Experimental investigation on the leading edge film cooling of cylindrical and laid-back holes with different radial angles

Abstract

Film cooling performances of the cylindrical film holes and the laid-back film holes on the turbine blade leading edge model are investigated in this paper. Experimental measurements have been carried out to investigate the influence of the inclined angle in the spanwise direction (i.e. radial angle for a blade in the engine) on the film cooling performances of these two kinds of holes. Three rows of holes are arranged in a semi-cylinder model which is used to model the blade leading edge. Two inclined angles and three blowing ratios are tested. Transient heat transfer measurement technique with double thermochromic liquid crystals is employed in the present experiment. The results show that the trajectory of the film jets in the leading edge region deviates from the mainstream direction to the spanwise direction gradually as the blowing ratio increases. Under large blowing ratio, more area can benefit from the film protection and the film cooling effectiveness distribution is more uniform than those under small blowing ratio, while the heat transfer coefficient is also higher. The basic distribution features of heat transfer coefficient are similar for all the tested models. The heat transfer coefficient in the region where the jet core flows through is relatively lower, while the heat transfer coefficient in the jet edge region is relatively higher. Compared with the cylindrical holes, the jets from the laid-back holes have better film coverage and meanwhile make more area have relatively higher heat transfer coefficient, especially under large blowing ratio. Under the same blowing ratio, the jets from film holes with small radial angle can attach on the wall surface better and give higher film cooling effectiveness in the region close to the hole exit than the film holes with large radial angle, while they also produce relatively higher heat transfer coefficient.