Spike-type disturbances due to inlet distortion in a centrifugal pump

Abstract

An inlet elbow installed upstream of centrifugal pump produces distorted suction flow. In this paper, numerical simulation is conducted to investigate interactions between impeller and inlet distortion, with emphasis on the consequent upstream disturbances. At the design point, velocity, pressure and swirling strength at the upstream section are extracted successively to describe the initial upstream disturbance, i.e., a spanwise vortex bubble (IVB1) on inner wall. Additionally, a detailed analysis allow identifications of flow separation and vortex: high incidence due to IVB1 generates two focus-type separations, then separations evolve into two concentrated separation vortices (CSV1 and 2) spanning from the suction surface to the upstream casing. Vortical flow field is further discussed to reveal CSV’s effect on the suction flow: casing-side end of CSV1 moves upstream to form a new vortex bubble (IVB2), which approaches to IVB1 and blocks impeller inlet; vortex-trail of CSV2 with an associated blockage induces another vortex bubble (IVB3) between IVB2 and CSV2. Therefore, new IVBs enhance upstream disturbances and exert a new pressure trace on inner wall, where a vortex bubble produces a rapid pressure drop followed by a sharp pressure rise due to a partial blockage. The resultant down-up waveform demonstrates enhanced disturbances are spike-type.