On the trajectory scaling of tandem twin jets in cross-flow in close proximity

An experimental study has been conducted on tandem twin jets in cross-flow (JICF) in close proximity to investigate the relationships between their trajectories, separation distances and velocity ratios. Results show that the front and rear jets, each with initially distinct jet trajectory, merge into a single trajectory shortly after they exhaust into the cross-flow. Furthermore, the merged tandem JICF attains deeper cross-flow penetration than that of a single JICF at the same velocity ratio. The front jet is also observed to provide ‘shielding’ for the rear jet such that the latter penetrates relatively deeper into the cross-flow, which corroborates observations made by earlier studies. In particular, the present study demonstrates that it is possible to collapse the tandem JICF merged trajectories by ‘rD’-scaling, where A and B coefficients show slight reductions and increments, respectively, with increasing separation distance. Collapsing the merged trajectories by using single JICF A and B coefficients leads to the notion of effective velocity ratio for tandem JICF, which enable the authors to propose a modification in the ‘rD’-scaling law for tandem JICF. Lastly, the modified ‘rD’-scaling law is applied to trajectory data from an earlier tandem JICF study, and its validity is demonstrated by the resulting good collapse.