Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session CG: Mini-Symposium on Computational Strategies for the Simulation of Nonlinear Waves and Turbulence in Environmental Flows |
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Chair: Peter Diamessis, Cornell University Room: Long Beach Convention Center 103B |
Sunday, November 21, 2010 1:00PM - 1:26PM |
CG.00001: Direct Numerical Simulations of Stratified Turbulence Invited Speaker: In the 1990's, computers became powerful enough to enable direct numerical simulations (DNSs) of turbulent flows which were fully consistent with laboratory data. Prior to that, low Reynolds number effects encouraged the belief that simulation results must be validated against physical measurements. Today, many researchers accept DNS as complimentary to laboratory data for studying engineering turbulence. We are now at a comparable breakthrough point with DNS of stratified turbulence. Whereas simulations with strong stratification just a few years ago could be run with a buoyancy Reynolds number, $\mathrm{Re}_b$, of about 20, it is now practical to simulate flows with $\mathrm{Re}_b > 50$, well beyond the value accepted for being relevant to the ocean or atmosphere. Statistics from DNS of forced homogeneous stratified turbulence run with 8.6 billion grid points are reported for a wide range of Froude numbers. Spectral energy balances are shown, as are the probability density functions of turbulent quantities. Preliminary results for runs with 69 billion points are also presented, along with an invitation for collaborative users of these data. [Preview Abstract] |
Sunday, November 21, 2010 1:26PM - 1:52PM |
CG.00002: Hydrostatic ma non troppo. Leptic expansion and Poisson solvers in thin domains Invited Speaker: The hydrostatic approximation of internal waves fails when the horizontal scale is comparable to the local depth. The resulting dispersion opposes nonlinear steepening. Theoretical models rely on approximations to achieve physically reasonable dispersion while ocean models rely on fully nonhydrostatic equations, whose solution involves expensive Poisson solvers. We show that even within numerical models there exists a continuum between hydrostatic and fully nonhydrostatic behavior. A formal expansion of the solution of the Poisson problem can be used to explore the grey area separating hydrostatic from nonhydrostatic scales. We show that an asymptotically correct amount of dispersion can be added to internal waves without incurring the full cost of a nonhydrostatic solution. We also show that if the full nonhydostatic equations are needed, the expansion can be used in lieu of a preconditioner. Since the expansion is derived analytically for an arbitrary elliptic operator, it is independent on the particular choice of spatial discretization. It can thus be readily adapted to structured, unstructured or coordinate mapping based models. [Preview Abstract] |
Sunday, November 21, 2010 1:52PM - 2:18PM |
CG.00003: On the Interaction of Buoyant Plumes With Ocean Mixed-Layer Fronts Invited Speaker: The ocean's surface mixed layer is notoriously complex due to high spatial and temporal gradients of density and velocity fields. The understanding and modeling of such flows have a wide range of applications. For instance, anomalous currents and density perturbations in the acoustic and optical environment can affect a variety of naval operations. These flows can also influence strongly the dispersion of surface and sub-surface pollutants. Large eddy simulations of an idealized mixed-layer problem are conducted using the spectral element model Nek5000. Sampling strategies of these fields are investigated using passive tracers and Lagrangian particles. These idealized fields are then used in order to explore the behavior of a buoyant plume through the water column, namely its surface and sub-surface dispersion, which is motivated by the Deepwater Horizon oil spill. [Preview Abstract] |
Sunday, November 21, 2010 2:18PM - 2:44PM |
CG.00004: Computational Investigations of Gravity and Turbidity Currents Invited Speaker: We will present an overview of high-resolution, Navier-Stokes based simulations of gravity and turbidity currents. The turbidity currents we consider are driven by particles that have negligible inertia and are much smaller than the smallest length scales of the buoyancy-induced fluid motion. For their mathematical description an Eulerian approach is employed, with a transport equation for the particle-number density. The governing equations are integrated numerically with high-order, compact finite difference techniques for rectangular geometries, and with second order finite difference methods for complex geometries. Arbitrary seafloor topographies are implemented via an immersed boundary method. We will discuss differences between two- and three-dimensional turbidity current dynamics in the lock-exchange configuration, and we will introduce some effects due to complex topography. Results will be shown regarding non-Boussinesq effects, and the unsteady interaction of a gravity current with a submarine structure, such as a pipeline. Furthermore, we will briefly discuss the linear stability problem of channel and sediment wave formation by turbidity currents. [Preview Abstract] |
Sunday, November 21, 2010 2:44PM - 3:10PM |
CG.00005: High resolution simulations of turbulent flows in open-channels Invited Speaker: The results of recent high resolution large-eddy simulations (LES) of selected turbulent open channel flows are presented and discussed. An efficient, finite volume based Navier-Stokes solver is employed to simulate the flow over a rough bed and through idealized emergent vegetation. The fluid phase is solved entirely on a Cartesian grid and different immersed boundary methods (IMB) are used to account for the solid, non-Cartesian roughness elements. First and second order statistics are compared to measurements and the accuracy of the different IMBs is assessed. The frequency of turbulence events (like sweeps, ejections) and their contribution to Reynolds stresses is quantified and the anisotropy of turbulence is described. Based on the turbulence statistics, the utilization of structures eduction methods and aided by visualizations and animations the generation and fate of the dominating coherent structures in the flows is discussed. [Preview Abstract] |
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