Heat Transfer, Adiabatic Effectiveness, and Injectant Distributions Downstream of a Single Row and Two Staggered Rows of Compound Angle Film-Cooling Holes

Abstract

Experimental results are presented that describe the development and structure of flow downstream of one row and downstream of two staggered rows of film-cooling holes with compound angle orientations. With the compound angle configuration, holes are inclined at 35 deg with respect to the test surface when projected into the streamwise/normal plane, and 30 deg with respect to the test surface when projected into the spanwise/normal plane. Within each row, holes are spaced 7.8 hole diameters apart, which gives 3.9d spacing between adjacent holes for the staggered row arrangement. Results presented include disributions of iso-energetic Stanton numbers, and adiabatic film cooling effectiveness deduced from Stanton numbers using superpositiion. Also presented are plots showing the streamwise development of injectant distributions and streamwise development of mean velocity distributions. Spanwise-averaged values of the adiabatic film cooling effectivenss, η, measured downstream of two staggered rows of holes are highest with a blowing ratio m of 0.5, and decrease with blowing ratio because of injection lift-off effects for x/d < 20. However, as the boundary layers convect farther downstream, η values for m = 0.5 are lower than values for m = 1.0, 1.5, and 1.74 since smaller amounts of injectant are spread along the test surface. These differences also result because injectant from the upstream row of holes eventually merges and coalesces with the injectant from the downstream row of holes (of the two staggered rows) at the higher m. With one row of holes, local effectivenss variations are spanwise periodic, where higher values correspond to locations where injectant is plentiful near the test surface. Local Stf/Sto data also show spanwise periodicity, with local Stf/So maxima corresponding to regions of higher mixing between streamwise velocity deficits. Spanwise-averaged iso-energetic Stanton number ratios downstream of both the one-row and two-row arrangements generally range between 1.0 and 1.25, and show little variation with x/d for each value of m tested. However, for each x/d Stf/StoValues increase with m. Additional discussion of these results is presented along with comparisons to ones obtained downstream of film cooling holes with simple angles in which holes are inclined at 35 deg with respect to the test surface in the streamwise/normal plane.