| The thermal radiation effect from hot parts of aircraft engines or gas turbines,as a critical factor,has become a significate factorin combustion process control and thermal protection system design.Ignoring its effects may cause problems such as over protection or lack of protection.To predict thermal radiation effects of high temperature parts has been a challenging issue nowadays.Generally,thermal radiation is full-field,non-gray and multi-field coupled,involving variations of gas temperature,species and concentration,and physical processes of fuel evaporation,atomization,combustion,soot production and turbulent fluctuation.Studies of thermal radiation effects for aircraft engines have been studied deeply in foreign countries in experimental data and numerical methods,but are still in itsinfan cyindomestic.Compared with the research level of combustion,flow and other heat transfer modes,the fully coupled simulation of thermodynamic processes of high temperature parts have not been matured.In contrast,the research level of understanding,mechanism of domestic engine hot end components heat radiation effect of basic data,efficient solution method research behind the combustion,flow and heat transfer in other ways,often become a short board of high temperature components of thermal process coupled simulation,thermal design theory is still not formed based on combustion,engine in a complete and reliable heat radiation.It is insufficient to provide a complete and reliable theoretical basis for the theory of heat transfer in engine combustion and thermal design.According to the above requirements,this paper mainly focuses on two terms: one is to develop a high-efficiency numerical technique for the radiation heat transfer in aircraft engines,and the other is to study the passive cooling structure.This paper consists of four parts as follows: calculation methodsof non-gray radiation propertiesof high-temperature gases,parallel solving technique for radiative transfer,validations,and coupling treatments of radiation heat environment and cooling structure.The treatment of non-gray characteristics of high-temperature gas is very crucial for efficiently solving the radiation problem in engine hot end parts.The non-gray characteristic calculation method must be well adapted to the typical working conditions of combustion products,improve the computing efficiency and ensure the computing accuracy at the same time.To calculate the high-temperature gas radiation characteristic parameters,we develop the gas-particle mixture combined with the narrow-band K-distribution model(CWNBCK)based on the narrow band merge method and the gas-particle cumulative K-distribution function merge method.The proposed model can handle the non-gray characteristics in wide spectrum range(even the full spectrum range)with high computational efficiency.The adaptability and reliability of the method to deal with the non-gray radiation of the engine are verified by the non-isothermal non-uniform,high temperature and high pressure,large gradient temperature/composition change and gas particle mixing medium.Radiation transmission parallel solution technology is important in the multi-physical field full coupling efficient simulation of the hot-end components based on the CFD framework.Therefore,we systematically study the parallel computing technology of participatory media thermal radiation transmission to be adapted to the spatial partitioning technology in CFD.By using the "transparent boundary" hypothesis and the "iterative delay method" for partitioned boundary data exchange,the problem of "numerical" boundary processing technology caused by the whole field characteristics of radiation transmission is solved.In order to solve the problems of convergence and slowdown in the parallel calculation of radiation transmission zoning,the "differential direction scanning order rule" is proposed to improve the transmission partition parallel computing convergence and the parallel efficiency by reducing the delay of data transmission between sub-regions according to the direction characteristics of radiation transmission.Based on the results of spectrum parallel and direction parallel and the hypothesis of spectral independence at the time of radiation balance,the band/partition combination multi-level parallel strategy is given when solving the participant media radiation transmission,which reduces the demand for memory and improves the flexibility of parallel computing.Finally,the numerical calculation scheme of the radiation transmission in the high-temperature parts of the engine is given through the combination of the radiation transmission band/partition parallel technology with the CWNBCK method for calculating the non-gray radiation characteristic parameters of the high-temperature gas.The reliability and efficiency of the numerical method are verified by analyzing different models and cases.In order to verify the reliability of the numerical solution technology of thermal radiation experimentally,the wall total heat flow and radiant heat flow data of the flame tube under different oil and gas ratio is measured by installing the heat flow meter and temperature measurement points at different positions on the wall of the flame tube.According to the experimental conditions,based on the CFD simulation results of combustion flow,the wall radiation heat flow calculated in this paper is compared with the experimental results to verify the reliability of this paper.At the same time,it is pointed out that under the experimental conditions,with the increase of oil-gas ratio the radiation ratio can be increased to 24%,in addition,the effect of carbon black particles on the radiation heat flow increases,can reach 25% and wall radiation heat flow circumferential unevenness is significantly less than the unevenness of temperature distribution,which is due to radiation transmission with a full range,making spatial distribution of radiation heat flow tends to average.Based on the numerical solution technology in this paper,for a certain type of aero engine,the radiation heat flow distribution characteristics of the combustion chamber wall,the outlet surface of the combustion chamber and the primary stator blade surface are analyzed.The results show that the unevenness distribution of radiation heat flow density at the outlet of the combustion chamber exacerbates the unevenness of the temperature distribution of the primary stator blade,so that the surface temperature of the stationary leaves which faced the high temperature zone of gas and high radiation heat flow area is higher than the average level by 200 ~ 300 K.In order to characterize the inhomogeneity of radiation heat flux density at the outlet of the combustion chamber,the Overall Radiation Distribution Factor(ORDF),Radial Radiation Distribution Factor(RRDF)and Circle Radiation Distribution Factor(CRDF)three parameters are used to quantitatively describe the two-dimensional inhomogeneity of the combustion chamber outlet heat flow density in the radial and circumferential directions.Thus the high heat flow density region of the combustion chamber can be determined.The paper further study the transfer effect law coupling thermal radiation and thermal barrier coating with a simple radiative heat transfer model,the results pointed out that both 8YSZ and Gd2 Zr O7(GZ)can obstruct the thermal radiation obviously with isolation effect.It should be paied attention that the projection radiation through the TBCs and the emission from TBCs can increase the total radiation arrivalling to the metal base,so the projected radiation and emission leve should both be consided when studying on the radiation from TBcs.At the same time,the paper also analyzed the heat transfer on the wall coupling radiation and the film cooling.The results pointed out that at the front of the film cooling,radiation could reduce the cooling efficiency significantly;however,in the downstream area of gas film,the radiation could enhance the cooling macroscopically,because the wall temperature increased here. |
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