Three-dimensional (3D) unsteady Reynolds-averaged Navier–Stokes (URANS) simulations are conducted to investigate the blade load and internal flow field for a low specific centrifugal pump operating as a turbine (PAT). Validation and grid independence of the simulation method are performed and ensured. A thorough inspection to flow variables in terms of pressure and radial velocity as well as circumferential velocity at strong rotor–stator interaction region is performed. Unsteady performance characteristics in terms of head and shaft power as well as transient blade loads are evaluated to assess the unsteady PAT performance. Significant decreasing of the blade load is revealed when impeller passage passes the volute tongue and associated with the strong vortex close to passage suction side caused by the sharp angle of suction side trailing edge with a discernible flow incidence angle. High negative radial velocity in the region close to suction side is originated from the vortex inducing velocity at the blade suction side and a high pressure gradient in the trailing edge region. The decrease of blade load is caused by periodical development and restriction of the vortex with an impeller passage passing tongue and a subsequent pressure variation on suction side that leads to temporally decreased blade loading. High positive radial velocity in pressure side region is originated from the blocking effect from the strong vortex at suction side, leading to the generation of a relatively weaker vortex fluctuating with impeller rotation at pressure side. That is the source of pressure variation on pressure side, contributing to the blade loading variation. These results provide a detailed insight into the complex overload flow field that might be utilized for an improved PAT design.

中文翻译：

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以非定常叶片载荷为重点的涡轮离心泵超载运行性能数值研究

进行三维 (3D) 非定常雷诺平均 Navier-Stokes (URANS) 模拟，以研究用作涡轮机 (PAT) 的低比离心泵的叶片载荷和内部流场。执行并确保仿真方法的验证和网格独立性。在强转子-定子相互作用区域对压力和径向速度以及圆周速度方面的流动变量进行了彻底检查。评估头部和轴功率以及瞬态叶片负载方面的不稳定性能特征，以评估不稳定的 PAT 性能。当叶轮通道通过涡舌时，叶片载荷显着降低，并与通道吸力侧附近的强涡流相关，该涡流由吸力侧后缘锐角和可识别的流动入射角引起。靠近吸力侧区域的高负径向速度源于叶片吸力侧的涡诱导速度和后缘区域的高压梯度。叶片负载的降低是由于叶轮通道通过舌部的涡流的周期性发展和限制以及随后的吸力侧压力变化导致叶片负载暂时降低。压力侧区域的高正径向速度源于吸力侧强涡的阻挡作用，导致在压力侧产生随叶轮旋转而波动的相对较弱的涡流。这是压力侧压力变化的来源，导致叶片负载变化。这些结果提供了对可用于改进 PAT 设计的复杂过载流场的详细了解。