Separate and Combined Effects of Surface Roughness and Turbulence Intensity on Vane Heat Transfer

A research and development program has been undertaken to ascertain the effects of surface roughness levels on vane external heat transfer, with varied conditions of inlet freestream turbulence intensity and vane Reynolds number. A transonic linear vane cascade was constructed to operate at a nominal overall pressure ratio of 1.86. Airfoil heat transfer distributions are measured using a thin-walled stainless steel airfoil having imbedded thermocouples. The methodology incorporates a thin-foil surface heater to provide a known heat flux condition, with room temperature mainstream air at approximately 5 atm pressure. Heat transfer is characterized for uniform surface average roughness levels of 0.4, 1.85, and 4.5 micrometers, with inlet turbulence intensity levels from 4 to 13%. Airfoil Reynolds number based on axial chord length and exit velocity ranges from 2.2 to 4.8 · 10⁶. Results show consistent individual and combined effects of Reynolds number, turbulence, and surface roughness changes. Higher roughness levels tend to dominate turbulence effects in most regions except the leading edge.