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This study aims to improve the survivability and maneuverability of the fighter,and study the stealth performance of fighter in the jet noise of aeroengine, it is of great significance to study the jet noise characteristics of double S-bend nozzles.

The multiparameter coupling and super-ellipse design methods are used to design the cross section of double S-bend nozzle. Taking unsteady flow information as the equivalent sound source, the noise signal at the far-field monitoring points were calculated with Ffowcs Williams–Hawkings (FW–H) method, and then, the sound source characteristics of the double S-bend nozzle are analyzed.

The results show that the internal flow of the S-bend nozzle with rectangular section is smoothed and the aerodynamic performance is better than super-ellipse section, the shear layer length of rectangular section is longer, the thickness is smaller and the mixing ability is stronger. The sound pressure level of the two S-bend nozzles decreases with the increase of the monitoring angle, and the sound pressure on the horizontal plane is greater than the vertical plane. In the direction of 40°–120°, the jet noise of rectangular nozzle is smaller, and the multiparameter coupled rectangular cross section structure is more applicable.

It is beneficial to reduce the jet noise of the engine tail nozzle and improve the stealth performance of the aircraft.

There is very little research on the jet noise characteristics of the double S-bend nozzle. The multiparameter coupling and the super-ellipse method are used to design the nozzle flow section to study the aerodynamic performance and jet noise characteristics of the double S-bend nozzle and to improve the acoustic stealth characteristics of the aircraft.

THE wind tunnel described in this report forms one of the major items of equipment of the Division of Aeronautics of the Council for Scientific and Industrial Research. The primary purpose of the tunnel is for tests of firms' designs. The size of the working section was chosen so that some full size aircraft components could be tested, while the power was selected so that the Reynolds number obtained at normal speed in tests of complete models would be great enough to avoid large‐scale effects. However, as it was the only tunnel to be built, at any rate for some time, research had to be borne in mind in the design, and in addition to the requirements already stated, the air flow was to be as uniform and free from random turbulence as possible.

By reducing the coating thickness of the weak scattering source, the coating weight of the absorbing material can be reduced by 35% with little effect on the RCS.

To alleviate the weight-increasing problem caused by a large number of coating of absorbing materials, a method for zonal coating of absorbing materials for a stealth helicopter was proposed. By appropriately reducing the thickness of the coating at the secondary scattering locations, the amount of coating used is significantly reduced.

Compared with the full-coated, the zonal coating scheme achieves the corresponding RCS reduction effect.

Zonal coating design can achieve the effect of reducing coating weight and cost.

The effects of different coating methods on RCS were verified by electromagnetic scattering simulation, and the applicability of the zonal coating design of the absorbing material to the stealth helicopter was verified.