Vorticity in OpenFOAM; Negative to when I compute from fvc::grad(U)

tzaht · February 5, 2020, 21:44

Hi there,

I output the values of the velocity gradient tensor, as well as, the vorticity for my simulation.

Let's just consider the rotation about the x-axis for simplicity.

The problem that I am having is that when I compute $\omega_x = \frac{\partial w}{\partial y} - \frac{\partial v}{\partial z}$ , this is the definition of curl in the OpenFOAM Programmer's guide 2.1.3. Howeber, I actually get the negative of the vorticity in the standard OpenFOAM output file.

Now, when I again follow the maths in the Progammer's guide, I see that OpenFOAM is actually computing the hodge dual of the rotation rate tensor, so for [math] \omega_x = \omega_{23}[\math]. This should indeed be $\omega_x = \frac{\partial w}{\partial y} - \frac{\partial v}{\partial z}$ .

Now, the only thing I can think of that I may be doing wrong is that I assume that OF is writing the VGT in the following order: $\partial_x{u} ,\partial_y{u},\partial_z{u},\partial_x{v}...$
Any help appreciated.

HPE · February 11, 2020, 17:18

is it possible for you to provide a test case?

February 5, 2020, 21:44	Vorticity in OpenFOAM; Negative to when I compute from fvc::grad(U)	#1
tzaht Member Tony Zahtila Join Date: Mar 2016 Posts: 33 Rep Power: 10	Hi there, I output the values of the velocity gradient tensor, as well as, the vorticity for my simulation. Let's just consider the rotation about the x-axis for simplicity. The problem that I am having is that when I compute $\omega_x = \frac{\partial w}{\partial y} - \frac{\partial v}{\partial z}$ , this is the definition of curl in the OpenFOAM Programmer's guide 2.1.3. Howeber, I actually get the negative of the vorticity in the standard OpenFOAM output file. Now, when I again follow the maths in the Progammer's guide, I see that OpenFOAM is actually computing the hodge dual of the rotation rate tensor, so for [math] \omega_x = \omega_{23}[\math]. This should indeed be $\omega_x = \frac{\partial w}{\partial y} - \frac{\partial v}{\partial z}$ . Now, the only thing I can think of that I may be doing wrong is that I assume that OF is writing the VGT in the following order: $\partial_x{u} ,\partial_y{u},\partial_z{u},\partial_x{v}...$ Any help appreciated.

February 11, 2020, 17:18		#2
HPE Senior Member Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 931 Rep Power: 13	is it possible for you to provide a test case? __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

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