关键词: 喷管;排气;辐射;数值分析

Abstract: A flow of exhaust gases from a helicopter infra-red suppressor is one of significant infra-red radiation sources. The infra-red radiation emission of the exhaust jet is related to exhaust temperature, velocity and composition concentration distribution. A numerical study is conducted to investigate radiation characteristic for design of the infra-red suppressor. A computational method for 3-D turbulent free flame jet exhaustedfrom a elliptical jet pipe of helicopter is described. It comprises a numerical solution technique for the time averaged governing partical differential equations and physics model for the turbulence and thermal radiation. The k-ε twin-equation turbulence model, which is based on Boussinesq’s effective viscosity hypothesir, is used here, because of its simplicity and compulation economy.lt is necessary to calculate radiative heat transfer for predicting radiation fluxes and temperature distribution. Many models have been proposed to account for radiation. In this sduty, a six-flux model has been used, principally because this method simulates radiative transfer by equations which are differential in form, and can, therefore, be easily incorporated into existing computation schemes for solving the simultaneous differential equations representing the balance of mass, momentum, energy and chemical specices. The SIMPLE algorithm and the formulation of the CTDMA, which is the assumption of cyclically repeating boundary conditions, are used to solve the finite-difference equatinos. Because of the parabolic feature of equations, solution may be achieved by a matching integration. Each or plane is visited in turn, the finite-difference equations are solved by a TDMA algorithm at each plane. Analytical results of exhaust gas temperature, velocity, composition concentration and radiarion flux are presented for reference of the design of the helicopter infra-red suppressor. The comparison of numerical results with experimental data shows that the numerical method presented here is generally feasible.

Key words: Nozzle;Exhaust gas;Radiation;Numerical analysis