MECHANISM OF TURBULENCE INTERMITTENCE IN THE SURFACE LAYER

L. Kh. Ingel

Attention is drawn to the fact that even fairly small deviations of an underlying surface from the horizontal (usually uncontrolled) can result in a noticeable intermittence of air flows in the surface layer, even under stationary external conditions. Richardson numbers (Ri) were estimated for slope flows over a cooled inclined surface. They show that the flows corresponding to the stationary Prandtl model can be unstable even under relatively small inclination angle of the underlying surface relative to the horizon. An alternative integral model of turbulence is discussed. It is shown that the stationary decisions are conceivable in this model only when the inclination angles are not too small. There is an interval of small angles in which the laminar (quasilaminar) Prandtl flow is unstable, but a stationary turbulent flow is absent. It might be supposed that within this interval of angles an autooscillation occurs by the following scheme: development of a laminar (quasilaminar) slope flow—loss of its stability—turbulization—slowing down of slope flow—turbulence decay—decrease in effective viscosity—acceleration of flow—unstability, etc. An attempt was made to estimate the period of such oscillations.

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