Porous Medium-entering D, F coefficients to code

Samsam2 · January 4, 2019, 09:36

I have calculated F and d coefficients for Darcy Forchheimer equation for my porous media and I have two scalars. I saw in code F and D should be entered like vectors:

type DarcyForchheimer;

d (500000 -1000 -1000);
f (0 0 0);

I dont know what those two -1000 mean and how I should calculate them!
I would appreciate it if any one could help me.

tomf · January 7, 2019, 04:24

Hi,

The -1000 is a way to do multiplication. As only a positive number is valid, OpenFOAM uses a negative number as a multiplier. So your D values are equivalent to:

d (500000 500000000 500000000);

This way, you can force directionality of your porous region (i.e. a radiator that typically shows higher resistance in cross-flow directions than in flow direction).

Regards,
Tom

Samsam2 · January 7, 2019, 08:46

Thank you so much Tom,
In cases that we are sure porous media is homogeneous and air permeability/resistance in all directions are same, should we enter (500000 50000 50000)?
Thank you,

tomf · January 7, 2019, 09:46

Yes, or alternatively

(500000 -1 -1)

January 4, 2019, 09:36	Porous Medium-entering D, F coefficients to code	#1
Samsam2 New Member Sama Join Date: Jan 2019 Posts: 16 Rep Power: 7	I have calculated F and d coefficients for Darcy Forchheimer equation for my porous media and I have two scalars. I saw in code F and D should be entered like vectors: type DarcyForchheimer; d (500000 -1000 -1000); f (0 0 0); I dont know what those two -1000 mean and how I should calculate them! I would appreciate it if any one could help me.

January 7, 2019, 04:24		#2
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 642 Rep Power: 32	Hi, The -1000 is a way to do multiplication. As only a positive number is valid, OpenFOAM uses a negative number as a multiplier. So your D values are equivalent to: d (500000 500000000 500000000); This way, you can force directionality of your porous region (i.e. a radiator that typically shows higher resistance in cross-flow directions than in flow direction). Regards, Tom Samsam2 likes this.

January 7, 2019, 09:46		#4
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 642 Rep Power: 32	Yes, or alternatively (500000 -1 -1) Samsam2 likes this.

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January 7, 2019, 08:46		#3
Samsam2 New Member Sama Join Date: Jan 2019 Posts: 16 Rep Power: 7	Thank you so much Tom, In cases that we are sure porous media is homogeneous and air permeability/resistance in all directions are same, should we enter (500000 50000 50000)? Thank you,