Film Cooling From Shaped Holes

Local and spatially averaged magnitudes of the adiabatic film cooling effectiveness, the iso-energetic Stanton number ratio, and film cooling performance parameter are measured downstream of (i) cylindrical round, simple angle (CYSA) holes, (ii) laterally diffused, simple angle (LDSA) holes, (iii) laterally diffused, compound angle (LDCA) holes, (iv) forward diffused, simple angle (FDSA) holes, and (v) forward diffused, compound angle (FDCA) holes. Data are presented for length-to-inlet metering diameter ratio of 3, blowing ratios from 0.4 to 1.8, momentum flux ratios from 0.17 to 3.5, and density ratios from 0.9 to 1.4. The LDCA and FDCA arrangements produce higher effectiveness magnitudes over much wider ranges of blowing ratio and momentum flux ratio compared to the three simple angle configurations tested. All three simple angle hole geometries, CYSA, FDSA, and LDSA, show increases of spanwise-averaged adiabatic effectiveness as the density ratio increases from 0.9 to 1.4, which are larger than changes measured downstream of FDCA and LDCA holes. Iso-energetic Stanton number ratios downstream of LDCA and FDCA holes (measured with unity density ratios) are generally increased relative to simple angle geometries for m⩾1.0 when compared at particular normalized streamwise locations, x/D, and blowing ratios, m. Even though this contributes to higher performance parameters and lower protection, overall film cooling performance parameter q˙″/q˙o″ variations with x/D and m are qualitatively similar to variations of adiabatic film cooling effectiveness with x/D and m. Consequently, the best overall protection over the widest ranges of blowing ratios, momentum flux ratios, and streamwise locations is provided by LDCA holes, followed by FDCA holes. Such improvements in protection are partly due to film diffusion from expanded hole shapes, as well as increased lateral spreading of injectant from compound angles. [S0022-1481(00)02202-7]