离心泵汽蚀过渡过程瞬态特性分析

Analysis on Transient Hydraulic Characteristics of Cavitation Process in Centrifugal Pumps

为了对离心泵汽蚀过渡过程的瞬态水力特性进行分析,采用全汽蚀模型且不考虑水中溶解性气体对汽蚀的影响,再通过计算流体力学软件CFX对离心泵叶轮流道内汽蚀过渡过程进行了数值模拟计算,并与试验结果进行了对比.结果表明:数值模拟结果与试验结果的变化趋势基本一致,汽蚀过渡过程中叶片背面气体体积分数随汽蚀余量的降低而逐渐增大,当叶片工作面的气体体积分数大于0时,汽泡相开始堵塞叶轮流道,进而影响叶轮内部能量的交换和传递;汽蚀引起的旋涡使得叶轮流道内的速度出现无规律波动,从而造成靠近旋涡区和叶片工作面通道内的速度和载荷增大;扬程在随汽蚀余量的降低而缓慢降至一定程度后再次急剧下降,不同工况下扬程波动的幅度有所不同,小流量时扬程波动幅度最大.

The full-cavitation model without considering the effect of the undissolved gas in water on cavitation was applied to study the transient hydraulic characteristics of the cavitation process in centrifugal pumps. The numerical simulation on vapor-liquid two-phase turbulence within whole flow passage of a centrifugal pump was performed by the computational fluid dynamics software CFX, and the comparison between the simulation results and the experimental data was conducted. The results show that the simulation results are in reasonable agreement with the experimental data. In the process of cavitation, the gas volume fraction at the blade back increases with the decrease in net positive suction head （NPSH）. However, when the gas volume fraction at the working surface of the blade is greater than zero, the bubbles begin to clog the impeller channel, thus affecting the energy exchange and transfer in the impeller. The velocity within the impeller fluctuates irregularly due to the vortex caused by cavitation, leading to the increase in the velocity and load near the region of the vortex and in the channel of the blade working surface. Head decreases slowly to a certain extent and then declines sharply with the decrease in NPSH. In addition, the head fluctuation amplitude is different under different conditions and has a maximum value at the lower flow rate.