Numerical Investigation On The Aerodynamics And Infrared Radiation Characteristics Of 2-dimensional Nozzles With Sheltering Baffles

The hot components and flume of aero-engine exhaust system are the significant infrared radiation sources for the aircraft. Compared with axisymmetric nozzle, the non-axisymmetric circular-to-rectangular nozzle is capable of suppressing the infrared radiation signature with less performance loss. The numerical simulations on the aerodynamics and infrared radiation characteristics of two-dimensional circular-to-rectangular nozzle (aspect is 3.33) fixed with sheltering baffle or delta-tabs were conducted based on CFD/IR methods. The effects of sheltering baffle and delta-tabs on the aerodynamics characteristics and infrared radiation suppression of the two-dimensional circular-to-rectangular nozzle were analyzed.The circular-to-rectangular nozzle fixed with sheltering baffle changes the symmetrical flow-field of the two-dimensional nozzle. Compared with common two-dimensional nozzle, total pressure loss changes weakly. As the sheltering distance increases for the double sheltering plates, it can get higher pumping coefficient insides the channel and lower temperature on the upper sheltering plate. When a series of slots are made on the upper sheltering plate for the case of 10mm sheltering distance, the pumping coefficient rises from 0.31% to 0.63%, and the pumping coefficient reaches to 1.45% for the slot cooling configuration with film guide tongue. The circular-to-rectangular nozzle fixed with delta-tabs decreases the length of hot jet core region, and increases the pumping coefficient about 4% related to the common two-dimensional nozzle. But the thrust coefficient decreases obviously owing to the blockage of delta-tabs to the jet flow. Among the configurations of delta-tabs studied in the present, the nozzle fixed with four delta-tabs whose tip angle is smaller have the best pumping coefficient.All the sheltering baffle structures are of suppressing effects on the exhaust plume from -90°to 0°in the vertical plane. The nozzle fixed double sheltering baffles suppresses the underside infrared radiation in the vertical plane and enhance the infrared radiation from 0°to 90°. The double-sheltering baffles with film slots on the upper sheltering baffle have more obviously infrared radiation suppression effect. The nozzle fixed with four tabs whose tip angle is smaller have the best infrared radiation suppression effect.In this paper, the aerodynamics and infrared radiation characteristics of the scaled two-dimensional nozzles with shelter are conducted by experiment. By measuring downstream temperature and velocity field distribution for the different nozzle structure, the effects of the delta-tabs on the aerodynamics are concluded. By measuring the infrared radiation intensity for the exhaust system with/without sheltering baffle, the infrared suppression characteristics are quantitative compared.