液力变矩器空化数值模拟及对性能的影响

Numerical simulation of cavitation in torque converter and analysis of its influence on performance

基于计算流体动力学,从是否考虑空化两个角度分别数值模拟液力变矩器流场并绘制外特性曲线,通过试验验证仿真结果准确性。为了深入剖析空化对于液力变矩器内/外特性的影响规律,基于Q准则涡识别方法提取三维涡结构特征,分析低速比工况下各叶片表面空化特征动态演化规律,重点研究导轮叶片处空化现象,阐明空化对流场时空结构分布及能量损耗的影响机理。结果表明:①考虑空化的数值模拟与试验结果吻合度高,外特性预测误差在3%以内;②不考虑空化的数值模拟结果中泵轮转矩系数与试验数据误差较大,启动工况下误差在20%以上,仿真结果严重失真;③泵轮转速为2000 r/min时,速比为0.4的工况是空化消失的临界点,随着速比降低,空化现象及其影响越发明显。研究结果可为液力变矩器高精度数值模拟提供理论指导。

The flow field in torque converter is numerically simulated based on computational fluid dynamics,and the external characteristic curves are drawn from the two perspectives of whether cavitation is considered or not.The accuracy of simulation results is verified by experiment.In order to deeply analyze the cavitation of torque converter for the influence law of internal and external characteristic,Q criterion of vortex identification method is used to extract the internal three-dimensional vortex structure characteristic.The dynamic evolution law of cavitation characteristic on each blade surface under low-speed ratio conditions is analyzed and clarified,and the cavitation phenomenon on stator blade is mainly studied,and the influence mechanism of cavitation phenomenon on spatiotemporal structure distribution of flow field and energy loss is analyzed and revealed.The results show that:①The numerical simulation considering cavitation is in good agreement with the experimental results,and the prediction error of external characteristics is less than 3%;②There is a large error between the torque coefficient of the pump and the test data in the numerical simulation results without considering cavitation,and the error is more than 20%on the braking condition,simulation results are seriously distorted;③When pump speed is 2000 r/min,the condition of 0.4 speed ratio is the critical point of cavitation disappearance,with the reduction of the speed ratio,cavitation phenomenon and its influence become more obvious.The research results can provide theoretical guidance for high precision numerical simulation of torque converter.