A Design Method for the Profiling of End Walls in Turbines

Abstract

The profiling of end walls in turbines has proved to be effective in reducing secondary flows and losses in turbines, both in cascades and in a turbine representative rig. This paper presents a simple method for the design of end walls using the philosophy that the blade (or rather flow) curvature causes the cross passage pressure gradient, so that mirroring the blade curvature on the end-wall should assist in canceling this effect. Three alternative end-wall profiles have been designed based on the camber line of the blades. From a CFD investigation into the effects of these profiles, they should all be effective in reducing the secondary flow within the cascade. The best profile extended upstream and downstream of the blades to attempt to overcome the problems associated with sharp curvature at inlet and exit from the blade row. For the best profile the CFD predicts a 6% reduction in secondary loss and a 61% reduction in secondary kinetic energy. Whilst the loss predictions are not expected to be accurate, the reduction in secondary kinetic energy is likely to be similar to that achieved if the profile were tested experimentally. Experience with testing of an earlier end wall (Hartland et al [1]) suggests that there is likely to be a substantial reduction in secondary loss accompanying this level of reduction in secondary kinetic energy.