Vortex dynamics in jets from V-notched nozzles

Abstract

Planar laser induced fluorescence technique was used to study the near-field flow structures of a free V-notched jet. The study shows that large-scale primary flow structures transit to turbulence earlier and time-averaged jet spread is significantly more extensive for a free V-notched jet compared to a free axisymmetric jet. The presence of peaks and troughs at nozzle lip initiates the formation of the streamwise vortices, in contrast to free axisymmetric jets where the streamwise vortices are formed as a result of natural shear layer instability. Furthermore, unlike in a free axisymmetric jet where streamwise vortices are formed at random positions, the streamwise vortices formed in a free V-notched jet are aligned to the peaks, the troughs and to locations halfway between a peak and a trough. Present investigation also reveals that all streamwise vortices at the peak and trough locations are outwardly-spreading, instead of agreeing with earlier results which showed peaks and troughs producing both outwards and inwards-spreading streamwise vortices. Despite the dissimilarity, the flow phenomenon was studied in detail with a possible flow model explaining the observations proposed. © 2004 by K.M.K. Lim, Temasek Laboratories.