Effects of indeterminate-origin collars on self-excited collared-jets

Abstract

An experimental study was carried out to investigate the use of V- and A-notched indeterminate-origin circular collars in self-excited circular collared-jets, in comparison with a non-notched circular collar. Hot-wire measurement results show that notched collars lead to an increase in the optimal collar length, as well as achieving higher centerline velocity decays, over the reference collar. Close to their optimal collar length, notched collars are shown to produce significant changes to the cross-stream velocity profiles. Notched collared-jets are more sensitive towards collar length changes than the reference collared-jet and demonstrate more significant variations in the half-jet widths. The half-jet width developments are also observed to be dependent upon the exact azimuthal plane of the notched collared-jets, though in general V-notched collar produces wider overall jet spreads than A-notched collar. Lastly, self-excitation behaviour is observed to be significantly suppressed when notched collars are used and postulated to be the result of the jet shear layer impinging upon the axially non-uniform collar lips. This disrupts self-excitations at the shear-layer tone frequency and may provide insights into reducing flow oscillations in similar flow scenarios. © 2010 Taylor & Francis.