Where is the grad computed in SIMPLE source code?

zizhou · September 15, 2019, 06:07

I have been trying to figure out how SIMPLE algorithm is implemented, but here: https://openfoamwiki.net/index.php/O...hm_in_OpenFOAM
it never mentions how the gradient of scalars is computed on an irregular mesh, and I haven't found where it is computed in source code. Is there anyone could tell me where is the function of grad computation? Thank you so much!

metalfox · September 16, 2019, 12:19

The explicit calculation of gradients in OpenFOAM usually involve invoking Gauss theorem:

$\int_{V}\nabla\phi\approx\frac{\sum_{f}\mathbf{S}_{f}\phi_{f}}{V}$

where $\mathbf{S}_{f}$ is the surface normal facing outwards, and $\mathbf{S}_{f}\phi_{f}$ represents the outer product of $\mathbf{S}_{f}$ with the tensor $\phi_{f}$ (for example, a rank 0 tensor, i.e. an scalar).

This calculation is valid for arbitrary polyhedrons.

The relevant piece of code is in gaussGrad.C (https://cpp.openfoam.org/v6/gaussGrad_8C_source.html).

September 15, 2019, 06:07	Where is the grad computed in SIMPLE source code?	#1
zizhou New Member zizhou huang Join Date: Jul 2019 Posts: 18 Rep Power: 7	I have been trying to figure out how SIMPLE algorithm is implemented, but here: https://openfoamwiki.net/index.php/O...hm_in_OpenFOAM it never mentions how the gradient of scalars is computed on an irregular mesh, and I haven't found where it is computed in source code. Is there anyone could tell me where is the function of grad computation? Thank you so much!

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September 16, 2019, 12:19		#2
metalfox New Member Join Date: Dec 2015 Posts: 24 Rep Power: 10	The explicit calculation of gradients in OpenFOAM usually involve invoking Gauss theorem: $\int_{V}\nabla\phi\approx\frac{\sum_{f}\mathbf{S}_{f}\phi_{f}}{V}$ where $\mathbf{S}_{f}$ is the surface normal facing outwards, and $\mathbf{S}_{f}\phi_{f}$ represents the outer product of $\mathbf{S}_{f}$ with the tensor $\phi_{f}$ (for example, a rank 0 tensor, i.e. an scalar). This calculation is valid for arbitrary polyhedrons. The relevant piece of code is in gaussGrad.C (https://cpp.openfoam.org/v6/gaussGrad_8C_source.html).