Large-Scale Vortex Instability in Helical Convective Turbulence
Various structures that can be observed in convective flows have recently become a subject of active research (see, e.g., Westfried and Zaleski, 1984). Convection has turned into a sort of laboratory for investigation of structures and structural transitions. Here we discuss a new principal possibility typical of the turbulent convection with non-vanishing mean helicity, i.e. with non-vanishing correlation <v·∇×v> ≠ 0. We show that in turbulent convection there exists a new type of instability that leads to generation of large-scale vortex structures with non-trivial topology of streamlines (see also Moiseev et al., 1988). Such structures can be called topological solitons. Below we consider a simplified version of the problem which, however, preserves all principal physical characteristics of this phenomenon. We consider the helical turbulence created by a random external force and weak deviations from linearity in equations of motion. From physical point of view, non-zero helicity means that turbulence is non-invariant with respect to reflec-tion, i.e. the number of vortices with right-handed screwedness is not equal to the number of vortices with the left-handed one. This is the case when the random external force F i is an axial vector.
KeywordsVelocity Field Internal Wave Reynolds Equation Turbulent Convection Horizontal Size
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