Investigation of turbulent characteristics of twin jet near the free surface was carried out experimentally at four offset height ratios of 1, 2, 3 and 4. The experiments were conducted using square orifice nozzle pair with separation ratio of 2.6 at Reynolds number of 3890. The effect of the free surface as well as the effect of the offset height ratio on the streamwise mean velocity, streamwise turbulence intensity and Reynolds shear stress were discussed. The velocity decay and jet spread were quantified in order to characterize the effect of offset height on entrainment and mixing performance. The flow dynamics at the free surface was characterized by observing the variation of streamwise mean velocity and turbulence intensities at the free surface. Proper orthogonal decomposition was performed and the role of the energetic structures in the surface attaching twin jet was discussed both qualitatively and quantitatively.

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