| 1. |
- Okda, Sherif, et al.
(författare)
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Testing of the Aerodynamic Characteristics of an Inflatable Airfoil Section
- 2020
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Ingår i: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 33:5
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Tidskriftsartikel (refereegranskat)abstract
- Inflatable structures are characterized by being light and easy to manufacture and deploy. Hence, they find many applications in aerospace and aeronautical engineering. In this paper, an inflatable segment with a The National Advisory Committee for Aeronautics (NACA) 0021 airfoil cross-section is designed, fabricated, and tested. The geometrical accuracy of the manufactured inflatable segment is measured using laser scanning. Measurements show that the average normalized error of the chord length and thickness are 2.97% and 0.554%, respectively. The aerodynamic behavior of the inflatable segment is then tested in a wind tunnel at different wind speeds and angles of attack. Lift forces are measured using a six-component balance, while the drag forces are calculated from the wake measurements. The lift and drag coefficients of the inflatable section are compared to those of a standard NACA 0021 airfoil. Finally, flow visualization is examined at different angles of attack using two methods: smoke and tufts. Both methods show that flow separation starts at 15° and full stall occurs at 25°. Results indicate that inflatables can find more applications in the design and construction of aerodynamic structures, such as wings.
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| 2. |
- Wadekar, Sandip, 1989
(författare)
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Large-Eddy Simulation of Gasoline Fuel Spray Injection at Ultra-High Injection Pressures
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gasoline direct injection is a state-of-the-art technique that reduces hydrocarbon and particulate emissions. However, further improvement is needed to meet current as well as future emission regulations. A prominent solution is to increase the fuel injection pressure which allows faster fuel droplet atomization, quick evaporation and improves fuel-air mixture formation under realistic engine conditions. In this work, the gasoline fuel injection process at ultra-high injection pressures ranging from 200 to 1500 bar was analyzed using numerical models. In particular, the Large-Eddy Simulation (LES) method, with the standard Smagorinsky turbulence model, was utilized using the Eulerian formulation for the continuous phase. The discrete droplet phase was treated using a Lagrangian formulation together with spray sub-models. In the first part of study, spray was injected into an initially quiescent constant volume chamber using two different nozzle hole shape geometries: divergent and convergent. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on spray development. The calibrated models were then used to investigate the impact of ultra-high injection pressures on mean droplet sizes, droplet size distribution, spray-induced large-scale eddies and entrainment rate. The results showed that, at ultra-high injection pressures, the mean droplet sizes were significantly reduced and the droplets achieving very high velocities. Integral length scales of spray-induced turbulence and air entrainment rate were better for the divergent-shaped injector, and considerably larger at higher injection pressures compared to lower ones. In the second part of the study, four consecutive full-cycle cold flow LES simulations were carried out to generate realistic turbulence inside the engine cylinder. The first three cycles were ignored, with the fourth cycle being used to model the injection of the fuel using the divergent-shaped injector only (which was found to be better in the previous part of this study) at different injection pressures. In addition to the continuous gas phase (Eulerian) and the dispersed liquid (Lagrangian), the liquid film feature (Finite-Area) was used to model the impingement of fuel spray on the engine walls and subsequent liquid film formation. The simulation results were used to evaluate spray-induced turbulence, fuel-air mixing efficiency and the amount of liquid mass deposited on the walls. The limitation of the high-pressure injection technique with respect to liquid film formation was optimized using a start of injection (SOI) sweep. Overall results showed that the mixing efficiency increased at high injection pressure and that SOI should occur between early injection and late injection to optimize the amount of mass being deposited on the engine walls.
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| 3. |
- Li, Xiaojian, 1991, et al.
(författare)
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Installation effects on engine design
- 2020
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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.
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| 4. |
- Ottersten, Martin, 1981, et al.
(författare)
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Inlet Gap Influence on Low-Frequency Flow Unsteadiness in a Centrifugal Fan
- 2022
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Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- In this study, unsteady low-frequency characteristics in a voluteless low-speed centrifugal fan operating at a high mass flow rate are studied with improved delayed detached eddy simulation (IDDES). This study is motivated by a recent finding that the non-uniformly distributed pressure inside this type of fan could be alleviated by improving the gap geometry. The present simulation results show that the velocity magnitudes of the gap have distinct low and high regions. Intensive turbulent structures are developed in the low-velocity regions and are swept downstream along the intersection between the blade and shroud, on the pressure side of the blade. Eventually, the turbulence gives rise to a high-pressure region near the blade’s trailing edge. This unsteady flow behavior revolves around the fan rotation axis. Additionally, its period is 5% of the fan rotation speed, based on the analysis of the time history of the gap velocity magnitudes and the evolution of the high-pressure region. The same frequency of high pressure was also found in previous experimental measurements. To the authors’ knowledge, this is the first time that the trigger of the gap turbulence, i.e., the unsteady local low velocity, has been determined.
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| 5. |
- Li, Xiaojian, 1991, et al.
(författare)
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A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
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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.
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| 6. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Transient torque reversals in indirect drive wind turblnes
- 2023
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Ingår i: Wind Energy. - 1099-1824 .- 1095-4244. ; 26, s. 691-716
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Tidskriftsartikel (refereegranskat)abstract
- The adverse effect of transient torque reversals (TTRs) оп wind turЬine gearboxes сап Ье severe due to their magnitude and rapid occurrence compared with other equipment. The primary damage is caused to the bearings as the bearing loaded zone rapidly changes its direction. Other components are also affected Ьу TTRs (such as gear tooth); however, its impact оп bearings is the largest. While the occurrence and severity of TTRs are acknowledged in the industry, there is а lack of academic literature оп their initiation, propagation and the associated risk of damage. Furthermore, in the wide range of operation modes of а wind turЬine, it is not known which modes сап lead to TTRs. Further, the interdependence of TTRs оп environmental loading like the wind is also not reported. This paper aims to address these unknowns Ьу expanding оп the understanding of TTRs using а high-fidelity numerical model of an indirect drive wind turЬine with а douЬly fed induction generator (DFIG). То this end, а multibody model of the drivetrain is developed in SIMPACK. The model of the drivetrain is explicitly coupled to state-of-the-art wind turЬine simulator OpenFAST and а grid-connected DFIG developed in MATLAB®'s Simulink® allowing а coupled analysis of the electromechanical system. А metric termed slip risk duration is proposed in this paper to quantify the risk associated with the TTRs. The paper first investigates а wide range of IEC design load cases to uncover which load cases сап lead to TTRs. lt was found that emergency stops and symmetric grid voltage drops сап lead to TTRs. Next, the dependence of the TTRs оп inflow wind parameters is investigated using а sensitivity analysis. lt was found that the instantaneous wind speed at the onset of the grid fault or emergency shutdown was the most influential factor in the slip risk duration. The investigation enaЫes the designer to predict the occurrence of TTRs and quantify the associated risk of damage. The paper concludes with recommendations for utility-scale wind turЬines and directions for future research.
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| 7. |
- Li, Xiaojian, 1991, et al.
(författare)
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A new method for performance map prediction of automotive turbocharger compressors with both vaneless and vaned diffusers
- 2021
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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
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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.
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| 8. |
- Malmek, Karolina, 1990, et al.
(författare)
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Rapid aerodynamic method for predicting the performance of interacting wing sails
- 2024
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Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 293
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Tidskriftsartikel (refereegranskat)abstract
- Rapid performance prediction tools are required for the evaluation, optimization, and comparison of different wind propulsion systems (WPSs). These tools should capture viscous aerodynamic flow effects in 3D, particularly the maximum propulsion force, stall angles, and interaction effects between the lift-generating units. This paper presents a rapid aerodynamic calculation method for wing sails that combines a semiempirical lifting line model with a potential flow-based interaction model to account for 3D interaction effects. The method was applied to a WPS that consisted of several wing sails with considerable interaction effects. The results were compared to CFD RANS simulations in 2D and in 3D. For the evaluated validation cases, the interaction model improved the prediction considerably compared to when the interaction was not accounted for. The method provided acceptable driving force, moments, and stall predictions, with negligible computational cost compared to 3D CFD simulations.
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| 9. |
- Marimon Giovannetti, Laura, et al.
(författare)
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Multi-wing sails interaction effects
- 2022
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Ingår i: SNAME 24th Chesapeake Sailing Yacht Symposium, CSYS 2022. - : The Society of Naval Architects and Marine Engineers.
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Konferensbidrag (refereegranskat)abstract
- The effects of multiple wings interacting and the change in efficiency due to those effects as well as optimal sheeting angles are becoming an important area of study with the advent of wind-propelled ships for goods transport. This research presents a first analysis of wind tunnel tests carried out at the University of Southampton R.J. Mitchell wind tunnel where three wings are subject to turbulent flow with Reynolds number in excess of 1 million. A range of possible variations of ship heading and apparent wind angles are tested taking into consideration the blockage effects and the geometrical characteristics of the working section. The forces and moments are captured on each individual wing as well as in the overall wind tunnel balance with 6-components dynamometers. Furthermore, pressure sensors and PIV data are recorded during the tests to provide the experimental campaign with results that can validate both qualitatively and quantitatively the numerical tools developed to aid the design stage of wind propelled vessels.
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| 10. |
- Ottersten, Martin, 1981
(författare)
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Numerical investigation of tonal noise sources from centrifugal fan
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heating, ventilating, and air conditioning systems (HVAC) are today an important part of many people's life. They provide a sufficient amount of airflow with the correct temperature, quality, and humidity. The negative side is the noise it produces. Many improvements have been made in building development to reduce noise from the environment. When so, the noise from the HVAC system becomes clearer. The dominant tonal noise in an HVAC system is produced by the fan. In this work tonal noises produced by a centrifugal fan is investigated to be able to understand the generation mechanism and identify their sources. The approach is to use the hybrid computational aeroacoustics (CAA) method, that couples a computational fluid dynamics (CFD) method with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy. Recirculating flows, which are responsible for reducing the fan efficiency and increasing the noise generation, are observed between the shroud and the blade trailing edges. It is found that the recirculating flows are associated with the gap between the shroud and the inlet duct. The recirculating flow causes large modeled turbulence kinetic energy (TKE). The TKE is unevenly distributed among the blades due to the unsteady recirculating flow. Moreover, the position of the largest TKE periodically varies among the blades. The period corresponds to approximately 4 times the fan rotation period, it was also found in acoustic measurements. Different pressure distributions among the blades are found and ascribed to the turbulence initializing from the inlet gap. The turbulence develops along the shroud wall and interacts with the blades at their leading edges. The interaction renders uneven surface pressure distributions among the blades as well as significant peak differences. As the distances to the inlet gap and the shroud increases, the difference of the pressure distributions among the blades decays. The wall-pressure fluctuations indicates that the locations of the tonal noise sources agree with the locations of the uneven surface pressure distributions and the significant pressure peaks, which are near the blade leading edges.
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