Numerical Simulation Study Of Low Reynolds Number Turbine Gas-thermal Coupling

With the continuous improvement of turbine performance,the aerodynamic load of turbine blades continues to increase,the thickness of the boundary layer of the blade suction surface increases,and it is easy to have flow separation,and when the aircraft is in a high-altitude cruising state,the turbine works in a low Reynolds number environment,and the internal flow of the turbine is more complex,so it is extremely important to accurately predict the internal flow field and temperature field of the turbine under low Reynolds number conditions.With the continuous development of computational fluid dynamics,gas-thermal coupling numerical simulation technology has become an important tool for turbine design.The main work of this paper is to carry out the numerical simulation calculation of gas-thermal coupling of high-pressure turbine guide vanes,and simulate and predict the influence of Reynolds number change on the flow field and temperature field in the turbine under low Reynolds number conditions.(1)In this paper,the NASA-Mark II high-pressure turbine guide vane with radial cooling channel is used as the research object,a numerical simulation calculation model is established,and different turbulence models and rotary models are used to simulate the gas-thermal coupling of the blades.The results show that the numerical calculation results of gas-thermal coupling using the transfer model are in good agreement with the experimental results.By simulating and simulating the blade surface flow characteristics and heat transfer characteristics under different turbulence models,the calculation results of different turbulence models on the blade surface pressure are basically the same.However,due to the insufficient simulation accuracy of the high Reynolds number Standard k-εmodel and the RNG k-εmodel on the flow of the boundary layer of the blade wall,the temperature calculated by the simulation of the high Reynolds number turbulence model is higher than the experiment,and the maximum difference in the temperature of the middle diameter section of the dimensionless blade is 0.175,and the absolute temperature difference is about 142K,which is relatively large,and the error of the heat transfer coefficient of the blade surface is also relatively large.The transition model can be used to predict the generation of transition in the boundary layer,and the calculation results are consistent with the experiment,and the accuracy is high.(2)Aiming at the problem that the change of Reynolds number has a significant effect on the surface flow and heat transfer of the guide vane of high-pressure turbine under low Reynolds number conditions,this paper achieves the purpose of changing the Reynolds number by proportionally adjusting the total inlet pressure and the outlet static pressure,and designs 12 groups of working conditions for simulation calculation and analysis.The results show that with the change of Reynolds number,the flow state of the fluid on the blade pressure surface does not change significantly,while on the blade suction surface,the flow separation zone of the blade wall gradually shrinks to almost disappear with the increase of Reynolds number.It was found that when the Reynolds number changed,the static pressure coefficient of the blade surface remained basically unchanged.In the range of Reynolds number Re=1.9×10~4to Re=5.8×10~6,with the increase of Reynolds number,the surface temperature of the blade generally showed a downward trend,the heat transfer coefficient gradually increased,and the dimensionless shear stress on the wall continued to increase.(3)The influence of inlet turbulence on turbine flow and heat transfer was studied,and under the condition of low Reynolds number,five sets of different mainstream inlet turbulence working conditions were designed,and the gas-thermal coupling numerical simulation was calculated respectively,and the results showed that within the calculated range,the mainstream inlet turbulence intensity had little effect on the flow and heat transfer of turbine guide vanes.The results show that the surface temperature of the blade is too high when the turbulence intensity of the cold flow inlet is Tu=1%,and the surface temperature of the blade decreases when the turbulence intensity of the cold flow inlet is greater than 3.2%,and the surface temperature of the blade decreases with the increase of turbulence inlet.(4)The influence of wall roughness on turbine flow and heat transfer was studied,and under low Reynolds number conditions,five groups of different wall roughness working conditions and smooth walls were designed to perform gas-thermal coupling numerical simulation calculation on the turbine guide vanes.The results show that the blade surface temperature is the lowest under smooth wall conditions,and the blade surface temperature gradually increases with the increase of wall roughness.