Internal waves generated from a turbulent mixed region

• Published in: Physics of fluids (1994) 2003-02, Vol.15 (2), p.488-498
• Main Authors: Dohan, K., Sutherland, B. R.
• Format: Article
• Language: English
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/1.1530159

Using two nonintrusive visualization methods, laboratory experiments are performed to examine the internal wave field underlying a turbulent region generated by a vertically oscillating grid. The first method uses dye-lines to mark the vertical motions of isopycnal layers and the second uses “synthetic schlieren” to visualize the entire wave field. In a range of experiments, the strength of the stratification is varied so that the buoyancy frequency N=0.33–1.40  s −1 . In all cases, large tank-scale standing wave modes are established which last throughout the experiment. The amplitudes of the isopycnal lines, A ξ , follow a power law relation A ξ ∼N −1.5 . The synthetic schlieren technique allows us to visualize turbulent eddy-scale waves and to isolate the properties of the strongest downward propagating waves at the base of the turbulent layer. These waves have a surprisingly narrow range of frequencies and vertical wavenumbers. The angles of wave propagation from the vertical for the dominant waves lie in the range Θ=42°–55°. The amplitudes in the wave field follow a relation A ξ ∼N −1.68 . These waves are of large amplitude: their vertical displacement is from 2% to 4% of their horizontal wavelength, a significant fraction of the breaking amplitude.