多级离心泵内部级间影响及压力脉动特征

Inter-stage interaction and unsteady flow characteristics in multistage centrifugal pump

为了研究多级离心泵内级间相互影响及流道内的瞬时流动特征,对一两级泵内部流动进行了三维定常与非定常数值计算,获得并分析了不同流量工况条件下流道内各个监测点的压力脉动特征.研究表明:首级导叶的存在是导致次级叶轮入口截面上不均匀流动状态的关键因素;在每级叶轮的出口与导叶进口联结处均存在剧烈的动静耦合作用;尽管整体流道的几何形状复杂,叶片通过频率仍支配着该两级泵内全流道的特征压力脉动,而导叶叶片数对压力脉动特征的影响较弱;叶轮内与叶频对应的压力脉动幅值自叶轮进口到叶轮出口逐渐增大,且在叶轮出口处达到极大值,导叶中的相应变化规律则与之相反;偏离最优流量工况,叶频仍占据统治地位,但整个流道内的压力脉动幅值增大,该趋势在小流量工况下尤为明显.

To analyze inter-stage interaction and transient flow characteristics in a multistage centrifugal pump,numerical simulations of both steady and unsteady,three-dimensional turbulent flow in a two-stage centrifugal pump are conducted. Pressure fluctuations at monitoring points in both the impeller and diffuser passages are obtained at different flow rates. The results show that the first-stage diffuser is the key factor for determining the non-uniform velocity distribution at the inlet of the second-stage impeller. There is a strong rotor-stator interaction between the impeller outlet and diffuser inlet in each stage. Even though the geometrical shape of the whole flow passage is so complicated,the blade passing frequency is still the dominating factor that decides the pressure fluctuation characteristics in the entire flow passage in the pump. By contrast,the pressure fluctuations are less affected by the number of diffuser vanes. The pressure fluctuation amplitude at the blade passing frequency within the impeller passages increases gradually from the impeller inlet to the outlet,but vice versa in the diffuser. The pressure fluctuation amplitude at the blade passing frequency is still dominated at low and high flow rates,however,the fluctuation amplitude is amplified,especially at the low flow rate.