为揭示2元圆转矩喷管尾喷流强化掺混的内在机制,应用大涡模拟(LES)方程对2种相同进、出口直径的喷管模型(轴对称、2元圆转矩)在Ma=0.8、高雷诺数(2×105)条件下进行了数值模拟计算.结果表明:与轴对称喷管相比,圆转矩喷管射流掺混效应增强,速度衰减快,核心区长度和高温区域面积减小.同时尾喷流拟序结构变化说明:2种喷管主要拟序结构均包含涡环、涡辫、发卡涡、螺旋涡等相似结构;但圆转矩喷管在射流近场诱导出的涡旋更丰富,边角剪切涡发展更快,形成明显的CVP结构,导致其射流柱失稳时刻提前、距离缩短;同时,喷管形式的改变使得射流剪切层内雷诺应力增大,速度脉动增强.拟序结构发展及雷诺剪切应力变化说明在射流流场中涡旋发展耗散速度增大、速度边界层脉动增强、射流柱易失稳是导致射流掺混增强的本质因素,为异形喷管的强化掺混机理提供了依据.%In order to reveal the internal mechanism of mixing enhancement of 2-D circle-rectangular transition nozzle,the numerical simulation by the Large Eddy Simulation (LES)equation of mixing characteristics of jet and environment were studied at two nozzle model with the same inlet and outlet diameters,which were symmetrical and circle-rectangular transition nozzle with low Mach number (Ma=0.8) and high Reynolds number(2×105).The results show that the circle-rectangular transition nozzle jet has the strengthening mixing effect,the faster velocity decay rate, the reduction potential core-length and the shrinking area of high temperature, comparing with the axial symmetric nozzle.The variations of coherent structure of the tail jet flow show that the main structures of two kinds of nozzle are vortex ring, vortex braid,Hairpin Vortex,spiral vortex and so on,but the circle-rectangular transition nozzle model produces a wide variety of vortexes in the near field of jet, the shear vortex develops faster and forms an obvious CVP, which causes the instability point of the jet column earlier and closer to the exit.In addition,the change of nozzle form makes the Reynolds stress in the jet shear layer increase,the velocity fluctuation is more intense and the mixing is enhanced. In the jet flow field, the rapider development of vortex, the increase of vortex dissipation rate and the increase of velocity boundary layer fluctuation are the essential factors leading to mixing enhancement,which also provide the basis for strengthening mixing mechanism of profiled nozzle.
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