EXPERIMENTAL STUDIES OF THE DEVELOPMENT OF QUASI-2-DIMENSIONAL TURBULENCE IN STABLY STRATIFIED FLUID

Quasi-two-dimensional turbulence was generated by towing an array of v ertical cylinders through a tank which was filled with a two-layer str atified fluid. Sugar and Epsom salts were used, to give matching refra ctive indices for the two layers. The interface between the two layers was seeded with approximately 1000 neutrally buoyant particles. The e volution of this quasi-two-dimensional turbulence was visualized by ph otographing the fluorescent particles illuminated by a horizontal lase r sheet traversing in the vertical direction. The three-dimensional pa rticle velocity was obtained by digitizing the streaks. The evolution of the velocity correlations, length scales, one-dimensional and two-d imensional velocity and vorticity spectra were obtained for N=5.72 s(- 1), N=4.43 s(-1), and N=2.55 s(-1) (where N is the Brunt-Vaisala frequ ency). The results showed the physical process of inverse energy casca ding and the formation of dominant vortical structures under the influ ence of density stratification. Compared with idealized two-dimensiona l turbulence, the flow is highly dissipative at high N, as a result of the frictional dissipation between the interface and the unstratified layers.