A parametric design method, which was based on super-elliptical transition and self-adaption infrared radiation shield for the double S-shaped nozzle, was introduced. The complete shielding of high-temperature components in the S-shaped nozzle was realized. Model experiments and numerical simulations were performed to investigate the effects of offset ratioS/D, the ratio of length to diameterL/D, and the aspect ratioW/Hon the aerodynamics and infrared radiation. The results showed that the total pressure recovery and thrust coefficients were improved initially, but dropped rapidly with the increase in offset ratios with the range of investigated parameters. There existed an optimal offset ratio for the aerodynamic performances. Considering the weight penalty, the length of nozzles should only be increased properly to achieve better aerodynamic performances. Both friction and viscous losses caused by large streamwise vortices dominated the aerodynamic performances of nozzles. The nozzle with the aspect ratio ofW/H=5.0was recommended for achieving optimal aerodynamics. The increase in aspect and offset ratios could effectively suppress plume radiation, which was, however, not sensitive to overall radiation. Compared to circular nozzles, double S-shaped nozzles reduced overall infrared radiation by over 50%, which proves significant stealth ability. A balance between aerodynamic performances and infrared radiation suppression could be reached for double S-shaped nozzles.

A proper-orthogonal-decomposition analysis was performed on the turbulent flow in the near-wake region of an S805 airfoil in deep stall at an angle of attack of 30 deg. The flow was measured using tomographic particle image velocimetry at a Reynolds number of 4600. Instantaneous turbulence structures, which were significant contributors to the first two proper-orthogonal-decomposition modes, were studied. These structures included the large-scale Kármán vortex and small-scale shear-layer vortices that were interacting with the Kármán vortex. An interesting correspondence was observed between the rotational vectors in proper-orthogonal-decomposition modes 4 and 5 and the locations of the leading-edge shear-layer vortices in the flowfields, which were major contributors to these two modes. Similarity was found in the autospectral functions computed from the velocity fields, which were significant contributors to the first five proper-orthogonal-decomposition modes. The wavelengths corresponding to the peak values of autospectral functions could be related to the size of the induced flows by the Kármán vortex and the streamwise spacing of the shear-layer vortices.

This paper considers supersonic oscillators, in which the widths of the power nozzle and throat are the significant geometric parameters in characterizing the different internal flow characteristics. Supersonic fluidic oscillators with different power nozzle and throat widths are studied through time-dependent numerical computations. Two characteristic parameters, namely the delay time for the initiation of oscillation t₀ and the oscillation period T, are selected to describe the physical mechanisms of the various oscillators. The Mach numbers and streamlines at different times are also used to investigate the flow characteristics. The results show that, when the power nozzle exit width is much smaller than the inlet width of the mixing chamber, the delay time decreases as the throat width increases. Changing the throat width of the oscillator does not significantly affect the delay time t₀ when the power nozzle exit width is equal to the inlet width of the mixing chamber. The oscillation period decreases gradually as the oscillator throat width increases. It is found that there exists a critical throat width which determines whether the oscillators work.

For the purpose of improving thrust and cooling the wall of the nozzle on a micro turbojet engine, the aerodynamic characteristics micro lobed ejector, which consists of a lobed nozzle and mixing, is studied using numerical calculations and experiments. Firstly, the aerodynamic performances of several lobed nozzle jectors with different geometries were calculated based on the Reynolds-averaged Navier-Stokes equations with k -ε turbulence model. The numerical results show that the pumping ratio is enhanced with the increase of lobe expansion angle in the range of 5 to 17 degrees. Firstly, the thrust gain increases and then decreases with the increase of lobe expansion angle. Secondly, taking into account of the aerodynamic performances and weight penalty, the thrust and the wall temperature of the nozzle of a micro turbojet engine with a lobed ejector of 5-degree expansion angle was measured. Experimental data demonstrate that the lobed ejector increases the thrust of the engine by 2.99% relative to the convergent nozzle. Moreover, the peak temperature of nozzle wall is decreased by 30%. At the same time, the pumping air mixed with the exhaust plume decreases the temperature of the plume. It is believed that the lobed ejector has another advantage of reducing the infrared radiation of the micro turbojet engine.