RBCC燃烧室超声速反应混合层特性的大涡模拟

Large Eddy Simulation of Supersonic Reaction Mixed Layer in a RBCC Combustor Model

以飞行马赫数为4.5 Ma的RBCC发动机典型工作状态为研究背景,采用大涡模拟研究了支板火箭射流和空气来流形成的超声速反应混合层的掺混燃烧过程,获得了燃烧室内详细的流场结构和流动特征,分析了强射流条件下超声速反应混合层的特性。结果表明由于速度梯度的存在,火箭射流进入燃烧室后与空气来流形成环形剪切层,剪切层内丰富的旋涡结构主导火箭射流和空气来流的掺混燃烧,随着湍流能量的串级输运,化学反应过程中释放的能量将被转化成细观尺度的湍流动能,大尺度旋涡将能量传递给小尺度旋涡并最终耗散,细小尺度的旋涡一方面能够促进燃烧反应物的掺混并强化燃烧过程,另一方面会给化学反应过程带来强烈的脉动,使得局部火焰淬灭,火焰结构表现出明显的非定常性。

Large eddy simulation is conducted to explore the flow field structure and to analyze the features of the supersonic reaction mixed layer formed between the strut rocket jet and the airstream in a RBCC combustor model with the flight Ma =4.5, which is a typical working state in the flight regime of the RBCC vehicle. The results show that the rocket jet interacts with the airstream because of the existence of velocity gradient forming an annular shear layer containing various vortex structures that play important roles in the turbulent mixing and combustion. With the turbulent energy cascade transport, chemical energy released during the reaction is converted into small-scale turbulent kinetic energy. Large-scale vortexes transfer the energy to small-scale ones that dissipate its energy eventually. On one hand, small-scale vortexes can promote mixing and enhance the combustion process. On the other hand, they can bring pulsation to the chemical reaction, making the local flame quenching and the flame structure unsteady.