Effects of Offset Height on the Turbulent Characteristics of Rectangular Twin Jets

Turbulent characteristics of a twin jet were experimentally investigated for offset heights, h = 1d and 3d where d is the nozzle diameter. The experiments were conducted using a pair of rectangular nozzles of an aspect ratio of 3, that is oriented in the minor plane and with a nozzle separation ratio of 2.3. The Reynolds number, based on jet exit velocity and nozzle diameter was maintained at 4622. The results show that confinement effect decreased the merging point of the jets by 30% but there is no significant effect on the combined points. Reduced confinement showed an 89% reduction in the acceleration of the mean streamwise surface velocity. Two-point streamwise velocity correlations were used to investigate the large-scale coherent structures. The results revealed enhanced streamwise stretching of the structures as the offset height ratio decreased. In the combined region, the structures are more inclined towards the free surface as the offset height ratio decreased.