Superposition methods for predicting overall cooling effectiveness of cooled nozzle guide vane endwalls subject to inlet radial temperature profile: accuracy and limitations

In this paper we evaluate the accuracy and limitations of superposition methods for predicting the overall cooling effectiveness distributions of cooled high-pressure nozzle guide vane (NGV) endwalls in the presence of non-uniform inlet radial temperature profiles. The requirement to use superposition approaches arises during the design process, when trying to combine data from separate evaluations of the impact of endwall film cooling and inlet temperature profile on overall cooling effectiveness. The process is analogous to the (perhaps more common) use of superposition for the design of multirow film cooling systems using data from individual-row experiments. Using infrared thermography, we measure the overall cooling effectiveness (so-called metal effectiveness) on the hub endwall of a nozzle guide vane. Four situations are studied: uniform inlet temperature without film cooling; uniform inlet temperature with film cooling; non-uniform inlet temperature without film cooling; and non-uniform inlet temperature with film cooling. Using a superposition method, we compare the overall cooling effectiveness inferred from decomposed experiments (no film cooling with uniform inlet temperature; film cooling with uniform inlet temperature; no film cooling with non-uniform inlet temperature) with that directly measured with both film cooling and non-uniform inlet temperature. Several limitations of such superposition approaches are discussed.