Problems at boundary conditions

Felipe Matos · May 4, 2010, 20:19

I'm simulating a incompressible flow inside a cylindrical pipe with Reynold 100 (laminar). I'm setting:
- prescribed velocity (5cm/s) at inlet
- prescribed pressure (0 Pa) at outlet (reference pressure 1 atm)
- No slip wall at the cylindrical wall
Althought these boundaries ARE NOT variabels, when I plot the values on the nodes at each boundary they ARE NOT the same that I prescribed.

Example: the velocity at the wall are not zero. The values are around 10-3 cm/s but not zero as suposed.
The same thing is happening to the velocity at the inlet and to the pressure at the outlet.

Anyone knows what can this be?
Thanks

Aero75 · May 5, 2010, 04:05

Felipe,

Are you showing the values as conservative or hybrid on the boundaries? Conservative values will show the values based on the average in the control volumes. Hybrid values will overwrite the values at the elements nearest to the boundaries with the boundary values - this is what you probably want to do for your plots...

You can look it up in the CFD-Post manual. Whether you use conservative or hybrid values can be set when plotting in Post.

Regards,

Aero75

May 4, 2010, 20:19	Problems at boundary conditions	#1
Felipe Matos New Member FM Join Date: Feb 2010 Posts: 14 Rep Power: 16	I'm simulating a incompressible flow inside a cylindrical pipe with Reynold 100 (laminar). I'm setting: - prescribed velocity (5cm/s) at inlet - prescribed pressure (0 Pa) at outlet (reference pressure 1 atm) - No slip wall at the cylindrical wall Althought these boundaries ARE NOT variabels, when I plot the values on the nodes at each boundary they ARE NOT the same that I prescribed. Example: the velocity at the wall are not zero. The values are around 10-3 cm/s but not zero as suposed. The same thing is happening to the velocity at the inlet and to the pressure at the outlet. Anyone knows what can this be? Thanks

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May 5, 2010, 04:05		#2
Aero75 New Member Join Date: Apr 2010 Posts: 4 Rep Power: 15	Felipe, Are you showing the values as conservative or hybrid on the boundaries? Conservative values will show the values based on the average in the control volumes. Hybrid values will overwrite the values at the elements nearest to the boundaries with the boundary values - this is what you probably want to do for your plots... You can look it up in the CFD-Post manual. Whether you use conservative or hybrid values can be set when plotting in Post. Regards, Aero75