EFFECTS OF LOCAL BLOCKAGE ON FILM COOLING EFFECTIVENESS OF A FAN-SHAPED HOLE FED BY CROSSFLOW

Effects of local blockage in the hole on film cooling effectiveness were investigated. The film cooling effectiveness (FCE) and heat transfer coefficient (HTC) of a fan-shaped hole was measured on a test rig of a flat plate with secondary crossflow in the coolant feeding passage. The blowing ratio was varied from 1 to 2 with a crossflow-to-mainstream momentum ratio of 0.4 and a blocking ratio of the hole was 25%. Results have revealed the difference of blockage effects at different locations. The blockage at the entrance side (Entr-side) and expansion side (Exp-side) walls concentrate the jet stream on one side, thus reducing the FCE values. Blockage on the laidback wall (Exp-back)slows down coolant velocity, leading to an accelerated dissipation of the film layer. The FCE values decrease as the blowing ratio is raised in the Entrside case. The Blockage of Entr-side and Exp-back increased the heat transfer coefficient compared to the no blockage condition(clean), but the blockage on the diffuser side wall reduced the heat transfer coefficient compared to the clean condition. The heat transfer coefficient ratio of all holes increases with the increase of the blowing ratio. Results are indicative to evaluate the performance uncertainty of a fan-shaped hole in a real operating environment.