was simulated using moving overlapping grids and dual time-stepping. The numerical method was verified through comparison with wind tunnel data (error <8%). The results reveal that the upstream braking plate significantly decreases the aerodynamic forces of the downstream plate during opening of the plates and causes the aerodynamic drag of the downstream braking plate to fluctuate significantly when it increases. The operation of the braking plate produces a small increase in the drag force of the train body (2.6%), but it significantly decreases the lift force of the train body (by up to 94%), especially during the opening of the braking plates. The flow field in the upper part of the train is significantly changed by the opening of the braking plate. In particular, the pressure in the cavity of the braking device changes sharply, and the surface is subjected to a large pulse pressure.
  •  
29.
  • Magrini, Andrea, et al. (författare)
  • A review of installation effects of ultra-high bypass ratio engines
  • 2020
  • Ingår i: Progress in Aerospace Sciences. - : Elsevier BV. - 0376-0421. ; 119
  • Tidskriftsartikel (refereegranskat)abstract
    • The adoption of ultra-high bypass ratio (UHBPR) engines has been long recognised to bring about reduction of specific fuel consumption and noise emission. In the need to fulfil ambitious environmental targets and mitigate the aviation sector impact, they represent a smoother technology change, compared to futuristic aircraft designs featuring electric, distributed and boundary layer ingesting propulsion. However, the challenges related to UHBPR adoption can prevent a real system performance improvement, due to interdependent counteracting factors and enhanced interference between engine and airframe. This paper reviews the installation effects on underwing-mounted UHBPR turbofan engines, first presenting the cycle design studies and how they are affected by considering integration. The advancements in nacelle components modelling and optimisation are then reviewed, where new numerical models, statistical methods and optimisation algorithms are employed to tackle the inherently multi-objective problems. The computational estimation of installation effects and the studies on optimal engine position are also presented, highlighting the overall effect on the aerodynamic characteristics. Finally, the wind tunnel tests using powered engine simulators are discussed. The tools developed to quantify the thrust and drag figures of installed propulsors and obtain indications on their best underwing location now allow quite accurate estimations, both in numerical and experimental simulations. The higher level of interaction and the increased mutual sensitivity of engine operation and wing flow field, however, suggest the need to elaborate closely coupled methods to correctly replicate these effects and an assessment of current wind tunnel practices for the design and operation of powered engine simulators.
  •  
30.
  • Mazeaud, Benoit, et al. (författare)
  • Application of SNGR Method to Compute Aero-Vibro-Acoustics of Heavy-Duty Rear-View Mirrors
  • 2019
  • Ingår i: 25th AIAA/CEAS Aeroacoustics Conference, 2019. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
  • Konferensbidrag (refereegranskat)abstract
    • Flow-induced noise inside cab interior (also termed aerodynamics-induced interior noise) is nowadays perceived as a key factor when assessing the quality of heavy-duty vehicles. In order to satisfy the turnaround time required for current product development, a simplified hybrid numerical approach has been adopted. It couples the SNGR (Stochastic Noise Generation and Radiation) method with a finite element method. The SNGR approach uses RANS (Reynolds Averaged Navier Stokes) for fast CFD (Computational Fluid Dynamics) computations, and is based on a stochastic model to synthesize turbulent velocity fluctuations. These fluctuations are then used to reconstruct aeroacoustic sources based on lighthill's equation. Several rear-view mirror configurations have been chosen to validate this numerical approach. The results are in good agreement with the experiments performed on track. The numerical approach is finally demonstrated as a fast method that can be applied to assess and rank early designs in a short time for the purpose of reducing aerodynamics-induced interior noise.
  •  
31.
  • Minelli, Guglielmo, 1988, et al. (författare)
  • An aeroacoustic study of the flow surrounding the front of a simplified ICE3 high-speed train model
  • 2020
  • Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 160
  • Tidskriftsartikel (refereegranskat)abstract
    • A numerical study using IDDES is carried out to investigate the aerodynamic and the aeroacoustic response of a simplified ICE3 high-speed train model. The work focuses on the front part of the train and, in particular, on the first bogie cavity. The choice is justified by a literature survey which shows that this part of the train is the principal contributor of critical noise pollution created at pass-by in populated areas. Detailed CFD can provide useful insight and be of great importance in the identification of noise generation mechanisms and their relation with the flow structures. Results show the formation of two main aerodynamic structures with a clear relation to the aeroacoustic response calculated on the train and ground surfaces. Simulations were made at Re=1.8×105 and M=0.058 to match the experimental observations found in literature and generate a set of benchmark data for future investigations.
  •  
32.
  • Minelli, Guglielmo, 1988, et al. (författare)
  • Using horizontal sonic crystals to reduce the aeroacosutic signature of a simplified ICE3 train model
  • 2021
  • Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 172
  • Tidskriftsartikel (refereegranskat)abstract
    • The design of noise barriers for high-speed trains is challenging due to the flow interaction between the train body and barriers. A failed design could affect the flow that in turn introduces additional aerodynamic loads to the train and generates extra noise. This study is the first investigation to numerically explore the detailed effects of noise barriers on high-speed trains. In particular, horizontal sonic crystals are compared to vertical, closed at the ground barriers in order to investigate the detailed effects of different noise screens on high-speed trains. The compressible IDDES is used to simulate the flow. The focus of this study is twofold. The first is to test if an alternative barrier typology can effectively reduce the noise signature, without having an impact on the train’s aerodynamic performance. The second is to explore the connection between the near-field velocity fluctuations and the far-field noise. A few specific tonal frequency components have been commonly reported but not clearly explained in the literature. It is unclear if the specific tonal components are less dependent on the Reynolds numbers, although, in general, energetic flow structures are dependent on inflow speeds. Concerning the noise reduction, the results show that the sonic crystal barrier case has a significantly better performance. A modal analysis is used to explore the causes of the tonal peaks and the association of the underbody swirling vortices to the far-field noise is described.
  •  
33.
  • Mingione, G., et al. (författare)
  • Airframe Noise Reduction Technologies applied to High-Lift Devices of Future Green Regional Aircraft
  • 2014
  • Ingår i: Greener Aviation 2014: Clean Sky breakthroughs and worldwide status.
  • Konferensbidrag (refereegranskat)abstract
    • Regional aircraft typically operate over airports located in the neighbourhood of densely populated areas, with high frequency of take-off / landing events and, hence, they strongly contribute to community noise and gaseous emissions. These issues currently limit further growth of traffic operated by regional airliners which, in the next future, will have to face even more stringent environmental constraints worldwide as prescribed by the civil aviation certification normative and local regulations as well.Therefore, in accordance with ACARE Vision 2020 toward a drastic reduction of air transport environmental impact over next decades, several mainstream technologies have been considered in the frame of Clean Sky JTI – Green Regional Aircraft (GRA) ITD project for application to next-generation regional aircraft. Such technologies are concerning: i) advanced aerodynamics and load control to maximise lift-to-drag ratio in both design and off-design conditions of the whole flight mission profile, thus reducing fuel consumption/ air pollutants emission and also allowing for steeper/ noise-abatement initial climb paths; ii) load alleviation to avoid loads from gust encounter and manoeuvre exceeding given limits, thus optimising the wing structural design for weight saving; iii) low airframe noise to reduce aircraft acoustic impact in approach flight condition.High-Lift-Devices (HLD) in fully-deployed settings represents one of the main sources of aircraft community noise during the approach flight phase and of consequent annoyance perceived by the resident population in the vicinity of airports. Therefore, in the overall scenario as above outlined, several HLD architectures, integrating either matured or more advanced low-noise concepts/technical solutions still preserving high-lift performances, have been investigated in the frame of the GRA ITD project. These HLD have been tailored to different classes/ configurations of future regional aircraft, ranging from high-wing 90-seat Turboprop to low-wing 130-seat Turbofan with different power-plant and engine installation.Technological studies of High-Lift Low-Noise devices carried out in the framework of the GRA ITD project have been presented. Both computational analyses and wind tunnel tests have been described in detail.Some passive acoustic devices have been firstly analysed with different numerical approaches. First of all, the use of conventional liners, as acoustic treatments carefully integrated with the wing, have revealed to be effective in noise detection for a wide range of frequencies. Also side-edge fences have demonstrated a promising aptitude in suppression of the turbulent vortex occurring around the flap side-edge. These encouraging results have been also confirmed during an extensive WT test campaign.Finally, multi-objective optimizations and the numerical assessment of several configurations have been performed by applying both aerodynamic and aeroacoustic methodologies. These studies have showed the successfully design of high-lift technologies with a low noise impact.The most promising among the addressed HLD technologies will be brought to the final demonstration phase within the GRA ITD work programme, in order to assess in a realistic experimental environment (TRL 5) the aircraft low-speed aerodynamic and aero-acoustic performances through WT tests on large-scale (say 1:6) complete A/C powered models.
  •  
34.
  • Mingione, G., et al. (författare)
  • Landing gear noise reduction technology development for future green regional aircraft
  • 2014
  • Ingår i: Greener Aviation 2014: Clean Sky breakthroughs and worldwide status.
  • Konferensbidrag (refereegranskat)abstract
    • One of the main objectives of the CS-JTI GRA ITD project - Low Noise Configuration domain is the aircraft noise reduction. It is well known that landing gear is one of main sources of airframe noise and therefore several previous projects have been carried out in USA and Europe to investigate relevant low-noise technologies.Nevertheless these studies have addressed mainly wing-mounted main landing gear (MLG) architecture of low-wing large aircraft which is quite different from the fuselage-mounted MLG of high-wing aircraft. Therefore, an activity plan has been defined to address noise reduction of MLG, and of nose landing gear (NLG) as well, for high-wing turboprop regional aircraft, aimed at identifying TRL 3 technologies and increase their maturity level up to TRL 5.The plan includes both numerical and experimental activities with the participation of European industries, research centers, SMEs and universities, as either GRA ITD Members or Partners of projects in the frame of Calls for Proposals (CfP).In 2012 MLG and NLG baseline configurations, being realistic CAD models of actual architectures, have been jointly delivered by Alenia Aermacchi and Messier-Bugatti-Dowty. In the course of 2013 low-noise technologies development is performed, from state-of-art survey and preliminary studies based on semi-empirical approach, to CFD/CAA analyses and basic wind tunnel tests on simplified mock-ups. Technologies under investigation are fairings, wheels hub caps, bay and doors acoustic treatments, partial closure of bay cavity (after gear lowering), spoilers, vortex disintegrators, etc.The paper describes to-date results and the criteria adopted to down-select landing gear low noise devices leading to the choice of best solutions for WT test demonstrations.
  •  
35.
  • Na, Wei, 1986, et al. (författare)
  • A slug length calculation for a contraction with mean flow between two half cylinders
  • 2022
  • Ingår i: Internoise 2022 - 51st International Congress and Exposition on Noise Control Engineering. - : The Institute of Noise Control Engineering of the USA, Inc..
  • Konferensbidrag (refereegranskat)abstract
    • A slug length is widely used to describe additional mass inertia at low frequencies in duct acoustics. It is often used in acoustic energy analysis, e.g. as one of the inputs for semi-analytical or empirical models to obtain the acoustic reflection and transmission coefficients. However, the calculation of slug length is usually empirical and limited to certain conditions, such as simple geometric configurations, low frequencies, no mean flow, etc. In this paper, the slug length at a contraction with mean flow between two half cylinders is calculated by different methods: solving the Laplace’s equation numerically, solving the Helmholtz equation, and using the Cummings – Fant equation based on the numerical results of frequency-domain linearized Navier-Stokes equations. Both the frequency-dependance and the mean flow effect are discussed. The calculated slug length can also be used as a crucial input, for example, in the Dowling and Hughes slit model and modified Cummings slit model to predict the acoustic scattering at tube rows in the presence of a cross mean flow.
  •  
36.
  • Na, Wei, 1986, et al. (författare)
  • A unified approach coupling linearized Navier-Stokes equations and Helmholtz equations to predict sound propagation with viscothermal losses in acoustic liners
  • 2023
  • Ingår i: Engineering Archive.
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper introduces a unified approach for coupling the classical linearized Navier-Stokes equations (LNSE), the original Helmholtz equation and a modified form of the Helmholtz equation for porous material modelling in frequency domain. This approach is termed the unified LNSE (ULNSE). It accounts for viscothermal losses of sound propagation in acoustic liners with small-scale perforation. This method also provides a possibility to switch from LNSE to the classical and modified Helmholtz equations depending on local acoustic properties. The ULNSE is validated and applied to simulation of conventional and hybrid liners in three dimensions (3D), and also compared to a semi-empirical model and experiments. The hybrid acoustic liner consists of a perforated plate, a porous foam layer, and a rectangular cavity. Unlike the hybrid liner, the porous foam is not mounted in the conventional liners. In the perforated plate where the viscothermal effect plays a role, sound waves are solved using the LNSE. The modified Helmholtz equation is formulated with a complex wavenumber to model the porous foam as an equivalent fluid model. In the liner cavity and external duct, the original Helmholtz equation is utilized. The ULNSE is cheaper than the classical LNSE since the Helmholtz equations, which consume less computational resources, are used locally where the viscothermal losses are negligible. Meanwhile, the ULNSE can maintain high numerical accuracy. The liners are analyzed in terms of critical parameters such as the porous foam material, and perforated plate thickness and porosity. The porous foam proves to be effective in sound absorption.
  •  
37.
  • Na, Wei, 1986, et al. (författare)
  • Design and analysis of conceptual acoustic metamaterials applied to mitigating cooling fan noise for heavy-duty vehicles
  • 2024
  • Ingår i: Inter Noise 2024.
  • Konferensbidrag (refereegranskat)abstract
    • The noise generated from cooling fans in heavy-duty vehicles like trucks poses challenges regarding environmental pollution and overall user comfort. To solve this problem, this study develops an acoustic metamaterial (AMM) that is constructed with small Helmholtz resonators in two layers. This concept can attenuate the noise in a broad frequency range. Furthermore, the particle swarm optimization (PSO) algorithm based on artificial intelligence (AI) is used to optimize the AMM structure. The key design parameters are discussed and analyzed. The installation strategies are put forth to examine the performance of the AMM. The proposed metamaterials, combined with the installation strategies, are numerically simulated using the finite element method. The results show that the current AMM is effective in reducing both tonal and broadband noise of interest. The findings shed light on the development of acoustic metamaterials for cooling-fan noise reduction in heavy-duty vehicles.
  •  
38.
  • Nebenführ, Bastian, 1984, et al. (författare)
  • Hybrid RANS/LES Simulations for Aerodynamic and Aeroacoustic Analysis of a Multi-Element Airfoil
  • 2013
  • Ingår i: 19th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102134 ; , s. 64-
  • Konferensbidrag (refereegranskat)abstract
    • A hybrid RANS/LES modeling approach is used for simulating the turbulent flow around a three-element airfoil in high-lift configuration. A detailed analysis of the flow is made, based on the simulation outcome. A comprehensive aeroacoustic analysis involving all three elements of the airfoil is also presented. To provide input data for acoustic analogies, the results of the simulation are sampled at a permeable stationary surface near the airfoil and at the airfoil itself. The far-field noise signature of the high-lift airfoil is computed with the help of the Kirchhoff integral surface method, the Ffowcs-Williams and Hawkings method for a stationary, permeable surface, and the Curle method. The sound pressure level spectrum exhibits a broad-banded shape with several narrow-banded tonal peaks at low Strouhal numbers. The broad-banded peak at high Strouhal numbers, which is typically associated with vortex shedding behind the blunt slat trailing edge, was also captured. Using Curle's acoustic analogy, the noise emission pattern of the three elements is explored, isolated from each other, revealing that both slat and flap act as dipoles. By refining the used grid, the flow results are significantly improved in terms of slat shear layer instability and resolved turbulent content as compared to our previous work.
  •  
39.
  • Niebles Atencio, Bercelay, 1979, et al. (författare)
  • Experiments and Lattice-Boltzmann Simulation of Flow in a Vertically Aligned Gearbox
  • 2023
  • Ingår i: Journal of Tribology. - 0742-4787 .- 1528-8897. ; 145:11
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a study of the oil flow in a vertically arranged FZG gearbox. The splash and churning losses are experimentally evaluated using measurements of the resistance torque. Using high speed imaging, the instantaneous oil splashing inside the gearbox is also presented and compared with Computational Fluid Dynamics (CFD) results from the Lattice-Boltzmann method (LBM), instead of the traditional grid-based finite volume method. Four different configurations, including a spur gear based on the standard FZG geometry and a disc pair wheel-pinion with the same tip diameters of the standard geometries are used. The experiments cover a range from 500 to 3000 rpm and three oil levels are studied. For the CFD simulations, the same oil levels and rotational speeds are used. The experimental results indicate torque differences depending on the oil level and the configuration. The splashing pattern is also different from the standard horizontal FZG case, which is typically studied in the literature. On the other hand, the CFD simulations and flow visualization experiments are in relative agreement with one another. The similarities and differences in the torque values for the different configurations and the splashing pattern for both experiments and CFD simulations are analyzed and discussed.
  •  
40.
  • Nilsson, Stefan, 1985, et al. (författare)
  • Conjunction of Aeroelasticity and Aeroacoustics in Transonic Cavity Flow
  • 2022
  • Ingår i: Proceedings of the International Forum of Aeroelasticity and Structural Dynamics 2022, IFASD 2022.
  • Konferensbidrag (refereegranskat)abstract
    • The effects of elastic cavity walls on noise generation at transonic speed are investigated for the generic M219 cavity. The flow is simulated with Spalart-Allmaras (SA) improved delayed detached-eddy simulation (IDDES) in combination with a wall function. The structural analysis software, which is strongly coupled with the flow solver, uses a modal formulation. The first 50 structural normal mode shapes are included in the simulation, spanning frequencies 468–2280 Hz. Results are compared with those from a reference simulation with rigid cavity walls. Spectral analysis of pressure fluctuations at microphones above the cavity evinces a distinct tone at 816 Hz, which is absent in the reference simulation. Moreover, the power of the 4th Rossiter mode at 852 Hz is depleted, implying a significant energy transfer from the fluid to the structure. Spectral proper orthogonal decomposition (SPOD) is employed for analyses of cavity wall pressure fluctuations and wall displacements. The SPOD mode energy spectra show results consistent with the spectra at the microphones, regarding the tone at 816 Hz and the depletion of the energy at the 4th Rossiter mode. In addition, the SPOD mode energy spectra show energy spikes at additional frequencies, which coincide with structural eigenfrequencies
  •  
41.
  • Nilsson, Stefan, 1985, et al. (författare)
  • Effects of Aeroelastic Walls on the Aeroacoustics in Transonic Cavity Flow
  • 2022
  • Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of elastic cavity walls on noise generation at transonic speed are investigated for the generic M219 cavity. The flow is simulated with the Spalart–Allmaras (SA) improved delayed detached-eddy simulation (IDDES) turbulence model in combination with a wall function. The structural analysis software uses a modal formulation. The first 50 structural normal mode shapes are included in the simulation, spanning frequencies of 468–2280 Hz. Results are compared with those from a reference simulation with rigid cavity walls. A spectral analysis of pressure fluctuations from a microphone array above the cavity evinces a distinct tone at 816 Hz, which is absent in the reference simulation. Furthermore, the power of the 4th Rossiter mode at 852 Hz is depleted, implying a significant energy transfer from the fluid to the structure. Spectral proper orthogonal decomposition (SPOD) is employed for analyses of cavity wall pressure fluctuations and wall displacements. The SPOD mode energy spectra show results consistent with the spectra of the microphone array with respect to the tone at 816 Hz and the depletion of the energy at the 4th Rossiter mode. Furthermore, the SPOD mode energy spectra show energy spikes at additional frequencies, which coincide with structural eigenfrequencies.
  •  
42.
  • Nilsson, Stefan, 1985, et al. (författare)
  • Effects of Viscosity and Density on the Aeroelasticity of the ONERA M6 Wing from Subsonic to Supersonic Speeds
  • 2022
  • Ingår i: AIAA AVIATION 2022 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
  • Konferensbidrag (refereegranskat)abstract
    • The effects of fluid viscosity and density on the aeroelasticity of the ONERA M6 wing over a wide range of free-stream Mach numbers, spanning 0.6–1.1, based on viscous and inviscid flow assumptions are studied. Both static and dynamic responses of the wing are examined. We employ a hybrid Reynolds-Averaged Navier-Stokes (RANS) - Large-Eddy Simulation (LES) method for viscous flow, namely Spalart-Allmaras Delayed Detached-Eddy Simulation (SA-DDES). The inviscid flow solver uses the Euler equations. A few selected cases are also analysed using Unsteady RANS (URANS). The flow solvers are strongly coupled to a structural analysis software, which uses a modal formulation. The structural responses are analysed using a constant free-stream density for all Mach numbers. In addition, higher densities are used for all Mach numbers in order to find the critical dynamic pressure where flutter is obtained. A substantial difference in the aeroelastic responses is found for Mach numbers ranging 0.8750–0.9500, when comparing viscous and inviscid flow simulations. Furthermore, it is shown that viscosity is of minor importance at subsonic and supersonic speeds. At Mach number 0.8395 it is shown that DDES provides close to identical structural responses as URANS. The largest difference of the predicted flutter boundaries is found in the transonic region. The flutter boundary for viscous flow stands out at Mach 0.9250 where it is 53 per cent higher than the flutter boundary predicted by inviscid flow. Simulations with URANS showed that it would predict a lower flutter boundary at Mach 0.9250, compared to SA-DDES.
  •  
43.
  • Nilsson, Stefan, 1985, et al. (författare)
  • On Viscosity and Density Affecting Aeroelasticity of ONERA M6 Wing from Subsonic to Transonic Regimes
  • 2023
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The effects of fluid viscosity and density on the aeroelasticity of the ONERA M6 wing over a wide range of free-stream Mach numbers, spanning $0.6$--$1.1$, based on viscous and inviscid flow assumptions are studied. Both static and dynamic responses of the wing are examined. We employ a hybrid Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) method for the viscous flow, namely Delayed Detached-Eddy Simulation (DDES) with the Spalart-Allmaras (SA) turbulence model. The inviscid flow solver uses the Euler equations. A few selected cases are also analysed using Unsteady RANS (URANS). The flow solvers are strongly coupled to a structural analysis software, which uses a modal formulation. The structural responses are analysed using a constant free-stream density for all Mach numbers. In addition, higher densities are used for all Mach numbers in order to find the critical dynamic pressure where flutter is obtained. A substantial difference in the aeroelastic responses is found for Mach numbers ranging $0.875$--$0.95$, when comparing viscous and inviscid flow simulations. Furthermore, it is shown that viscosity is of minor importance at subsonic and supersonic speeds. At Mach number $0.8395$ it is shown that DDES provides close to identical structural responses as URANS. The largest difference of the predicted flutter boundaries is found in the transonic region. The flutter boundary for viscous flow stands out at Mach $0.925$ where it is $53 \%$ higher than the flutter boundary predicted by inviscid flow. Simulations with URANS showed that it would predict a lower flutter boundary at Mach $0.925$, compared to DDES.
  •  
44.
  • Niu, Jiqiang, et al. (författare)
  • Aerodynamic simulation of effects of one- and two-side windbreak walls on a moving train running on a double track railway line subjected to strong crosswind
  • 2022
  • Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 221
  • Tidskriftsartikel (refereegranskat)abstract
    • High-speed railway lines are widely distributed worldwide. The surrounding wind environment of such railway lines is complex, which significantly affects the safety of high-speed train operations. Using a combination of the computational fluid dynamics method of improved delayed detached eddy simulation and sliding grid technology, the effects of one- and two-side windbreak walls on the unsteady aerodynamic performance of a high-speed train running under a crosswind on a double-track railway line with an embankment and the flow-field characteristics around the train were systematically studied. The grid independence and numerical methods used in this study were verified. The results showed that when the windbreak wall was absent, the aerodynamic performance of the train running on the upstream railway line was the poorest, while the train running on the downstream railway line exhibited large aerodynamic fluctuations. The windbreak wall significantly reduced the aerodynamic force and its fluctuation; the one- and two-side windbreak walls had different effects on the unsteady aerodynamic performance of trains running on the upstream and downstream railway lines under a crosswind. The one-side windbreak wall could restrain the aerodynamic fluctuation of the train more and is thus preferred from the perspective of construction effort and cost.
  •  
45.
  • Niu, Jiqiang, et al. (författare)
  • Investigation of aerodynamic behaviour of a high-speed train on different railway infrastructure scenarios under crosswind
  • 2022
  • Ingår i: Wind and Structures, An International Journal. - 1598-6225 .- 1226-6116. ; 35:6, s. 405-418
  • Tidskriftsartikel (refereegranskat)abstract
    • The aerodynamic behaviour of a CRH high-speed train under three infrastructure scenarios (flat ground, embankment, and viaduct) in the presence of a crosswind was simulated using a 1/8th scaled train model with three cars and the IDDES framework. The time-averaged and instantaneous flow field around the model were examined. The employed numerical algorithm was verified through a wind tunnel test, and the grid and timestep resolution analyses were conducted to ensure the reliability of the data. It was noted that the flow around the rail line was different under different infrastructure scenarios, especially in the case of the embankment, which degraded the aerodynamic performance of the train under the crosswind. The flow around the train on the flat ground and viaduct was different, although the aerodynamic performance of the train was similar in both cases. Moreover, the viaduct accidents were noted to have the most critical consequences, thereby requiring the most attention. The aerodynamic performance of the train on the windward track of the embankment under the crosswind was worse than that of the train on the leeward track. But for the other two infrastructure scenarios, the aerodynamic performance of the train on the windward track is relatively dangerous, which is mainly caused by the head car. These observations suggest that the aerodynamic behaviour of the train on an embankment under a crosswind must be carefully considered and that certain wind protection measures must be adopted around rail lines in windy areas.
  •  
46.
  • Niu, Jiqiang, et al. (författare)
  • Numerical investigation on application of train body airflow diversion device to suppress pressure waves in railway high-speed train/tunnel system
  • 2023
  • Ingår i: International Journal of Rail Transportation. - : Informa UK Limited. - 2324-8386 .- 2324-8378. ; 11:4, s. 490-507
  • Tidskriftsartikel (refereegranskat)abstract
    • The development of the high-speed maglev train (HSMT) is important for the future of high-speed rail transit. A pressure wave (PW) is a common aerodynamic effect in high-speed railway tunnels. For HSMTs with a speed of 600 km/h, the amplitude of PW in the tunnel can be very big, which maybe far exceed the current design strength standard of the train body structure and seriously threatens the safety of the railway train/tunnel structure and passenger ear comfort. Therefore, aerodynamic PWs caused by a two-dimensional axisymmetric model with an ellipsoidal nose passing through a tunnel was investigate, and the numerical method adopted in this study was validated by two scaled moving model tests. The PWs caused by trains in four cases and the effects of train speed and tunnel length were analysed and compared. Some results show that diversion device significantly reduces the amplitude of the PWs (Delta C-p) on the train surface and tunnel wall. The diversion device on the train tail (C4) not only changes Delta C-p, but also changes the waveform. The diversion device on the train tail (C3) and diversion device on both train head and tail which are connecting each other (C2) mainly reduced the Delta C-p. When the decrease in both PWs on the train surface and tunnel wall is considered, C2 has the best effect. With an increase in the train speed, the effect of C2 on restraining the PW on the train surface and tunnel wall increases to a certain extent. However, the restraining effect on the micro-pressure wave (MPW) at the tunnel exit does not exceed 5%. The suppression effect of C2 on Delta C-p on the train surface and tunnel wall decreases with an increase in the tunnel length. However, it does not change the distribution law of Delta C-p along the train and tunnel. This study can provide a reference for the design of the body of HSMTs and the suppression of PW in tunnels.
  •  
47.
  • Ottersten, Martin, 1981, et al. (författare)
  • A new strategy of designing micro vortex generators to mitigate tonal noise generation from voluteless centrifugal fan
  • 2022
  • Ingår i: Proceedings of the International Congress on Acoustics. - 2226-7808 .- 2415-1599.
  • Konferensbidrag (refereegranskat)abstract
    • Low-speed voluteless centrifugal fans are typically used in ventilation systems. The negative side of the fans is noise, particularly tonal noise of which the dominant tone is at the blade passing frequency (BPF). One of the important noise contributors is the gap between the rotating shroud and the stationary inlet duct. Previous studies have shown that the flow passing through the gap causes turbulence that interacts with the blade leading edge (BLE), rendering surface pressure fluctuations that are the tonal noise sources at BPF. In this study, a method of assembling micro vortex generators (MVGs) to control the turbulence for voluteless centrifugal fans is proposed for the first time. The assembling is made in two different ways: 14 add-ons on the shroud surface at the gap, and 7 ones on the BLE surface near the shroud. The effects of the MVGs are investigated using the hybrid computational aeroacoustics method, which couples the improved delayed detached eddy simulation method with the Ffowcs Williams and Hawkings acoustic analogy. Our simulations show that the MVGs are effective to control the turbulence and mitigate the tonal noise. The assembled array of 7 MVGs achieves more reduction of the tonal noise than the 14-MVGs array.
  •  
48.
  • Ottersten, Martin, 1981, et al. (författare)
  • Inlet Effect on Tonal Noise Generated from a Voluteless Centrifugal Fan
  • 2022
  • Ingår i: FAN 2022.
  • Konferensbidrag (refereegranskat)abstract
    • In this study, three voluteless centrifugal fans are compared for their aeroacoustic performances. The tonal noise is predicted by coupling the IDDES with Formulation 1A of Farassat. The sources of the tonal noise at the blade passing frequency (BPF) are identified. It is found that the sources are related to the fan inlet gap that introduces the turbulence interacting with the blade leading edge. By redesigning the gap, the tonal noise at the BPF is reduced effectively.
  •  
49.
  • Ottersten, Martin, 1981, et al. (författare)
  • Inlet Gap Effect on Aerodynamics and Tonal Noise Generation of a Voluteless Centrifugal Fan
  • 2022
  • Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 540
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the gap effects on the aerodynamics and tonal noise generation of voluteless centrifugal fans are studied based on different gap geometries. The study is motivated by the state of the art of this type of fan, for which the tonal noise generation due to the gap turbulence has not been addressed concerning the gap geometry, while a recent study reported that there is tonal noise at the blade passing frequency (BPF) from the gap turbulence. We simulate the configurations using a hybrid method coupling the improved delayed detached eddy simulation (IDDES) with Formulation 1A of Farassat. Our simulation shows regions with high vorticity magnitudes in the channel between two blades near the trailing edges close to the shroud. The turbulence renders a uniform pressure rise. By changing the gap design, the turbulent regions can be reduced. The configurations show a similar trend of the root mean square (RMS) pressure on the blade leading edge (BLE), largest at the shroud, and decays when the distance to the gap increases. The gap designs affect the amplitude of the RMS pressure, which is connected to the BPF. Spectral analysis is performed for the surface pressure fluctuations and the sound pressure upstream of the fan. The surface pressure fluctuations show that, for all cases, the regions with high energy are identical to the locations where the gap turbulence evolves and accounts for the impingement on the BLE. The amplitude of the tonal noise at the BPF differs between the cases.
  •  
50.
  • Ottersten, Martin, 1981, et al. (författare)
  • Inlet Gap Effect on Tonal Noise Generated from a Voluteless Centrifugal Fan
  • 2022
  • Ingår i: International Journal of Turbomachinery, Propulsion and Power. - : MDPI AG. - 2504-186X. ; 7:4
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, three voluteless centrifugal fans are compared for their aeroacoustic performances. The tonal noise is predicted by coupling the IDDES with Formulation 1A of Farassat. The sources of the tonal noise at the blade passing frequency (BPF) are identified. It is found that the sources are related to the fan inlet gap, which introduces higher velocity intensities and turbulent fluctuations interacting with the blade leading edge. By redesigning the gap, the tonal noise at the BPF is reduced effectively.
  •  
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