TR-PIV measurement of the turbulent submerged jet and POB analysis of the dynamic structure

The flow field of a submerged turbulent jet interacting with a free surface was measured using laser-induced fluorescence and time-resolved PIV techniques,and the dynamics of the flow structures were examined further using the proper orthogonal decomposition (POD)a-nalysis technique.The jet axis was located at the depth of H/D =4 below the free surface and the Reynolds number was 5600.The LIF results show that the jet flow exhibits an upwelling motion due to the existence of the free surface.The time-averaged flow field shows that the upper half portion of the jet flow spreads faster and the maximum velocity is located towards the free sur-face.The typical off-axis double peaks distribution of stream-wise turbulent intensity disappears as the downstream distance increases.The POD results show that the upstream well-organized coherent structures rise up rapidly when the jet is about to approach the free surface and the sub-sequent strong interaction occurrs.The dominant large-scale structures begin to develop down-ward in the further downstream due to the confinement in the vertical direction.