Research On Structure And Performance Of A Trapped-vortex Ramjet Combustor

Compared with traditional swirl burner, the trapped-vortex combustor has the advantages of simple structure, high combustion efficiency, combustion stability and so on, which is considered to be the most promising rich hydrogen fuel combustion. Trapped vortex combustor constructs a double-vortex structure using cavity and anterior and posterior wall injection, to play the role of ignition and stabilizing flame. The deputy vortex can protect the ma in vortex from the influence of the main flow, and promote the material and energy exchange between the vortex area and the main stream. The length of cavity, height of anterior and posterior wall and the injection position are important parameters which influence the flow field structure and the performance of combustor. This article mainly aims at the ratio of cavity length and the anterior wall height, and posterior wall injection position, to research the influence to the combustor performance of different length height ratio and different injection position and the mechanism, which can provide theoretical basis for the design and optimization of the structure of the trapped-vortex combustor.This paper is based on the trapped-vortex combustor in a certain type of ramjet. After the numerical method was verified, 4 different length height ratio schemes were proposed. Cold and hot state numerical simulation was carried out, and the performance of different length height ratio of cavity was compared and analyzed. Based on this, 6 different injection position schemes were put forward, and hot state numerical calculation was carried out. Finally, numerical simulation was carried out with different injection position under different conditions to study the performance of combustor under different working conditions.The study results show that: a stable double- vortex structure gradually formed and the scale increases with length height ratio increasing. But after the length height ratio increases to a certain value, the double-vortex structure is broken into a number of small scale vortices. When the length height ratio is 1.2, a stable double vortex structure is constructed and the scale is larger enough to make more fluids involved in the trapped vortex flow, and the total pressure recovery coefficient is higher than others; the temperature of the combustor and the main combustion zone is highest of the four structures, so the combustor of 1.2 length height ratio is considered as the best combustor. When the posterior wall injection position is close to the top of the wall, the injection fluid can’t participate in flow in trapped-vortex area very well; while the injection position is near the cavity bottom, trapped vortex area flame is impacted by the posterior wall injection fluid, the temperature in the trapped-vortex area is reduced, the maximum temperature decreased gradually. When the injection position located at 40% position, the double- vortex is stable, and temperature in trapped-vortex area is high, which is considered as the best case with high total pressure recovery coefficient and high combustion efficiency.