On the flow interactions of multiple jets in cross-flow

Direct numerical simulations have been performed to study the behaviour of multiple square jets issuing normally into a cross-flow. The jets are arranged side-by-side in spanwise direction in twin jet configuration and with addition third jet downstream along the centre line in tandem jets configuration. The simulations are carried out for the jet-to-jet adjacent edge distances of 1D and 2D in twin jets case and 2D for in tandem jets case, where D is the jet width. The simulation uses the jet to cross-flow velocity ratio of 2.5 and the Reynolds number based on the free-stream quantities and the jet width is 225. The predicted flow features show that the downstream merging between the two counter rotating vortex pairs (CRVP) in the twin jets configuration is strongly dependent on the jet-to-jet edge distance. Further downstream, the far-field of sideby-side jets is mostly dominated by a larger CRVP accompanied with a smaller inner vortex pair. The originally inner vortex is found no longer to be survived and it has been almost dissipated before exiting the computational domain. The obtained results are in good qualitative agreement with the experimental findings in the literature. The resulting flow structures associated with both the twin and the tandem jets in cross-flow configuration show complex flow interactions between individual jets. Indeed, the interactions between the three jets and cross-flow cases have led to a complex vortex system in which six vortex pairs can be identified. The evidence of these flow structures could provide valuable information for related industrial applications. Key-Words: Direct numerical simulation, Multiple jets in cross-flow, Jet-to-jet spacing, Vortex structures, Cross-flow entrainment.