透平工况动静叶栅内固液两相流动压力脉动特性

Pressure fluctuation of solid-liquid flow in stator and rotor cascades of pump as turbine

为了研究泵作透平过流含沙水时动静叶栅内非定常流动所引起的压力脉动特性情况,以径向导叶式离心泵反转作液力透平为研究对象,对全流道进行结构化六面体网格划分,采用大涡模拟(large eddy simulation,LES)与Mixture多相流模型相结合的方法进行了三维非定常数值计算.分别对清水介质和固液两相介质3个流量工况下的压力脉动进行了监测.结果表明:清水介质和固液两相介质下,动静叶栅交界面处监测点P3和导叶内监测点P6由于受到叶轮内压力梯度的交替变化影响,时域脉动周期性明显,且与叶片通过周期一致.小流量工况下,颗粒的存在减少了尾水管回流,使得压力脉动较清水介质更稳定,大流量工况下,颗粒的存在加剧流场紊乱.压力脉动频域分布结果显示,不同工况的主频均为叶片通过频率,谐频为叶频的倍数,其幅值呈指数形式衰减.在小流量工况下,叶轮内部涡流诱导了明显的二次谐波,流体介质中的颗粒使得此处的高频压力脉动得到了增强.大流量工况下,流体介质中的颗粒使得此处的高频压力脉动得到了削弱.

In order to study the pressure fluctuation characteristics of solid-liquid flow in stator and rotor cascades of pump as turbine,the centrifugal pump with space diffuser as turbine was chosen,and then the unsteady 3 D flow field was simulated based on the large-eddy simulation（ LES） and Mixture multiphase flow model with structured hexahedral mesh generated in ICEM. The pressure fluctuations under three different flow in water and solid-liquid two-phase were monitored in the numerical calculation. The results show that the point P3 between the stator and the rotor and the point P6 in the guidevane are due to the pressure gradient alternating change in the impeller under the water and solid-liquid two-phase,the periodicity of the pressure fluctuations in time domain is obvious,and consistent with the blade passing period. The presence of particles reduces the backflow of the draft tube,which makes the pressure fluctuation more stable at the small flow rate,and the existence of particles increases the flow field disturbance at the large flow rate. The results of the pressure fluctuations in frequency domain reveal that the main frequency are of the blade passing frequency（ BPF） and the harmonic frequency is a multiple of the blade passing frequency under different conditions,and its amplitude shows exponential decay. The vortex induces second-harmonic in the impeller obviously. The particles enhance the high-frequency pressure fluctuation at the small flow rate but weaken it at the large flow rate.