侧流道泵叶轮轴径向间隙内流动特性数值模拟与验证

Numerical simulation and verification on flow characteristics of impeller axial and radial gaps in side channel pump

为了研究侧流道泵叶轮周围间隙质量流量交换规律,该文利用数值计算方法研究了侧流道泵在最高效率工况点下叶轮间隙处的流动规律,具体分析了其脉动扬程、交换质量流量、间隙处压力脉动情况、轴向速度变化等。结果表明,每旋转一个叶轮流道（18°）,扬程出现一次完整的波动周期,每个周期内扬程最大值与最小值相差0.07 m左右;间隙外缘监测点的瞬时压力值明显大于其他4个监测点,顶部监测点压力值最大,在整个周期内的平均压力值大约是最小压力监测点的2.8倍;右侧间隙靠近外缘处的流体交换最激烈,该处速度绝对值最大;流体主要是在右侧间隙外缘大约0.8-1倍间隙半径处向侧流道流入,在0.53-0.8倍间隙半径处从侧流道流出至叶轮中;净交换流曲线近似呈三角函数图像变化,交替出现减小增大反复趋势,并且净交换流的波动导致侧流道泵扬程曲线的波动。该研究可为进一步提高侧流道泵的水力性能提供理论依据。

Side channel pump is a kind of vane pump and has a small volume with low flow rate but high head. The specific speed of the pump is super low and usually it is used in the occasions that centrifugal pumps can’t meet the requirements. In order to analyze the exchange mass flow in the gap between the impeller and the side channel, numerical calculation was applied to investigate flow characteristics in the gap under the operating condition with the highest efficiency in this paper. After simulating through commercial software CFX14.5, the head pulsation, exchange mass flow, pressure fluctuation and axial velocity in the gap were obtained in detail. At last, the hydraulic performance of the side channel pump was tested, and a comparison of hydraulic performance between simulation and test results was applied. Overall good agreement between the two results could be observed and the comparison verified the validity in simulating the flow characteristics of the impeller axial direction and radial gaps in the side channel pump. The simulation results showed that there was a fluctuation circle of the head when the impeller rotated by 18° and the head difference between maximum and minimum was about 0.07 m. The circulation flow between side channel and impeller changed in circumferential direction. One indicator for the form of the circulation flow was the exchange mass flow. The exchange mass flow under the maximum head operating condition was larger than that under the minimum head operating condition. Through the exchange mass flow’s distributions in the right gap between the impeller and the side channel, it could be found that the fluid flowed from the impeller to the side channel in the outer radius of the right gap, and it flowed from the side channel to the impeller in the inner radius of the right gap. The transient pressure near the outer radius of the gap was larger than that in the inner radius, and the average maximum pressure was 2.8 times larger than the average minimum pressure during the whole rotating circle. It showed that the total pressure in the right gap increased sequentially along the direction of impeller rotation and in comparison, the pressure rose stronger in circumferential direction under the maximum head operating condition than under the minimum head operating condition. Because of circumferential flow, many vortexes were generated near the inlet of the impeller. The radial vortex affected the flow pattern of the side channel pump inevitably but the axial vortex was good for the energy transfer. Under the minimum head operating condition the streamlines were scattered more greatly than those under the maximum head operating condition, so it caused more flow loss during the pump’s operation. As the flow exchange was the strongest in the outer radius of the right gap, the absolute value of velocity here was the largest, while the velocity in the left gap and inner radius kept an extreme small value. Net exchange flow decreased and increased alternatively like a trigonometric function image during the period of rotating circle, and the fluctuation of exchange flow led to the head pulsation of the side channel pump. The research results can provide a theoretical reference for improving the hydraulic performance of side channel pumps.