The Effect of Casing Coolant Injection on Aerodynamic Loss in a Linear Turbine Cascade With Tip Clearance

Abstract

Abstract Deviation and loss have been measured and numerically analyzed in a linear turbine cascade with tip clearance and upstream casing coolant injection. Compared to the case without coolant injection, when a coolant flow of 0.5% of the mainstream mass flow rate with a non-dimensional swirl of 100% is injected into the mainstream, the following changes occur. The mass-averaged deviation decreases by 2.4 degrees. The decrease in deviation occurs mainly because the underturning and overturning due to the passage vortex (PV) and trailing shed vortex (TSV) increase; and the centers of both vortices move toward the midspan and pressure side. The mass-averaged loss increases by 15.9% primarily because the losses associated with the PV and TSV increase. Multiple vortices are formed at the exit of the coolant slot due to the Kelvin-Helmholtz instabilities. These slot exit vortices strengthen the PV and increase the associated loss, but they have little direct interaction with either tip clearance vortex (TCV) or TSV. The TSV is strengthened by both tip unloading and PV strengthening, and thus the associated loss increases. The loss due to the TCV decreases slightly due to the reduced incidence and decreased tip clearance flow rate. When the coolant is injected with less swirl — with non-dimensional swirl values of 85% and 70% — the loss increases are reduced to 9.3% and 6.7%, respectively, relative to the case without coolant. The change in loss with decreasing swirl is mainly due to the decreases in PV and TSV losses. The loss in the tip region is not sensitive to the coolant swirl.