泵轮叶片削剪对液力变矩器性能的影响

削剪泵轮叶片是优化液力变矩器性能的一种手段。为了研究泵轮叶片削剪程度对液力变矩器性能的影响规律，该研究基于计算流体动力学，采用应力混合涡湍流模型（stress-blended eddy simulation，SBES）对液力变矩器内部流场进行仿真模拟，依托外特性试验验证仿真结果的准确性。通过Q准则涡识别方法，甄选合适阈值重构叶片削剪前后泵轮流道三维涡系结构，定性分析多尺度涡动力学特性，量化提取二维流场图谱信息，揭示流速场时空演化规律。结果表明：泵轮叶片设计流线从出口处经过10%、20%和30%的削剪后，液力变矩器的变矩比逐渐增大，由原型变矩器的1.77增大到叶片削剪30%的2.33，泵轮转矩系数降幅明显，由原型变矩器的5.51降低到叶片削剪30%的3.39，叶片削剪10%后变矩比增大4.34%，泵轮转矩系数降低10.73%，降幅明显；随着泵轮叶片削剪程度加剧，叶片对流体的推动作用减弱，流体动能减小，多尺度涡运动趋势衰减，流道中部涡结构特征改变，流道出口高能小尺度“脱落涡”现象减弱；泵轮流道出口流速随叶片削剪程度增大而减小，由原型变矩器的23 m/s降低到叶片削剪30%的19 m/s，泵轮进口流速几乎不变，因进出口流速的变化，泵轮转矩系数降低。研究结果可为液力变矩器叶片设计与性能优化提供指导性建议。

Effects of pump blade cutting on the performance of a hydraulic torque converter

This study aims to investigate the impact of different cutting schemes on the internal flow field and external characteristics of the impeller blade in the hydraulic torque converter pump. A systematic analysis was carried out to explore the evolution of vortex structure and energy conversion. The internal flow field was also numerically simulated in the automotive punch-welded hydraulic torque converter under different cutting schemes using computational fluid dynamics and stress-blended eddy simulation (SBES). The accuracy of the simulation was verified using external characteristic experiments. A full channel model was established after that. The weights of blades were cut by 10%, 20%, and 30% than before in the hydraulic torque converter pump. The optimal threshold was selected to reconstruct the three-dimensional vortex structure using Q-criterion vortex identification. The feature extraction was also performed on the internal three-dimensional vortex structure in the pump wheel flow channel under different cut schemes. The multi-scale vortex dynamics were qualitatively analyzed in this case. The two-dimensional flow field was intercepted at different spatial positions. The flow map was then quantitatively extracted from the flow velocity field, in order to reveal the spatiotemporal evolution of the multi-scale flow field. Qualitative and quantitative interactive analysis was used to clarify the influence of the cut degree of the pump impeller blade on the internal/external characteristics of the hydraulic torque converter. The results show that the torque ratio of the pump impeller blade gradually increased after three cuts of 10%, 20%, and 30% on the pump impeller blade, particularly from 1.77 of the prototype hydraulic torque converter to 2.33 of the 30% cutting. By contrast, the torque coefficient of the pump wheel significantly decreased, from 5.51 of the prototype torque converter to 3.39 of the 30% cutting. Once the pump impeller blade was cut by 10%, the torque ratio of the hydraulic torque converter only increased by 4.34%, but the torque coefficient of the pump decreased by 10.73%. A better performance was achieved to reduce the torque coefficient of the pump. When the pump blade was cut by 20% and 30%, the torque ratio of the hydraulic torque converter increased by 16.78%, and 7.81%, respectively, whereas, the torque coefficient of the pump decreased by 18.88% and 15.08%, respectively. Furthermore, the area and thrust of pump impeller blades, and the kinetic energy of the fluid decreased, as the cutting degree of pump impeller blades increased, indicating the weak trend of multi-scale vortex motion. Some changes were found in the vortex structure in the middle of the flow channel, with the gradual weak merging of multi-scale vortices. There was also the weak high-energy small-scale vortex shedding at the outlet of the pump impeller flow channel. In the two-dimensional flow field, the outlet velocity of the impeller channel decreased with the increase of blade cutting degree, from 23 m/s in the prototype to 19 m/s in the impeller blade cutting of 30%. The inlet flow velocity of the pump impeller channel remained basically unchanged, while there was the slight reduction in the high and low flow velocity area at the turbine channel inlet. The low flow velocity area of the suction surface was reduced in the stator, where the average flow velocity decreased from 22% of the prototype to 16 m/s when the pump impeller blade was cut by 30%. The flow velocity of the channel changed significantly under blade cutting, resulting in a decrease in the torque coefficient of the pump impeller. This finding can provide some guiding suggestions for the design and performance optimization of hydraulic torque converter blades.