Recently, due to the development of the weapon system, the scope of aircraft''s mission has been expanded. The survivability of the aircraft in the modern war environment is an important factor that occupies the superiority of air warfare. Stealth technology that reduces the possibility of detection is required to improve aircraft survivability. In particular, high temperature exhaust gas emitted from propulsion engines can be a target of IR seekr. To reduce the infrared signal of the exhaust gas, it is very important to mix core gases uniformly with by-pass air. In this study, an experimental study was conducted to know the infrared signal reduction characteristics of the lobed mixer according to the bypass ratio.
In order to understand the mechanism of the infrared signal reduction, micro turbojet engine was modified and used for experiments. By-pass air was used by high-pressure air stored in an external high-pressure tank. A certain amount of compressed air is supplied through an external duct mounted on the micro turbojet engine exhaust to simulate bypass flow, which is mixed with high temperature core air and ejected to the atmosphere. The exhaust nozzle used in the experiment is a lobed mixer with a lobe of sinusoidal shape and is designed to have a penetration of 0.2. Exhaust gas temperature and infrared signal are measured according to distance from nozzle outlet under conditions of bypass ratio of 0.5, 1.0 and 1.4. Infrared reduction rates are compared with micro turbojet core gas only case.
As a result, as the bypass ratio increased, the infrared signal of the exhaust gas and the temperature decrease with bypass ratio. In the case of the bypass ratio 1.4, the effect of the temperature reduction is very large compared to other case. In addition, when compared to infrared signal results without a lobed mixer, the lobed mixer has an excellent effect on reducing the temperature of the exhaust gas and reducing the infrared signal than the cone nozzle. Also, the structure of mixed jet flow is verified through Schlieren visualization.