Influence of cooling air jets on the aerodynamic and aerothermal losses and cooling effectiveness of air-cooled radial flameholder

Abstract

The flow losses of flameholder are associated with the combustion performance of augmented combustor. After introducing cooling air, the changing flow field and mixture temperature will significantly affect the flow losses and wall temperature of air-cooled flameholder. In this study, experimentally verified CFD simulation methods were adopted to investigate the influence of the cooling air jet angle and aerodynamic conditions on the flow losses and cooling effectiveness. Firstly, the impact of the cooling air jet angle combination and size on the injection and mixing losses, kinetic energy loss, thermal energy loss, and cooling effectiveness of air-cooled flameholder was analyzed. Then the cooling scheme with low flow losses and excellent cooling effectiveness was discussed under different cooling air and mainstream conditions. Results show that the angle combination affects the mixing losses slightly but the injection losses greatly; the angle size has a notable influence on both losses. When the cooling jet angle between cooling holes and the back wall of flameholder exceeds 60°, total pressure loss and thermal energy losses change lightly. Noticeably, there are apparent disparities of flow fields in the near-field wake region under different cooling air jets angle combinations and sizes, resulting in the different flame structures, wall temperature distributions, and cooling effectiveness. Overall, when all cooling air jets are injected perpendicular to the back wall, air-cooled flameholder has the minimum flow losses and the best cooling effectiveness, whereas it has the weakest flame stability. In addition, the total pressure losses increase with improving the flow rate and temperature of cooling air and the mainstream velocity, but that decreases with increasing mainstream temperature. The kinetic energy and thermal energy losses are raised with the increased coolant flow rate, mainstream temperature, and mainstream velocity but reduced with the enhanced cooling air temperature.