ARTICLE:

• Coherent Fine Scale Eddies in Turbulence Transition of Spatially-Developing Mixing Layer  download article

Y. Wang
Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan

Mamoru Tanahashi
Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, Japan

Toshio Miyauchi
Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, Japan

ABSTRACT

To investigate the relationship between characteristics of coherent fine scale eddies (CFSEs) and turbulence transition, a direct numerical simulation (DNS) of spatially-developing turbulent mixing layer with Re_w,0 = 700 was conducted. The large-scale coherent structures; Kelvin-Helmholtz roller and rib vortex, do not disappear in the transition process and in the fully-developed state, however they are composed of lots of CFSEs. The most expected diameter of the CFSEs is about 8η and does not change in the process of the turbulence transition, while the most expected maximum azimuthal velocity of CFSEs decreases from 2.0u_k to 1.2u_k. The strain rate acting on the center of CFSEs tends to become weak during the transition, whereas the most expected eigenvalues ratio is maintained to be α : β : γ = −5 : 1 : 4. In addition, the phase averaged energy dissipation rate on the major axis of CFSE becomes low during the turbulence transition.

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