Flow visualization and free surface length scales measurements in a horizontal jet beneath a free surface

In the context of the recent studies on turbulence/free surface interactions of Brocchini and Peregrine [M. Brocchini, D.H. Peregrine, The dynamics of strong turbulence at free surfaces. Part 1. Description, J. Fluid Mech. 449 (2001) 225–254; M. Brocchini, D.H. Peregrine, The dynamics of strong turbulence at free surfaces. Part 2. The boundary conditions, J. Fluid Mech. 449 (2001) 255–290] and Murzyn et al. [F. Murzyn, D. Mouaze, J.R. Chaplin, Optical fibre probe measurements of bubbly flow in hydraulic jumps, Int. J. Multiphase Flow 31(1) (2005) 141–154], this paper presents flow visualizations and free surface measurements of the flow generated at the free surface by a horizontal jet beneath this air/water interface. The main goal is focused on the free surface motion. The shadowgraph technique is used for the first part of this study and two wire gauges have been built to describe the free surface oscillations. Description of typical free surface length scales and frequencies are also obtained and shown through a correlation technique for different positions of the jet beneath the air/water interface. Comparisons of the flow visualizations with free surface length scales confirm that this shadowgraph technique is well defined for this kind of flows and very promising. Front velocity of the jet is deduced from the pictures taken with a digital camera and a comparison is made with theoretical work of Brocchini and Peregrine [M. Brocchini, D.H. Peregrine, The dynamics of strong turbulence at free surfaces. Part 1. Description, J. Fluid Mech. 449 (2001) 225–254; M. Brocchini, D.H. Peregrine, The dynamics of strong turbulence at free surfaces. Part 2. The boundary conditions, J. Fluid Mech. 449 (2001) 255–290] to define the nature of the flow.