Random Turbulence Versus Structured Turbulence

Abstract

The turbulence flows involve more or less the intermittent behavior of motions in two aspects. The first one is the so-called external intermittency associated with what is called partially turbulence flows, especially with the strongly irregular and convoluted structure (little understood) and random movement of the boundary between the turbulent and non-turbulent fluid. The second aspect is the so-called scale (small wave numbers) inertial or intrinsic intermittency and associated with spotty temporal (“bursting phenomenon”) and spatial patterns of the small scale structures at the fluid – solid interface. This structured turbulence of molecular thermal nature is called Lagrangian turbulence, in which a volume-preserving flow has flowlines which fill up regions of space ergodically. The origin and the self – sustaining mechanism of the structured turbulence are described in the sequel by means of the starting impact inducing three self-sustaining wave configurations which further are propagated in the flow field as vorticity wave packets of soliton type. The result of the whole process is easily observed in the form of hairpin vortex packets so-called 𝛺 – shaped coherent vortical structures, but is extremely difficult to interpret understand and explain. In this paper it is shown that hairpin vortex generation mechanism is governed by principle of “𝛺” momentum – energy invariance for elastic collisions constrained to slide frictionless on the contact surface.

Keywords

• Laminar-Turbulent Transition
• Shear Turbulence
• Coherent Hydrodynamic Structures
• Vortex Dynamics