Impulsively excited disturbances in non-uniform boundary layers

Results will be reviewed for the linearized disturbance impulse response of non-uniform boundary layers. Two distinct forms of boundary layer non-uniformity have been studied. First, we consider the global behaviour of impulsively excited disturbances in temporally steady rotating-disc boundary layers, where there is a spatial inhomogeneity which stems from the radially increasing circumferential velocity. We then consider the oscillatory Stokes layer that is driven by the time-periodic in-plane motion of a bounding flat plate. This provides a second type of boundary layer non-uniformity, which allows us to address the effects of base-flow unsteadiness upon the global development of disturbances.