| y+值对MIRA模型气动参数计算精度的影响 |
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| 引用本文： | 刘海涛.y+值对MIRA模型气动参数计算精度的影响[J].交通运输工程学报,2019,19(4):125-136. |
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| 作者姓名： | 刘海涛 |
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| 作者单位： | 华东交通大学机电与车辆工程学院,江西南昌,330013 |
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| 基金项目： | 国家自然科学基金项目51765017江西省青年科学基金项目20161BAB216136江西省教育厅科学技术研究项目GJJ150497 |
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| 摘 要： | 为研究量纲为1的参数y+值对车辆气动参数计算精度的影响, 以阶梯背MIRA模型为基础, 在保证模型网格数量与质量相近的情况下调整近壁网格尺寸, 构建不同y+值的流场仿真模型; 考虑到不同的湍流模型对车辆外流场仿真的y+值具有不同的适用范围, 选取SST κ-ω和LES两种常用的湍流模型对阶梯背MIRA模型外流场进行稳态和非稳态仿真分析; 将气动参数仿真结果与试验结果进行对比分析, 得出合适的y+值取值范围; 结合仿真速度云图和车身表面受力曲线分析了边界层首层网格厚度对仿真精度的影响; 建立了方背MIRA模型在2种湍流模型下的外流场仿真模型, 进行不同流速下气动参数的计算, 从而对y+值取值范围进行验证。研究结果表明: 针对车辆外流场数值仿真, 采用SST κ-ω模型时对应的合适平均y+值取值范围为20~50, 而采用LES模型时对应的合适平均y+值取值范围为5~10;当边界层首层近壁网格厚度过大时, 数值仿真无法准确捕捉边界层中速度梯度的变化, 造成边界层流场流动信息丢失, 而当边界层首层近壁网格厚度过小时, 边界层网格会严重畸变, 2种情况下气动参数计算误差都超过5%, 从而影响车辆外流场数值仿真精度; 根据所获得的y+值取值范围, 方背MIRA模型计算的气动参数误差小于5%, 说明了2种湍流模型平均y+值取值范围的正确性。
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| 关 键 词： | 车辆工程 流体数值仿真 y+值 湍流模型 气动参数 MIRA模型 误差分析 |
| 收稿时间： | 2019-02-15 |
Influence of y+ value on calculation accuracy of aerodynamic parameters of MIRA model |
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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. |
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| Authors: | LIU Hai-tao |
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| Affiliation: | School of Mechanotronics and Vehicle Engineering, East China Jiaotong University, Nanchang 330013, Jiangxi, China |
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| 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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