Generation and Transport of Tip Clearance Vortices in a High Reynolds Number Axial Flow Rotor

The current paper describes a detailed investigation of the fundamental mechanisms involved in the formation of the rotor tip clearance vortex in a high Reynolds number axial-flow rotor, and the interactions of the tip clearance vortex with the main passage flow and a rotor trailing edge separation vortex. Flow fields through a highly-loaded rotor in a high Reynolds number pump facility (HIREP) with various rotor tip clearances are used for the study. Experimental measurements of the rotor tip flow obtained at one particular tip clearance are compared with the flow fields at seven additional clearances numerically analyzed with a three-dimensional Navier-Stokes code. The measured and the calculated flow fields are used to understand the development of the tip clearance vortical structure. The current study shows that the strength and the trajectory of the tip clearance vortex and the residual lift inside the tip gap are all dependent on the clearance size. A trailing edge separation vortex, due to strong radial flow on the suction side of the trailing edge, interacts with the tip clearance vortex. Before this interaction, however, the tip clearance vortex has fully developed, and the trajectory of the tip vortex is only mildly affected by this interaction. An existing similarity model for tip vortex trajectory is examined with respect to the current flow, and a possible generalization of the model is proposed.