基于表面粗糙度修正的冷却风扇数值模拟方法研究

为了进一步提高冷却风扇多重参考坐标系(MRF)模型的数值模拟精度,结合壁面函数进行粗糙度修正,并分析MRF模型的影响因素。首先,以黏性底层中第一层网格离壁面的无因次速度u~+与距离y~+相等为依据,得到粗糙度常数、粗糙度高度与y~+之间的代数关系;根据实际壁面类型,得到修正后的y~+值与第一层网格高度,将其带入标准壁面函数进行近壁面修正。最后,以某型号冷却风扇为例,研究湍流模型、网格数量、表面粗糙度修正等因素对风扇数值模拟结果的影响。结果表明,模型可以更好地处理高应变率及流线弯曲程度较大的流动,更适合风扇的旋转流动,对风扇等旋转机械的模拟具有更高的准确性;过密的网格数量会使得计算结果出现波动;表面粗糙度修正改善了性能曲线上的一些畸点,在风扇常用工况范围内,使得试验值与仿真值的偏差由5%降低到修正后的3%以内。

Numericals simulation method of cooling fan based on surface toughness correction

In order to further improve the numerical simulation accuracy of the multi-reference frame(MRF) model of cooling fan, the roughness of the model was modified by the wall function, and the influential factors of the MRF model were analyzed. Firstly, the algebraic relationship among roughness constant, roughness height and y⁺ was obtained based on the dimensionless velocity u⁺ and distance y⁺ of the first layer mesh from the wall in the viscous sublayer. Then, according to the actual wall type, the revised y⁺ value and the first layer mesh height were obtained, and they were substituted into the standard wall function for near wall correction. Finally, taking a cooling fan as an example, the effects of turbulence model, mesh number and surface roughness correction on the numerical simulation results of the fan were studied. The results show that the model can better deal with the flow with high strain rate and bending streamline, and is more suitable for the rotating flow of fans, and has higher accuracy for the simulation of rotating machinery such as fans. Over-dense mesh number will make the calculation results fluctuate. Surface roughness correction improves some abnormal points on the performance curve, and within the range of fan common operating conditions, the deviation between test values and simulation values reduced from 5% to 3% after correction.