Abstract
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.
Highlights
Booming development of technologies in infrared detection for infrared signatures has severely threatened aircraft powered by aero-engines, one of which is the portable infrared radiation (IR) seeking missiles for military use [1]
This study demonstrates integrated procedures to form a double S-shaped nozzle based on the complete line-of-sight shielding principle
(1) By the method introduced in this paper, the geometric shape of double S-shaped nozzles with a super-elliptical transverse section can be established with the input of inlet and outlet parameters of nozzles
Summary
Booming development of technologies in infrared detection for infrared signatures has severely threatened aircraft powered by aero-engines, one of which is the portable infrared radiation (IR) seeking missiles for military use [1]. It is considered that the exhaust system of engine is the most important radiation source in the near infrared band, and most aircraft with a function of stealth must deploy a low-level IR signature nozzle [3]. For an axisymmetric convergent-divergent nozzle, hightemperature units, such as center plug, flame holder, liner, and strut, are exposed of a considerable radiation intensity at some particular lines of sight. As well known, shielding of radiation is another effective way to decreasing IR signature which spreads from the cavity of the exhaust system. The two-dimensional nozzle can shield part of radiation of the center plug and flame holder. The axis-symmetric plug nozzle can shield the entire radiation originating from the exhaust cavity. Infrared suppression consideration leads to serpentine nozzles to provide line-of-sight blockage of the exhaust system. The highly efficient embedded turbine engine (HEETE) plan presented the serpentine inlet and exhaust nozzle, which could shield the fan and high-temperature rin International Journal of Aerospace Engineering am bm
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