Manipulation of Vortical Structures in Noncircular Jets.

Statistical Properties of Turbulent Free Jets Issuing from Nine Differently-Shaped Nozzles

“…These jets are identified to generally entrain ambient fluid(s) more effectively than comparable circular jets, and this is taken to also imply more effective mixing [14]. Previous experimental studies have revealed several features of the increased entrainment of noncircular jets issuing from elliptic nozzles (e.g., [17,19,20]) and nozzles with corners (e.g., [15,43,44,51]). The increased entrainment capability of these jets is thus believed to be associated either with the non-uniform curvature of the jet's initial perimeter, relative to the evenness for the circular configuration, or with the instabilities produced by the initial perimeter's sharp corners through the asymmetric distribution of pressure and mean flow field.…”

“…rectangular, triangular, star-shaped ( [15,42,51]) have observed a phenomenon of 'axis-switching': namely, as the jet spreads, its cross-section can regularly evolve through shapes similar to those of the jet nozzle but with axes successively rotated at angles characteristic of the jet geometry. This main underlying mechanism for the increased entrainment properties of noncircular jets, relative to comparable circular jets, results from self-induced deformation of vortex rings with non-uniform azimuthal curvature and interaction between azimuthal and streamwise vorticity [14].…”

“…Since the smallest radius of the ring occurs in the major axis plane whereas the largest occurs in the minor axis plane, the minor axis grows more rapidly than the major, thus leading to the 'axis switching' at a certain distance downstream from the nozzle exit (e.g. [15,17,20,21,25,40,48,51,53]). Previous experiments on (momentum dominated) flames from several non-circular jets by Gutmark et al [15] also show the phenomenon of axis switching.…”

Mixing enhancement in non-circular jets

“…Laboratory studies using elliptic nozzles (Husain and Hussain, 1983;Ho and Gutmark, 1987) and using nozzles with corners, e.g., rectangular, triangular, starshaped (Gutmark et al, 1989b;Toyoda andHussain, 1989, Quinn, 1992), have observed that as the jet spreads, it can regularly evolve through shapes resembling that at the jet-exit but with axis successively rotated at angles characteristic of the jet geometry (denoted as axisswitching phenomena). This main underlying mechanism for the enhanced entrainment properties of non-circular jets relative to comparable circular jets, results from self-induced Biot-Savart deformation of vortex rings with non-uniform azimuthal curvature, and interaction between spanwise and streamwise vorticity.…”

Spray and atomization of a common rail fuel injector with non-circular orifices

“…rectangular, triangular, star-shaped [12][13][14] have shown that as the jets move downstream, their cross-sections change similarly to the shape of the orifice geometry but with axes successively rotating at the angle characteristic of the orifice geometry. This phenomenon is a result of self-induced Biot-Savart deformation of vortex rings with nonuniform azimuthal curvature and interaction between azimuthal and stream-wise vorticity [15].…”