Author(s)

A. Tamburrino & A. Mourgues

Abstract

Results of an experimental study about the flow structure in the near free surface region of a tank agitated by jets located in the bottom are presented in the paper. Flow visualization and PIV techniques were used to compute instantaneous velocity fields, mean velocity profiles, turbulence intensities and turbulent kinetic energy distribution. Velocity spectra and autocorrelations were also calculated from the data collected. A succession of events in the near air-water interface, forming a quasi-periodical pattern, was inferred from flow visualization and measurements. The most relevant event corresponds to a horizontal sweep, usually preceded by an upwelling of fluid. It is postulated that these events are associated to the renewal phenomenon, which is important in the gas transfer process across the interface. Velocity spectra and autocorrelations showed some dominant frequencies associated to large scale motions in the tank. Isotropy loss and damping of the vertical velocity fluctuation was inferred from the velocity spectra. Ascending vortices deform when they approach to the free surface, increasing their horizontal size and diminishing the vertical one, or breaking down in smaller ones.

Keywords