Reduction in Secondary Flows and Losses in a Turbine Cascade by Upstream Boundary Layer Blowing

Abstract

The effect of upstream tangential blowing on the secondary flows has been studied in a turbine cascade of rotor blades. The aim is to reduce the secondary flows and losses, but in the evaluation an accounting procedure for the energy for blowing is required. The experimental results show that the effect of the increasing blowing is first to thicken the inlet boundary layer, giving greater secondary flow and more loss, and then as re-energisation of the inlet boundary layer takes place together with increasing counter streamwise vorticity, the passage vortex is progressively weakened, with a corresponding reduction in loss. Low rather than high angle blowing is shown to be more effective as the jet is kept closer to the end wall, and strong similarities could be obtained with the flow patterns from previous work with a skewed inlet boundary layer. However when the energy for inlet blowing is included, no net gain is achieved due mainly to the mixing loss of the injected air. Overall gains may be achievable, if combined with such features as injection for film cooling.