高速可压缩来流与凹腔驻涡相互作用及其物质输运特性研究

Interaction of High-Speed Compressible Incoming Flow and Trapped Vortex in Cavity and Its Mass Transport Characteristics

关键词:  双模态冲压发动机  可压缩流  凹腔  物质输运  驻涡  数值模拟

Key words:  Dual-mode ramjet  Compressible flow  Cavity  Mass transportation  Trapped vortex  Numerical simulation

摘要:

为了深入认知凹腔驻涡与高速可压缩来流之间的相互作用过程以及来流马赫数对上述动力学过程的内在影响规律，对长深比为1.0的单凹腔基础构型在常温、常压、Ma=0.3~0.7的高速可压缩来流下进行冷态非定常数值模拟，并基于拉格朗日视角研究来流与凹腔驻涡相互作用及其物质输运特性。结果表明：凹腔上方剪切层内旋涡结构仍然具有类似自由剪切层的周期性演化过程，主流与凹腔通过三次掺混进行物质输运；随着主流马赫数的增加，旋涡运动方式及凹腔-主流物质掺混机制都发生了本质上的改变，剪切层内旋涡和凹腔主涡涡量均呈现数量级式增长，剪切层旋涡结构脱落频率近似线性增长并逐渐卷吸至凹腔中部，进入凹腔的主流流体占比降低，但扩散程度和速度加快；此外，源于凹腔的流体流出唇口线后经剪切层的夹带作用回流占比增大，降低了凹腔-主流的整体质量交换水平；驻留参数整体衰减，高马赫数时仅为低速工况的1/2，显著降低了回流区对于流体驻留作用的贡献。

Abstract:

In order to deeply understand the interaction process between the trapped vortex of the cavity and the high-speed compressible incoming flow and the internal influence of the incoming flow Mach number on the above dynamic process， the cold unsteady state numerical simulation was carried out for the single basic cavity configuration with a length-depth ratio of 1.0， the inflow conditions are high speed compressible flow of Ma=0.3~0.7 at room temperature and atmospheric pressure， both the interaction between the main flow and the trapped vortex and its mass transport characteristics have been studied based on the Lagrangian perspective. The results show that the vortex structure in the shear layer still has a periodic evolution process similar to the free shear layer， the main flow and the cavity are mixed for three times for mass transport. With the increase of the mainstream Mach number， the vortex motion mode and the cavity-mainstream mass mixing mechanism have undergone essential changes， both the vortex in the shear layer and cavity increases by orders of magnitude， the shedding frequency of the vortex structure in the shear layer increases approximately linearly and gradually entrains to the middle of the cavity， the proportion of the mainstream fluid entering the cavity decreases， but the degree and speed of diffusion are accelerated. Moreover， after the fluid originating from the cavity flows out of the lip line，the mass fraction of reflux flow increases by the entrainment effect of shear layer， which reduces the overall mass exchange level between the cavity and the mainstream. The residence parameter attenuates as a whole， it is only 1/2 of low-speed operating conditions at high Mach number， which significantly reduces the contribution of the recirculation zone to fluid retention.