Evaluation of Heat Transfer Coefficients for an Impingement Cooling Cascade: Experimental Challenges and Preliminary Results

In this paper, a modification of the widely used transient liquid crystal heat transfer measurement technique for impingement cooling is presented, in which a constant heat flux at the surface is used to drive the experiment, instead of a step change in the flow temperature. This method, already employed for film cooling, is used for the first time in a narrow impingement channel of an impingement cooling cascade which is characterized by complex and three dimensional vortical structures. The results are compared to the traditional heater mesh method (i.e. a temperature step in the flow drives the experiment). With both methods similar results are obtained, with the associated differences that can be attributed to entrainment effects or different surface roughness. An uncertainty analysis shows also that a transient experiment with constant surface heat flux improves the accuracy in the high heat transfer regions, e.g. stagnation points, which are the most uncertain regions in the heater mesh method.