Prediction and Control of Turbulence Based on Turbulent Elementary Vortices

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To understand elementary vortex in turbulence and to apply it for engineering problems, characteristics of the elementary vortex in various turbulent flows are investigated by direct numerical simulations. It is shown that the characteristics of the elementary vortex are independent of a type of turbulent flows and Reynolds number, and that they create large-scale clusters in high Reynolds number turbulence. Large scale DNS of plane-channel flow reveals that vortices in near-wall region are universal and that the far-wall field is characterized by streaky structures. In addition, such a structure was not sustained but roll-cell vortices appeared in the numerical experiment, in which spanwise width of computational domain was strictly restricted. Scalar transport mechanism by the elementary vortex and fractal characteristics of scalar surface in turbulence are also clarified. R&D studies on active feedback control of wall turbulence are performed by using DNS. Investigation on the Reyno … More lds number dependency of the control effect reveals the effectiveness of the proposed control for high Reynolds number flows appearing in real applications, too. It is shown that the existing control algorithms are also valid for a turbulent pipe flow, and we demonstrate the possibility of drag reduction based on the information measurable on the walls only. A prototype feedback control system with arrayed sensor and deformable-membrane-type magnetic actuators placed in a matrix is also developed and evaluated. Turbulent flow fields modulated by additives, manipulation at the wall or pressure gradient were investigated by means of DNS. Namely, influences of the non-uniformity of particle distribution and particle rotation in particle-laden flows, effect of fabric planting, and spatially developing field with acceleration or deceleration were analyzed. To develop new SGS model, hierarchical structure of turbulence and energy transfer mechanism between different scales are investigated using DNS of high Reynolds number turbulence. Less