Rrsearch On IR Suppressant Of Hot Exhaust With The Spherical Particles

During the last 40 years, infrared radiation (IR) guided missiles have been the leading killer of combat aircraft. The aero engine is one of the most important IR sources of aircraft and it becomes to be much more distinct with the increase of its performance. This results in a great challenge of IR suppression of combat aircraft especially the aero engine. Thus understanding and controlling aircraft IR signature are the essential and significant element in addressing the mission effectiveness of future conflicts.Aerosol obscure is one of effectual techniques of IR suppression, which has been applied to decrease the IR signature of hot air exhausted from aero engine in a few countries. Scattering and absorbing of IR energy can be combined together with the small particles suspended in obscure, and the transmission of IR will be reduced according to those.All the results show that the IR signature of exhausted hot air from aero engine is affected by the optical characters of discrete particles and the distributions of discrete particles in aerosol at the same time. And the basal parameters of optical character is complex index of refraction, which is decided by extinction efficiency factor, asymmetry factor and forward scattering factor. The distribution of discrete particles in aerosol is decided by the diameter, velocity, thermal conductivity and thickness of discrete particles.It was found in investigations that the rule of IR signature affected by the diameter of discrete particles was the most complicated. And there existed the best IR signature extinction when the diameter of particles was in the range of 1.0μm.The results presented that the IR signature is much more sensitive to the imaginary part of complex index of refraction than the real part. Better IR signature was achieved when the imaginary part of complex index of refraction equals 3.0.Among these three parameters of velocity, thermal conductivity and thickness of discrete particles, the IR signature was decreased greatly in the case of higher thickness and it decreased a certain extant in the case of larger velocity. The diameter of discrete particles is so small that the IR signature was affected by thermal conductivity faintly.Experimental and numerical results also demonstrated that the chosen of discrete particle in aerosol should confirm the diameter by wavelength firstly, select the material whose extinction efficiency factor is higher, and pick out the material whose asymmetry factor, forward scattering factor are lower followed.