Jet preferred mode vs shear layer mode

The effect of acoustic excitation on a low Reynolds number jet with constant centerline velocity u0 but varying velocity profile u(y) is investigated experimentally by particle imaging velocimetry. Different initial conditions at the nozzle orifice are here used with the intent to characterize the relation between the jet preferred mode fp and the natural shear layer mode fn. The jet response to acoustic excitation is described in terms of the centerline velocity decay and the downstream increase in momentum thickness. This study intends to shed some light onto the duality of the two most fundamental flow instabilities and their controversial dependency on each other.