Spatiotemporal characteristics of flow in the bend and return channel perturbed by rotor–stator interaction

Abstract

The flows in turbomachinery systems are strongly perturbed by the rotor–stator interaction (RSI) between the rotating and stationary through-flow components, generating the fluctuating flows. This work presents a numerical investigation of a flow in a test centrifugal pump system consisting of an impeller, diffuser, bend, and return channel at the designed and low flow rates. Both vaneless and vaned diffuser models are considered to determine the perturbation of the diffuser vanes on the flow. The objective is to quantitatively assess the impacts of two influential factors, i.e., the diffuser type and the flow rate, on the spatiotemporal characteristics of the transient flow in the various through-flow components. Particular attention is paid to the generation of the reversed flow, circulating vortices, and temporal fluctuations of the velocity field. It is found from the numerical data that both the flow rate and the diffuser type affect the temporal fluctuations of the flow, primarily via the impact of the RSI-induced large-scale vortices generated in the passages of the impeller and the vaned diffuser. The flow in the bend experiences the streamline curvature on the solid walls; thus, the peak values of the fluctuating amplitude of the streamwise and transverse velocities and the reversed flow may shift between the two halves of the channel close to the inner and outer wall. The boundary layer flow patterns are mainly determined by the flow rate at the low flow rate and by the diffuser vanes at the designed flow rate. This work comprehensively reveals the transient behaviors and unsteadiness of the flow which was not provided in the experimental investigation for the test centrifugal pump system which was widely studied since the essential flow physics are included. The numerical data in the stationary bend and return channel are first provided, which are of engineering significance for this type of centrifugal turbomachinery.