Authors & Affiliations
A.I. Leypunsky Institute for Physics and Power Engineering, Obninsk, Russia
The conditions and mechanisms of events in a moving fluid are analyzed, leading to the apparent disorder of unsteady flow, known as turbulence. The method of analysis is the use of different forms of equations of motion and transfer of characteristics, the selection of stable formations in the flow structure and a description of the interaction between them. The non-trivial results of previous works are used. The transfer and transformation of disturbances of a vortex distributed in the flow is analyzed, the conditions under which insulated tubes with a helical flow appear inside the shear flow. An important condition is the short duration of vortex disturbances. Equations are obtained that describe the interaction of the main shear flow and the vortex tube, the features of which lead to flow instability. The existence of two mechanisms for the development of turbulence is shown – the autogeneration of local decelerations and the instability of stretching of vortex tubes. The self-generation mechanism is the transfer of kinetic energy from the main flow to an annular vortex with the generation of a new annular vortex. This is the main mechanism that ensures the propagation of instability downstream, arises first when the Re number increases. The tensile instability leads to the splitting of the vortex tube into independent sections, the generation of many annular vortices that fill the space and drift in it. The vortex multiplication factor in each generation increases with the Re number and can reach many thousands. The role of ordered unsteady flows in the initiation of turbulence is shown.
fluid mechanics, turbulence, disordered flows, vortex tube stretching, local braking, equations of motion, feedback in flow
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