An Integration Of Subgrid Physics Into Coarse Grid Simulations Of River Models
Abstract
In river flows, the large eddies scale on river width and depth, thus the uncertainties and inhomogeneities in river boundary structure have length scales only slightly smaller the large-eddy scale. Consequently, the turbulence generated by the river bottom inhomogeneity is hydrodynamically significant. Conventionally, uncertainty and inhomogeneity in large-scale river modeling are generally addressed together by calibrating a roughness coefficient. However, this kind of calibration is inherently grid dependent due to nonlinearity associated with local flow inhomogeneity. In other words, the work to calibrate a model at one grid scale is lost if the model grid is altered, and such grid-dependent calibration cannot provide insight into the unresolved processes or features. To address the grid dependence, a Coarse Grid Simulation (CGS) framework is proposed (Fu and Hodges, 2005). The CGS will provide a model structure for representing the relationship between empirically-known subgrid features and grid-resolved flow. Therefore, the CGS will lessen the calibration efforts associated with changing model grid scales. In the present work, we demonstrate that grid resolution must affect turbulence calibration for inhomogeneous subgrid-scale physics in standard RANS formulations. Examples are provided to show that through use of the proposed CGS formalism, fine-scale process observed in a fine-grid model can be represented at arbitrary grid scales in a coarse-grid model without ad hoc calibration. Reference Fu, S. and B.R. Hodges (2005), ¡°Grid-scale dependency of subgrid-scale structure effects in hydraulic models of rivers and streams,¡± Mechanics and Materials Conference (McMat 2005), June 1-3, 2005, Louisiana State University, Baton Rouge, Electronic Proceedings (CD-ROM), 5 pgs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.H21A0171F
- Keywords:
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- 1839 Hydrologic scaling;
- 1846 Model calibration (3333);
- 1847 Modeling;
- 1849 Numerical approximations and analysis