Multi-parameter influence on combined-hole film cooling system

Combined-hole film cooling system is a promising way to improve cooling efficiency of gas turbine. New combined-hole systems, such as double-jet [14], anti-vortex design [16] and NIKOMIMI [15] are developed to overcome the kidney vortexes. Round-hole and double-jet, which are typical in design of combined-hole film cooling system, are investigated in this study experimentally and numerically. It is observed that the anti-kidney vortexes produced in double-jet film cooling system are controlled by the pitch and compound angle of the two holes. The pitch of double-jet unit determines the formation of anti-kidney vortexes led by the interaction between two vortexes, while the compound angle affects the strength of each branch of anti-kidney vortexes. Being two of the most important factors for film cooling of gas turbine, blowing ratio and density ratio, vary in degree of influence on film cooling effectiveness, and the key point is whether the cooling gas has blown off from the surface. It is possible to achieve high film cooling effectiveness with a combined-hole system when the geometry parameters, (compound angle, pitch, etc.), and aerodynamic parameters, (blowing ratio, density ratio, etc.) match well on local flow structure.