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LIU Hai-tao. Influence of y+ value on calculation accuracy of aerodynamic parameters of MIRA model[J]. Journal of Traffic and Transportation Engineering, 2019, 19(4): 125-136. doi: 10.19818/j.cnki.1671-1637.2019.04.012
Citation: LIU Hai-tao. Influence of y+ value on calculation accuracy of aerodynamic parameters of MIRA model[J]. Journal of Traffic and Transportation Engineering, 2019, 19(4): 125-136. doi: 10.19818/j.cnki.1671-1637.2019.04.012
shu

Influence of y+ value on calculation accuracy of aerodynamic parameters of MIRA model

doi: 10.19818/j.cnki.1671-1637.2019.04.012

  • School of Mechanotronics and Vehicle Engineering, East China Jiaotong University, Nanchang 330013, Jiangxi, China

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  • Author Bio:

    LIU Hai-tao(1986-), male, lecturer, PhD, liuht_2005@163.com

  • Received Date: 2019-02-15
  • Publish Date: 2019-08-25
    Abstract
  • In order to study the influence of dimensionless parameter y+ value on the calculation accuracy of aerodynamic parameters of vehicles, based on the step-back MIRA model, the size of near-wall grids was adjusted under the condition that the number and quality of model grids were similar, and the flow field simulation models with different y+ values were constructed. Considering that different turbulence models have different applicable ranges of y+ values for the external flow field simulation of vehicles, two common turbulence models of shear stress transmission (SST) κ-ω and large eddy simulation (LES) were selected to simulate the steady and unsteady external flow field of the step-back MIRA model. The simulation results of aerodynamic parameter were compared with the experimental results, and the appropriate ranges of y+ value were obtained. Combining the velocity nephogram and the carbody surface stress curve from the flow field simulation results, the influence of grid thickness of the first layer of boundary layer on the simulation accuracy was analyzed. The external flow field simulation models for the square-back MIRA model under the two turbulence models were established, the aerodynamic parameters were calculated at different flow velocities, and the ranges of y+ value were verified. Analysis result shows that the appropriate average y+ value range of SST κ-ω model is 20-50 for the external flow field numerical simulation of vehicles, and the appropriate average y+ value range of LES model is 5-10. When the thickness of the first near-wall grid of boundary layer is too large, the numerical simulation can not accurately capture the change of velocity gradient in the boundary layer, which leads to the loss of flow information in the flow field of boundary layer. When the thickness of the first near-wall grid is too small, the boundary layer grid will be seriously distorted. In both cases, the calculation errors of aerodynamic parameter exceed 5%, which will affect the numerical simulation accuracy of external flow field of vehicles. According to the obtained ranges of y+ value, the errors of aerodynamic parameter calculated by the square-back MIRA model are less than 5%, which illustrates the correctness of ranges of average y+ value for the two turbulence models.

     

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