Understanding Scramjet Combustion using LES of the HyShot Ⅱ Combustor: Stable Combustion and Incipient Thermal Choking

摘要

Unsteady combustion phenomena in scramjet combustors are challenging to understand and difficult to study computationally and experimentally. The most important unsteady phenomena are dual-mode ramjet/scramjet transition and onset of inlet unstart, of which the latter can be caused by either aerodynamic phenomena associated with the inlet flow itself or processes taking place in the combustor. Both these processes are complicated, and will typically involve situations in which the Mach number locally falls below unity, and the flow temporally becomes thermally choked. In this study we focus on deepening our knowledge about stable scramjet combustion and creating fundamental know-ledge about incipient unstart, primarily by means of thermal choking. For the purpose of this study we use the HyShot II model combustor, for which experimental data for both stable combustion and incipient thermal choking is available. The computational methods used consist of Large Eddy Simulation (LES) models and skeletal reaction mechanisms. The LES predictions are successfully validated against the experimental data and used to analyze the combined flow, mixing and combustion processes involved. The tools used include conventional as well as modern methods such as Takeno Flame Index and Chemical Explosive Model Analysis. These methods give a concise description of the flow, fuel-air mixing and combustion, identifies the factors contributing to the thermal choking and stabilization of the shock-system.