Influence of tip leakage flow and inlet distortion flow on a mixed-flow pump with different tip clearances within the stall condition

Abstract

In order to investigate the effect of impeller tip clearance on internal flow fields and the rotating stall inception impacted by tip leakage vortex and inlet unsteady flow in a mixed-flow pump, mixed-flow pump models with tip clearances of 0.5 mm, 0.8 mm, and 1.1 mm were numerically calculated, and then the energy performance curves and internal flow structures were obtained and compared. The results show that the pump efficiency and the internal flow fields of numerical calculation are in good agreement with experimental results at design flow rate and near-stall condition. A portion of the positive slope segment appears in the energy performance curves under different tip clearances. The lowest head of the mixed-flow pump in the positive slope region decreases with the increase of the tip clearance while the highest head shows an opposite situation indicating that mixed-flow pumps are easier to stall under small tip clearance. At the design flow rate condition, the tip leakage vortex is relatively stable under different tip clearances and appears as a “snail shell” shape, whereas in rotating stall conditions, the “snail shell” shape disappear and the tip leakage flow on blade front forms a “flat” vortex structure. The inlet swirl flow not only affects the tip leakage flow in rotating stall conditions under different tip clearances, but also blocks the fluid from the inlet pipe. Under the circumstance of the same tip clearance, the main frequency amplitude of pressure pulsation coefficient gradually shifts away from blade passing frequency (96.67 Hz) to the axial frequency (24.17 Hz) when the pump operates in the stall condition.

Influence of different blade numbers on the performance of “saddle zone” in a mixed flow pump

“…Using the same grid topology, the grid quality is consistent with the changing of the grid nodes number on the topology line and adjusting the identical nodes. According to the study of Tan et al 35,36 and our previous study, 18 the local flow velocity and pressure on point TCM (in middle position along the blade chord in the tip region) are selected to evaluate the independence test of mesh density, as shown in Table 2. The relative changes from Case 5 to Case 4 are estimated to be (H 5 �H 4 )/H 1 ¼ 0.34%, (g 5 �g 4 )/g 1 ¼ �0.16%, (P TCM,5 �P TCM,4 )/P TCM,1 ¼ 0.11%, and (V TVM,5 �V TVM,4 )/V TVM,1 ¼ 0.01%.…”

“…[15][16][17] It has been shown that the unsteady characteristics of the tip leakage flow under off-design conditions are closely related to the occurrence of rotational stalls. 4,18 Although the classical stall theory proposed by Emmons 19 can explain the stall propagation phenomenon in most rotating machines, the possible factors causing the stall have not been discussed much. After decades of research by many scholars, it has been found that for rotating machinery with different structures, the precursor characteristics induced by rotating stall are also different.…”

Transient characteristics of internal flow fields of mixed-flow pump with different tip clearances under stall condition

“…The transient characteristics of the impeller flow fields can be analyzed by considering the pressure pulsations in time domain or frequency domain; this approach has been proven to be effective in the unsteady flow analysis of mixed-flow pumps. [40][41][42][43][44] In this study, the time domain and frequency response of pressure pulsations at different monitoring points in the impeller tip region located at the inlet, middle and outlet of the impeller are analyzed. The transient flow features of the mixed-flow pump for various tip clearances are compared.…”

Experimental Study of Pressure Pulsation in a Mixed-Flow Pump with Different Tip Clearances Based on Wavelet Analysis

“…Lei et al [26] calculated the influence of T-shape tip clearance on performance of a mixed-flow pump and found that the leakage flow with T-shape blade end decreases by 15.95% compared with original blade end. Besides, pressure pulsation has been extensively investigated in mixed-flow pumps for several years, including pressure pulsation generated by inlet swirling flow [27] and RSI [28][29][30]. Miyabe et al [31] used Dynamic Particle Image Velocimetry (PIV) and pressure pulsation measurements to investigate the propagation mechanism of a rotating stall.…”