Investigation of End-Wall Vortex Cavitation in a High Reynolds Number Axial-Flow Pump

摘要

Relative motion of a turbomachinery blade row and the casing requires finite clearance between the rotor tips and the end-wall to avoid rubbing. Presence of this gap, relative motion of the blade tip and the end-wall, and pressure difference across the blade give rise to tip clearance flow which causes many adverse effects, including end-wall vortex cavitation. The vortex is formed by interaction of the clearance flow with the through flow on the suction side of the blade. This report formulates a correlation of the appropriate variables which predict the inception of end-wall vortex cavitation using the following approach: 1) identification of necessary parameters and relationships; 2) experimental measurements of the parameters in the High Reynolds Number Pump facility, a 42-inch diameter pump specifically designed for this purpose; 3) formulation of the correlation model from relationships among the measured variables; and 4) verification of the model with existing databases. The resulting model provides guidance to turbomachinery designers. The model of end-wall vortex cavitation successfully correlates the subject data existing databases. An optimum tip clearance has been theoretically identified. The correlation model contains the boundary layer, lift coefficient, tip clearance, vortex core size, and tip geometry as input variables. Submodels have been developed for the core radius and tip lift coefficient as a function of tip clearance. Laser velocimeter measurements show that additional circulation is shed into the tip vortex from the suction side trailing edge. Water tunnels. (edc)