基于整车风洞试验的MIRA车型数值计算
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摘要
为了明确稳态数值计算对于整车气动力,特别是车身表面压力的预测能力,首先以全尺寸MIRA车型整车风洞试验数据为基准,进行网格方案研究并得出结论、车身面网格为10mm、5层边界层网格且第1层网格无量纲高度Y+=30可以满足网格无关性要求。然后,基于该网格方案进行数值计算后得到:无偏航工况下,阻力系数CD与试验值误差为0.34%,升力系数CL误差为1.06%;3°～20°偏航工况下,CD和侧向力系数CS误差分别不超过5%和9%,表明气动力计算准确性较高;车身表面254个测压点中,压力系数CP预测误差大于50%的测点个数基本不超过20%,其中误差较大的测点主要位于车身底部以及背风侧等流动较为复杂的区域。
The prediction capability of steady numerical simulation on aerodynamic forces and surface pressure of generic vehicles was clarified. First,a detailed study on mesh scheme for MIRA reference car model was carried out with baseline data derived from full-scale wind tunnel test. Results show that the gridindependent strategy requires 10 mm for car surface mesh,Y+=30 for the first layer grid and 5 layers around the car. Based on this mesh scheme,aerodynamic force calculation of MIRA model could yield satisfactory predictions,that at 0° yaw,the error of drag coefficient CDfrom test data was 0.34%,error of lift coefficient CL1.06%,and at 3° ～20° yaw conditions,error of CDand side force coefficient CSwere respectively no more than 5% and 9%,which indicate the reliability of aerodynamic forces computation for simplified cars like MIRA model. For surface pressure,of all 254 pressure taps all over the car,error of CP over 50% are less than 20%,while surface pressure was poorly calculated mostly where flow is so complicated that separation or reattachment tends to happen,such as the underbody and the leeward side..
The prediction capability of steady numerical simulation on aerodynamic forces and surface pressure of generic vehicles was clarified. First,a detailed study on mesh scheme for MIRA reference car model was carried out with baseline data derived from full-scale wind tunnel test. Results show that the gridindependent strategy requires 10 mm for car surface mesh,Y+=30 for the first layer grid and 5 layers around the car. Based on this mesh scheme,aerodynamic force calculation of MIRA model could yield satisfactory predictions,that at 0° yaw,the error of drag coefficient CDfrom test data was 0.34%,error of lift coefficient CL1.06%,and at 3° ～20° yaw conditions,error of CDand side force coefficient CSwere respectively no more than 5% and 9%,which indicate the reliability of aerodynamic forces computation for simplified cars like MIRA model. For surface pressure,of all 254 pressure taps all over the car,error of CP over 50% are less than 20%,while surface pressure was poorly calculated mostly where flow is so complicated that separation or reattachment tends to happen,such as the underbody and the leeward side..
引文
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[2]姜乐华,谷正气. CFD在汽车空气动力学研究中的应用[J].湖南大学学报, 1997, 24(4):5256.Jiang Lehua, Gu Zhengqi. The application of CFD methods to automobile aerodynamics[J]. Journal of Hunan University, 1997, 24(4):5256.
[3]傅立敏,王靖宇.汽车三维分离流动特性的数值研究[J].汽车工程, 2000, 22(6):361364, 376.Fu Limin, Wang Jingyu. Numerical study of separated flow around afterbody of road vehicle[J]. Automotive Engineering, 2000, 22(6):361364, 376.
[4]严鹏,吴光强,傅立敏,等.轿车外流场数值模拟[J].同济大学学报, 2003, 31(9):10821086.Yan Peng, Wu Guangqiang, Fu Limin, et al. Numerical simulation of flow field around car[J]. Journal of Tongji University, 2003, 31(9):10821086.
[5]吴军,钟志华,谷正气.汽车外流场数值仿真的进一步研究[J].机械工程学报, 2003, 39(9):110113.Wu Jun, Zhong Zhihua, Gu Zhengqi. Further study on numerical simulation of flow around automobiles[J]. Chinese Journal of Mechanical Engineering,2003, 39(9):110113.
[6] Shih T H, Liou W W, Shabbir A, et al. A new kεeddy viscosity model for high Reynolds number turbulent flows:model development and validation[J].Computers and Fluids, 1995, 24(3):227238.
[7]张英朝,薛学栋,丁伟,等.某两厢车气动外形减阻自动优化设计[J].同济大学学报, 2016, 44(11):17711776.Zhang Yingchao, Xue Xuedong, Ding Wei, et al.Automobile shape optimization of hatchback to reduce aerodynamic drag[J]. Journal of Tongji University,2016, 44(11):17711776.
[8]朱晖,杨志刚.两方程模型计算轿车气动性能的适用性研究[J].汽车工程, 2016, 38(11):12831287,1337.Zhu Hui, Yang Zhigang. A study on the applicability of twoequation models to the calculation of aerodynamic performance of Sedan[J]. Automotive Engineering, 2016, 38(11):12831287, 1337.
[9] Ashton N, Revell A. Comparison of rans and des methods for the drivaer automotive body[C]∥SAE Paper, 2015011538.
[10] Palaskar P M, Kumar V, Vaidya R. Methodology development to accurately predict aerodynamic drag and lift for passenger vehicles using CFD[C]∥SAE Paper, 2016011600.
[11] Ahmad N E, AboSerie E, Gaylard A. Mesh optimization for ground vehicle aerodynamics[J]. CFD Letters, 2010, 2(1):5465.
[12] Gaylard A P, Baxendale A J, Howell J P. The use of CFD to predict the aerodynamic characteristics of simple automotive shapes[C]∥SAE Paper, 980036.
[13] Zhang Yingchao, Ding Wei, Zhang Yu. Aerodynamic shape optimization based on the MIRA reference car model[C]∥SAE Paper, 2014010603.
[14] Le G G M, Garry K P. On the use of reference models in automotive aerodynamics[C]∥SAE Paper, 2004011308.
[15] Lawson A A, Dominy R G, SimsWilliams D B, et al. A comparison between onroad and wind tunnel surface pressure measurements on a midsized hatchback[C]∥SAE Paper, 2007010898.
[16] Gu Zhengqi, Song Xin, Jian Yejie, et al. Optimization of the realizable k-εturbulence model especially for the simulation of road vehicle[C]∥SAE Paper,2012010778.
[17] Wang Y, Xin Y, Gu Z, et al. Numerical and experimental investigations on the aerodynamic characteristic of three typical passenger vehicles[J]. Journal of Applied Fluid Mechanics, 2014, 7(4):659671.
[18]龚旭,谷正气,李振磊,等.侧风状态下轿车气动特性数值模拟方法的研究[J].汽车工程, 2010, 32(1):1316.Gong Xu, Gu Zhengqi, Li Zhenlei, et al. A study on the numerical simulation of car aerodynamic characteristics under crosswind conditions[J]. Automotive Engineering, 2010, 32(1):1316.