Investigations of film-cooling effectiveness on the squealer tip with various film-hole configurations in a linear cascade

An experimental investigation is performed to study the effect of film-hole configurations on the blade tip film cooling performance in a five-blade linear cascade. Six film-hole configurations are taken into consideration under four typical blowing ratios. In Type-A, Type-B and Type-C, the film holes are arranged in a single row along the middle-camber line with different hole-to-hole pitches. Type-D, Type-E and Type-F have the same film-hole number of 13 as Type-B. For Type-D, the film holes are also arranged in a row, but they are located close to the suction-side squealer. For Type-E, the film holes are arranged in two rows. For Type-F, two rows of 8 holes are concentrated at the leading edge, and the rest 5 holes are arranged in a line at the middle chord region of the blade tip. Besides, some numerical simulations are conducted to provide detailed coolant jet trajectory. The results show that film-hole arrangement has a great impact on the tip film-cooling effectiveness. The coolant issuing from middle-camber holes are suctioned by the vortex structures inside squealer cavity to flow towards the pressure side, producing good film coverage at the local zone between the middle-camber line and pressure-side squealer for Type-A, Type-B and Type-C. For Type-F, as more film holes are concentrated at the leading edge, the film coverage on the front tip surface is well improved compared to the other film-hole arrangements. Under the same coolant usage, Type-F obtains the most favorable film cooling performance except for the trailing edge, and Type-C produces wider film coverage extending to trailing edge.