基于修正PANS模型的轴流泵空化特性数值模拟

为了研究轴流泵空化问题,利用CFX软件二次开发技术对湍流模型进行了修正,通过编写CCL语言实现了PANS模型中参数f_k的动态定义,使其可以瞬时地根据当地网格条件和湍流长度尺度修改其值;利用修正后的湍流模型对轴流泵全流道进行空化数值计算,得出临界汽蚀余量为5.37 m,经试验可知实际临界汽蚀余量为5.68 m,两者误差是由试验条件及试验系统引起的,且在合理范围内,并通过拍摄空泡图验证了该湍流模型在轴流泵空化计算中的可靠性.分析数值计算结果,得出了不同工况下轴流泵的空化特性,随着汽蚀余量的减少,轴流泵叶轮内空泡体积分数变大,涡量变大,叶片表面压力和流速在空泡产生和溃灭的位置处发生相应波动;随着流量的增大,轴流泵临界汽蚀余量减少,空泡分布的整体量变大,叶轮内部湍动能值变大,湍流耗散变严重,与空化的发生溃灭有直接关系.

Cavitation characteristics of axial-flow pump based on modified partially-averaged Navier-Stokes model

In order to study the cavitation problem of axial flow pumps, the secondary development technology of CFX software was used to modify the turbulence model, and realize the dynamic definition of the parameter f_k in the PANS model by writing CCL language, so that it can be defined according to local grid conditions and turbulence lengths. The revised turbulence model was used to numerically calculate the cavitation in the entire flow channel of the axial-flow pump. According to the calculation results, the critical NPSH of the axial flow pump was 5.37 m. The test shows that the actual critical NPSH is 5.68 m, and the error between the two is caused by the test conditions and the test system, and is within a reasonable range. And the reliability of the turbulence model in the cavitation calculation of the axial flow pump was also verified by taking the cavitation diagram in the test. By analyzing the numerical calculation results, the cavitation characteristics of the axial flow pump under different working conditions were obtained. As the decrease of NPSH, the volume fraction of cavitation in the impeller of the axial flow pump increases, the vorticity increases, and the surface pressure and flow velocity of the blade fluctuate correspondingly at the position where the cavitation occurs and collapses. With the increase of flow rate, the critical NPSH of axial flow pump decreases, the overall amount of cavitation distribution becomes larger, the value of turbulent kinetic energy inside the impeller becomes larger, and the turbulent flow dissipation becomes serious, which is directly related to the occurrence and collapse of cavitation.