In-service turbine airfoils generally have surface roughness much greater than new airfoils due to deposition, erosion, and spallation. This surface roughness has the effects of promoting early transition and increasing surface friction and heat transfer rates. When film cooling is used on the airfoil, the surface roughness affects film cooling performance by changing the approach boundary layer flow, and by increasing the turbulent mixing downstream of coolant injection. Previous studies of surface roughness effects on film cooling performance have used flat surface wind tunnel facilities. The present study was unique in using a simulated vane test facility. Hence it is the first study of surface roughness effects on film cooling of a highly curved surface. In our experiments, effects of roughness upstream and downstream of coolant injection were studied. Combined effects of leading edge showerhead injection and high mainstream turbulence levels were also investigated. In this study, determination of the effects on film cooling performance was limited to measurements of adiabatic effectiveness. Each configuration was tested over a range of blowing ratios and with a density ratio of 1.6. In each case roughness caused a significant degradation in adiabatic effectiveness. Roughness was observed to have a much greater effect on adiabatic effectiveness on the vane geometry than previous studies had observed using flat surfaces.

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