涡带工况下轴流泵装置内部脉动特性数值分析

Analysis on Pressure Fluctuation in Axial-Flow Pumping System Under Partial Load

为研究涡带工况时立式轴流泵装置内部流场压力脉动情况,开展了立式轴流泵装置非定常数值模拟,通过设置监测点,获得了不同位置的压力脉动结果,并进行了频谱分析.通过物理模型试验及PIV流场测试技术验证了数值计算结果的有效性,重点分析了叶轮进口及箱涵式进水流道底部的压力脉动特性.研究结果表明,涡带工况时叶轮进口的脉动主频已不再受轴频控制.不同工况时叶轮进口的相同监测点的脉动主频存在差异性.大流量工况时叶轮进口的脉动相对幅值较大,且涡带诱发的脉动主频与轴频相同.各工况时箱涵式进水流道底部水力脉动均为低频涡带脉动.在大流量工况时,箱涵式进水流道底部的脉动压力主频与轴频相同,次主频与叶频相同,扭矩变化主频与叶轮的轴频相同.

The three-dimensional, unsteady Reynolds-averaged Navier-Stokes equations with RNG k-6 turbulent model were solved to investigate the pressure fluctuation of axial-flow pumping system under partial load by used ANSYS CFX. The pressure fluctuations at nine representative locations under off-design condition were obtained, and the time-domain and frequency-domain of each monitoring point were analyzed. Such an understanding was critical to predict and eventually control cavitation and noise as well as vibration in pumping system, and improve hydraulic performance of pumping system. Comparison of calculated unsteady hydraulic performance parameters and flow field contours with the test results by energy test and PIV （Particle Image Velocimetry ） verified that the inner flow characteristic simulated by this calculation method was comparatively accurate. The numerical results show that the frequency of pressure fluctuation at impeller inlet is not dominated by the shaft frequency under partial load. The dominant frequency of same monitor is different in different operating conditions. The relative pressure amplitude is larger at impeller inlet, and the dominant frequency induced by submerged vortex is the same as shaft frequency at large flowrate condition. The pulsation frequency is low frequency fluctuation at the bottom of cube-type inlet passage under different operating conditions. The dominant pulsation frequency and the dominant frequency of torque is the same as shaft frequency, the secondary frequency is the same as the blade passing frequency at large flowrate condition. The numerical results can provide certain theoretical references to reveal the pressure fluctuation in the axial-flow pumping system under partial load.