轴流式水泵非定常湍流数值模拟的若干关键问题

Some Key Issues of Unsteady Turbulent Numerical Simulation in Axial-flow Pump

为准确捕捉轴流式水泵不稳定流场特征,采用雷诺时均法和大涡模拟方法对轴流泵非定常湍流进行数值模拟,并就相关问题进行深入研究。研究发现,与其他湍流分析方法相比较,大涡模拟方法在轴流泵非定常流场分析中具有更高的计算精度;同时将轴流泵进水流道与泵段一起进行流场计算后,发现叶轮进口的流动是极不均匀的,靠近弯肘形流道内侧的速度明显大于其他部位,这一现象与通常假定的轴流泵进口流动是均匀的设计与分析理论有很大区别。研究还发现,为了获得轴流泵流场内不同压力脉动频率成份,脉动计算的采用样时间应不少于8个旋转周期;轴流泵内部的水压力脉动幅值在叶轮附近区域沿半径逐渐增大,而在导叶出口之后沿半径逐渐减小。

In order to predict the unsteady flow feature in axial-flow pump, the Reynolds-averaged Navier-Stokes （RANS） method and large eddy simulation （LES） method are used to perform the 3D unsteady turbulent simulation. The key issues in the simulation including the turbulence model, interaction between suction box and impeller, pressure fluctuation distribution pattern and pressure amplitude spectrum are investigated. It is found that LES could give more accurate simulation result over other turbulence models. The flow pattern at the suction box outlet is not uniform if the interaction between the suction box and impeller is considered. The velocity at the side of suction box near the inlet is larger than other areas. The ununiformity is quite different from the conventional supposition in which the flow at impeller inlet is considered to be uniform in the design and analysis of axial-flow pump. The investigation also shows that the sampling time should not be less than eight rotating cycles in order to ensure the capture of all the dominated frequencies of pressure fluctuations. The pressure amplitude increases gradually along the radius at the impeller region, and it decreases gradually along the radius after the outlet of guide-vane.