The elliptic whistler jet

Elliptic jets have decided advantages for technological applications over c ircular jets; this paper explores further advantages achieved by jet forcin g due to self-excitation. Using hot-wire measurements and flow visualizatio n, we have studied an elliptic whistler (i.e. self-excited) air jet of 2 : 1 aspect ratio which, in contrast to an elliptic jet issuing from a contour ed nozzle, displays no axis switching, but significantly increased spread i n the major-axis plane. Its near-field mass entrainment is considerably hig her (by as much as 70%) than that of a non-whistling jet. Flow visualizatio n reveals unexpected dynamics of the elliptic vortical structures in the wh istler jet compared to that in the non-whistling jet. Vortices rolled up fr om the lip of the elliptic pipe impinge onto the collar, producing secondar y vortices; interaction of these two opposite-signed vortices is shown to c ause the different behaviour of the whistler jet.