Spatiotemporal characteristics of three-dimensional vortex structure of centrifugal pump based on modal decomposition method

Abstract

To investigate the spatiotemporal characteristics of vortex structures within a centrifugal pump and explore the application of modal decomposition techniques in three-dimensional vortex feature extraction, this study employs computational fluid dynamics (CFD) to numerically simulate the unsteady flow in a centrifugal pump under flow rates of 80 m³/h (low-flow condition), 100 m³/h (design flow condition), and 120 m³/h (high-flow condition). By integrating the Omega-Liutex method with modal decomposition techniques, including Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD), a detailed characterization of the vortex structures is performed. The results indicate that, compared to other vortex identification criteria, the Omega-Liutex vortex identification technique effectively captures the flow structures within the centrifugal pump. By applying the POD method to analyze the vortex characteristics in the impeller region under three different flow conditions, the analysis revealed that tip vortices and wake vortices dominate the energy distribution across all flow conditions, with an energy proportion ranging from 34.7% to 40.3%. Additionally, under both low-flow and design-flow conditions, the first and second-order modal structures of the vortex in the impeller region demonstrate periodic behavior. The dominant vortex structures in the volute region exhibit significant variations under different flow conditions. Under low-flow and design-flow conditions, the primary vortex structures in the volute region include the tongue-shedding vortex and the wall-attached vortex, with a nonlinear interaction observed between the first and second-order modes. Under high-flow conditions, the primary energetic vortex structure in the volute region is the recirculating vortex in the diffuser section. A comparison of the vortex areas for all modes in the impeller and volute regions under three different flow conditions reveals that the primary mode exhibits the smallest vortex area. The first-order mode obtained through the DMD method clearly reveals the overall flow characteristics within the centrifugal pump. Among the first four modes, there are always two modes exhibiting identical vortex structures. In the comparison of vortex feature extraction, the POD method can identify large-scale vortices with relatively low energy in the impeller and volute regions, whereas the DMD method extracts vortex structures more clearly and comprehensively.