Grid-scale dependency of subgrid-scale structure effects in hydraulic models of rivers and streams

by Shipeng Fu and Ben R. Hodges

Fu, S. and B.R. Hodges, Grid-scale dependency of subgrid-scale structure effects in hydraulic models of rivers and streams, Mechanics and Materials Conference 2005 (McMat 2005), June 1-3, 2005, Louisiana State University, Baton Rouge, Electronic Proceedings (CD-ROM), 5 pgs.

Abstract

A key difficulty in applying numerical models for engineering hydraulics is coping with subgrid-scale heterogeneity in both benthic structure and fluid flow. This difficulty is exemplified by the effects of Large Woody Debris (LWD) on stream and river hydrodynamics. In the past, LWD effects have typically been modeled by calibrating eddy viscosities or Manning’s ‘n’ to approximate the increased drag. However, the spatial structure of flow near LWD contributes to viability of aquatic habitat, so the prior methods are unsuitable for hydraulic models used for instream-flow habitat analysis. Furthermore, resolving the flow field around LWD with Large Eddy Simulation (LES) techniques would require an impractical amount of computer power, and coarse-grid Reynolds-averaged Navier Stokes (RANS) models lead to grid-dependency of the drag effects for subgrid-scale structure. To address these problems, a new conceptual model is developed. The new approach applies a spatial filter to the Reynolds-averaged Navier-Stokes equation, effectively creating a combination of RANS and LES. The advantage of this approach is the heterogeneity in subgrid-scale turbulence structure can be directly modeled without a grid-scale dependency.

©2005 Ben R. Hodges	• last updated July 22, 2005	• UT • College of Engineering • Dept of Civil Engineering • CRWR • EFM Home •
©2005 Ben R. Hodges	• last updated July 22, 2005