Inviscid Transient Growth on Horizontal Shear Layers with Strong Vertical Stratification

Abstract : We report an investigation of the three-dimensional stability of an horizontal free shear layer in an inviscid fluid with strong, vertical and constant density stratification. We compute the optimal perturbations for different optimization times and wavenumbers. The results allow comparing the potential for perturbation energy amplification of the free shear layer instability and the different mechanisms of transient growth. We quantify the internal wave energy content of the perturbations and identify different types of optimal perturbations. Intense excitation of gravity waves due to transient growth of perturbations is found in a broad region of the wavevector plane. Those gravity waves are eventually emitted away from the shear layer.