Closed-loop control of a spatially developing shear layer

Participant : Christophe Collewet.

This study is led within a strong collaboration with Diemer Ando-Ondo and Johan Carlier of the Acta team (Irstea Rennes). It aims at controling one of the prototypical flow configurations encountered in fluid mechanics: the spatially developing turbulent shear layer occuring between two parallel incident streams with different velocities. Closed loop control is achieved to maintain the shear-layer in a desired state of interest for industrial applications, and thus to reject upstream perturbations. The industrial and scientific contexts advocates first for the use of image sensor to measure the flow velocity fields and second for applying the control on the upstream boundary condition. The optimal control was performed using a linear control law designed from a reduced linearized state space model of the Navier-Stokes equations. A steady desired state was first considered leading to a linear time-invariant system. The resulting feedback control law was validated on a powerful and realistic numerical Navier-Stokes 3D solver, which will be useful to anticipate the control of the shear layer in a dedicated wind tunnel. Two conference papers on this work have been submitted to the "16th European Control Conference" and "8th AIAA Flow Control Conference". We are now considering the case of an unsteady desired state to control the large roller vortices developing in the shear layer and that are the main contributor to entrainment and mixing processes.