The paper presents parametric studies of the first and second azimuthal absolute modes in annular non-swirling and swirling jets. The spatio-temporal linear stability analysis is applied to investigate an influence of governing parameters including axial velocity gradients in inner and outer shear layers, back-flow velocity, swirl number and shape of the azimuthal velocity. A new base flow is formulated allowing a flexible variation of the shape of axial and azimuthal velocity profiles. It is shown that the first helical absolute mode is governed mainly by the back-flow velocity and swirl intensity. A steepness of the inner shear layer can control the absolute mode frequency. The velocity gradient in the outer shear layer and the shape of the azimuthal velocity have rather limited impact on the absolute mode characteristics. Finally, it is shown that the second helical absolute mode can dominate the flow with a stronger swirl intensity.

中文翻译：

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环形射流的绝对不稳定性：局部稳定性分析

本文介绍了环形非旋流和旋流射流中第一和第二方位绝对模式的参数研究。应用时空线性稳定性分析来研究控制参数的影响，包括内外剪切层的轴向速度梯度、回流速度、涡流数和方位速度的形状。新的基流被制定，允许灵活变化轴向和方位角速度剖面的形状。结果表明，第一螺旋绝对模式主要由回流速度和涡流强度控制。内剪切层的陡度可以控制绝对模式频率。外剪切层的速度梯度和方位速度的形状对绝对模式特性的影响相当有限。最后，