HR: 0830h
AN: OS41C-0809    [PDF]
TI: Non-hydrosatatic Effects in Exchange Flows
AU: * Kanarska, Y
EM: kanarska@ukrpost.net
AB: An important class of stratified flows is exchange flows in which fluids of different densities move in opposite directions through a channel. These flows are studied mainly in the frame of an internal hydraulic theory. However geophysical flows are more complicated than a two-layer hydraulic solution. In this paper the hydrodynamics of exchange flows is investigated with focusing on the role of non-hydrostatic effects, friction, mixing and an impact of an unsteady barotropic tide forcing on hydrodynamics of water exchange in the straits. Special attention is given to design of physically relevant time-dependence boundary conditions at the open boundaries. The numerical tool for investigations is a three-dimensional, non-hydrostatic, numerical model of free surface stratified flows (Kanarska Y., Maderich V, 2003). The model is a non-hydrostatic extension of the free-surface primitive equation POM model. A mode splitting technique, decomposition of pressure and velocity fields into hydrostatic and non-hydrostatic components and sequential calculation of these components are the base of numerical algorithm of the model. At first the model is used to investigate different regimes of exchange flows ranging from dispersive gravity waves in the seiche flows to shear instability in the lock-exchange flows including transition regimes where both mechanisms occur. The investigation of the energetics and the resulting diapycnal mixing is carried on the base of the analysis of available potential energy. Then the model is applied for an investigation of the exchange flows in a long and narrow strait with a sill or contraction for the configuration of experiments of Maderich (2000) and to the simulation of the water circulation in the Dadanelles strait. Calculations and analysis based on a three-layer decomposition with an intermediate layer of variable density showed the importance of entrainment and friction in the long straits. As a result the composite Froude number is significantly lower in comparison to predictions of two-layer hydraulic theory. Developed time-dependent boundary conditions at the open boundaries allow simulating the unsteady exchange with barotropic tidal forcing. For the first time the seasonal changes for the water exchange in the Dardanelles were simulated. The obtained results show strong mixing in most narrow zone of the strait. It was found that both baroclinic an barotropic variability are important for flow hydrodynamics.
DE: 3210 Modeling
DE: 3220 Nonlinear dynamics
DE: 4255 Numerical modeling
DE: 4512 Currents
DE: 4568 Turbulence, diffusion, and mixing processes
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting