Investigation of Transient Technique for Turbine Vane Heat Transfer Using a Shock Tube

An investigation was made of a transient technique for determining heat transfer and flow conditions in a cascade of turbine vanes. A shock tube was used to establish, behind a reflected shock, temperature ratios between the gas the vanes simulating the severe operating conditions of modern gas turbines. Heat transfer and flow conditions at five locations (leading edge and 1/4 and 1/2 chord positions on suction and pressure surfaces) were determined by a heat flux gage and by flow visualization with a Mach-Zehnder interferometer. The heat flux gage was a thin-film semiconductor type thermocouple used to measure the surface temperature of a semi-infinite solid as a function of time. Then a transient analysis using a finite difference scheme was used to calculate the heat transfer. The validity of the transient technique was established by measurements with the thin-film gage mounted on the shock tube wall. Analytical results for steady, turbulent heat transfer to a flat plate are somewhat less than the measured results, the difference decreasing with increased shock strength. Analysis of the transient flow conditions in the shock tube provides an explanation of this behavior. The heat transfer conditions for the turbine vane are believed to be established rapidly enough to represent valid steady state measurements for the simulated turbine vane flow conditions.