CFD investigation and PIV validation of flow field in a compact return diffuser under strong part-load conditions

The internal flow fields in a compact return diffuser under strong part-load conditions are investigated both numerically and experimentally. For numerical simulation, three-dimensional unsteady Reynolds-Averaged Navier-Stokes equations are solved on high-quality structured grids in conjunction with the shear stress transport k-ω turbulence model by employing the computational fluid dynamics (CFD) software ANSYS-Fluent 14.5. For flow field measurements, a special test rig is designed and the two-dimensional particle image velocimetry (PIV) measurements are conducted in the diffuser midplane to capture the complex flow field and for validation of the CFD results. The analysis of the results has been focused on the flow structure in the diffuser, especially under part-load conditions. The detailed comparison between CFD and PIV results is performed. Vortical flow and recirculation flow patterns in the diffuser are captured and analyzed. Large flow separation and backflow appear under the part-load flow conditions. This paper provides a good data set for developing as well as evaluating the accuracy of various CFD models for capturing the complex flow field in a compact return diffuser used with multistage pumps.