类后视镜钝体尾迹分析
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摘要
后视镜是汽车前侧窗区域重要的气动噪声源,认识后视镜尾迹特征对研究后视镜气动噪声的产生机理有重要意义.搭建类后视镜钝体尾迹风洞试验平台,通过表面油流、热线风速仪和粒子成像测速仪(Particle Image Velocimetry,PIV)测量了类后视镜钝体的时均和瞬时尾迹.通过本征正交分解(Proper Orthogonal Decomposition,POD)识别后视镜尾迹中的大尺度相干结构.试验结果表明:受有限长度特征影响,后视镜尾迹与有限长柱体的尾迹特征类似,尾迹中存在交替涡脱落,尾迹涡脱落特征频率小于0.2.受端部下洗气流的影响,尾迹涡脱落特征频率在流向和展向分布不均.POD分析结果验证了交替涡脱落的存在,交替的涡脱落导致了尾迹回流区的流向和展向振荡现象.因此,后视镜尾迹与有限长柱体的尾迹类似,尾迹涡脱落主要受有限长特征的影响.
Rearview mirror is an important source of aerodynamic noise in the front window area of the car. It is of great significance to study the characteristics of the wake of rearview mirror to understand the mechanism of aero-dynamic noise of rearview mirror. The wind tunnel test platform was built to measure the time-averaged and instan-taneous wake of the rearview mirror bluff body by surface oil streamline, hot wire anemometer, and Particle Image Velocimetry(PIV). Proper Orthogonal Decomposition(POD)was used to identify the large-scale coherent structures in the wake of the rearview mirror. The experimental results show that, due to the finite length feature, the wake of the rearview mirror is similar to that of the finite-length cylinder. Alternating vortex shedding exists in the wake,whose characteristic frequency is less than 0.2. Under the influence of the downwash airflow at the top end, the char-acteristic frequency of the vortex shedding is unevenly distributed in the streamwise direction and the spanwise direction. The POD analysis results verify the existence of alternating vortex shedding, which leads to the streamwise and spanwise oscillation of the wake recirculation zone. Therefore, the wake of the rearview mirror is similar to that of the finite length cylinder, and the wake vortex shedding is mainly affected by the finite length characteristics.
Rearview mirror is an important source of aerodynamic noise in the front window area of the car. It is of great significance to study the characteristics of the wake of rearview mirror to understand the mechanism of aero-dynamic noise of rearview mirror. The wind tunnel test platform was built to measure the time-averaged and instan-taneous wake of the rearview mirror bluff body by surface oil streamline, hot wire anemometer, and Particle Image Velocimetry(PIV). Proper Orthogonal Decomposition(POD)was used to identify the large-scale coherent structures in the wake of the rearview mirror. The experimental results show that, due to the finite length feature, the wake of the rearview mirror is similar to that of the finite-length cylinder. Alternating vortex shedding exists in the wake,whose characteristic frequency is less than 0.2. Under the influence of the downwash airflow at the top end, the char-acteristic frequency of the vortex shedding is unevenly distributed in the streamwise direction and the spanwise direction. The POD analysis results verify the existence of alternating vortex shedding, which leads to the streamwise and spanwise oscillation of the wake recirculation zone. Therefore, the wake of the rearview mirror is similar to that of the finite length cylinder, and the wake vortex shedding is mainly affected by the finite length characteristics.
引文
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[17] WANG H F,CAO H L,ZHOU Y. POD analysis of a finite-lengthcylinder near wake[J]. Experiments in Fluids,2014,55(8):1790.
[2]李启良,杨志刚,王毅刚.汽车后视镜气动噪声的影响参数[J].同济大学学报(自然科学版),2011,39(8):1204—1207.LI Q L,YANG Z G,WANG Y G. Influence parameters of aerody-namic noise for automotive rearview mirror[J]. Journal of TongjiUniversity(Natural Science),2011,39(8):1204—1207.(In Chi-nese)
[3]陈鑫,冯晓,沈传亮,等.车外后视镜造型对气动噪声影响的实验研究[J].汽车工程,2017,39(2):206—213.CHEN X,FENG X,SHENG C L,et al. An experimental study onthe effects of exterior rearview mirrors styling on aerodynamic noise[J]. Automotive Engineering,2017,39(2):206—213.(In Chinese)
[4] CHEN K H,JOHNSON J,DIETSCHI U,et al. Wind noise measure-ments for automotive mirrors[J]. SAE International Journal of Pas-senger Cars-Mechanical Systems,2009,2(1):419—433.
[5]杨博,胡兴军,张英朝.汽车后视镜区域非定常流场与气动噪声研究[J].机械工程学报,2010,46(22):151—155.YANG B,HU X J,ZHANG Y C. Study on unsteady flow field andaerodynamic noise of the automobile rearview mirror region[J].Journal of Mechanical Engineering,2010,46(22):151—155.(InChinese)
[6]杨博,傅立敏.稳态数值模拟在轿车外气动噪声源预测中的应用[J].吉林大学学报(工学版),2007,37(5):1005—1008.YANG B,FU L M. Application of steady state numerical simulationto prediction of sedan exterior aeroacoustic sources[J]. Journal ofJilin University(Engineering and Technology Edition),2007,37(5):1005—1008.(In Chinese)
[7] CHEN K H,JOHNSON J,DIETSCHI U,et al. Automotive mirrorwind noise simulations and wind tunnel measurements[C]//14th A-IAA/CEAS Aeroacoustics Conference. Vancouver,DOI:10.2514/6.2008—2906.
[8] BUSCARIOLO F F,ROSILHO V. Comparative CFD study of out-side rearview mirror removal and outside rearview cameras propos-als on a current production car[C]//22nd SAE Brasil InternationalCongress and Display.Warrendale,PA:SAE,2013:2013-36-0298.
[9] HOELD R,BRENNEIS A,EBERLE A,et al. Numerical simulationof aeroacoustic sound generated by generic bodies placed on aplate. I-Prediction of aeroacoustic sources[C]//5th AIAA/CEASAeroacoustics Conference and Exhibit.Bellevue,DOI:10.2514/6.1999—1896.
[10]SIEGERT R,SCHWARZ V,REICHENBERGER J. Numerical sim-ulation of aeroacoustic sound generated by generic bodies placed ona plate. II-Prediction of radiated sound pressure[C]//5th AIAA/CEAS Aeroacoustics Conference and Exhibit. Bellevue,DOI:10.2514/6. 1999—1895.
[11]王汉封,邹超,王启文,等.均匀流中悬臂圆柱体气动力雷诺数效应[J].湖南大学学报(自然科学版),2015,42(5):65—71.WANG H F,ZOU C,WANG Q W,et al. Reynolds number effectson the aerodynamic forces of a cantilevered circular cylinder in uni-form flow[J]. Journal of Hunan University(Natural Sciences),2015,42(5):65—71.(In Chinese)
[12] FREDSOE J,SUMER B M. Hydrodynamics around cylindricalstructures[M]. London:World Scientific,1997:10.
[13]SIROVICH L. Turbulence and the dynamics of coherent structures.[J]. Quarterly of Applied Mathematics,1987,45(3):561—590.
[14]MEYER K E,PEDERSEN J M,OZCAN O. A turbulent jet in cross-flow analysed with proper orthogonal decomposition[J]. Journal ofFluid Mechanics,2007,583:199—227.
[15]NOACK B R,MORZYNSKI M,TADMOR G. Reduced-order mod-elling for flow control[M]. Italy:Springer,Vienna,2011:121—124.
[16]NOACK B R,AFANASIEV K,MORZYNSKI M,et al. A hierarchyof low-dimensional models for the transient and post-transientcylinder wake[J]. Journal of Fluid Mechanics,2003,497:335—363.
[17] WANG H F,CAO H L,ZHOU Y. POD analysis of a finite-lengthcylinder near wake[J]. Experiments in Fluids,2014,55(8):1790.