  A new topography adapted mesh generation process tailored to simulate
Atmospheric Boundary Layer (ABL) flows on complex terrains is presented. The
mesher is fully automatic given: the maximum and minimum surface mesh size, the
size of the first element of the boundary layer, the maximum size in the
boundary layer and the size at the top of the domain. The following
contributions to the meshing workflow for ABL flow simulation are performed.
First, we present a smooth topography modeling to query first and second order
geometry derivatives. Second, we propose a new adaptive meshing procedure to
discretize the topography based on two different metrics. Third, the ABL mesher
is presented, featuring both prisms and tetrahedra. We extrude the triangles of
the adapted surface mesh, generating prisms that reproduce the Surface Boundary
Layer. Then, the rest of the domain is meshed with an unstructured tetrahedral
mesh. In addition, for both the surface and volume meshers we detail a hybrid
quality optimization approach, analyzing its impact on the solver for
high-complexity terrains. We analyze the convergence of the triangle adaptive
approach, obtaining quadratic convergence to the geometry and reducing to one
half the error for the same amount of degrees of freedom than without
adaptivity and optimization. We also study the mesh convergence of our RANS
solver, obtaining quadratic mesh convergence to the solution, and using a 30%
of the degrees of freedom while reducing a 20% of the error of standard
semi-structured approaches. Finally, we present the generated meshes and the
simulation results for a complete complex topographic scenario.
