Building on the success of his flow visualization techniques studying turbulence in turbomachinery and LES applications, Professor Joe Katz and Professor Tom Osborn of JHU’s Department of Earth and Planetary Sciences have taken the Particle Image Velocimetry (PIV) technique under the sea to explore the flow near the bottom of the ocean. (For details of the PIV technique, see Turbomachines, in the Aerospace and Marine Systems section). Ocean flow dynamics have a huge impact on weather, climate, and marine life. And because the ocean is relatively shallow, especially in coastal areas (its horizontal extent is far larger than its vertical extent), turbulence generated at the bottom and the free surface plays a large part in the flow dynamics. To be able to predict ocean flows and energy budgets accurately, researchers need a good measure of the amount of dissipation and shear stress occurring at the surface, in the form of wind shear, and at the ocean floor, in the form of boundary layer turbulence.

There are currently no reliable data on the shear stresses at the ocean floor and their relation to large scale forcing (such as tides, currents and waves). Past experiments, done with point measurements, lack sufficient resolution, and are not capable of separating waves from turbulence. In experiments conducted off the coast of New Jersey, Professors Osborn and Katz used a submersible PIV system to record instantaneous spatial velocity distributions and sediment entrainment, initially within a 20x20 cm sample area and then in two 50x50 cm samples simultaneously, over a range of elevations from 10 cm to 1.4 m above the bottom. A new platform can scan up to 40 feet above the bottom. Because the PIV technique resolves a spatial, instead of a temporal, picture of the flow, it is possible to distinguish the wave dynamics from the turbulence. They have probed the complex interaction between turbulence and waves, and found that the turbulence in this boundary layer appears to be anisotropic at all scales. Current models assume that turbulent flow in the oceans is isotropic (the statistics are the same in all directions), and without data to the contrary, there was no reason to challenge that assumption. But the PIV data generated by Professors Katz and Osborn provides modelers with a more accurate scenario, one they can work with to develop more realistic representations of ocean flow.

[Welcome & Overview] [People] [Research] [Seminars, Events & Positions] [Undergraduate Programs] [Graduate Programs] [Student Groups] [Campus Life] [Home]