Performance of a Turbine Airfoil With Multiple Film Cooling Stations: Part II — Aerodynamic Losses

Abstract

In the present study the aerodynamic performance of a turbine NGV airfoil was investigated, cooled from several showerhead, pressure and suction side stations. Film cooling heat transfer and effectiveness on this airfoil was examined in part I of this paper. Tests were conducted in a linear cascade at an exit Reynolds number of 1.45e6 and an exit Mach number 0.8. Density ratio effects were studied with air and CO2 injection, matching the densities by correctly adjusting the coolant temperature. In terms of a primary loss coefficient, neglecting the coolant kinetic energy, coolant injection increased the losses by 20–30% compared to solid blade losses, but depended only weakly on the coolant mass flow rate. A slight loss increase for increasing injection up to 2% coolant mass flow was noted, followed by a weak decrease for further augmented coolant mass flow rates. The primary losses appeared to be independent of the coolant medium and temperature. Thermodynamic loss coefficients including the loss of coolant kinetic energy, monotonically increased with coolant mass flow rates. To check the validity of CO2 injection for the simulation of high density ratios, the latter has been matched using strongly cooled air and heated CO2. The thermodynamic losses did not match at constant density ratio, but at constant coolant Mach number, when compared at constant coolant mass flow rates. Reporting the losses to the total pressure ratio (momentum flux ratio) yielded excellent scaling emphasizing the usefulness of the momentum flux ratio for film cooling loss scaling.