Research On Novel Cooling Structure And Mixing Mechanism Of High Heat Load Air-cooled Turbine

During the " 14th Five-Year Plan" period,the hanging temperature of China’s turbine blades has reached 2200K,while the withstand temperature of turbine blade materials is only about 1500K.Therefore,in the absence of ultra-temperature-resistant blade materials,it is necessary to rely on advanced turbine blade cooling technology to ensure the normal operation of gas-cooled turbines with high heat load.In aero-engines and gas turbines,the leading edge of the turbine guide vane is first subjected to high-temperature gas scour,and the normal jet and film composite cooling method with high cooling effectiveness is usually used.The research hotspots of leading edge impingement cooling of turbine blades are not only normal jet cooling and tangential jet cooling(also known as vortex cooling),but also sweeping jet.Because of its advantages of uniform heat transfer effectiveness and wide coverage,it is a new type of high efficiency impingement cooling method.However,the current research on sweeping jet cooling only stays on the smooth surface,and has not yet covered the influence of the presence of film holes on the aerodynamic heat transfer characteristics.Therefore,this paper focuses on the cooling of the leading edge of turbine blades,and studies the mixing mechanism of coolant and hot gas in the sweeping jet and film composite cooling structure,so as to improve the cooling effectiveness of the leading edge of the blades,reducing the amount of coolant used.The main work includes:(1)The sweeping jet and film composite cooling structure was proposed and applied to flat plate models,semi-cylindrical leading edge model,and actual blade leading edge,respectively.The results show that the overall cooling effectiveness of sweeping jet and film composite cooling is higher than that of traditional normal jet and film composite cooling,and sweeping jet and film composite cooling also has the advantage of uniform heat transfer performance.However,the advantage of high overall cooling effectiveness of sweeping jet and film composite cooling on the leading edge model decreases with the increase of blowing ratio.In addition,the results also show that the total pressure loss coefficient of sweeping jet and film composite cooling is high,the influence of the inclination angle of the film holes and temperature ratio on the mixing of gas and coolant and cooling effectiveness of the sweeping jet and film composite cooling is small.(2)The influence of impinging distance(P/D)on the leading edge model of turbine blades on the aerodynamic heat transfer characteristics of sweeping jet and film composite cooling was further studied.The difference in the overall cooling effectiveness under each impinging distance is small,indicating that the impinging distance.as an important parameter of impingement cooling effectiveness,cannot affect the overall cooling effectiveness of the sweeping jet and film composite cooling structure within the range of 3-5,so the influence of the impinging distance can be ignored when applying this composite cooling structure.However,it is found that the coolant flowing out of the middle film holes always tends to flow to the left or right,which affects the uniformity of the distribution of overall cooling effectiveness.(3)The relative size of the velocity and turbulence intensity of the mainstream(hot gas)and film is the dominant factor for the inclination of the coolant flowing out of the middle film holes.The flow structure is more sensitive to changes in turbulence intensity when the mainstream velocity is higher.The flow structure is greatly affected by the mainstream velocity,which determines the severity of external mixing and the total pressure loss coefficient,as well as the coolant outlet velocity of the film holes.When the mainstream velocity is low,the mainstream and the film are in a "stalemate" phase,and the coolant from the middle film holes flow towards the lower pressure side.When the mainstream velocity is large,the mainstream with the higher momentum to suppress the film to the outer surface,and the coolant flowing out of the middle film holes can flow evenly to both sides.(4)The proportions of internal cooling effectiveness,convective cooling effectiveness inside film holes,and external cooling effectiveness in the leading edge model were calculated,and the calculation method was validated.The results show that it is reasonable to use the time-averaged results to analyze the ratio of impingement cooling effectiveness,convective heat transfer effectiveness inside the film holes,and external cooling effectiveness in the overall cooling effectiveness.In the leading edge model,the average ratio of impingement cooling effectiveness to overall cooling effectiveness is 64.33%,and the average ratio of convective heat transfer effectiveness inside film holes is 38.02%.As the blowing ratio increases,the ratio of external cooling effectiveness gradually changes from positive to negative.(5)Considering the negative effects of the random inclination of the coolant flowing from the middle film holes and the external cooling effectiveness,the application of sweeping jet and film composite cooling to the high-pressure blade focused on the location,aspect ratio,and inclination angle of the film holes,and conducted POD(Proper Orthogonal Decomposition)and DMD(Dynamic Mode Decomposition)analysis of the mixing of mainstream and coolant in the leading edge region.The above research conclusions and methods can provide data support and basis for the adoption of novel and efficient cooling structures for actual blade leading edges.enrich the cooling schemes for air-cooled turbine blades,and have significance in supporting the development of high efficiency aero-engines and gas turbines.