离心泵汽蚀非稳定流动特性数值模拟

Numerical Simulation on Cavitation Unsteady Characteristics in Centrifugal Pump

为研究离心泵发生汽蚀时流道内部变化规律,通过三维软件Pro/E对离心泵内部流道进行三维造型,利用雷诺时均N-S方程和RNG k-ε两方程及SIMPLEC算法,采用全空化模型并考虑水中未溶解气体对空化的影响,应用计算流体力学软件CFX对离心泵全流道内的气液两相湍流进行了数值模拟计算,分析了离心泵内部发生汽蚀时的非定常流动的规律。结果表明:在汽蚀初生到临界汽蚀余量这一区间范围内,气体体积分数主要集中在无量纲径向位置为0.2附近的一段区间内。随着汽蚀余量的降低,气体体积分数的密度会相应地增加,受叶轮和蜗壳的耦合作用呈现不对称分布,在汽蚀初生时叶轮流道内压力波动呈正弦周期性变化。随着汽蚀余量的降低和气体分数的增加,叶轮流道内压力呈现不规则变化,压力脉动从隔舌处开始沿着叶轮旋转方向逐渐衰落。

In order to study internal flow variation when centrifugal pump cavitations occur, three-dimensional modeling was used for centrifugal pumps internal flow through three-dimensional software Pro/E. Based on the Reynolds-averaged N -S equations with the RNG k-ε turbulence model and SIMPLEC algorithm, the full-cavitation model was used considering effects on cavitations when the gas was not dissolved in the water. By using the computational fluid dynamics software CFX, the numerical simulation calculation of vapor-liquid two-phase turbulence within whole flow passage of centrifugal pump was conducted and the laws of the unsteady flow when centrifugal pump cavitations occur were analyzed. The results show that within this range from the newborn to the critical cavitations NPSH, the gas volume fraction mainly begins from dimensionless radial position 0.2, and the gas volume fraction density correspondingly increases with the lower of NPSH. Affected by asymmetry distribution under the effect of the impeller and volute coupling, in the newborn of cavitations, impeller pressure fluctuations were sinusoidal periodic variation. With the lower of NPSH and gas volume fraction increasing, impeller pressure is changing irregularly. From the beginning of the tongue, along the impeller rotating direction, pressure fluctuation gradually declines.