| 1. |
- Shao, Xinyuan, 1997, et al.
(författare)
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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
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Ingår i: Journal of Ocean Engineering and Science. - 2468-0133. ; 8:4, s. 446-460
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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. |
- Andersson, Josefin, 1994, et al.
(författare)
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Propulsion Installation Modelling for geared Ultra-high bypass ratio engine cycle design
- 2020
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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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| 3. |
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| 4. |
- Chen, Zheng wei, et al.
(författare)
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Reducing the aerodynamic drag of high-speed trains by air blowing from the nose part: Effect of blowing speed
- 2023
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - 0167-6105. ; 238
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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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| 5. |
- Chroneer, Zenitha, et al.
(författare)
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Prediktering av extern flödesakustiks påverkan på hyttbuller
- 2019
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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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| 6. |
- Eliasson, P., et al.
(författare)
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Assessment of high-lift concepts for a regional aircraft in the ALONOCO project
- 2012
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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
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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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| 7. |
- Fares, Omar, 1992, et al.
(författare)
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Numerical Investigation of Narrow-Band Noise Generation by Automotive Cooling Fans
- 2020
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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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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| 8. |
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| 9. |
- Guo, Chunyu, et al.
(författare)
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Influence of jet flow on hydrodynamic performance of a ducted propeller
- 2023
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Ingår i: Physics of Fluids. - 1070-6631 .- 1089-7666. ; 35:12
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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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| 10. |
- Guo, Chunyu, et al.
(författare)
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Numerical investigation of the scale effects of pump-jet propulsor with a pre-swirl stator
- 2023
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1089-7666 .- 1070-6631. ; 35
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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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