| Radiative heat transfer is an important method of heat transfer in the natural world,which is widely used in daily life,industrial production,and national defense technology.In the previous studies,the actual surface was always treated as diffuse or specular surface for the convenience of calculation,but these treatments can not accurately simulate the actual working condition.The bidirectional reflectionce distribution function(BRDF)can accurately describe the reflection characteristics of the actual surface so that the radiation calculation of the multi-dimensional graded index medium coupled with BRDF surface can make the radiative heat transfer analysis more accurate and practical.The main work of this article is as follows:The radiative transfer calculation in a one-dimensional graded index media coupled with BRDF surface can not accurately describe the influence of BRDF surface on radiative transfer in a multi-dimensional graded index media.Therefore,this paper uses Minnaert model to simulate the BRDF surface and extends the DRESOR method to solve the radiative heat transfer problem in a two-dimensional rectangular graded index medium coupled with BRDF surface on the basis of one-dimensional system.The comparison between the calculated results and literature data verifies the correctness of DRESOR method.Meanwhile,the effect of different BRDF surfaces on radiative transfer in a two-dimensional rectangular system is discussed.And the influence of BRDF surface under different optical thicknesses and scattering albedo is also analyzed.It is found that the more deviation from the diffuse characteristics the BRDF surface has,the larger difference of the radiative heat flux and intensity between the BRDF and diffuse surface there exits.The increased optical thickness and scattering albedo both decrease the deviation of the radiative heat flux maded by the BRDF surface,which proves that the absorption and scattering effects of the medium can weaken the influence of the boundary condition on the radiative heat transfer in the system.The effect of BRDF surface on radiative transfer in a cylindrical medium is also studied.The cylindrical coordinate system is able to better describe the cylindrical boundary,and considering the radiation characteristics of cylindrical surface will make radiative heat transfer analysis more accurate in the cylindrical medium.Therefore,this paper analyzes the influence of BRDF surface on the radiative transfer in a two-dimensional cylindrical graded index medium under the cylindrical coordinate system.Here,the Minnaert model and the Torrance-Sparrow model are used to simulate different types of BRDF surfaces.The BRDF surface modeled by the Torrance-Sparrow model(T-S surface)contains specular and diffuse reflection components that makes the research more practical.Then,the effect of BRDF surface on radiant heat flux and radiation intensity distribution in a two-dimensional cylindrical system is discussed based on the accurate comparison benchmark.It is found that with the increase of the difference of reflection characteristics between the BRDF surface and diffuse surface,the difference of the radiative heat flux and intensity distribution significantly increases,the radiative heat flux deviation maded by the BRDF surface is up to 19.94%,and the radiative intensity distribution exists the regular change under different boundary conditions.In addition,the influences of the specular and diffuse component of TS surface on radiation intensity distribution are also discussed in detail,it can be found that the specular reflection of T-S surface plays the leading role within larger reflection angles. |
