Spiral instability and screech effect in supersonic jet flows

The present paper is devoted to the effect of the discrete tone sound, which is generated by gaseous jet flows. It is known in scientific literature as the effect of jet screech. Thanks to the works by A. Powell, the modern theory explains this effect as the interaction between the jet shock waves and the vortical structures, which are developed at the jet boundary. In the recent work by I. Menshov, I. Semenov, and I. Akhmedyanov (Doklady Akademii Nauk, 420, 3, 2008) by means of the method of numerical modeling it was shown that there exist a correlation between the quantitative characteristics of the screech and the spiral instability developing in the jet flow, which gave occasion to the authors to doubt the validity of Powell's theory. In the present paper the analytical analysis of the stability of an axisymmetric jet flow is carried out. The results obtained provide solid grounds in the favor of the hypothesis of spiral instability as the basic mechanism of the jet screech.