Calculation of Aircraft Exhaust System Infrared Radiation Using Temperature Corrected Turbulence Model

Abstract

The standard two-equation turbulence model has no provision for large density gradient when used to compute the mean flow and the infrared radiation of hot jet. Stability consideration indicates that density gradient in a turbulent flow would add to instability due to local accelerations in the turbulent velocity field. Such instability would lead to faster mixing and spreading of jet flow. By choosing the total temperature gradient to represent the density gradient, a temperature corrected two-equation turbulence model would take into account the spatial instability. The coupled calculations for flow field, species concentration field and gas radiation transfer/energy equations based on Narrow Band k-distribution in non-gray absorbing-emitting were employed to simulate accurately the infrared signature of the aircraft exhaust system. The final infrared signature has considered the atmosphere effect, and homochromous atmospheric transmittance under various conditions was obtained by LOWTRAN 7. The standard two-equation model, Jones-Launder k-ɛ formulation, was also investigated for comparison with the temperature corrected turbulence model. All of the models were investigated for a reference nozzle producing heated jets at a low Mach number to avoid complications of large compressibility effects. The primary deficiency of the standard models was the delayed initial jet mixing rate relative to experimental data. The temperature corrected turbulence model provided improved mean flow and infrared radiation predictions relative to the standard models.