AN EXPERIMENTAL-STUDY OF FILM-COOLING EFFECTIVENESS NEAR THE LEADING-EDGE OF A TURBINE BLADE

A flame ionization technique based on the heat/mass transfer analogy h as been used in an experimental investigation of film cooling effectiv eness. The measurements were made over the surface of a turbine blade model composed of a semi-cylindrical leading edge bonded to a flat aft er-body. The secondary flow was injected into the boundary layer throu gh four rows of holes located at +/-15 and +/-44 deg about the stagnat ion line of the leading edge. These holes, of diameter d, had a 30 deg spanwise inclination and a 4d spanwise spacing. Adjacent rows of hole s were staggered by 2d, and perfect geometry symmetry was maintained a cross the stagnation line. Discharge coefficients and flow division be tween the 15 and 44 deg rows of holes have also been measured. The str ong pressure gradient near the leading edge produces a strongly nonuni form flow division between the first ( +/-15 deg) and the second (+/-4 4 deg) row of holes at low overall mass flow ratios. This produced a t otal cutoff of the coolant from the first row of holes at mass flow ra tios lower than approximately 0.4, leaving the leading edge unprotecte d near the stagnation line. Streamwise and spanwise plots of effective ness show that the best effectiveness values are obtained in a very na rrow range of mass flux ratios near 0.4 where there is also considerab le sensitivity to changes in Reynolds number. The effectiveness values deteriorate abruptly with decreasing mass flow ratios, and substantia lly with increasing mass flow ratios. Therefore, if was concluded that the cooling arrangement investigated has poor characteristics, and so me suggestions are made far alternate designs.