Experimental Investigations of the Effect of Scheme Exit Height and Double Row Injection on the Film Cooling Performance of a Micro Tangential Jet Scheme: Part II — Suction Side

This paper presents experimental investigations of the effect of scheme exit height and double jet injection on the film cooling performance of a Micro-Tangential-Jet (MTJ) scheme on the suction side of a gas turbine vane using the transient Thermochromic Liquid Crystal (TLC) technique. In part I of the present paper the investigations over the pressure side are presented. The MTJ scheme is a micro-shaped scheme designed so that the micro-sized secondary jet is supplied tangentially to the vane surface. In order to investigate the effect of scheme exit height, one row of the MTJ scheme with exit height of 1.5 hole diameters was investigated and compared with the case of 1.0 hole diameter scheme exit height. Meanwhile, to investigate the effect of double injection, one row of the MTJ scheme in staggered arrangement with one row of fan-shaped scheme was investigated. The investigations were conducted at a blowing ratio, calculated based on the scheme exit area, ranging from 0.25 to 0.625. The average density ratio during the investigations was 0.93, and the Reynolds Number was 1.4E+5, based on the free stream velocity and the main duct hydraulic diameter. The pitch to diameter ratio of the cooling holes is 6.5, and the turbulence intensity during all investigations was 8.5%. The increase in the MTJ scheme exit height did not result in significant change in the Mach number distribution. Moreover, increasing the scheme exit height resulted in enhanced effectiveness performance. The enhanced effectiveness was accompanied with Heat Transfer Coefficient (HTC) ratio augmentation as well. As a result, a reduction in the Net Heat Flux Reduction (NHFR) accompanied increasing the scheme exit height from 1.0 to 1.5 hole diameters. Besides, adding a row of shaped schemes in front of the MTJ scheme result in significant effectiveness reduction, compared to the case of single row injection. The latter was attributed to the presence of the shaped scheme inclination angle that result in enhanced secondary stream loss due to the perpendicular momentum component to the vane surface accompanying the shaped scheme secondary jet.