Dimensioned Scalar Help

physics1 · January 8, 2014, 13:22

I am solving a transport equation ddt(n)+div(n,U)=0 for a ciruclar density area. As it transport the density begins to break up. We have fixed this by inputing a diffusion coefficient into the equation making it ddt(n)+div(n,u)-k*laplacian(n)=0, where k is defined as a dimensioned scalar. The issue is that at k=10,000 the diffusion works and the density does not break up but if i increase it to k=100,000 the density structures again. Ive compared it to the case where k=0 and they look identical. Is there a maximum value for a dimensioned scalar that i am hitting when i increase k from 10,000 to 100,000? If so how can i make that value larger?

Bernhard · January 9, 2014, 02:23

ddt(n)+div(n,U) is not the way to implement a scalar transport equation in OpenFOAM. You would need ddt(n)+(phi,n). Have a look at the scalarTransportFoam solver.

physics1 · January 9, 2014, 11:34

The transport equation is working correctly (i just mistyped it) i just need help with understanding what a dimensioned scalar is. It seems like im maxing out the value possible for a dimensioned scalar since it works for 10000 but not 100000.

January 8, 2014, 13:22	Dimensioned Scalar Help	#1
physics1 New Member Join Date: Jul 2012 Posts: 13 Rep Power: 13	I am solving a transport equation ddt(n)+div(n,U)=0 for a ciruclar density area. As it transport the density begins to break up. We have fixed this by inputing a diffusion coefficient into the equation making it ddt(n)+div(n,u)-k*laplacian(n)=0, where k is defined as a dimensioned scalar. The issue is that at k=10,000 the diffusion works and the density does not break up but if i increase it to k=100,000 the density structures again. Ive compared it to the case where k=0 and they look identical. Is there a maximum value for a dimensioned scalar that i am hitting when i increase k from 10,000 to 100,000? If so how can i make that value larger?

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January 9, 2014, 02:23		#2
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 21	ddt(n)+div(n,U) is not the way to implement a scalar transport equation in OpenFOAM. You would need ddt(n)+(phi,n). Have a look at the scalarTransportFoam solver.

January 9, 2014, 11:34		#3
physics1 New Member Join Date: Jul 2012 Posts: 13 Rep Power: 13	The transport equation is working correctly (i just mistyped it) i just need help with understanding what a dimensioned scalar is. It seems like im maxing out the value possible for a dimensioned scalar since it works for 10000 but not 100000.