Research On A Convective Cooling Turbine Blade Model Considering The Heat Conductivity In The Radial Direction

With the improvement of the aircraft engine performance,the thermal efficiency and the output power ascend,the temperature at turbine inlet gets higher and the working condition of turbine blades also gets worse.However,particularly high temperature can contribute to the increase of thermal load and stress of turbine blades.It can also lead to the appearance of blade ablation,affecting the turbine blade performance and shortening the blade working life.Therefore,it is common practice to apply cooling techniques to the turbine blades in order to tackle these problems.Normally,turbine blade cooling can be divided into two main types:the internal cooling and the external cooling.And the internal cooling is the foundation of the external cooling.Meanwhile,common research methods for turbine cooling include network method,three-dimensional simulation method and experiment etc.In this thesis,the internal cooling research is developed on turbine blades,and the fluid network,whose research object is the internal cooling fluid in turbine,as well as the blade one-dimensional and the two-dimensional heat transfer model,of which the research object is the blade,are all established.Besides,the calculation results of all the three models are respectively compared with results of three-dimensional simulation.The main tasks of this thesis are as follows:1)Based on the conservation law of momentum,energy and mass,element momentum equations,element energy equations,node continuity equations and node energy equations are all derived.By the given experimental correlations for heat transfer coefficients and friction coefficients in internal cooling elements and impingement cooling elements,a fluid network model of internal cooling air in impingement-cooled turbine vane channels is built up with the pressure balance and temperature balance of nodes and elements as solving conditions.The change rule of coolant temperature solved by this model is relatively close to the results of aero-thermal interaction CFD simulation,which shows that the fluid network method can be applied to the calculation of internal cooling channel fluid in impingement-cooled turbine vanes.2)With the blade as the research object,a blade one-dimensional heat transfer model is set up considering the heat conductivity in the direction normal to the blade wall.In accordance with the simplified one-dimensional heat transfer schematic sketch,an infinitesimal element is cut out at certain height.Via the application of theoretical analysis method,the differential relation of the coolant temperature along the blade span can be deduced with the assistance of internal cooling coolant energy equation,after blade coolant-side wall convective heat,gas-side wall convective heat and internal conductive heat of the infinitesimal element are all obtained.When given the inlet temperature of internal coolant,the analytic expressions of coolant-side wall temperature,gas-side wall temperature and coolant temperature can be acquired.Moreover,the comparisons of model calculated results with reference data and three-dimensional CFD simulation results respectively are conducted.It indicates that the one-dimensional heat transfer model can cost little time and is able to predict the blade wall temperature quickly.3)A blade two-dimensional heat transfer model is proposed,in which radial uneven temperature at inlet and cooling at blade tip and root are all taken into account with the consideration of the heat conductivity both in the radial direction and in the direction normal to the blade wall.On the basis of the two-dimensional heat transfer infinitesimal element simplified after considering radial heat conductivity,two-dimensional heat conductivity equation in the element is set up and given by theoretical analysis.The boundary conditions for the equation include heat transfer coefficients of the gas-side blade wall,the temperature of gas and the heat flux through the blade tip and root etc.Among them,the heat transfer coefficients of the gas-side blade wall and the temperature of gas are obtained from the three-dimensional CFD simulation flow field at blade designing stage by the boundary condition of adiabatic solid wall.In order to boost the usability of the model,the blade is divided into several partitions in the light of the location and number of internal cooling channels,and each partition is segmented further in radial direction.Every segment of blade is set the same calculation conditions.By adopting finite difference method(FDM),the difference expressions of two-dimensional heat conductivity equation,gas-side boundary condition,coolant-side boundary condition,blade tip boundary condition,blade hub boundary condition and coolant equation are all derived.The model is then applied to a high-pressure turbine vane of E3 and the contrast between the two-dimensional model results and three-dimensional CFD simulation results is carried out.It suggests that this model can be appropriate for the turbine blades where there is temperature difference between the inner wall and the outer wall.The blade gas-side wall temperature distribution tendency predicted by the model is similar to that by the three-dimensional CFD with almost exactly the same maximum temperature locations and minimum temperature locations.What's more,the maximum calculated error is no more than 6.5%,and the time cost in the calculation can be decreased by 95%.Besides,by contrast to the results of the one-dimensional,it proves that the blade two-dimensional transfer model has smaller calculation error.Overall,the blade two-dimensional heat transfer model is able to confirm the turbine blade convective coolant flow requirement,and can be employed to acquire the blade temperature of gas-side wall accurately and rapidly.