Feasibility Study of Film Source Coupling Transpiration and a Row of Cylindrical Film Holes

The present study assesses the performance of a film cooling source, composed of a segment of permeable wallinstalled near a row of cylindrical film holes. Coolant is introduced through both the permeable wall and the film holes resulting in a downstream film composed of both transpired and discretely injected coolant. The aerodynamic performance and cooling downstream of this coupled sourceare studied analytically, experimentally andnumerically. The sensitivity of transpiration blowing ratio, discrete hole blowing ratio, discrete hole pitch, transpiration slot width, and the relative positioning of the two sources on these global parameters of interest is the end result. The analytical results are used to get a basic understanding of the issue and design the test matrix for the numerical study. A range of design parameters are studied numerically in a Box-Behnken test matrix to yield global results which are then combined into one parameter, β. A second order response surface of the parameter βallows for a more complete understanding of the coupled source. This numerical analysis is compared with experimental results from two different coupled sources in order to assess the predictions. The results indicate that coupling of the two sources allows a more efficient use of coolant by generating a more uniform initial film. One coupled case in particular shows a 170% increase in cooling over the baseline cylindrical row, a 22% reduction in aerodynamic losses over the baseline transpiration source, all with a 51% reduction in mass flow as compared with the same cylindrical row baseline. Further study and optimization will allow this technique to provide more effective thermal protection at a lower cost of aerodynamic losses and spent coolant.