The current paper presents a theoretical analysis of swirl flow stability, both inside a tube (vortex tube) and in a free annular swirl flow. The starting concept is the study of the evolution of velocity and temperature fluctuations. Methods of non-equilibrium thermodynamics are used to describe the magnitude of fluctuations and their properties. The important role of the total enthalpy follows from a variational analysis. Moreover, the thermodynamic criterion of the stability is formulated using the total enthalpy, and compared with experiments, numerical results and classical Rayleigh theory support its applicability. It was shown that the solid body vortex is at the margin of stability, which is experimentally observed. Analogously, the potential vortex is by the thermodynamic criterion stable; however, by the Rayleigh criteria it is on the onset of stability. The classical Taylor experiment of flow between two rotating cylinders is analysed from the point of view of this criterion. These results are underlined by swirl tube experiments at the Institute of Aerospace Thermodynamics at Stuttgart University and the annular nozzle experiments performed in the Institute of Thermomechanics CAS in Prague. Both independent experiments confirm the transformation of the initial annular vortex into a stable potential-type vortex. The results of this theory can also be used to explain the exceptional stability of tropical cyclones.

本文提出了管内（涡流管）和自由环形旋流中旋流稳定性的理论分析。起始概念是研究速度和温度波动的演变。非平衡热力学方法用于描述波动的幅度及其性质。总焓的重要作用由变分分析得出。此外，利用总焓制定了稳定性的热力学判据，并与实验进行了比较，数值结果和经典瑞利理论支持了其适用性。结果表明，固体涡旋处于稳定边缘，这是实验观察到的。类似地，位涡根据热力学准则是稳定的；然而，根据瑞利准则，它正处于稳定期。从该判据的角度分析了两个旋转圆柱体间流动的经典泰勒实验。斯图加特大学航空航天热力学研究所的涡流管实验和布拉格 CAS 热机械研究所进行的环形喷嘴实验强调了这些结果。两个独立的实验都证实了初始环形涡旋转变为稳定的势型涡旋。该理论的结果也可以用来解释热带气旋的异常稳定性。