Influence of time-varying flow on dynamic flame characteristics in VCE: Numerical and experimental study

Abstract

Afterburner shows obvious transient characteristics in variable cycle engines (VCEs), herein, a compact flame holder and injection device with well performance coordinating a rear variable bypass injector (RVABI) were designed and investigated under variable inlet conditions. Inlet aerodynamic parameters were dynamically simulated and adjusted from small to large to investigate the matching law of bypass ratio and guiding angle, flow structure, and combustion characteristics. A typical case was experimentally verified well, and the coherent modes of the transient velocity field were identified using snapshot proper orthogonal decomposition(POD). It is found from POD that the first modes contributing to the total fluctuation energy are decreased by 15% when the guiding angle increased to 31.92°. The inlet conditions have little effect on the vortex structure near the pilot, while the red-blue alternating vortex structures in the rear of the strut are mainly influenced by the coupling of back pressure between the strut and the pilot. The air entrainment strength guided by RVABI will affect the three-dimensional vortex system built by the flame holder, and cause flow separation or local flameout when the velocity distortion is out of 0.5–1.2. Increased air-entrainment strength generates high turbulent energy, which can improve flow separation and increase radial flame development's instability. Moreover, a guiding angle of nearly 5° has the same effect on air entrainment strength as a bypass ratio of 0.2.