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ISSN オンライン: 2642-0554

GLOBAL INSTABILITY ANALYSIS OF A ROUND JET

Shintaro Takeuchi
Department of Mechanical Engineering, Osaka University, 2-1 Yamada-oka, Suita-city, Osaka 565-0871 Japan

Yutaka Miyake
Department of Mechanical Engineering, Graduate School of Engineering, Osaka University 2-l,Yamadaoka, Suita, Osaka, 565-0871; Department of Mechanical Engineering Fukui University of Technology 3-6-1, Gakuen, Fuki, 910-8505 Japan

要約

In order to investigate the diversity of the evolution of near-field of a round jet observed in experiments and in numerical simulations by different authors, the secondary stability is analyzed which appears in the early stage of spatial development of a round jet in its near field. The secondary instability which is characterized by generation of streamwise vortices in a braid region between neighbouring vortex rings is analyzed by a global instability analysis. Unstable modes of disturbances are identified by the analysis in a base flow of an axial segment of one pitch of a round jet between one pair of vortex rings. The linear bound of their evolution as well as the interaction of each mode are investigated by introducing these disturbances on the base flow. The key of the role of these disturbances in the spatial evolution of a round jet is examined by introducing modes into the baseflow and the wavelet analysis, etc. It turned out that the most probable cause of the diversity of the evolution is a non-uniform concentration of disturbances in the azimuthal direction, which is dependent on environmental disturbances and hence non-deterministic. This non-uniformity looks like a result of delicate local receptivity of disturbance.