26 research outputs found
Comparison of OpenFOAM and EllipSys3D for neutral atmospheric flow over complex terrain
The flow solvers OpenFOAM and EllipSys3D are compared in the case of neutral
atmospheric flow over terrain using the test cases of Askervein and Bolund
hills. Both solvers are run using the steady-state Reynolds-averaged
Navier–Stokes k–ϵ turbulence model.
One of the main modeling differences between the two solvers is the
wall-function approach. The OpenFOAMÂ v.1.7.1 uses a Nikuradse's sand
roughness model, while EllipSys3D uses a model based on the atmospheric
roughness length. It is found that Nikuradse's model introduces an error
dependent on the near-wall cell height. To mitigate this error the near-wall
cells should be at least 10Â times larger than the surface roughness. It is
nonetheless possible to obtain very similar results between EllipSys3D and
OpenFOAMÂ v.1.7.1. The more recent OpenFOAMÂ v.2.2.1, which includes the
atmospheric roughness length wall-function approach, has also been tested and
compared to the results of OpenFOAMÂ v.1.7.1 and EllipSys3D.
The numerical results obtained using the same wall-modeling approach in both
EllipSys3D and OpenFOAMÂ v.2.1.1 proved to be almost identical.
Two meshing strategies are investigated using HypGrid and SnappyHexMesh. The
performance of OpenFOAM on SnappyHexMesh-based low-aspect-ratio unstructured
meshes is found to be almost an order of magnitude faster than on HypGrid-based structured and high-aspect-ratio meshes. However, proper control of
boundary layer resolution is found to be very difficult when the
SnappyHexMesh tool is utilized for grid generation purposes.
The OpenFOAM is generally found to be 2–6Â times slower than EllipSys3D in
achieving numerical results of the same order of accuracy on similar or
identical computational meshes, when utilization of EllipSys3D default grid
sequencing procedures is included