Turbulence Within the Tip-Leakage Vortex of an Axial Waterjet Pump

Abstract

Stereoscopic particle image velocimetry measurements are performed in an optical refractive index matched facility to investigate the evolution of turbulence in the tip region of an axial waterjet pump rotor. Presented analysis of mean flow velocity, vorticity, Reynolds stresses, and turbulence production/transport within the rotor passage focus on the tip-leakage vortex and associated flows. Turbulence production peaks in the shear layer that connects the blade-tip suction side with the vortex as well as in a region of flow contraction situated at the casing wall. Flow separation occurring there, as the leakage backflow meets the throughflow, detaches the boundary-layer vorticity, which is entrained into the tip-vortex perimeter. Upon the inclusion of turbulence transport in the analysis, a discrepancybetweendistributions of turbulent stresses andassociated production vanishes, except at the vortex core. There, the elevated turbulent energy (but relatively low production of Reynolds stresses) is presumably due to low dissipation. Within the aft part of the rotor passage, shortly after vortex bursting, the tip-leakage backflow reaches the neighboring blade. There, radial motion induced by the tip-vortex residual swirl detaches the pressure-side boundary-layer vorticity and injects it into the rotor passage.