A turbulent circular jet with variable density caused by the mixing of air with gases of different densities (air, helium, and carbon dioxide) is studied. The Reynolds number is fixed for all cases: Re = 5300. Using proper orthogonal decomposition and direct numerical simulation data, a comparative analysis of the three gases under consideration is carried out. It is shown that with a decrease in the ambient gas density, the frequency of coherent structures formation drops, and the number of proper orthogonal decomposition (POD) modes necessary for constructing a low-dimensional flow model decreases.

中文翻译：

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混合不同密度气体时湍流圆形射流近场的POD分析

研究了一种由空气与不同密度的气体（空气，氦气和二氧化碳）混合引起的，具有可变密度的湍流圆形射流。在所有情况下，雷诺数都是固定的：Re =5300。使用适当的正交分解和直接数值模拟数据，对所考虑的三种气体进行了比较分析。结果表明，随着环境气体密度的降低，相干结构形成的频率降低，并且构建低维流动模型所需的适当正交分解（POD）模式的数量减少。