摘要:
针对三维时间发展可压缩氢/氧非预混燃烧反应平面自由剪切混合层,采用5阶迎风/6阶对称紧致混合差分格式以及3阶显式Runge-Kutta时间推进方法,直接数值模拟了伴随燃烧产物生成和反应能量释放, 流动受扰动激发失稳并转捩的演化过程. 在转捩初期, 获得了${\it\Lambda}$涡、马蹄涡等典型的大尺度拟序结构,观察到了流动失稳后发生双马蹄涡三维对并的现象, 大尺度结构呈较好的对称性.在流动演化后期, 大尺度结构逐次破碎形成小尺度结构, 混合层进入转捩末期,呈明显的不对称性.
Abstract:
A fifth-order upwind/sixth-order symmetriccompact hybrid difference scheme coupled with a third-order explicitRunge-Kutta time-marching method is used as a direct numerical simulationalgorithm to investigate a three-dimensional temporally-developingcompressible plane free shear mixing layer with H$_{2}$/O$_{2}$ non-premixedcombustion. The reacting mixing layer with product formation and energyrelease is perturbed by a pair of conjugate oblique waves, and henceexperiences an instable transitional evolution. At the beginning oftransition, some well-known large scale coherent structures, such as${\it\Lambda}$ vortex and horseshoe vortex, are found, and a three-dimensionalparing phenomenon of two horseshoe vortices following flow instabilities isalso revealed. Furthermore, these large scale structures are approximatelysymmetric. At the last stage of the development of this flow, large scalestructures break down continuously, and small scale structures gradually getdominant. The reacting mixing layer finally behaves very similar toturbulence and shows clear asymmetry. On the analogy of the stability theoryfor incompressible boundary layer, the large scale structures obtained hereare due to a subharmonic secondary instability mechanism, which is wellknown as Herbert type secondary instability.
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