Sig WindE/Validation Cases
Page under construction
The aim of this page is to hold validation cases for ABL (Atmospheric Boundary Layer) flows that are of interest to anybody starting to model ABL flows in OF. The simulations I perform, and refer to mainly in this text are RANS with k-epsilon turbulence closure models, using simpleFoam. Most of the first simulations that are placed in this page were done according to the excellent Martinez 2011 Ms.C. thesis [1] All of the boundary conditions and mesh creation suggestions were followed by from his work and the references within it.
(0) Maintaining a logarithmic inlet profile over a 2D domain
The wall function boundary condition implemented in OF is the Nikuradse's grain of sand roughness. It produces an anomaly in the k profile in the first cell above the ground which propagates upwards and down-flow. This is discussed extensively in the literature, and alternative wall functions have been suggested such as Richards and Hoexy 1993 (RH). There has lately been a very good documentation of testing this anomaly by Martinez in his Ms.C. thesis [2].
File:BL2D.tar checked on OF 2.1
Attached case ("BL2Dtemplate") has python scripts using the pyFoam library to run different z0 values (all files included in this page require the pyFoam library). run with ./Allrun .
(1) Flow over Isolated 2D Hill (checked on OF 2.1)
The 2D simple hill from Martinez 2011 whose shape is given by
![y\left(x\right) = -\frac{H}{6.04844}\left[J_0(\Lambda)I_0(\Lambda\frac{x}{a})-I_0(\Lambda)J_0(\Lambda\frac{x}{a})\right] \; \mathrm{for} \; |x-x_0| \leq a](/images/math/0/b/b/0bbf895b595d82a846ee581595d56349.png)
The mesh is created with blockMesh, and a template file, and also a python script that writes the hill shape as a polyline object in the blockMeshDict. The mesh grading was done by breaking the control box into 3 segments - upwind, hill area and downwind (unlike the Martinez mesh grading tanh scheme). The case with the python script, ready to run (./Allrun) is attached here
File:2DBump.tar (checked on OF 2.1)
It compares the results with figures 21a,21b and 21c from Martinez 2011.
Another 2D case I tried simulating though unsuccessfully is mentioned here Sig_WindE_-_Validation_Cases_RUSHIL.
(2) Flow over Isolated 3D Hill (checked on OF 2.1.1)
The same geometry as used by Martinez 2011, with the same recommendations. The mesh is created by snappyHexMesh. The STL file is created in salome with this python script File:3DBump salome script.tar. The case with an Allrun file is attached here
File:3DBump.tar (checked on OF 2.1.1)
(3) Flow over real terrain - Askervein hill (checked on OF 2.1.1)
The Askervein hill [3] and [4] is a low isolated eliptic hill located in the island of south Uist in Scotland. In 1982-3 a measurement campaign was conducted there, and it has since been used as a bench mark case for linear and non-linear (CFD) models for flow and pollutant dispersion simulations. A simulation case is presented here with use of the meshing recommandations from Martinez 2011. The terrain is massaged using SAGA GIS open source software, as will be described below.
Creating the STL surface
In this case a real terrain is used. This means that the source of data is some DTM, and an additional step of smoothing the boundaries of the terrain has to be taken, in order to incorporate the boundary conditions used so far in the previous simulation, since they are appropriate only to flat terrain.
