Investigation On Flow Mechanism And Performance Estimation Of Fixed-geometric Thrust Vectoring Nozzle

Thrust vectoring is one of the most critical technologies for 4th generation or later fighter, which can be used to enhance the agility and maneuverability in post stall regime, and will re-duce or eliminate the need for horizontal and vertical tails. Compared with mechanical thrust vectoring system, the fixed-geometry fluidic vectoring system has simpler structure, lighter weight, and quicker vector response, therefore, it has come into the consideration of exhausting systems all over the world. So the paper emphasizes on the high nozzle pressure ratio exhausting system for larger thrust-to-weight aero-engine, and investigates the working mechanism, flow-field characteristics, multi-parameters affecting principle and performance estimation. The research contents are as follow:1. Base on numerous CFD and model experimental study, the working mechanism of Shock Vectoring Controlling (SVC) nozzle was proposed, and concluded that the unbalanced pressure distributing on nozzle walls, caused by transverse injection, is essential vector source. The main flow-field characteristic of SVC nozzle is dominated by the restriction of confined space and positive pressure gradient. It is found that the flow separation and shear layer cause the unsteady of SVC nozzle, and the frequency of unsteady flow is about 2.0KHz and 4.0KHz. Effect of aerodynamic and geometric parameters, including nozzle pressure ratio (NPR), sec-ondary pressure ratio (SPR), Ma number of free stream, secondary injection angle and position, on vector performance and flow-field were exposed, so was the dynamic response performance, and Results show that maximal increase of thrust vector performance of 46% can be achieved by the change of NPR; when the outer flow is on condition of transonic, a decrease of 16% in vec-tor performance may happen; and by changing the secondary injection angle, a increase of 50% in vector performance can be obtained. In order to enhance the vectoring efficiency, two meth-ods were considered:mechanical/SVC nozzle and assistant injection, which showed good be-havior in wide working range, meanwhile the thrust coefficient exceedes 2.07°/% and the thrust coefficient is larger than 0.90.2. Analytical method and CFD were used for investigating the mechanism of fluidic throat area control of fixed-geometry fluidic vectoring nozzle, and the flow-field characteristics of flow separation and velocity distribution were exposed. Critical affecting parameters on ration of throat area control (RTAC) were investigated, and found the optimal secondary injection (Xj=-0.05) and angle (θ=130°). By using assistant injection, the RTAC of 50% is achieved under the restriction of corrected secondary flow ratio of 15%. The fluidic throat control dynamic re-sponse and time was obtained, which is about 10ms, and the disturbance spreading of injection and no-injection was studied, and the fluctuation frequency in mass flow of nozzle inlet is about 2 kHz and 0.4 kHz.3. Base on Discrete Transfer Method (DTM) and C++ language, the program for estimating infrared radiation character of SVC nozzle was established, which can separate the effect of in-frared radiation intension of every nozzle part on the special observation point. The infrared ra-diation character of SVC nozzle for small bypass ratio aero-engine was researched, and pointed out high temperature gas and wall, and the inner inlet face are important factors. The essence of reducing infrared radiation intension for SVC nozzle is faster cooling and diffusion of hot gas by the streamline vortex, which caused by secondary injection. And in large observation angle, a decrease of 58% on infrared radiation intension is obtained. The influence of secondary position was investigated (Xj=0.516 and 0.688), and results show that, at larger observation an-gles(｜α｜[40°-90°) of narrow and wide plane, the infrared radiation intension of 0.516 model is larger than model ofXj=0.688 by 18%-100% and 40%-107%, respectively.4. For the coupling and performance estimation of fixed-geometry fluidic vectoring nozzle with aero-engine, a new method was proposed, based on Design of Experiment (DOE), Re-sponse Surface Methodology (RSM) approximate model and aero-engine performance simula-tion model with air extraction from fan or compressor. For the approximate model of fluidic vector and fluidic throat control, interaction effects were declared, and under the restriction of corrected secondary flow ration and thrust coefficience (Cfg≥0.90, ω(?)≤0.15),optimal vector angle (δp.max=19.81°) and maximal throat control performance (RTAC=54.83%) are obtained. By the balance of pressure and mass flow, the coupling model of SVC model and throat control model with aero-engine model were established, and the effect of different of air extraction po-sitions and air extraction ratios on the co-working point of aero-engine and fixed-geometry flu-idic vectoring nozzle were investigated. Results show that for vector control condtion,15% air exratction from fan discharge may produce vecor angle of 16.50°, cuase thrust derease by 19% and make specific fule consumption (SFC) to increase by 18.7%, while for fluidic throat control contidion,18% air extraction flow fan exit obtains RTAC of 35%,12% decrease in thrust and 16% increase in SFC.