Comparative analysis of flow physics in axial-flow pump predicted through the advanced unsteady numerical techniques

Appropriate numerical methodologies should be selected for accurate, efficient computational simulations. This study is a comprehensive comparative analysis of the flow phenomena within an axial-flow pump that are predicted using numerical approaches: unsteady Reynolds-averaged Navier–Stokes (URANS), detached-eddy simulation (DES), and large-eddy simulation (LES). The shear stress transport k−ω turbulence model, combined with reattachment modification, is used for URANS prediction, while the wall-adapting local eddy-viscosity model for subgrid-scale (SGS) closure is used for LES. The grid resolution is verified to minimize the dependence of LES predictions on the SGS model. The numerical predictions are compared with the experimental data to assess the accuracy and reliability of the three approaches. The flow characteristics of the axial-flow pump involve cavitation and vortex structures generated by separation flows, tip leakage vortices (TLV), and trailing-edge (TE) vortices and their wake. In URANS, these phenomena are underestimated and have simple structures, limited spatial resolutions, and reduced temporal dependence. URANS predicts the TLV as a nearly straight structure, whereas DES and LES resolve it as an intricate spiral vortex. However, DES overpredicts vortex structures and vorticity intensities in certain regions. LES provides the most detailed and comprehensive depiction of flow phenomena, capturing numerous small-scale, highly convoluted vortex structures that illustrate their formation, evolution, and dissipation. URANS and DES exhibit limitations in resolving complex TE vortices, but LES effectively captures them as vortex shedding that gradually dissipates downstream. Additionally, LES reproduces the laminar–turbulent transition in near-wall flows, which cannot be achieved by URANS and DES.