Flow separation prevention around a NACA0012 profile through multivariable feedback controlled plasma actuators

In the present paper, the problem of controlling the unsteady flow separation over an aerofoil, using plasma actuators, is addressed. Although a plasma flow is essentially a two-phase flow, it has been proved that a local force term may be successfully considered within a flow solver in order to mimic the effect of a local acceleration (see [63]). By exploiting the Chimera Overlapping Grids technique to allow the inclusion of one or more actuators, accurate numerical simulations have been carried out with the in-house Finite Volume solver Xnavis. The effects of varying both number and position of the actuator/sensor pairs along the aerofoil are investigated by focusing on the dynamic control of the boundary layer separation. The capabilities of the proposed control strategy are also examined by showing how the practical flow separation control problem can be formulated as a simple output regulation problem, so that a simple control strategy may be used. Several numerical simulations of incompressible flows around a pitching NACA0012 at Reynolds Re = 20, 000 illustrate the effectiveness of the proposed approach, in the presence of time-varying angles of attack and complex non-linear dynamics, which are neglected in the control design. The present work extends the former paper of Broglia et al. [2], where the control algorithm was applied to the simple case of single input/single output regulation and implemented in a Finite Elements numerical code; in that work the boundary layer control of an airfoil at fixed angle of attack was addressed. In the present paper a multi input/multi output approach is theoretically developed and numerically implemented. Robust and fast flow reattachment is achieved, along with both stabilisation and increase/reduction of the lift/drag, respectively. A major advantage of the presented method is that the chosen controlled outputs can be easily measured in realistic applications. (C) 2019 Elsevier Ltd. All rights reserved.