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OPTIMAL CONTROL OF TURBULENT CHANNEL FLOW USING AN LES REDUCED-ORDER MODEL

Laurent Cordier
Department Fluides, Thermique, Combustion, CEAT Institut PPRIME, CNRS-Universite de Poitiers-ENSMA, UPR 3346 43 rue de I'Aerodrome, F-86036 Poitiers CEDEX, France

Ali El Shrif
Department of Mechanical Engineering Almeurgueb University Alkhoums, Libya

Аннотация

Optimal control was successively implemented using Large Eddy Simulations, as a reduced-order model. The application of optimal control is targeting the drag reduction on the channel upper and lower walls. Three different cost functionals (drag, terminal turbulent kinetic energy, mean turbulent kinetic energy) have been tested and the strategy was applied to flows going from Reτ = 100 to Reτ = 360. Wall transpiration (unsteady blowing/suction) with zero net mass flux is used as a control. At Reτ = 100, control managed to fully relaminarize the flow (drag reduction of about 57%) by considering as cost functional the terminal kinetic energy. For this same cost functional, an important drag reduction of about 50% is still obtained at Reτ = 180 but without reaching the relaminarization. Our results show that to minimize the flow drag, it is more efficient to consider the kinetic energy as cost functional than directly the drag. Lastly, it is essential for the convergence of the minimization that the optimality system is solved on a sufficiently long time horizon.