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本文目的是研究声激励对自由射流流场结构的影响。采用多重网格方法对声激励下三维自由射流(Re=2200)的空间演化做大涡模拟。比较了无激励情况和不同频率声激励下射流涡量场的改变。计算表明,当声激励频率接近射流优势频率时,涡量场结构变化显著。周向涡量集中卷起形成大的涡环,射流径向扩展增大。当激励频率接近优势频率两倍时,有涡合并现象,说明出现次谐波。当激励频率远高于优势频率时,流场结构与无激励情况差别不大。本文还给出在接近优势频率的激励下射流中的流向涡量的分布,定性上与实验观察相同。
The purpose of this paper is to study the effect of acoustic excitation on the free-jet flow field structure. Large-eddy simulation of the spatial evolution of a three-dimensional free-jet (Re = 2200) under acoustic excitation is performed using a multi-grid approach. The variation of jet vorticity field under no excitation and different excitation frequencies was compared. The calculation shows that when the acoustic excitation frequency is close to the jet dominant frequency, the structure of vorticity field changes significantly. The circumferential vorticity is rolled up to form a large vortex ring, and the jet radial expansion increases. When the excitation frequency close to the dominant frequency twice, there is vortex merger, indicating the emergence of subharmonic. When the excitation frequency is much higher than the dominant frequency, the structure of the flow field is not much different from the non-excitation case. This paper also gives the distribution of the flow vorticity in the jet near the dominant frequency, qualitatively the same as the experimental observation.