Bilal Ozkan Lafci, website username login: StratifiedLake
Member of the following CSDMS groups
- Terrestrial Working Group
- Cyberinformatics and Numerics Working Group
- Hydrology Focus Research Group
Signed up for the mailing list: yes
An internal bore is a type of large-scale geophysical flow where a shock-like height discontinuity propagates along an interface between two fluids of different densities. Internal bores are responsible for many complex and interesting atmospheric and oceanographic phenomena. The most visually striking and well-known example of an internal bore is the Morning Glory cloud formation off the northern coast of Australia (pictured at left), which is formed by the interaction of a sea-breeze with a temperature inversion layer. Internal bores can also be formed in the atmosphere by cold outflows from thunderstorms. In marine environments, internal bores can arise from several mechanisms such as the interaction of the tides with ocean floor topography, or by gravity current flows past submarine obstacles.
For the last 60 years, people have been developing and refining analytical models to describe the propagation of internal bores. If the densities of the two fluids are very different, as is the case for a tidal bore, which propagates along an interface between water and air, a very accurate model describing a bore's propagation as a function of its size can be obtained by conserving mass and momentum across a control volume encompassing the more dense layer of fluid. However, if the densities are very similar, the upper fluid cannot be neglected. In this case, there is not enough information to come up with a closed form model from a control volume analysis unless we make some assumption about the energy loss across the bore.
That's where we come in. To gain insight into how energy evolves and dissipates within an internal bore, we simulate them using two and three-dimensional direct numerical simulations. An example of one of our two-dimensional simulations is shown below. These simulations allow us to directly measure the energy and how it evolves as the bore propagates. Based on our results, we are able to propose a new analytical model for internal bores which takes into account mixing at the interface between the two layers. Our new model accurately predicts internal bore's propagation velocities, and can also predict the amount of energy lost to mixing. These results will soon be published in the Journal of Fluid Mechanics. We are now working on extending our model and simulations to non-Boussinesq internal bores so we can bridge the gap between Boussinesq and single-layer bores.