含气率对液力透平影响的非定常分析

为了研究含气率对液力透平内部压力的影响，以比转速为84.5的单级单吸离心泵反转作液力透平并对其内部流场进行CFD瞬态数值模拟，获得了气体在液力透平内的分布规律以及气液两相介质下透平内部流场的压力脉动变化规律。结果表明:从蜗壳进口到叶轮出口,含气率逐渐增加，含气率等于0.2时蜗壳出口、叶轮进口气体的尾迹效应明显，分布不够均匀。叶轮出口有气体聚集现象，气体体积分数越高，聚集现象越明显。进口含气率对透平蜗壳、叶轮内各点的相对压力分布影响明显，各点的相对压力随着透平进口含气率增加而降低。含气率小于0.05时其对透平内各监测点的压力脉动主频幅值影响不大，含气率大于0.05后其对液力透平内各监测点的压力脉动主频幅值有影响，含气率越高，压力脉动主频幅值越小。不同含气率下液力透平蜗壳周向、径向以及叶轮内的压力脉动主频均等于叶轮叶片的转动频率。 

Unsteady analysis of effect on hydraulic turbine under variable gas content

In order to study the effect of gas content on the internal pressure in hydraulic turbine,CFD technology was used to simulate the flow field in a pump with the specific speed of 84.5 as turbine,the distribution of gas and the effect of gas content on pressure fluctuation in hydraulic turbine were clarified.Results showed that from volume inlet to impeller outlet,the gas content increased gradually,when the gas content was equal to 0.2,the gas distribution was not uniform,and in volume outlet and impeller inlet the wake effect was obvious.The gas gathered in impeller outlet,the higher gas rate indicated the more obvious gathering phenomenon.The influence of gas content on the distribution of relative pressure was obvious,the relative pressure of each point in hydraulic turbine decreased with the increase in gas rate.The gas content had little effect on the pressure fluctuation amplitude of the monitored point at the main frequency when the inlet gas content was less than 0.05,but when the inlet gas content was greater than 0.05,the effect was obvious.The bigger gas content meant the smaller pressure fluctuation frequency amplitude.In different gas content the main frequencies of pressure fluctuation in turbine volute and impeller were equal to the rotation frequency of the impeller blades.