Transition in a plane channel flow in the presence of a magnetic field.

We investigate the linear evolution of perturbations in a magnetohydrodynamic channel flow with electrically insulating channel walls and a spanwise magnetic field. Linear optimal perturbation are computed. When the Hartmann number increases, dominant optimal perturbations are no more the classical streamwise modes. Performing direct numerical simulations using as initial condition optimal modes plus three-dimensional noise, we investigate how the transition to turbulence is affected by the magnetic field