On the receptivity of free shear layers to two-dimensional external excitation

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Abstract
In this paper, we study the receptivity of a typical free shear layer to pulse-type and periodic excitation. We do this by solving the initial-value problem completely and studying its long-time behaviour. This leads to a wave packet for the pulse. By the superposition of many wave packets, we generate a spatial instability mode when the flow is convectively unstable. This establishes a general and simple relationship between the receptivities for pulse-type and sinusoidal excitations. We find that a shear layer is very receptive to high-frequency disturbances that are generated near the centreline of the layer.