The Interaction Between Gravity Currents and Breaking Internal Waves: Berkeley Fluids Seminar

Seminar | October 21 | 12-1 p.m. | 3110 Etcheverry Hall

 Professor Jeffrey R. Koseff, William Alden Campbell and Martha Campbell Professor of Engineering, Department of Civil and Environmental Engineering, Stanford University

 Department of Mechanical Engineering (ME)

Abstract: Gravity currents moving along the continental slope, such as cold river inflows into lakes or brine effluent from desalination plants, can be influenced by internal waves shoaling on the slope resulting in mixing between the gravity current and the ambient fluid. Whilst some observations of the potential influence of internal waves on gravity currents have been made, the process has not been studied systematically. Professor Koseff will present the results of laboratory experiments, and some initial numerical simulations, in which a gravity current descends down a sloped boundary through a pycnocline at the same time as an internal wave at the pycnocline shoals on the slope. The waves are generated in a two-layer thin-interface ambient water column under a variety of conditions characterizing both the waves and the gravity currents. Professor Koseff will also present results over a full range of Froude number (characterizing the waves) and Richardson number (characterizing the gravity current) conditions, and will discuss the mechanisms by which the gravity current is mixed into the ambient environment including the role of turbulence in the process. Measurements of the downslope mass flux of the gravity current fluid in cases with different amplitudes of the incident internal wave will also be discussed. For the parameter regime considered, the mass flux in the head of the gravity current was found to reduce with increasingly larger incident amplitude waves. This reduction was effectively caused by a “decapitation” process whereby the breaking internal wave captures and moves fluid from the head of the gravity current back up the slope. The significance of the impact of the internal waves on gravity current transport, strongly suggests that the local internal wave climate may need to be considered when calculating gravity current transport.

Biography: Jeff Koseff, founding co-director of the Stanford Woods Institute for the Environment, is an expert in the interdisciplinary domain of environmental fluid mechanics. His research falls in the interdisciplinary domain of environmental fluid mechanics and focuses on the interaction between physical and biological systems in natural aquatic environments. Current research activities are in the general area of environmental fluid mechanics and focus on: turbulence and internal wave dynamics in stratified flows, transport and mixing in estuarine systems, phytoplankton dynamics in estuarine systems, coral reef, sea-grass and kelp-forest hydrodynamics, and the role of natural systems in coastal protection., 510-642-5942