Adiabatic Effectiveness of Film Cooling with Compound Angle Holes-The Effect of Blowing Ratio and Freestream Turbulence

These photographs show the strong effects of blowing ratio and freestream turbulence on the adiabatic effectiveness of film cooling with compound angle holes. The photographs on the left are for three different blowing ratios (M = 0.5, 1.0 and 1.5 respectively) with low freestream turbulence levels (Tu = 0.1%) and those on the right are for the same blowing ratios with high freestream turbulence levels (Tu = 10%). The surface in these photographs is insulated (Styrofoam) and is airbrushed with black paint and microencapsulated thermochromic liquid crystals (TLCs). The hole is oriented with a compound angle of 45 deg and with an injection angle of 30 deg from the flat plate surface. The colors are the hue values for the TLCs and are calibrated against temperature, thus the photographs represent the surface temperature distribution. When slightly corrected for radiation and a small amount of conduction, this is the adiabatic wall temperature. The jet is heated above the freestream temperature. The adiabatic effectiveness is defmed as the ratio of the difference between the adiabatic wall temperature and the freestream temperature to the difference between the jet temperature and the freestream temperature. Thus the colors (hues) in these photographs represent the adiabatic effectiveness directly. Adiabatic effectiveness is important in determining the total heat transfer for film cooling. These photographs show that both blowing ratio and freestream turbulence have significant effects on the adiabatic effectiveness. Increased blowing ratio decreases the area over which cooling occurs, while freestream turbulence increases this area.