Experimental Investigations On The End Wall Film Cooling At Large Temperature Ratio And Combination Cooling With Film Hole And Vortex

The increase in the inlet temperature of gas turbines can directly improve the efficiency of aerial engines or heavy duty gas turbines.Currently,the inlet temperature has been higher than 1800?,which is far exceeded the permissible temperature of gas turbine end-wall material.Therefore,it is important to develop more efficient cooling technologies in order to maintain a reasonable operation life of the components with high thermal loads at a high efficiency.However,the surface of end-wall is directly washed by the complex secondary flow of the cascade channel,which leads in a serious non-uniform distribution of heat transfer coefficient and brings a challenge for us to rationally design the arrangement of film holes on the end-wall.Multiple rows of film holes are usually laid out at the end-wall to achieve an entire coverage of cooling air in the design of the advanced turbine cascade.It is well known that the end-wall film cooling characteristics are influenced by the high temperature mainstream environment,the secondary flow of the cascade channel,and the vortices at the exits of film hole.Among them,the temperature ratio of the mainstream to cooling air is a crucial factor,which affects the end-wall cooling performances.The temperature ratio is usually greater than 2.0 in real advanced gas turbines.However,in the observation of domestic and foreign published literatures concerned with end-wall film cooling in the recent decades,most of the experiments are carried out in the small temperature difference between the mainstream with cooling air,of which there are some experiments of film cooling using profiled gases to simulate the density ratio of hot gas to cooling air for no temperature difference.However,in actual fact,as the researchers of Wright-Patterson air force institute of technology of USA discussed,the temperature ratio reflects not only the density difference of cooling air and mainstream,but also the variations of thermal conductivity,specific heat capacity,viscosity and other physical properties.Therefore,under the permissible experimental conditions,an investigation on the effects of the temperature ratio on film cooling characteristics can help us accurately understand film cooling characteristics,and is also of great significance to optimize the cooling design for turbine end-walls.In this paper,ten rows of compound cylindrical holes are evenly arranged in the axial direction of a first-stage vane end-wall surface to achieve an entire coverage of cooling air.The experiments are carried out in a precise controllable hot wind tunnel to investigate the effects of mainstream temperature on the heat transfer of the end-wall surface,and the effects of mainstream-to-coolant blowing ratios,temperature ratios and the mainstream inlet Reynolds number on the whole film-cooling characteristics using infrared thermography.These experimental results reveal the differences of end-wall film cooling characteristics under large and small temperature ratios.On the basis of above studies,the tetrahedral ramp is arranged upstream or downstream of a cylindrical to change the interaction of coolant with mainstream in order to improve the coverage area of cooling air.In order to highlight the pure mixing characteristics of cooling air with mainstream regardless of the effect of thermal conductivity of solid structure,the experiments are carried out in the conditions of no temperature difference.The effects of height,orientation and location of tetrahedral ramp on the film coverage characteristics are discussed at different blowing ratios from three-dimensional angle by PLIF(Planar Laser Induced Fluorescence)technique.The aim of this experimental investigation is to provide a reference for the next research in optimizing cooling structures at large temperature ratios.