Journal of Jilin University(Engineering and Technology Edition) ›› 2019, Vol. 49 ›› Issue (4): 1043-1053.doi: 10.13229/j.cnki.jdxbgxb20180226

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Aerodynamic calculation of MIRA model correlated with wind tunnel test

Hua ZHOU1,2(),Zhi⁃gang YANG1,2,3(),Hui ZHU1,2   

  1. 1. Shanghai Automotive Wind Tunnel Center, Tongji University, Shanghai 201804, China
    2. Shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal Management Systems, Shanghai 201804, China
    3. Beijing Research Center, Commercial Aircraft Corporation of China, Beijing 102200, China
  • Received:2018-03-22 Online:2019-07-01 Published:2019-07-16
  • Contact: Zhi?gang YANG E-mail:zhouhua0987826@163.com;zhigang.yang@sawtc.com

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Abstract:

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 grid-independent 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 C D from test data was 0.34%, error of lift coefficient C L 1.06%, and at 3°~20° yaw conditions, error of C D and side force coefficient C S were 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 C P 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..

Key words: vehicle engineering, aerodynamic force, surface pressure, numerical simulation, MIRA reference car model, wind tunnel test, mesh scheme, yaw conditions

CLC Number: 

  • U467.1

Fig.1

Schematic diagram of MIRA notchback model dimensions"

Fig.2

Schematic diagram of wind tunnel with an open?jet test section"

Fig.3

MIRA notchback model in the wind tunnel"

Fig.4

Distribution of surface pressure taps"

Fig.5

Static pressure measurement tubes inside the car model"

Fig.6

C D variation with wind speed"

Fig.7

Domain dimensions for numerical simulation"

Table 1

Boundary conditions and parameters setup"

边界条件 参数设置
近壁面处理 非平衡壁面函数
阻塞比/% 1.6
MIRA车型正投影面积/m2 1.858
速度入口/（km·h-1） 80
压力出口 一个标准大气压
MIRA车身表面和地面 固定壁面
计算域侧面和顶面 对称壁面

Table 2

Parameters for grid independence study"

变化参数 变化范围
车身面网格尺寸/mm 5~15
车身表面网格Y +值 30~90
车身边界层网格层数 3~10
体网格数量/万个 1361~3753
网格加密形式 尾部加密和整车加密

Table 3

Error of C D and C L for different surface"

面网格尺寸/mm 网格数/万个 ΔC D/% ΔC L/%
15 884 1.35 8.51
10 1726 -0.34 1.06
7.5 2731 -0.34 -1.06
5 5544 0.68 1.06

Fig.8

Error of C P for different surface mesh size"

Table 4

Error of C D and C L for different wall Y + over the car surface"

车身表面Y + ΔC D/% ΔC L/%
30 -0.34 1.06
45 0 13.83
60 -0.68 26.60
90 -2.03 40.43

Fig.9

Error of C P for different wall Y+ over the car"

Fig.10

C P distribution along upperbody centerline"

Fig.11

C P distribution along underbody centerline"

Table 5

Error of C D and C L for different boundary"

边界层层数 边界层厚度/mm ΔC D/% ΔC L/%
3 3.47 -0.34 6.38
5 6.74 -0.34 1.06
8 13.73 0.68 3.19
10 20.30 1.01 -2.13

Fig.12

Error of C P for different boundary layer mesh"

Table 6

Error of C D and C L for different grid density"

体网格总数/万个 ΔC D/% ΔC L
1361 0 -14.89
1726 -0.34 1.06
2662 0 -4.26
3753 -0.68 1.06

Fig.13

Error of C P for different mesh density"

Fig.14

Different mesh refinement types"

Table 7

Error of C D and C L for different types of mesh refinement"

加密方式 网格数/万个 ΔCD/% ΔCL/%
不加密 1726 -0.34 1.06
尾部加密 2834 -0.34 4.26
整车加密 3621 -0.34 1.06

Fig.15

Error of C P for different types of mesh refinement"

Fig.16

Static pressure distribution on backlight"

Fig.17

Static pressure distribution on boot deck"

Fig.18

Static pressure distribution on rear end"

Fig.19

Hybrid grid pattern at longitudinal symmetric plane of flow domain"

Fig.20

Pressure taps where error of C P>50%"

Fig.21

Wall shear stress streamlines over car model"

Fig.22

Velocity streamlines of flow domain at longitudinal symmetric plane"

Fig.23

Boundary setup under yaw conditions"

Fig.24

Comparison between CFD and test results of C D and C S under yaw conditions"

Fig.25

Pressure distribution over MIRA model and on horizontal plane of Z=0.5 m"

Fig.26

Error of C P under different yaw angles"

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