混流泵非均匀轮缘间隙流场数值计算

Numerical Calculation of Internal Flow Field in Mixed-flow Pump with Non-uniform Tip Clearance

摘要:

为了研究非均匀轮缘间隙下混流泵叶轮内部流场，基于RNG k—ε模型，采用SIMPLEC算法对混流泵在0、0.3、0.5mm偏心距下的内流场进行数值模拟，对比分析了有、无偏心状态下混流泵外特性、叶片表面静压分布、周向压力和湍动能分布以及轮缘间隙流场的流线分布。研究结果表明，数值模拟采用的网格类型、湍流模型能够较为准确地计算混流泵的内部流动特性。0.5mm偏心距下混流泵扬程最大下降了9.8%，设计工况点效率下降了4.3%，高效点向大流量偏移；偏心对混流泵叶轮进出口压力分布影响较大，靠近偏心一侧的叶片出口轮缘处压力分布呈现沿径向梯度分布趋势且周向压力分布严重不均；非均匀轮缘间隙严重干扰了端壁区流场，使轮缘间隙流场的泄漏流、二次流等不稳定流动现象明显增多，湍动能耗散随着偏心距增大不断加剧，水力损失增大，是造成效率下降的主要因素。

Abstract:

In order to study the impeller internal flow field of the mixed-flow pump with nonuniform tip clearance, the internal flow field in mixedflow pump with two eccentricities which were 0, 0.3mm and 0.5mm was numerically simulated based on the standard RNG k—ε turbulence model and SIMPLE algorithm. Besides, the external characteristic, static pressure distribution on blade surface, tangential pressure, turbulent kinetic energy distribution and streamline distribution near the tip clearance of mixed-flow pump were compared under the conditions with or without eccentricity. The results showed that the type of numerical simulation grid and the turbulence model can accurately predict the internal flow characteristics of the mixed-flow pump. The maximum decrease of head in mixed-flow pump was 9.8%, the efficiency at the design point in mixed-flow pump was dropped by 4.3% and the high efficient point was swung to the large flow rate when eccentricity e was 0.5mm. The pressure distribution of inlet and outlet of mixedflow pump impeller was affected greatly by eccentric, and pressure distribution near the eccentric side of the blade outlet flange showed a trend which was gradient distribution along the radial and circumferential pressure distribution was greatly imbalanced. Non-uniform tip clearance seriously interfered with the end wall region flow, which led to the unsteady flow phenomenon of the leakage flow and the secondary flow in the flow field of the tip clearance was obviously increased, the turbulent kinetic energy dissipation was increased with the increase of eccentricity and hydraulic loss, which was the main factor resulting in a decline in the efficiency of mixed-flow pump. The research results had reference meaning for revealing the internal flow characteristics of impeller in mixed-flow pump with non-uniform tip clearance.