Inlet, free-stream, conditions for RSM model

Eslam Reda · February 15, 2010, 06:01

Hello guys,
I am solving a turbulent flow through duct problem.Can any one tell me the best inlet and boundary conditions for the Reynolds' stresses i.e. u'u', u'v', u'w' and so on.
Thanks a lot.

harishg · February 17, 2010, 18:27

A simple and commonly used boundary condition at outlet is zerogradient. At the inlet, the boundary conditions have to be consistent with the flow physics. At wall and symmetry its straight forward.

Eslam Reda · February 18, 2010, 01:10

Thanks (harishg) for your precious reply. I am using OpenFOAM, Launder-Gibson RSM model. OF automatically sets a wall and inlet value of 1e-15 for u'u', v'v' and w'w'. This may be understood. But the trouble with other stresses u'v', u'w',... etc. They are zeros at inlet but I can't find out how OF sets their values at the wall

. Surely k is given a fixed value of 1.5e-15 at both inlet and walls. While epsilon and nu are calculated from wall functions.
Please help me solve this annoying problem.

harishg · February 24, 2010, 17:56

All the Reynolds stresses are zero at the wall. However if yplus is in the log layer, the wall functions have to be calculated accurately even for the stresses. The values cannot be set to 1e-15 at the wall. Check the book of Wilcox.

artemiss1984 · February 26, 2010, 13:42

you can use experimental data for a duct or pipe.for free stream this components are very amall.
as a suggestion if you have a 3d geometry first use a simpler model like k-e then switch to RSM model to have better convergence.

February 15, 2010, 06:01	Inlet, free-stream, conditions for RSM model	#1
Eslam Reda New Member Eslam Reda Join Date: Jun 2009 Posts: 19 Rep Power: 16	Hello guys, I am solving a turbulent flow through duct problem.Can any one tell me the best inlet and boundary conditions for the Reynolds' stresses i.e. u'u', u'v', u'w' and so on. Thanks a lot.

February 18, 2010, 01:10	Wall Boundary Conditions	#3
Eslam Reda New Member Eslam Reda Join Date: Jun 2009 Posts: 19 Rep Power: 16	Thanks (harishg) for your precious reply. I am using OpenFOAM, Launder-Gibson RSM model. OF automatically sets a wall and inlet value of 1e-15 for u'u', v'v' and w'w'. This may be understood. But the trouble with other stresses u'v', u'w',... etc. They are zeros at inlet but I can't find out how OF sets their values at the wall . Surely k is given a fixed value of 1.5e-15 at both inlet and walls. While epsilon and nu are calculated from wall functions. Please help me solve this annoying problem.

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February 17, 2010, 18:27		#2
harishg Senior Member N/A Join Date: Mar 2009 Posts: 189 Rep Power: 17	A simple and commonly used boundary condition at outlet is zerogradient. At the inlet, the boundary conditions have to be consistent with the flow physics. At wall and symmetry its straight forward.

February 24, 2010, 17:56		#4
harishg Senior Member N/A Join Date: Mar 2009 Posts: 189 Rep Power: 17	All the Reynolds stresses are zero at the wall. However if yplus is in the log layer, the wall functions have to be calculated accurately even for the stresses. The values cannot be set to 1e-15 at the wall. Check the book of Wilcox.

February 26, 2010, 13:42		#5
artemiss1984 Member Join Date: Apr 2009 Posts: 38 Rep Power: 17	you can use experimental data for a duct or pipe.for free stream this components are very amall. as a suggestion if you have a 3d geometry first use a simpler model like k-e then switch to RSM model to have better convergence.