Numerical Investigation On Pneumatic Performances And Infrared Radiation Characteristics Of An S-shaped Tunnel Single Expansion Ramp Nozzle

Some of the potential payoffs attributed to the single expansion ramp nozzles(SERN). These payoffs not only include a reduction in weight and cruise drag through improved integration and an increase in aircraft maneuverability and agility through the application of thrust vectoring and reversing, but also include a increase in stealth and survivability aspects of the aircraft through a reduction of nozzle infrared signature and radar cross section. The using of the single expansion ramp nozzle is one of the key strategies for suppressing infrared radiation signature. So a large number of countries pay great attentions to it. Basing on CFD/IR numerical calculations, the influence of different structures on nozzles'pneumatic performances and infrared radiation characteristics for the SERN are revealed, including making gaps on ramp,changing angle of the ramp or changing the area ratio.First of all, an experiment on the analytical prediction of pneumatic performances and infrared radiation characteristics for the scaled single expansion ramp nozzle is performed. Through comparing these data with the computational data basing on FLUENT, we can prove the turbulent model is reasonable and the program of calculating the infrared radiation characteristics is correct. Then we could use the reasonable turbulent model and the program of calculating the infrared radiation characteristics to compute the real sized single expansion ramp nozzle.The results show that: After making gaps on the ramp, the peak value of plume infrared radiation intensity is decreased 25.2% at coordinate of YOZ plane and 26.4% at coordinate of XOZ plane. The plume infrared radiation intensity also is decreased at other angles. The average temperature of the ramp is decreased too, from 643K to about 335K. Because of these, the total infrared radiation intensity of the nozzle is decreased a lot. At the same time, the pneumatic performances are improved, including a increase in axial thrust ratio and a reduction in thrust-vector angle. With the increasing of ramp's angle, the effect of the covering of the ramp on the inner-wall and plume is weakened between the angle of -10o and -30o at coordinate of YOZ plane. With the increasing of the area ratio the nozzle's infrared radiation intensity is decreased but at the same time the thrust of the nozzle is decreased too. The change of NPR has a little influence on nozzle's infrared radiation intensity.