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为增加对高度欠膨胀射流物理流动规律,特别是对其近场瞬态结构特征的认识,利用基于Open FOAM函数库开发的可压缩流动求解器astro Foam,对喷压比(NPR)分别为5.60,7.47,9.34,11.21,雷诺数Re约105的高度欠膨胀射流进行了三维大涡模拟。首先讨论了射流近场的时均流动特征,发现大涡模拟计算成功捕捉到了高度欠膨胀射流近场的典型结构,并与实验测量和文献结果吻合较好。重点研究了高度欠膨胀射流近场的瞬态非定常特征,给出了实验难以测量的射流近场波系结构的建立过程,发现其主要受初始条件的主导,喷压比的影响较为有限。揭示了马赫桶内精细的小尺度胞格结构,并通过高速脉冲纹影图片予以初步证实。定量地研究了射流马赫盘的振荡特征,发现其具有强瞬态和高非线性的特点,不同喷压比下马赫盘的振荡周期相同,主要受f=5.298k Hz的轴对称模态的主导。
In order to increase the understanding of the law of physical structure of highly underexpanded jet, especially its near-field transient structure, compressible flow solver astro Foam was developed based on Open FOAM library. The pressure-to-pressure ratio (NPR) was 5.60 , 7.47, 9.34, 11.21, and Reynolds number Re about 105, respectively. Firstly, the characteristics of mean-time flow in near-field jet are discussed. It is found that the large-eddy simulation model successfully captures the typical structure of the near-field due to high-expansion jet and is in good agreement with the experimental data and the literature results. Focusing on the transient unsteady characteristics of the near-field in a highly underexpanded jet, the establishment process of the jet near-field wave structure, which is difficult to measure experimentally, is given. It is found that the jet is dominated by the initial conditions and the jet pressure ratio is relatively limited. The fine small-scale cell structure in Mach’s barrel was revealed and initially confirmed by high-speed pulsed smear images. The oscillation characteristics of jet Mach disk are quantitatively studied and found to have the characteristics of strong transient and high nonlinearity. The oscillation period of Mach disk under the same jet pressure ratio is dominated by the axisymmetric modal at f = 5.298 k Hz .