Near-field developments of elliptic jets in crossflow

Abstract

An experimental study has been carried out for aspect ratio AR = 0.3 and 3 elliptic jets in crossflow, with the results being compared to a circular jet in crossflow using the digital particle image velocimetry technique. Results show that for AR = 0.3 and 3 elliptic jets, which are significantly streamlined and blunt with respect to the crossflow respectively, unsteady foci observed earlier in AR = 0.5 and 2 elliptic and circular jet lee-side regions are either non-existent or not well defined. Mean peak vorticity values along leading-edge and lee-side shear layers are also observed to be higher for elliptic jets than for the circular jet, regardless of aspect ratio. Intriguingly, AR = 0.3 elliptic jet had lower vorticity values than its AR = 0.5 counterpart along the shear layers and could be due to rapid vortex entanglements of the leading-edge vortices within short distances away from the AR = 0.3 elliptic jet exit. Velocity plots also show ‘bifurcations’ for the transverse velocity component and demonstrated reduced activities associated with the counter-rotating vortex pair formation as the aspect ratio increases. Analysis of the velocity profile developments downstream of the jets shows multiple velocity maxima and minima associated with various features of the jet in a crossflow phenomenon and that crossflow recovery at the lee-side regions will be slower for high aspect ratio jets. Lastly, results also show that although stronger flow reversals occur for high aspect ratio jets, they do not lead to more intense counter-rotating vortex pair formations over the low aspect ratio elliptic jets.

Keywords:

• elliptic jet
• jet in crossflow
• particle image velocimetry

Acknowledgement

This project is financially supported by the National University of Singapore through Academic Research grant no. RP950638.