Jets and plumes in a crossflow are characterised by a contra rotating vortex pair that dominates the deflected jet. Much of my research work in this area has been to examine the development and subsequent decay of these vortices and the associated circulation.
Flow visualisation of smoke seeded jets has been a powerful tool for determining the growth of the jets and their trajectory for different configurations, such as twin in-line and side-by-side jet nozzles of different centre-to-centre spacings
Smoke flow visualisation clearly reveals the time-averaged shape of the contra-rotating vortex pair, although this flow feature does not appear in instantaneous snapshots of the flow field.
Velocity measurements in planes across the jet allow determination of the distribution of the streamwise vorticity component associated with each vortex and the overall circulation by integration of these distributions.
The circulation decays with distance downstream of the nozzle and further studies, for both single and twin jets, have shown how this is related to turbulent vorticity transport across the jet centre-line.
The overall circulation determined from integrated vorticity is strongly correlated with that determined by a simple line integral of the vertical velocity component on the jet centre-line (for full paper click here).
Acknowledgements: Prof N Toy, Dr V Kolar, Prof S Okamoto, Dr P J Disimile