Effect Of Calculation Method Of Gas Thermalparameters And Characteristics On Turbineheat Transfer

One of the important factors to improve aero-engine performance is to increase gas temperature in front of turbine.To overcome temperature limitation that turbine blades withstand,it is necessary to investigate the convective heat transfer over the turbine blades.Due to the limitations of theoretical analysis and experimental research,it is necessary to study the convective heat transfer rate over the turbine blades by numerical simulations at present.Existing methods do not consider the influence of the multi-component characteristics of hot gas on the performance of the propulsion system.The working substance of the present results adopted is hot air,but the working substance in the combustion chamber is multi-component gas.Convective heat transfers over aero-engine component walls or mixtures of cooling air and hot gas involve multi-component gas transport processes.The effects of thermal properties,transport and diffusion of multi-component gas on convective heat transfer are then systematically studied over flat plates and turbine cascades in this paper.First,to study the influence of gas thermal parameters on incompressible convective heat transfer,calculation method of gas thermal parameters for the combustion of hydrocarbon fuel and air was proposed.Using part of the gas thermal parameters given by this method as input conditions,numerical simulations of convection heat transfer over the flat plate and the turbine cascades at different inflow temperatures were performed,and the simulation results of convection heat transfer of air as the working substance were then performed for comparisons.The results show that when the other conditions are the same,the local Nusselt number of multi-component gas is greater than the Nusselt number of air over the flat plate and turbine cascades.With the increase of the inlet temperature,the difference of the local Nusselt number between air and hot gas becomes larger.Compared with air as the working substance,the Nusselt number over the flat plate increases from 2.8% to3.6%,and the Nusselt number increases from 7.25% to 9.69% over the cascades.Secondly,an algorithm for calculating the influence of different gas component transport coefficients on incompressible convective heat transfer was proposed.Based on this method,four commonly used methods for calculating gas transport coefficients such as molecular viscosity coefficient and thermal conductivity were selected for analysis.The results show that the calculation methods for the transport coefficients of different gas components have certain effect on the convective heat transfer over the flat plate and the cascades.At given inlet temperature of 1000 K and 2200 K,the maximum difference between the Nusselt numbers of the upper and lower boundaries over the flat plate increases from 2.7% to 4.0%,and the largest differences in the Nusselt numbers over the turbine cascades increase from 4.58% to 9.70%,respectively.Thirdly,for compressible convective heat transfer,the influence of gas thermal parameters on compressible convective heat transfer was studied based on the above analysis of incompressible convective heat transfer.The results show that when the other conditions are the same,the local Stanton number of multi-component gas is slightly smaller than that of air.For the flat plate convection heat transfer,as inlet Mach number increases,the difference of the local Stanton number between air and gas becomes larger.Within the given range of inlet Mach numbers,compared to the air as working substance,the local Stanton number of the hot gas increases from 2.1%to 5.2% over the flat plate.Under given conditions,the local Stanton number increases to 3.32% over the turbine cascades.For compressible convective heat transfer,the effects of different combinations of calculation methods for different component of gas transport coefficients on compressible convective heat transfer were then studied.The results show that the calculation methods for the transport coefficients of different gas components have certain effect on the convective heat transfer over the flat plate and turbine cascades.When the incoming Mach number increases from 0.3 to 1.2,the difference between the upper boundary of gas Prandtl number and the local Stanton number by Sutherland’s law increases from 5.756% to 5.9%,and the difference between the lower boundary and Sutherland increases from 5.665% to 5.73% over the flat plate on the average,respectively.When the incoming Mach number is 0.22,and the ratio between inlet and out pressure is 1.3,the difference between the upper boundary of the gas Prandtl number over the back of the turbine cascades,and the local Stanton number by Sutherland’s law is 3.404% over the lower boundary,the largest difference is 3.725%.Finally,summarizations were conducted,and the direction of further research was suggested in the paper.