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Article

DNS and LES of estimation and control of transition in boundary layers subject to free-stream turbulence

Authors: Monokrousos, A M, Brandt, L.B., Schlatter, P., Henningson, D.S.H.
Document Type: Article
Pubstate: Published
Journal: Int. J. Heat and Fluid Flow
Volume: 29, Issue 3   841-855
Year: 2008

Abstract

The aim of this study is to perform numerical simulations to apply feedback control to transitional boundary-layer flows. An efficient pseudo-spectral numerical code is used and modern control theories are incorporated into the controller design. Control of wall-bounded transitional and turbulent flows is the object of the present investigation owing to the high potential benefits. Any reduction of the skin-friction, for example, implies relevant savings of the operational cost of commercial aircrafts and cargo ships. Numerical simulations and in particular direct numerical simulations (DNS) and large-eddy simulations (LES) have provided physical insight into the phenomena of transitional and turbulent flows, despite the fact that they are limited to simple and moderate Reynolds-number flows. Recently, much effort is put in the combination of computational fluid dynamics and control theory (Bewley, 2001 and Kim, 2003). While early attempts of flow control were based on physical intuition or on a trial-and-error basis, more systematic approaches are now followed. Linear feedback control is considered in this project. Results from the application of linear optimal control theory confirm the importance of linear mechanisms in the nonlinear flows under consideration (Högberg and Henningson 2002). However, in the feedback perspective, full information on the flow is needed to compute the optimal control. This information is extracted from wall-measurements and the flow based on those the full flow field is estimated. The information problem is a limiting factor in the success of a control scheme, since, as a first step, it affects the whole procedure. Investigations are also be performed on this matter.