Spatial Optimal Disturbances in Three-Dimensional Boundary Layers

A parabolised set of equations is used to compute spatial optimal disturbances in Falkner-Skan-Cooke boundary layers These disturbances associated with maximum energy growth initially take the form of vortices which are tilted against the direction of the mean crossflow shear. They evolve into bended streaks while traveling downstream and finally into crossflow disturbances when entering the supercritical domain of the boundary layer. Two physical mechanisms. namely the lift-up and the Orr-mechanism. can be identified as being responsible for non-modal growth in three-dimensional boundary layers A parametric study is presented where. amongst others, the influences of pressure gradient and sweep angle on optimal growth are investigated. It turns out that substantial disturbance growth is at found in regions of the flow where modal disturbances are damped.