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2002 LAPCOD Meeting
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A Lagrangian stochastic model for dispersion in unsteady inhomogeneous sub-filter scale turbulence
C. Coulliette, A. Reynolds
California Institute of Technology
chad@caltech.edu(Abstract received 11/01/2002 for session B)
ABSTRACT
In many applications from the fluid dynamics laboratory to oceanographic flows, computer modelling or observational data typically results in a discretized velocity field. The knowledge we have of the flow under study is limited by the spacing between grid points in space and time. In a laminar flow, this limited knowledge may be adequate to sufficiently describe how particles are advected through this flow. But, in a turbulent flow, we need a way to determine the effect of the sub-grid or more generally, sub-filter scale, below which structure is not resolve, on particle advection. Many attempts in oceanographic and other fields have been made to model the unresolved Lagrangian dynamics as an Ornstein-Uhlenbeck process by assuming homogeneity and stationarity of the velocity statistics at the sub-grid scale. We overcome this limitation through the employment of a more sophisticated Lagrangian stochastic (LS) model capable of capturing inhomogeneous and unsteady effects. This LS model is used to investigate the relationship between small-scale turbulent dispersion and Lagrangian coherent structures in a quasigeostrophic double-gyre model and in HF radar velocity data of Monterey Bay. The existence of coherent structures mandates the use of a LS model which adapts to temporal and spatial variations in the prescribed flow.
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2002 LAPCOD Meeting, Key Largo, Florida, December 12-16, 2000