半开叶轮离心泵叶顶间隙非定常流动特性研究

Unsteady Flow Characteristics of Tip Clearance in Semi-open Impeller Centrifugal Pump

摘要:

为研究半开式离心泵叶顶间隙区域的非定常流动特性，应用SST k-ω两方程模型，对半开式离心泵进行了全流道数值模拟，利用快速傅里叶变换（FFT）将各监测点的时域值转换为频域值,并分析了泄漏涡轨迹与叶片载荷的相关机理以及泄漏涡的频谱特性。结果表明：泄漏涡涡核与叶片骨线的夹角θ随着叶尖载荷的变化发生了周期性脉动；泄漏涡加剧了叶尖处的流动分离，在叶片前缘形成了连接叶片表面与泵壳的涡管；在流量为0.75Qd时，叶顶前缘间隙处扰动主信号为0.51fB，该频率与二次泄漏以及叶尖处涡管的非定常脉动特性相关；随着流量减小，扰动信号频率有所波动，叶尖泄漏涡破碎位置向叶片前缘移动。

Abstract:

Transient pulsation of tip leakage vortex is an important factor for flow instability and stall of centrifugal impeller. To get an insight into the unsteady flow characteristics in the tip region of a semi-open centrifugal pump, the SST k-ω two-equation model was used to solve the N-S equation. And the fast Fourier transform (FFT) was used to transform the time domain value of vorticity of each monitoring point into frequency domain value, so as to monitor the frequency domain characteristics. The correlation mechanism between the leakage vortex trajectory and the blade loading was studied and the spectral characteristics of the leakage vortex were analyzed. The results showed that the angle θ between the leaking vortex core and the blade bone line was changed periodically with the tip blade loading. The leakage flow accelerated the flow separation at the tip, forming a vortex tube extending from the tip blade surface to the shroud. At 0.75Qd, the 0.51fB in the tip region was the main disturbance signal, which was closely related with the secondary leakage and the unsteady pulsation of the vortex tube. As the flow rate decreased, the disturbance frequency was changed, and the tip leakage vortex crushing position was moved toward the leading edge of the blade. Under the near-stall operating points, the unsteady fluctuation of the leakage flow was aggravated by the pulsation and shedding of the vortex tube, and the tip leakage vortex crushing position was extended to the leading edge of the blade. The unsteady characteristics of the tip leakage flow of the semi-open centrifugal pump were researched, which provided a theoretical basis for the optimal design of the semi-open impeller and the capture of stall signal.