Computing complex flows on coarse grids using vorticity confinement

Abstract

Many flows of interest are characterized by large regions of concentrated (and turbulent) vortical structures that persist and can convect over long distances. Flows of this nature include those associated with aircraft, but also include flows associated with ships, automobiles, bridges, and buildings. Conventional CFD methods tend to dissipate vortical structures, degrading the overall accuracy of the computed flow. This dissipation can be reduced through the use of fine grids, but at the expense of greatly increased computational demands. In addition, no conventional CFD method produces the unsteady chaotic flow associated with turbulence except on extremely fine grids and in very small regions. The vorticity confinement method prevents ~ Senior Research Scientist 0 Research Scientist *Professor Copyright © 2002 by Flow Analysis, Inc. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. the dissipation of vortical structures on coarse grids, and approximately produces the unsteady small-scale features (down to grid-cell scale) associated with physical turbulence. In this paper, vorticity confinement is used to model a turbulent wake behind a cylinder. Comparisons with data demonstrate the potential of vorticity confinement to predict mean wake flow and Reynolds stresses accurately and efficiently, even on a coarse grid. In addition, computations are performed on a realistic ship configuration; the resulting velocity field and bow vortex trajectory are shown to agree well with wind tunnel measurements.