Transient growth in a right-angled streamwise corner

The linear nonmodal mechanisms with respect to an incompressible right-angled unbounded corner flow are investigated under the parallel flow assumption. For a null streamwise wavenumber αα, the initial optimal perturbation is shown to take the shape of strong counter-rotating vortices, positioned with a symmetric or anti-symmetric arrangement along the bisector, yielding to high- and low-speed streaks at finite times. This mechanism is explained by a classical lift-up effect. Both symmetric and anti-symmetric configuration lead to higher optimal gain in energy than the one associated with a Blasius boundary layer. The maximum gain is obtained for the anti-symmetric arrangement. As αα is increasing, the short-time regime is dominated by an Orr mechanism. The kinetic energy production is proved to be mainly caused by the work of the mean shear flow along the streamwise direction with the Reynolds stress as in a Blasius boundary layer. Finally, optimal perturbations with respect to large times are computed for α≠0α≠0 and compared with the Orr mechanism.