Wall Pressure and Temperature Distribution in Bent Oblong Exhaust Ejectors

Abstract

In aerospace industry ejectors are employed to reduce infrared signatures of hot exhaust gases and ducts. The ambient air, entrained from the surrounding, acts as a cushion between hot exhaust and the ejector walls. This reduces the temperature and hence the infrared signature of exhaust ducts. In many applications the ejectors are bent upward to hide the hot engine from heat seeking missiles. Due to the bend, the hot gases from the turbine hit the side walls leading to hot spots on the ejector walls. This study was aimed to see the effectiveness of a series of bent oblong ejectors as infrared signature suppressors. Wall temperatures were measured with infrared thermal imaging camera and pressures were measured with static wall taps. The wall static pressure shows rise in pressure along the length of the ejector. It also identifies areas of flow separation and the areas where the primary flow hits the ejector walls and produces hot spots. Wall temperature distribution shows that the oblong nozzle has a detrimental effect by creating hot spots on the ejector surface. Wall temperature of the ejectors increased with the degree of bend. The normalized maximum wall temperature (T*w(max)) of 67.5° bent ejector was 45% higher than the straight ejector. The swirl in the primary flow also increased the wall temperature. On a straight ejector the T*w(max) with the 30° swirl was 35% higher than the no swirl case.