Strategies for Reduction of Turbulent Viscous Drag

Abstract

In this talks new (and not so new) ideas and strategies, which may help to reduce turbulent viscous drag, will be discussed. Focal point is the wall bounded flow with its characteristic turbulent boundary layer and associated characteristic turbulent structures of different scales within. Special attention is paid to the problem of self-formation process of turbulent structures, the derivation of suitable control strategies, their realization and, finally, their evaluation in regard to drag reduction. Addressing the fundamental properties of turbulence in boundary layers the talk starts with basic observations stemming from experiments and numerical simulation which elucidate the decay of flow structures and the transport of energy to smaller scales but also the formation of large scale turbulent structures and the associated process of turbulent self-regeneration cycle. Based on that an analytical approach is presented which has been used to derive one direction of technical concepts for turbulent drag reduction. Another direction of turbulent flow control technologies is associated with properties of the large scale turbulent flow structures in the log-layer region of the boundary layer. In this case control concepts have to face the problem of manipulating structures not close to the wall anymore. Hereto a new approaches are presented and discussed.