车身非光滑表面边界层流场特性分析

为了研究非光滑车身表面边界层流场特性,采用大涡模拟与Realizable k-ε湍流模型对车身外部瞬态和稳态流场进行数值模拟计算,对比分析了非光滑模型与光滑模型边界层内速度、粘性底层厚度、壁面剪切力、表面摩擦阻力因数、湍流强度和湍流耗散率等流场参数,解析了非光滑表面对车身流场流动特性的影响.研究结果表明,非光滑模型边界层内速度明显高于光滑模型,边界层厚度、壁面剪切力、表面摩擦阻力因数、湍流强度、湍流耗散率都比光滑模型有所减小.非光滑表面的引入加剧了车身尾迹气流的参混效应,防止外界的高速流对内部低速流的引射作用,从而减少了车身流场能量的损失.

Study on the Characteristics of Non-smooth Car Surface Boundary Flow Field

In order to study the flow field characteristics of a boundary layer on non-smooth car body surface, large eddy simulation and realizable turbulence model were used for the numerical simulation and calculation of external car body flow field in both transient-state and steady-state. Then, the flow field parameters, such as velocity, thickness of viscous sub-layer, wall shear stress, surface friction coefficient, turbulence intensity and turbulence dissipation rate within the boundary layer of both non-smooth and smooth model, were compared and analyzed. The influence of the non-smooth surface upon the flow field characteristics of the car body was analyzed. The results show that the velocity within the boundary layer of the non-smooth model is obviously higher than that of the smooth model, and boundary layer thickness, wall shear stress, local frictional resistance coefficient, turbulence intensity and turbulence dissipation rate are also less than the smooth model. The introduction of non-smooth surface contributes to the mixing effect of the wake flow of the carbody, preventing the ejector effect upon outside high-speed flow to internal low-speed flow, thus reducing the loss of energy of the car body flow field.