椭圆截面喷管排气辐射热流数值分析

本文对直升机红外抑制器椭圆截面喷管排气的辐射热流进行数值分析,并预估排气温度分布速度和燃气成分分布对辐射热流的影响。为了正确计算辐射热流,本文采用六热流辐射模型来考虑尾焰对周围环境传热的影响。紊流模型采用修正的双方程k—ε模型。由于喷管出口截面为椭圆形,因此排气为三元自由射流,控制方程为抛物型偏微分方程,可采用前进积分求解。计算结果与试验结果基本一致,说明本计算方法是可行的。

A Numerical Study of the Radiation Characteristic of an Elliptical Exhaust Jet

The flow- of exhaust gases from a helicopter infra-red suppressor is one of the significant infra-red radiation sources. The infra-red radiauve emission of the exhaust jet is related to exhaust temperature,velocity and composition profiles. A numerical study is conducted to investigate radiation characteristics for the design of the infra-red suppressor. A computational method for 3-D turbulent free flame jet exhausted from an elliptical jet pipe of a helicopter is described. It comprises a numerical solution technique for the time averaged governing partial differential equations and physical models for the turbulence and thermal radiation. For considering the effect of density changes in the exhaust jet,a modified k ?two equation turbulence model is used here, because of its simplicity and computational economy. It is necessary to caicualate the radiative heat transfer for predicting radiation fluxes and temperature distributions. Many models have been proposed to account for radiation. In this study, a six-flux model has been used, principally because this method models the radiative transfer by equations which are differentia! in form, and can, therefore? be easily incorporated into existing computation schemes for the solution of simultaneous differential equations which represent the balance on mass, momentum, energy and chemical species. The SIMPLE algorithm and the formulation of the CTDMA,which is the assumption of cyclically repeating d boundary conditions,are used to solve the finite-difference equations. Because the parabolic type is a feature of the equations,solution may be achieved by a marching integration. Each 6r plane is visited in turn,at which the finite-difference equations are solved by a TDMA algorithm. Analytical results of exhaust gas temperature. velocity ,composition and radiation flux are presented for reference of the design of the helicopter infraered suppressor. The comparison of numerical results with expert mental data shows mat the numerical method presented is generally feasible.