工质黏度对导叶式液力透平压力脉动特性的影响

Influence of medium viscosity on pressure pulsation characteristics of pump as hydraulic turbine with guide vane

为探究液力透平内压力脉动受工质黏性的影响,基于雷诺时均N-S方程和标准k-ε湍流模型,以带导叶的离心泵反转作液力透平为研究对象,选取清水及2种黏油作为对比工质进行三维瞬态数值模拟,并对模拟结果进行时域及频域分析.结果表明:清水工质下叶轮部分流道内存在和叶轮同向的非定常涡,而黏油工质下叶轮及尾水管内流场结构显著改善,黏性作用下,动静叶栅的相干作用仍是透平内压力脉动的主因.导叶内的平均压力脉动最强,叶轮内次之,尾水管内相对最弱,且此规律不受工质黏度影响.随着工质黏度的增大,各监测点的压力脉动峰峰值及最大压力脉动幅值均减小,且与导叶、尾水管内各测点主频及次主频幅值的变化趋势均同步,而与蜗壳、叶轮内各测点主频及次主频幅值的变化趋势差异较大,但与二者之和趋势吻合.同时,工质黏度越大,蜗壳、导叶和叶轮内各测点的时均静压越低.

In order to explore the influence of medium viscosity on the pressure pulsation characteri-stics of hydraulic turbine,based on the Reynolds time averaged N-S equation and standard k-εturbulence model,a centrifugal pump with guide vane reversed as turbine(PAT)was chosen as the research object,water and two kinds of viscous oil were taken as the contrast medium,three-dimensional transient numerical simulation was carried out,and then the simulation results were analyzed in the time domain and frequency domain.The results show that there are unsteady vortices with the same direction of rotation as the blade in partial impeller passages under clean water,while the flow field structure of the impeller and draft pipe under viscous oil is significantly improved.Under viscous action,coherent interaction of dynamic and static cascades is still the main inducement for pressure pulsation in the PAT.The mean pressure pulsation in the guide vane is the most intense,followed by the impeller,and the draft pipe is the least,and this law is not affected by the viscosity.With the medium viscosity increasing,the peak-peak value and the dimensionless maximum pressure pulsation amplitude at each monitoring point decrease,which synchronize with the basic frequency amplitude and the secondary basic frequency amplitude at monitoring points in the guide vane and the draft pipe,however,it is quite different from those at monitoring points in the volute and impeller,which synchronizes with the sum amplitude of them.At the same time,the greater the viscosity,the lower the mean static pressure of each measuring point in the volute,guide vane and impeller.