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On the application of passive flow control for cavitation suppression in torque converter stator

INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID flow 2019年第1期29卷 204-222页

作者： Liu, Cheng Wei, Wei Yan, Qingdong Weaver, Brian K. Wood, Houston G. Beijing Inst Technol Dept Mech Engn Beijing Peoples R China Beijing Inst Technol Sch Mech Engn Dept Vehicle Engn Beijing Peoples R China Univ Virginia Charlottesville VA USA Univ Virginia Dept Mech & Aerosp Engn Charlottesville VA USA

Purpose The purpose of this paper is to study the transient cavitation process in torque converters with a particular focus on cavitation suppression with a passive flow control technique. Design/methodology/approach The transient fluid field in a torque converter was simulated by RANS-based computational fluid dynamics (CFD) in a full three-dimensional (3D) model. A homogeneous Rayleigh-Plesset cavitation model was used to simulate the transient cavitation process and the results were validated with test data. Various secondary flow passages (SFP) were applied to the stator blade. The cavitation behavior and hydrodynamic performance were simulated and compared to investigate the effect of SFP geometries on cavitation suppression. Findings Presented results show that cavitation in the torque converter is highly unstable at stall operating condition because of the combination of a high incidence angle and high flow velocity. The addition of an SFP to the stator blade produces a disruption of the re-entrant jet and reduces the overall degree of cavitation, consequently inhibiting the unstable cavitation and reducing performance degradation. Originality/value This paper provides unique insights into the complicated transient cavitation flow patterns found in torque converters and introduces effective passive flow control techniques useful to researchers and engineers in the areas of fluid dynamics and turbomachinery.

关键词： Cavitation control passive flow control

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passive flow-field control using dimples for performance enhancement of horizontal axis wind turbine

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ENERGY 2023年 271卷

作者： Azlan, F. Tan, M. K. Tan, B. T. Ismadi, M. -Z. Monash Univ Malaysia Sch Engn Mech Engn Discipline Jalan Lagoon Selatan Bandar Sunway 47500 Selangor Malaysia

This paper investigates the effectiveness of dimples on the aerodynamic performance of NREL Phase VI wind turbine. Computational fluid dynamics (CFD) was conducted to simulate the turbulent flow and all the forces acting on the rotor. k-omega shear-stress transport (SST) turbulence model was selected to complete the governing equations and multi-reference frame was used as the computational domain. The computational results were compared with the experimental data and previous studies to ensure its reliability. The effect of different dimple configurations, placed at the suction side of the rotor, on the aerodynamic performance of the rotor blade was investigated in terms of the output torque and axial thrust, coefficient of pressure, and the flow field around the blade cross section in the spanwise directions. The results revealed that, dimpled-surface blade could generate up to 8.41% higher output torque compared to the original blade. The results showed no significant deviation in the axial thrust with the addition of the dimples. The modified surface blade with dimples was proven to enhance the operating performance of a wind turbine.

关键词： NREL Phase VI wind Turbine flow separation Wind turbine dimples passive flow control Pitch angle

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Peak lift-to-drag ratio enhancement of the DU12W262 airfoil by passive flow control and its impact on horizontal and vertical axis wind turbines

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ENERGY 2020年 201卷

作者： Acarer, Sercan Izmir Katip Celebi Univ Dept Mech Engn Fac Engn & Architecture Izmir Turkey

Recent studies have revealed that passive leading-edge slots on the pressure side has the potential to increase both the peak and overall C-L/C-D of airfoils and may possess an advantage over active methods. This work pursues application of such novel slots to the modern DU12W262 airfoil with a flexible slotshape parametrization coupled with an optimizer to allow other slot concepts as well (suction side and trailing edge slots). Experimentally validated Computational Fluid Dynamics (CFD) simulations are employed for this purpose. It is shown that 16% peak C-L/C-D improvement and overall alpha-C-L/C-D rise are observed without any penalty in stall range. Implications of these are demonstrated on Horizontal- and Vertical-Axis Wind Turbines (HAWT and VAWT) by CFD. It is shown that, HAWT peak C-p of increases by 3.2%. Alternative BEM simulations predict this as high as 7.5%. For the VAWT, the peak C-p remains unchanged, however high tip-speed-ratio (lambda > 3, low wind speed) C-p increases between 3.5 and 9.6% throughout the operational range. This may directly reflect into VAWT urban operation. In summary, the concept is highly successful in improving peak and overall C-L/C-D of a modern airfoil, and this yields to significant enhancements in both HAWTs and VAWTs. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： passive flow control Slot Airfoil HAWT VAWT Wind turbine

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Effect of passive flow control on the aerodynamic performance, entropy generation and aeroacoustic noise of axial turbines for wave energy extractor

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OCEAN ENGINEERING 2018年 157卷 262-300页

作者： Shehata, Ahmed S. Xiao, Qing Kotb, Mohamed A. Selim, Mohamed M. Elbatran, A. H. Alexander, Day Univ Strathclyde Dept Naval Architecture Ocean & Marine Engn Glasgow G4 0LZ Lanark Scotland Arab Acad Sci Technol & Maritime Transport Coll Engn & Technol PO 1029 Alexandria Egypt Univ Alabama Birmingham Mat Sci & Engn Birmingham AL USA

Wells turbine is the simplest type of an axial flow self-rectifying air turbine that can be used in conjunction with Oscillating Water Column (OWC) system in the extraction of ocean wave energy. It has been noticed that this turbine is subjected to early stall. As a consequence, several attempts for improving the energy extraction performance of Wells turbine within the stall regime have been investigated. One of these attempts was using an inclined slot as a passive flow control to obtain a delayed stall. In the following study, the impact of varying the angle for the slot on the performance of Wells turbine in the stall regime was investigated. Furthermore, the first law of thermodynamics and the entropy analysis has been used to examine the effect of the slot angle on the entropy generation features around the turbine blade. Moreover, Investigation of slot angle effect on the aerodynamics noise emission from Wells turbine airfoil during the normal operation and the stall regime is covered in this study. The blade of turbine with optimum angle of slot was investigated using the OWC based on actual data from the Egyptian Northern Coast. It was found that the optimum slot angle is 10 degrees clockwise which results in 3% improvement in the torque coefficient before the stall and 15% after the stall as compared to the 0 degrees slot. Otherwise, it gives a lower global entropy generation rate than the 0 degrees slot by 4% before the stall and 3% after the stall. Furthermore, using airfoil of blade turbine with a slot resulted in a reduction of aeroacoustic noise by -21.2% at the stall regime under oscillating flow conditions.

关键词： Oscillating flow Wave turbine passive flow control Entropy generation Aeroacoustic noise Egyptian coasts

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A critical study on passive flow control techniques for straight-bladed vertical axis wind turbine

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ENERGY 2018年 165卷 12-25页

作者： Zhu, Haitian Hao, Wenxing Li, Chun Ding, Qinwei Wu, Baihui Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Peoples R China Univ Plymouth Sch Engn Plymouth Devon England

The wind energy has positioned itself as a most promising sustainable energy. The straight-bladed vertical axis wind turbines (SB-VAWTs), as a common turbine for harvesting wind energy, have broad prospects of development. However, the SB-VAWTs are usually influenced by dynamic stall which can cause the aerodynamic losses and fluctuating load. Therefore, the passive flow control (PFC) technique is appreciated for SB-VAWTs due to its low cost and no additional energy consumption. Current paper presents the review of PFC techniques which have been used or are worth being utilized in SB-VAWTs. Furthermore, based on the validation of computational model, a numerical uniform-parameter-criterion study using TSST turbulence model has been conducted to present the research prospects of some novel PFC techniques for SB-VAWTs, including Gurney flap (GF), dimple-GF, leading-edge airfoil-slat (LEAS), flow-deflecting airfoil (FDA), non-circular gap (NCG). (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Vertical axis wind turbine passive flow control Numerical simulation Aerodynamic performance

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Modal analysis of passive flow control for the turbulent wake of a generic planar space launcher

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CEAS SPACE JOURNAL 2018年第2期10卷 189-202页

作者： Loosen, S. Statnikov, V. Meinke, M. Schroeder, W. Rhein Westfal TH Aachen Inst Aerodynam Wullnerschtr 5A D-52062 Aachen Germany Forschungszentrum Julich High Performance Comp JARA D-52428 Julich Germany

The turbulent wake of a generic planar space launcher equipped with two passive flow control devices is simulated using a zonal RANS-LES method and analyzed by dynamic mode decomposition (DMD). In the first approach, the effect of a classical boat tail on the wake is examined. In the second concept, a flow control device consisting of semi-circular lobes integrated at the base shoulder of the main body is used. The objective of the two concepts is to reduce the reattachment length and thus the lever arm of the forces as well as to stabilize the separated shear layer. Using a boat tail, the reattachment length can be reduced by 50%. Furthermore, it is shown that the semi-circular lobes enhance the turbulent mixing and the shear layer growth rate. Hence, they significantly reduce the reattachment length by about 75%. The semi-circular lobes partially reduce undesired low-frequency pressure fluctuations on the nozzle surface. However, this reduction is achieved at the expense of an increase of high-frequency pressure fluctuations due to intensified small turbulent scales. The DMD analysis of the velocity field reveals that the large-scale coherent structures featuring a wave length of two step heights observed in the reference configuration without flow control can be suppressed by the lobes. The spanwise wave length of the coherent structures seems to depend on the geometry of the lobes, since all detected spatial DMD modes show a spanwise periodicity being equal to the distance between two lobes.

关键词： Backward-facing step passive flow control Space launcher wake Zonal RANS-LES Dynamic mode decomposition (DMD)

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NUMERICAL INVESTIGATION OF passive flow control USING WAVY BLADES IN A HIGHLY-LOADED COMPRESSOR CASCADE

NUMERICAL INVESTIGATION OF PASSIVE FLOW CONTROL USING WAVY B...

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ASME Turbo Expo: Turbomachinery Technical Conference and Exposition

作者： Wang, Bo Wu, Yanhui Liu, Kai Northwestern Polytech Univ Sch Power & Energy 127 Dongxiang Rd Xian 710129 Shaanxi Peoples R China

ISBN: (纸本)9780791850992

Driven by the need to control flow separations in highly loaded compressors, a numerical investigation is carried out to study the control effect of wavy blades in a linear compressor cascade. Two types of wavy blades are studied with wavy blade-A having a sinusoidal leading edge, while wavy blade-B having pitchwise sinusoidal variation in the stacking line. The influence of wavy blades on the cascade performance is evaluated at incidences from -1 degrees to +9 degrees. For the wavy blade-A with suitable waviness parameters, the cascade diffusion capacity is enhanced accompanied by the loss reduction under high incidence conditions where 2D separation is the dominant flow structure on the suction surface of the unmodified blade. For well-designed wavy blade-B, the improvement of cascade performance is achieved under low incidence conditions where 3D corner separation is the dominant flow structure on the suction surface of the baseline blade. The influence of waviness parameters on the control effect is also discussed by comparing the performance of cascades with different wavy blade configurations. Detailed analysis of the predicted flow field shows that both the wavy blade-A and wavy blade-B have capacity to control flow separation in the cascade but their control mechanism are different. For wavy blade-A, the wavy leading edge results in the formation of counter-rotating streamwise vortices downstream of trough. These streamwise vortices can not only enhance momentum exchange between the outer flow and blade boundary layer, but also act as the suction surface fence to hamper the upwash of low momentum fluid driven by cross flow. For wavy blade-B, the wavy surface on the blade leads to a reduction of the cross flow upwash by influencing the spanwise distribution of the suction surface static pressure and guiding the upwash flow.

关键词： highly-loaded compressor cascade corner separation cross flow wavy blade passive flow control

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Aerodynamic performance enhancement analysis of horizontal axis wind turbines using a passive flow control method via split blade

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JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 2017年 167卷 148-159页

作者： Moshfeghi, Mohammad Shams, Shahrokh Hur, Nahmkeon Sogang Univ CFD Engn Res Ctr Seoul 121742 South Korea Univ Tehran Fac New Sci & Technol Dept Aerosp Engn Tehran 439955941 Iran Sogang Univ Dept Mech Engn Seoul 121742 South Korea

Horizontal axis wind turbines (HAWTs) are being widely used for green energy generation. Hence, aerodynamic performance enhancement of these machines is a key point for their overall performances. This paper numerically investigates effects of a passive flow control method on aerodynamic performance of a HAWT by splitting its blades along the span. First, 2-D simulations are conducted on 5809 airfoil in order to study effects of split width and Reynolds. Later, original blade (without split) and two split blades are simulated, and effects of split location on power coefficient, low speed shaft torque and flow patterns are investigated at different tip speed ratios. The results reveal that for an attached flow, torque value are sensitively dependent upon split location and injected flow angle. This is because injected flow triggers an early separation and reduces aerodynamic performance. For a partially separated case, results show that split location may impose either positive or negative effects on torque generation. Finally, for highly separated/stall situations, blade aerodynamic performance becomes less sensitive to the location of split. Also, torque per unit span analysis shows that as tip speed ratio decreases the split part of the blade generates a higher share of the total power.

关键词： Split blade passive flow control Horizontal axis wind turbine NREL Phase VI

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Investigation of passive flow control on the bluff body with moving-belt experiment

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INTERNATIONAL JOURNAL OF AERONAUTICAL AND SPACE SCIENCES 2016年第2期17卷 139-148页

作者： Rho, Joo-Hyun Lee, Dongho Kim, Kyuhong Hyundai Rotem Co R&D Ctr High Speed Train Dev Team Uiwang 16082 South Korea Seoul Natl Univ Dept Mech & Aerosp Engn Seoul 34818 South Korea Seoul Natl Univ Dept Mech & Aerosp Engn Inst Adv Aerosp Technol Seoul 34818 South Korea

The passive control methods such as horizontal and vertical fences on the lower surface of the bluff body were applied to suppress the vortex shedding and enhance the aerodynamic stability of flow. For investigating the effects of the passive control methods, wind tunnel experiments on the unsteady flow field around a bluff body near a moving ground were performed. The boundary layer and velocity profiles were measured by the Hot Wire Anemometer (HWA) system and the vortex shedding patterns and flow structures in a wake region were visualized via the Particle Image Velocimetry (PIV) system. Also, it is a measuring on moving ground condition that the experimental values of the critical gap distances, Strouhal numbers and aerodynamic force FFT analyses. Through the experiments, we found that the momentum supply due to moving ground caused the vortex shedding at the lower critical gap distance rather than that of fixed ground. The horizontal and vertical fences increase the critical gap distance and it can suppress the vortex shedding. Consequently, the stability characteristics of the bluff body near a moving ground could be effectively enhanced by the simple passive control such as the vertical fences.

关键词： passive flow control Moving belt experiment Vortex shedding

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THE IMPROVEMENT OF DRAG FORCE ON A TRUCK TRAILER VEHICLE BY passive flow control METHODS

ISI BILIMI VE TEKNIGI DERGISI-JOURNAL OF THERMAL SCIENCE AND...

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ISI BILIMI VE TEKNIGI DERGISI-JOURNAL OF THERMAL SCIENCE AND TECHNOLOGY 2016年第1期36卷 133-141页

作者： Akansu, Yahya Erkan Bayindirli, Cihan Seyhan, Mehmet Nigde Univ Muhendisl Fak Makina Muhendisligi Bolumu TR-51240 Nigde Turkey Nigde Univ Nigde Tekn Bilimler Meslek Yuksekokulu Motorlu Araclar & Ulastirma Teknol Bolumu TR-51240 Nigde Turkey Karadeniz Tech Univ Muhendisl Fak Makina Muhendisligi Bolumu TR-61080 Trabzon Turkey

In this study, the drag force measurements were carried out for a 1/32 scaled heavy vehicle model, consisted of truck and trailer, placed in the wind tunnel. The wind tunnel tests were also performed for 9 different free stream velocities in the range of Reynolds number between 113 000 and 453 000. The drag coefficients (CD) of the truck and trailer combination were experimentally determined. In the experimental studies, kinematic similarity was provided except moving road and blockage effect is ignored due to the small blockage ratio of 3%. The independence of Reynolds number was used for the dynamic similarity condition. The regions forming aerodynamic resistance on the truck trailer were determined and aerodynamic improvement was obtained with passive flow control methods. In the case of model 1 of truck and trailer, the aerodynamic improvement is obtained as % 15,71 by improving geometry of spoilers. % 22,46 aerodynamic improvements is also obtained by using passive air channel with a spoiler for the case of model 2. For the case of model 3, by adding a redirector to the model 2, the improvement is reached to % 25,58.

关键词： The drag force coefficient passive flow control air channel redirector wind tunnel

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