Q. With a porous region in CFX10, is it enough to specify the Volume Porosity or do I have to specify a resistance as well?
A. Yes you do. If you only specify the volume porosity, then you only get a pressure drop in the region due to Bernoulli from the increase in velocity of the fluid through the porous region. The pressure would then recover when the fluid exist the porous region. You need to specify a resistance, through loss coefficients or quadratic/linear resistance conefficients, so that you get a pressure drop from forcing the fluid through the region. Deriving appropriate coefficients isnt easy, but there is a technical note on this: just look for "porous flow modelling in cfx10" in the knowledge base.
Q. With a porous region in CFX10, is it enough to specify the Volume Porosity or do I have to specify a resistance as well? A. Yes you do. If you only specify the volume porosity, then you only get a pressure drop in the region due to Bernoulli from the increase in velocity of the fluid through the porous region. The pressure would then recover when the fluid exist the porous region. You need to specify a resistance, through loss coefficients or quadratic/linear resistance conefficients, so that you get a pressure drop from forcing the fluid through the region. Deriving appropriate coefficients isnt easy, but there is a technical note on this: just look for "porous flow modelling in cfx10" in the knowledge base. 

