A Novel Transient Technique to Determine Recovery Temperature, Heat Transfer Coefficient, and Film Cooling Effectiveness Simultaneously in a Transonic Turbine Cascade

Abstract

The study presented in this article provides detailed description about a newly developed experimental technique to determine three key convective heat transfer parameters simultaneously in hot gas path of a modern high pressure turbine–recovery temperature (Tr), heat transfer coefficient (HTC), and adiabatic film cooling effectiveness (Eta). The proposed technique, dual linear regression technique (DLRT), has been developed based on the 1D semi-infinite transient conduction theory, is applicable toward film cooled heat transfer experiments especially under realistic engine environment conditions (high Reynolds number along with high Mach numbers). It addresses the fundamental three temperature problem by a two-test strategy. The current popular technique, curve fitting method (CFM) (Ekkad and Han, 2000, “A Transient Liquid Crystal Thermography Technique for Turbine Heat Transfer Measurements,” Meas. Sci. Technol., 11(7), pp. 957–968), which is widely used in the low speed wind tunnel experiments, is not competent in the transonic transient wind tunnel. The CFM (including schemes for both film cooled and nonfilm cooled experiments) does not provide recovery temperature on the film cooled surface. Instead, it assumes the recovery temperature equal to the mainstream total temperature. Its basic physics model simplifies the initial unsteady flow development within the data reduction period by assuming a step jump in mainstream pressure and temperature, which results in significant under prediction of HTC due to the gradual ramping of the flow Mach/Reynolds number and varying temperature in a transient, cascade wind tunnel facility. The proposed technique is advantageous due to the elimination of these added assumptions and including the effects of compressible flow physics at high speed flow. The detailed discussion on theory and development of the DLRT is followed by validation with analytical calculation and comparisons with the traditional technique by reducing the same set of experimental data. Results indicate that the proposed technique stands out with a higher accuracy and reliability.