dear Fluent Users/Enthusiasts,

please, how good is fluent for incompressible, slow flows, and how good will it be in treating porous media flows

We've been using FLUENT for low velocity incompressible flows through porous media for years. Once we worked out good underrelaxation ranges to use, there have been no problems.

Hallo Evan, I also work with porous media, and I have often the problem that the residuals of continuity does not decrease under 0,003. What can I do and what underrelexation ranges do you use?

Yours Armin

Hi!

Unfortunately, Fluent cannot do transient flow through porous media. It is only an approximation through resistances and the porosity iteslf is not taken into account.

This can cause serious errors in the transient term.

I know it is approximated by the law of Darcy. But I am interested in Evan`s underrelaxation ranges...

Yours Armin

Thanks for your message Evan. please, do your simulations have free surfaces in them. And do you know more about the transient problem, the other contributor has mentioned about

We don't use the free surface model. We just use a wall with a slip BC and use the PRESTO! pressure scheme. Experience with actual equipment tells us we have very little water motion near the surface, so it works for us.

We haven't had any trouble with transients, although we don't do that many. Yes, it's an approximation. But it's not a bad approximation for some conditions. Our velocities are practically diffusion flow, so it works OK.

As for underrelaxations (for Armin) we try to stick with values near the following:

Pressure = 0.3, Momentum = 0.7, Energy = 1, TKE = 0.6, Dissipation = 0.6, Visc = 0.6, Den = 0.95, BF = 0.95

These are used with very high IRFs and buoyancy-dominated flows, so they may not work at all for you.

Be aware that there is no true turbulence in terms of energy cascading from large to small eddies if the bed porosity is too low. In that case unimpeded eddies of arbitrary size are impossible and conventional k-e models are not applicable. A specific turbulence model is required to account for the occurrence of void and pseudo vortices and to account for the size limitations of eddies (canot be bigger than the biggest opening in porous medium). This model is not available in Fluent.

Hi, Mr. Erwin, can you provide me some references about the model you mention?

Thanks

Newbie

Sorry for my late reply, I was on a trip.

References: Turbulence Model for flow through porous media - T. Matsuoka and Y. Takatsu - Int. J. Heat Mass Transfer, Vol.39, No 13, 1996

A general two-equation macroscopic turbulence model for incompressible flow in porous media - B. Antohe, J. Lage - Int. J. Heat Mass Transfer, Vol.40, No 13, 1997

Thanks for the information.

Regards

newbie

[luckycao]

hi， Erwin
i am simulating the flow that thorough the perforated plate，now i am stumped to determine the direction vectors of the resistance coefficient. my plate is wave-shaped，so the direction vectors is not simple to define as X Y or Z，i don't know how to deal with this ，could you help me？
thanks ，sincerely

[luckycao]

hi， Erwin
i am simulating the flow that thorough the perforated plate，now i am stumped to determine the direction vectors of the resistance coefficient. my plate is wave-shaped，so the direction vectors is not simple to define as X Y or Z，i don't know how to deal with this ，could you help me？
thanks ，sincerely