Turbulent Structures in Gravity and Turbidity Currents and Their Implications from Spreading Rates and Sediment Deposition Patterns
Mariano I. Cantero1, Marcelo H. Garcia2, Gary Parker1, S. Balachandar3, and James Best1
1Departement of Geology, University of Illinois at Urbana-Champaign, Urbana, IL
2Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaig, Urbana, IL
3Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL
This work focus on the study of turbulent structures in gravity and turbidity currents and the characteristics that they imprint on macroscopic features of the flow. Large-scale, highly-resolved numerical simulations of planar and cylindrical currents are conducted for flows where the density difference with the ambient fluid is small enough that the Boussinesq approximation can be adopted. Simulations are performed with over 130 million degrees of freedom, for which no sub-grid turbulence closure is needed.
As the flow evolves a sharp density interface forms between the heavy fluid in the current and the lighter ambient fluid. For large Reynolds numbers the interface rolls up forming strong Kelvin-Helmholtz vortices which are responsible for the entrainment of ambient fluid into the current. These vortices present a complex dynamics during the different phases of spreading and their interaction with the front of the current eventually influences the spreading rate.
The near-bed region of the flow presents turbulent structures which resemble those commonly observed in boundary layer flows. Hairpin-like vortices oriented with the flow direction populate the near-front region with a preferential pattern which can be associated to the lobes and clefts at the front of the current. This near-bed flow pattern leads to preferential sediment pick-up zones that are believed to promote the development and formation of grooves and furrows by the current front.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas