Scaling Flat Plate Overall Effectiveness Measurements

Abstract

Low temperature experiments are often performed on models of cooled turbine components in order to predict the temperature of the actual turbine component at engine conditions. Designing the scaled experiment properly takes care beyond simply matching the freestream Reynolds number. For instance, it is well known that for the overall effectiveness to match that at engine conditions, the Biot number of the experimental model must match that of the engine component. Somewhat less clear is the method by which one must scale the coolant flowrate. Widely used coolant flowrate parameters have generally been informed based on the results of adiabatic effectiveness experiments and it remains unclear how well these parameters also allow for matched overall effectiveness, which is highly dependent on internal cooling. In the present work, overall effectiveness distributions were measured on a flat plate with three rows of zero-degree compound angle 7-7-7 shaped holes. The influence of various thermodynamic gas properties was examined using several foreign gases as the coolant while matching coolant flowrate parameters M, I, and ACR. It is shown that the thermal conductivity of the coolant plays an outsized role in the overall effectiveness, but this is not accounted for with any of the traditional coolant flowrate parameters. With significant thermal conductivity variations possible between the coolant and freestream gas at both engine and experimental conditions, consideration of this effect is of vital importance to the experimentalist.