Wave-tank study of internal waves

Abstract

Internal waves, generated in an approximate two-layer system of miscible fluids by flow over a submarine ridge, were examined. The investigation was conducted in a wave tank 3.0 m long and 0.3 m wide in which total water depth varied between 7.3 cm and 15.2 cm. To determine visually the interface deformations, the lower saline layer was colored with Rhodamine "B" dye. Neutrally buoyant particles, consisting of a solution of carbon tetrachloride and benzene, were introduced in the vicinity of the pycnocline to indicate particle motion. Subsequent particle motion and interface deformations were photographed with a 16 mm motion picture camera. Analysis of the film yielded particle trajectories and internal wave characteristics such as wave-length, period, amplitude and phase velocity. The observed motions were compared with those predicted by internal wave theory. Observed phase velocities differed from the theoretical phase velocities in all cases, with a maximum difference in one case of 44 percent of theoretical value. The discrepancies may be due either to the superposition of the observed progressive wave on a standing wave or to the observation of non-conserved wave crests in a dispersive medium. However, observed phase velocities did decrease in magnitude with a decreasing layer density difference as predicted by theory.