High Resolution Measurements of Local Heat Transfer Coefficients by Discrete Hole Film Cooling

Abstract

Local heat transfer coefficients on a flat plate surface downstream a row of cylindrical ejection holes were investigated. The parameters blowing angle, hole pitch, blowing rate, and density ratio were varied in a wide range emphasizing on engine relevant conditions. A high resolution IR-thermography technique was used for measuring surface temperature fields. Local heat transfer coefficients were obtained by a Finite Element analysis. IR-determined surface temperatures and backside temperatures of the cooled testplate measured with thermocouples were applied as boundary conditions in a heat flux computation. The superposition approach was employed to obtain the heat transfer coefficient hr referring to adiabatic wall temperatures in the presence of film cooling. Therefore, heat transfer results with different wall temperature conditions and adiabatic film cooling effectiveness results of identical flow situations (constant density ratios) were combined. Characteristic surface patterns of the locally resolved heat transfer coefficients hf depending on the various parameters were recognized and quantified. The detailed results are used to discuss the specific local heat transfer behavior in the presence of film cooling. They also provide a base of surface data essential for the validation of the heat transfer capabilities of CFD-codes in discrete hole film cooling.