Double-contraction-expansion type tail nozzle structure with three injection ducts

A double-contraction-expansion type tail nozzle structure with three injection ducts comprises a tail cone, a lobe mixer, an inner nozzle, an outer nozzle and a nacelle rear end shell, the outer nozzle is arranged in the nacelle rear end shell, the inner nozzle is arranged in the outer nozzle, and the lobe mixer is arranged in the inner nozzle. Under the working conditions of takeoff, subsonic speed, transonic speed and supersonic speed, the mixed flow of the core flow and the secondary flow expands in the inner spray pipe, the third flow expands in the third flow channel between the inner spray pipe and the outer spray pipe, and the speed difference of the two jet flows is small and is basically the same as the speed of the surrounding atmosphere flowing through the shell at the rear endof the nacelle; therefore, the problem that the aerodynamic performance and noise performance of the supersonic passenger plane are deteriorated due to insufficient expansion of the spray pipe under transonic and supersonic w