Infrared radiation signature of three bearing swivel nozzle

In view of the three bearing swivel nozzle （3BSN） for turbofan engines，numerical simulation method was used to study the spatial distribution of infrared radiation signature of three bearing swivel nozzle under the working conditions of vertical take-off and landing （VTOL） and cruise（non-vectorial and 90° vectorial conditions），and the influence mechanism was also analyzed.The results showed that under non-vector state，the local high temperature area appeared on the lower wall of 3BSN due to the special geometry surface，and the jet shape became an elliptical cone，resulting in a maximum increase of 44.6% in wall infrared radiation from positive detection angle over negative detection angle at vertical plane，and the gas radiation on horizontal detection plane was greater than that on vertical detection plane.Under 90° vector state，the total radiation peak was only 43.3% of the non-vector state due to the shielding effect of deflected 3BSN structure on the front high-temperature components.The vector deflection of 3BSN reduced the gas velocity on the side far from curvature center and increased the temperature.A large local high temperature area appeared on the outside of the nozzle，which caused the wall radiation in negative detection angle range larger than that in positive detection angle on vertical detection plane，and the maximum relative difference was up to 71.9%.The deflection also obstructed the high temperature gas inside the nozzle.The negative detection angle of vertical detection plane can only cover the high temperature gas area at the nozzle exit，which was significantly smaller than the positive detection angle，resulting in the maximum relative difference of 20% in gas radiation.