Study On The Heat Transfer And Film Cooling Characteristics Of The W Shaped Hole On A Turbine Vane

In order to obtain higher aeroengine performance,the temperature of the inlet gas of the turbine component increases continually,and this brings more challenges to the cooling technology.As a high-efficiency cooling technology,film cooling is widely used in turbine vanes/blades.Designing new film cooling structures with high film cooling effectiveness and carrying on the film cooling researches are of great significance to the establishment and improvement of the aeroengine design system of our country.The experimental film cooling data in the nearly realistic aeroengine working conditions is especially important.Compared with the basic film cooling researches carried on flat plates,there is a relative shortage of the three dimensional film cooling characteristics researches on the twisted turbine vanes and the applied researches on the film cooling characteristics on turbine vanes in the nearly realistic aeroengine aerodynamic working conditions.Therefore,the research emphasis of this thesis is to apply the new W shaped film cooling holes on the first stage turbine guide vane of a verification aeroengine,and make further study of the flow,heat transfer and film cooling characteristics in the middle section region on the straight vane under the nearly realistic aeroengine working conditions and the regions near the end walls on the three dimensional turbine vane.Three parts are studied by numerical simulation and experiment in this thesis:(1)The external heat transfer and flow characteristics of the turbine vane without film cooling are studied.Then the film cooling characteristics of the vanes with single row of W shaped holes and the full coverage film cooling vanes with W shaped or cylindrical holes are studied.The effects of the coolant blowing ratio,mass flow rate ratio,mainstream Reynolds number and turbulence intensity on the film cooling effectiveness and heat transfer coefficient are analyzed,which provide the necessary data to support the design of turbine vane.(2)In order to obtain the heat transfer and film cooling characteristics in the three dimensional flow areas on the full-span twisted turbine vane,the film cooling characteristics in the regions near the end walls on the three dimensional full coverage film cooling turbine vanes with W shaped or cylindrical holes are studied.This supports the elaborate design of film cooling which concerns the three dimensional flow near the end walls.(3)Moreover,a comparative study of the film cooling results of the full coverage film cooling turbine vane in high and low speed wind tunnel is done to analyze the influence mechanism of the high or low speed states on the film cooling characteristics,which provides reference of the designs of the subsequent film cooling experiments and the engineering applications of the experimental results in low speed conditions.The flow and film cooling characteristics in the mid-span region of the turbine vane are studied in the nearly realistic aeroengine aerodynamic working conditions firstly.The mainstream Reynolds number is the main factor which influences the heat transfer of turbine vane without film cooling,and it determines the states and the transition point of mainstream boundary layer.Compared with the dust-pan shaped holes,the W shaped holes effectively restrain the lift-off of the coolant.Moreover,the advantages of W shaped holes become more obvious at middle and high blowing ratios.The coolant is guided to the spanwise areas by the two troughs of the W shaped outlet.The ridge of the W shaped hole weakens the low-velocity vortex in the diffusion section,which reduces the lift-off influence of low-velocity vortex on the coolant jets.The mainstream turbulence intensity has obvious effects on the film cooling performance of the single row film cooling holes.At low blowing ratios,the coolant attaches to the wall surface.The high turbulence enhances the mixing of coolant and mainstream,which aggravates the coolant dissipation and decreases the film cooling effectiveness.However,at high blowing ratios,the coolant lifts off the wall surface.The high turbulence enhances the diffusion of the coolant to the vane surface,which increases the film cooling effectiveness.The full coverage film cooling effectiveness of the W shaped hole vane is generally higher than that of the cylindrical hole vane.The film cooling effectiveness on the pressure and suction sides of the cylindrical hole vane decreases with the mass flow rate ratio increasing.For the W shaped hole vane,the mass flow rate ratio has different effects on the film cooling effectiveness distributions in different regions of the vane surface.In the most regions of the W shaped vane and cylindrical hole vane,mainstream Reynolds number has little effects on the film cooling effectiveness generally.The total pressure loss coefficient of the W shaped hole vane is higher than that of the cylindrical hole vane.The full coverage film cooling characteristics of the three dimensional twisted turbine vane are studied in the low speed wind tunnel.The film cooling effectiveness of cylindrical hole vane generally increases with the coolant mass flow rate ratio increasing.However,at low turbulence condition,the coolant flows to the bottom region due to the compound angle at high mass flow rate ratio,which decreases the film cooling effectiveness in the regions near the top end wall.For the W shaped hole vane,at low turbulence condition,the film cooling effectiveness in the top region of suction side decreases with mass flow rate ratio increasing.Mainstream turbulence has different effects on the film cooling effectiveness in different regions of the cylindrical hole vane.The film cooling effectiveness of the W shaped vane decreases with the turbulence increasing.The W shaped hole decreases the velocity of coolant and diffuses the coolant in the spanwise direction,which makes the coolant dissipate in high mainstream turbulence conditions.In the near downstream region,the heat transfer coefficient of the W shaped hole is higher than that of the cylindrical hole,however,in the far downstream region,the heat transfer coefficient of the W shaped hole is lower.The comparative study of the heat transfer and film cooling results of the full coverage film cooling turbine vane in high and low speed wind tunnels is done.For the cylindrical hole full coverage vane,the variation trends of film cooling effectiveness in the high and low speed wind tunnels are similar,while the film cooling effectiveness value in the high speed wind tunnel is 20% lower than that in the low speed wind tunnel generally.The reason is that there is a distinct low pressure area in the obtuse angle side of the cylindrical hole outlet in the high speed wind tunnel,which makes the coolant accelerate in the hole outlet.Meanwhile,the coolant is in compressible flow state.The coolant density decreases and the momentum ratio increases.Therefore,the coolant on the pressure and suction sides of the vane in high speed wind tunnel is easier to lift off the vane surface,especially at high mass flow rate ratios.For the pressure and suction sides of the W shaped hole vane,the film cooling effectiveness in the low speed wind tunnel shows good agreement with that in the high speed wind tunnel.The reason is that the coolant diffuses in the W shaped hole,which decreases the coolant velocity and weakens the influence of the coolant lift-off on the film cooling effectiveness in the high speed wind tunnel.The coolant of the leading edge film cooling holes in the low speed cascade is easier to be affected by the mainstream blocking effect,so the less coolant on the leading edge leads to the lower film cooling effectiveness.The effects of the coolant on the heat transfer of the full coverage vane are related to the mainstream boundary layer sate on the vane surface.