CFD SIMULATION OF THREE-DIMENSIONAL AIRFLOW OVER A VEGETATED SOIL SURFACE

The PAR3D code [1] represents a continuation of work that began with the MAC3D code [2] which was developed for simulating flow and transport in deep water. PAR3D retains the original capabilities of MAC3D, but it also incorporates parallel processing, which reduces CPU time and increases allowable resolution (problem size). Since water and air can both be regarded as incompressible fluids at flow velocities much less than the speed of sound, PAR3D has been extended to facilitate simulations of air flow and heat transfer over irregular terrain. PAR3D is limited to incompressible flow in particular, which means that the fluid density may be altered slightly by temperature but not by pressure. Variations in density create buoyant forces for which PAR3D employs the Boussinesq approximation. Thus, density variations are neglected in the continuity equation but not in the momentum equation. The code uses a finite-volume scheme with curvilinear marker-and-cell (MAC) grids to compute the transport of mass and momentum through flow regions of arbitrary shape. The MAC designation indicates that vector components are computed normal to the cell faces, while scalar quantities are computed exclusively at the cell centers. The grids are subdivided into multiple components called grid blocks, and each block is assigned to a single processor. Shared information is communicated between processors via the standard message-passing interface (MPI) library discussed by Gropp et al. [3].