基于BRDF的排气系统红外辐射特征计算研究

Computational Investigation of Infrared Radiation Characteristics of Exhaust System Based on BRDF

为了提高涡扇发动机排气系统红外辐射强度的计算精度,研究了壁面反射特性对计算结果的影响。红外辐射特征的计算采用反向蒙特卡罗(RMC)法,壁面反射采用双向反射分布函数(BRDF)和漫反射两种模型,并将计算得到的红外辐射强度与模型试验测试结果进行了对比。通过研究BRDF模型参数的变化对计算结果的影响确定了所采用模型中参数的取值。结果表明:壁面反射采用BRDF模型是提高红外辐射计算精度的有效途径。对于本文的试验模型,采用BRDF模型后,明显减小了以低发射高反射部件辐射为主的方向上红外辐射强度的计算误差。

In order to improve the computational precision of infrared radiation of a turbofan engine exhaust system, the effect of surface reflection characteristics on computational results is investigated. The reverse Monte Carlo （RMC） method is adopted to compute the infrared characteristics, and both bidirectional reflectance distribution function （BRDF） and the diffuse reflection models are employed. The computational infrared radiation intensities of a model engine exhaust system are compared with the experimental results. The parameters of the BRDF model are determined by investigating the effect of the parameters on computational results. The study shows that the adoption of BRDF model is an effective way to improve the computational precision of infrared radiation. For the case studied in this paper, the computational error of infrared radiation is obviously reduced at the orientation where the radiation mainly comes from low emittance and high reflectance surface when BRDF model is adopted.