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Alessio Malli
This work studies by direct numerical simulations (DNS) the skin-friction drag reduction obtained in a turbulent channel flow by steady spanwise forcing realized via standing waves. While the effectiveness of the forcing intended as a boundary condition for the DNS solver has been already proved by several past studies, the aim of the present work is to focus on the (detrimental) effects introduced by the unavoidable presence of a number of discrete Dielectric Barrier Discharge plasma actuators. Hence the DR technique is gradually modified to better describe the field of body forces realistically produced by suitable actuators. The spanwise-discrete nature of the actuators is modeled at increasing level of complexity: discrete spanwise velocity boundary conditions, the Suzen-Huang model for the body force and electro-hydro-dynamics plasma simulations. The effects of discretization are addressed by performing about ten DNS simulations for each of the three cases, where the actuator spacing is varied. The results indicate that drag reduction can still be achieved after spanwise discretization is accounted for.