Unsteady flow characteristics and mechanisms of a centrifugal pump with impeller translation

Abstract

This study investigates the influence of impeller translation on the internal flow of a centrifugal pump, with a focus on how translation-induced effects redistribute flow structures and modulate unsteady characteristics. Non-concentric impeller motion represents a critical off-design condition that exacerbates pressure pulsations and unsteady radial forces, increasing shaft stress and the risk of fatigue failure. Therefore, it is essential for operational reliability to characterize the interplay between impeller translation and the evolution of the internal flow. A computational fluid dynamics framework for generalized impeller eccentric rotation is proposed to capture this motion, employing a vibration intensity number (VIN) to quantify different eccentric operating conditions. The radial force, outlet pressure spatiotemporal evolution, and relative velocity fields are systematically analyzed. In addition, dynamic mode decomposition (DMD) is applied to identify the corresponding frequency-domain flow features. The results demonstrate that impeller translation significantly alters the radial force and the spatiotemporal evolution of the outlet pressure. Specifically, the outlet pressure exhibits distinct low-frequency, high-pressure propagation features, whose direction, phase relation, and circumferential distribution vary with the translational state. Mechanistically, the pressure field is governed by a coupled dual effect of kinematic and dynamic influences. Under bi-directional translation, the final pressure pattern is determined by the dominant directional component when these effects are in opposition. For the VIN = 1 case, the fixed relationship between translational velocity and acceleration produces a highly ordered evolution of flow variables. The DMD results further confirm this flow reorganization in the frequency domain. In particular, impeller translation modifies the harmonics of shaft-frequency pressure modes within the impeller while inducing a strong shaft-frequency response superimposed on the stable blade-passing frequency in the volute. Overall, eccentric motion does not introduce new flow structures; instead, it reshapes the spatiotemporal organization and frequency response of the internal flow through the coupling of rotational motion with translation-induced effects. These findings provide physical insight into flow instability and vibration response under non-concentric pump operation.