A computational investigation of 3-D flow separation in a vaneless diffuser

摘要

Computational analyses based on the momentum integral (MI) method and a turbulent flow simulation with the low Reynolds-number turbulence model (LRN k-epsilon) were conducted to investigate the 3-D alternating flow separation in a vaneless diffuser at small flow rates. The obtianed numerical results show that the LRN k-epsilon calculation works well in reproducing the reverse flow in the vaneless diffuser, while the MI-method behaves relatively poor although it captures the overall flow pattern correctly. It is clarified that a small gradient in the inlet tangential velocity distribution with respect to diffuser depth is the key factor, which dominates the reverse flow in the vaneless diffuser at small flow rates, as demonstrated in the experiment. And suppression of flow separation could be achieved by an increase in inflow turbulence or by a wall treatment with locally increasing the surface roughness of hub wall where the reverse flow occurs. Comparison indicates agreements in velocity distributions within 3-D boundary layer between the LRN k-epsilon calculation and the experiment are satisfactory.