Role of the backward-facing steps at two struts on mixing and combustion characteristics in a typical strut-based scramjet with hydrogen fuel

Scramjet is one of the most promising propulsion systems for the new generation supersonic/hypersonic air-breathing flight vehicles. To achieve sufficiently high combustion efficiency and relatively low total pressure loss, developing a new strut is an attractive approach. In this study, we focus on the backward-facing steps and investigate the geometry parameters of the backward-facing steps of the two struts. In this work, Reynolds averaged Navier-Stokes equation coupled with the one-step H-2-air reaction finite-rate/eddy-dissipation model is adopted to simulate all the two-strut cases, then this code is validated by the available experimental data. Next, we investigate the effects of different lengths and heights of the backward-facing steps on the two-strut based scramjet performance. For cold flow, enhancing the length of the backward-facing step can promote partly the mixing process with few extra total pressure losses. Further, the mixing process is weakened with increasing the height of the backward-facing steps to certain content, meanwhile, the total pressure loss is increased. In terms of reacting flow, increasing the length enhances the combustion efficiency, whereas the total pressure loss relatively decreases and thereafter increases. Enhancing the height of the backward-facing steps makes the combustion efficiency relatively decreases and thereafter increases, moreover, the total pressure loss increases as a result. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.