速度环量对大型轴流泵站水力性能的影响

摘要

To study the effect of inner rotational flow on hydraulic performance of large axial-flow pumps caused by cavitation, based on SST (shear−stress transport) k−ωturbulence model, the pumps internal cavitation was described by applying Rayleigh−Plesset model. The rotational flows of pumps under cavitation and non-cavitation condition were calculated by velocity circulation theory, combined with the model pump experimental study. The flow deviation angle (γ) of two different working conditions was compared, and the effect of velocity circulation on the hydraulic performance was discussed. The results show that under the optimal conditions, the head error is 3.58%while the efficiency error is 3.31%, which indicates the correctness of SST k−ωturbulence model, and the critical cavitation pressure (Pc) and fracture cavitation pressure (Pf) are also obtained. Under off design conditions, the cavitation increases the flow deviation angles, the velocity circulation and internal passage hydraulic loss. Under off design conditions, the γ values become large, especially larger at small flow coefficient, the cavitation further increases the flow deviation angles (γ), the velocity circulation and internal passage hydraulic loss, reducing the hydraulic performance of large axial-flow pumps.%为了研究大型轴流泵装置内部由空化引起的有旋流动对机组水力性能的影响，基于 SST(shear−stress transport)k−ω湍流模型，应用Rayleigh−Plesset模型对泵站内部空化进行描述，并用速度环量分别对非空化和空化2种状态的有旋流动进行计算，结合模型泵试验研究等方法对泵内有旋流动进行分析。比较2种工作状态下流体流动偏移角(γ)，研究速度环量对水力性能影响的规律。研究结果表明：在设计工况下，扬程相对误差为3.58%，效率相对误差为3.31%，验证了湍流模型的适用性，并得到泵站装置临界空化压力(Pc)和断裂空化压力(Pf)；在设计工况下，空化会增大流体流动偏移角，增大速度环量，增加内部流道水力损失；在偏离设计工况下，会增大流体流动偏移角(γ)。其中，在小流量系数条件下较大，此时空化进一步增大流动偏移角(γ)，并增加由此引起的速度环量变化量以及进出口流道内部损失，使大型轴流泵站性能下降。