Investigation of flow separation in a centrifugal pump impeller based on improved delayed detached eddy simulation method

Abstract

The mechanism of flow separation in the impeller of a centrifugal pump with a low specific speed was explored by experimental, numerical, and theoretical methods. A novel delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm combined with a rotation and curvature correction method was developed to calculate the inner flow field of the original pump for the large friction loss in the centrifugal impeller, high adverse pressure gradient, and large blade curvature. Boundary vorticity flux theory was introduced for internal flow diagnosis, and the relative velocity vector near the surface of the blade and the distribution of the dimensionless pressure coefficient was analyzed. The validity of the numerical method was verified, and the location of the backflow area and its flow features were determined. Finally, based on flow diagnosis, the geometric parameters influencing the flow state of the impeller were specifically adjusted to obtain a new design impeller. The results showed that the distribution of the boundary vorticity flux peak values, the skin friction streamline, and near-wall relative velocities improved significantly after the design change. In addition, the flow separation was delayed, the force applied on the blade was improved, the head under the part-load condition was improved, and the hydraulic efficiency was improved over the global flow ranges. It was demonstrated that the delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm was capable to capture the separation flow in a centrifugal pump, and the boundary vorticity flux theory was suitable for the internal flow diagnosis of centrifugal pump.

Numerical simulation of complex flow structures and pressure fluctuation at rotating stall conditions within a centrifugal pump

“…The unsteady calculation for this study is carried out by the DDES method. DDES has proved promising in resolving flow separation and turbulence, as shown from the findings of these references 25,28,29 …”

“…DDES has proved promising in resolving flow separation and turbulence, as shown from the findings of these references. 25,28,29 A trade-off between DDES and SST models: From Figure 4, the superiority of DDES to resolve the finer details of flow over SST is demonstrated. At t = 0.8280 s,…”

“…This is expressed to satisfy incompressible flows as described herein as an incompressible form. 18,22,30 This is a build-up on the k-ω SST RANS 12,28,31 and is summarized as follows The turbulent eddy viscosity is computed as:…”

Study on performance of thrust disk as auxiliary impeller

“…The rotation speed, impeller, and volute all have very important influences on the performance of centrifugal pump. [17][18][19] Also, it is necessary to take into account the cavitation. 20,21 Cavitation affects the hydraulic performance, causes strong vibration and equipment damage in serious cases.…”

Dynamic Instability Analysis of a Double-Blade Centrifugal Pump

“…Recently, the flow instability of a multistage centrifugal pump a off-design conditions was investigated by Shibata et al [13]. Pressure pulsations at dif fuser inlet were measured and rotating stall phenomenon was observed with CFD tools In addition, some studies were carried out to do the deep analysis on the unsteady flow phenomena in centrifugal pump, for instance, flow separation [14][15][16], rotating stall [17 19] and recirculation [20,21]. Those directly cause the formation of flow instability pressure pulsations and pump vibration.…”