Extended Abstract (128K)P3.10
Dynamic evaluation of drag coefficients for flow over scale-similar complex boundaries
Stuart Chester, Johns Hopkins University, Baltimore, MD; and C. Meneveau and M. Parlange
This talk will present results from preliminary simulations of flow over complex, self-similar boundaries with a dynamically determined drag coefficient. In traditional simulations of flow over complex terrain with unresolved surface features, the effect of the small-scale geometry is often parameterized using a drag coefficient determined in an ad-hoc fashion. Conversely, by defining an appropriate test-filtering operation, we show that the drag coefficient can be obtained dynamically from the smallest resolved scales of the surface, in a similar framework to that used in the dynamic model of Germano et al. (1991). The approach assumes scale-similarity of the boundary and also assumes a simple Reynolds number dependence for the drag coefficient. Results are obtained by performing numerical simulations of flow over Koch curve-shaped geometries of varying order, over a range of Reynolds number. In the high Reynolds number cases, a simple mixing-length turbulence model is used tentatively, along with an assumed inertial scaling (i.e. Reynolds number independence) of the drag coefficient. A priori tests done with fully resolved geometry show reasonable agreement between exact drag coefficients and dynamically determined values, at certain scales. A posteriori tests done with partially resolved geometry and a dynamically determined drag coefficient will also be discussed. The present preliminary simulations are limited to 2-D flow over 2-D geometry, and are performed on a structured grid. Imposed body forces (Mohd-Yusof, 1997) are used to represent the effect of the geometry. Several interpolation schemes are tried with the body forces to accurately represent the desired boundary conditions.
Poster Session 3, Fundamental Studies
Tuesday, 16 July 2002, 2:00 PM-2:00 PM
Previous paper Next paper