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

Experimental investigation has been performed to study the film cooling performance of cylindrical and laid-back film holes on the turbine blade leading edge. Four test models are measured for four blowing ratios to investigate the influence of film hole shape and hole pitch on the film cooling performance. Film cooling effectiveness and heat transfer coefficient are obtained using transient heat transfer measurement technique with double thermochromic liquid crystals. As the blowing ratio increases, the trajectory of jets deviates to the spanwise direction and lifts off gradually. However, more area can benefit from the film protection under large blowing ratio, while the heat transfer coefficient is also higher. The basic distribution features of heat transfer coefficient are similar for all the four models. Heat transfer coefficient in the region where the jet core flows through is relatively lower, while heat transfer coefficient in the jet edge region is relatively higher. For the models with small hole pitch, the laid-back holes only give better film coverage performance than the cylindrical holes under large blowing ratio. For the models with large hole pitch, the advantage of laid-back holes in film cooling effectiveness is more obvious in the upstream region relative to the cylindrical holes. For the cylindrical hole model and the laid-back hole model with the same hole pitch, the laterally averaged heat transfer coefficients are nearly the same with each other under the same blowing ratios. Compared with the models with large hole pitch, the laterally averaged film cooling effectiveness and the laterally averaged heat transfer coefficient are larger for the models with small hole pitch because of larger proportion of film covering area and strong heat transfer region.