Progress in Generalizing the Immersed Boundary Method in WRF for Flow over Complex Terrain

The immersed boundary method (IBM) allows representation of arbitrarily complex terrain on a background Cartesian grid. Velocity values near the immersed surface are updated at each time step to account for the presence of the boundary and its influence on the flow. A ghost-cell IBM was previously implemented into WRF (Lundquist et al. 2010, 2012) to allow representation of complex urban geometries for urban dispersion simulations. In this presentation, recent progress in the generalization of the IBM method in WRF to flow over complex terrain is described.

Simulations over complex, mountainous terrain typically require the use of Monin-Obukhov similarity theory to provide the momentum flux at the lower boundary. Accurately accommodating these surface fluxes is the goal of this work, which examines several different possible implementations of these flux boundary conditions into our previous WRF-IBM code. Test cases over flat terrain and idealized valleys are used to demonstrate the sensitivity of the flow simulations to the details of the boundary condition representation.