Particle Layer Effects on Flowfield and Infrared Characteristics of Aircraft Exhaust Plume

Abstract

Most existing plume infrared (IR) suppression techniques are difficult to apply to an already established aircraft system and cannot be applied in an active way. As an alternative solution, the present study explores an active technique for shielding IR signals by injecting particles into the engine exhaust plume. A Eulerian-Lagrangian-based discrete phase method was used to calculate a multiphase flow composed of exhaust gas and injected particles. To analyze the characteristics of thermal flow and particle distribution under flight conditions, a cruise condition of Mach number 0.7 at an altitude of 20,000 ft was considered. Water droplets and carbon particles with diameters of 5 and 10 mu m were considered, and placed randomly within the particle layer. To analyze the shielding effect according to particle size, material type, and distribution pattern, the transmittance of IR electromagnetic waves of 3-5 mu m wavelength was analyzed using a Maxwell multilevel fast multipole method. When the total mass was kept the same, 5 mu m water droplets in wavelength bands below 3.5-3.7 mu m, and 10 mu m water droplets or 5 mu m carbon particles in wavelength bands above 3.5-3.7 mu m were more effective for shielding. If the single-layer transmittance information obtained in the present study is extended to actual particle layers of several tens of centimeters, it is expected that the shielding effect will be significantly higher.