Effect Of Hole Configurations On Film Cooling Performance And Optimal Design

Gas turbine as a kind of power equipment with high thermal efficiency and low pollutant emission have been widely applied in many industrial fields such as aeronautical propulsion and land power generation.The inlet temperature of the gas turbine is constantly raised to achieve higher thermal efficiency and power output.However,this brings great difficulties to the protection of its hot components.Film cooling has been widely used in the protection of hot components of gas turbines.The factors that affect the film cooling performance can be divided into two categories: geometric parameters(hole diameter,hole length,inclination angle,etc.)and aerodynamic parameters(blowing ratio,density ratio,turbulence intensity,etc.).It is essential to obtain the influence of each factor on the film cooling effectiveness quickly and accurately.In this paper,the Taguchi method is introduced into the research field of film cooling.Taguchi method is used to optimize the geometric parameters of the double-row film holes.The optimal combination of parameters for double-row holes is obtained,i.e.,the combination of the upstream hole(inclination angle 45° and angle of orientation 60°)and downstream hole(inclination angle 75° and angle of orientation-65°).The optimal scheme with double-row holes achieved the highest overall average film cooling effectiveness of 0.27.The hole configuration has an important effect on the film cooling effectiveness.In this paper,the effects of three hole configurations with constant outlet area(conical hole,fan-shaped hole,and combined hole)on the film cooling effectiveness were studied by experiments and numerical simulations.It is found that small holes on both sides of the combined hole can effectively inhibit the generation of kidney vortices.The combined hole has the best improvement on the cooling performance,and the improvement effect is more obvious as the blowing ratio increases.The fan-shaped hole and conical hole have similar effects on improving cooling effectiveness.Although the complex hole configuration can effectively improve the film cooling performance,it is actually difficult to be processed and cannot be used.Therefore,the method of improving the film cooling performance by using backward injection hole is proposed.In addition,two types of hole configurations,backward injection holes and forward injection holes,are combined and arranged on the plate in a staggered manner.Three different combinations of the perforated plate structures are designed.For the backward injection hole,the exit momentum of the jet flow is small,the velocity boundary layer near the wall is thin,and the strength of the kidney vortices is also weak.These factors are conducive to improving the film cooling performance.The backward hole with2.5D hole length and 35° inclination angle obtains the best film cooling effectiveness at the blowing ratio of 2.0.The inclination angle is the parameter that has the greatest effect on the film cooling effectiveness for the backward injection hole.The forward hole is arranged in the middle area of the perforated plate,and the obtained transverse film cooling effectiveness will form a "triangle" distribution,which is not conducive to obtaining uniform film cooling effectiveness.The combination of all backward holes installed on the perforated plate(combination 3)can reduce the wall temperature to the greatest extent,and the temperature distribution on the wall is also very uniform.