Effects of non-uniform streamwise spacing in low aspect ratio pin fin arrays

Pin fin arrays are commonly used to cool the trailing edge of gas turbine airfoils. While the majority of pin fin research focuses on uniformly-spaced arrays, the goal of the present work was to determine if non-uniform spacing in the streamwise direction could be utilized to maintain high heat transfer while simultaneously extending the array footprint. The uniqueness of the work lies in the basis for selecting the non-uniform spacing pattern. The non-uniform arrangement was chosen to exploit previously published row-by-row heat transfer development where the initial rows showed little variation with streamwise spacing. As such, a non-uniform array was considered where the initial rows had spacing of 3.46 diameters and the inner rows gradually decreased to a final spacing of 1.73 diameters. Three seven-row arrays were considered having constant streamwise spacing of 2.16, 2.60, and 3.03 pin fin diameters. All configurations had constant spanwise spacing of two diameters and constant pin height of one diameter. Three Reynolds numbers of 3.0e3, 1.0e4, and 2.0e4 were considered based on pin fin diameter and minimum area velocity. At high Reynolds numbers, heat transfer and pressure drop measurements were in agreement for the nonuniform array and for a closely spaced array having 2.16 diameter streamwise spacing. While array performance was similar, the non-uniform array covered 16.8% more streamwise distance than the closely spaced array. At low Reynolds numbers, however, the non-uniform array was outperformed by the closely spaced array.