Second Law Analysis of Aerodynamic Gains Associated with Simple Angle and Compound Angle Full Coverage Film Cooling


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International Journal of Thermophysics


Entropy generation is employed to quantify second law losses, and aerodynamic gains, which are associated with a film cooled boundary layer produced by a unique full-coverage compound angle hole configuration. With this arrangement, an alternating sign for the compound angle β is employed from one streamwise row of holes to another, such that compound angle β is + 300 in one row of holes, followed by − 300 in the next row of holes. Results from this arrangement are compared to simple angle arrangement with β = 00. Determined from isothermal flow field measurements of local total pressure variations from film cooling, are the entropy change, entropy generation, and mass-averaged overall exergy destruction, relative to the freestream flow outside of the boundary layer. Because stagnation pressure values, associated with film cooling in the boundary layer, are higher than freestream stagnation pressure values, the present film arrangements and conditions produce aerodynamic gains relative to the freestream flow. Film cooling blowing ratio values range from 2.9 to 6.0, and mainstream Reynolds numbers range from 89 000 to 141 000. Entropy generation and exergy destruction are compared for the compound and simple angle full-coverage film cooling arrangements. Variations of these quantities are evident with boundary layer location, and as the blowing ratio, streamwise development location, and main flow Reynolds number vary. Differences for the two film cooling configurations, as these parameters vary, are a consequence of significantly different film cooling behavior and characteristics, as related to entropy generation and exergy destruction distributions.

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