Porous sheet with thin holes at a given angle

zog · July 22, 2019, 14:46

Hey there !

I am trying to set up porous media condition to compute the effects of a thin sheet with holes at (fe) 45 degrees. I have the data of the pressure loss for a given flux which i fitted to get the permeability and inertia lots coefficients.

I then tried various method but none gave satisfying results. I tried source terms with a calculated new porosity matrix given by a rotation of 45 degrees. It worked but i had to use the porous jump in fluent and remove said jump in the udf along with the rotation to make it work. I also tried to use the direction vector, setting dir 1 to the 45 degrees direction of the holes and dir 2 to the orthognal vector in the sheet plane. It worked too.

However both methods leave me puzzled as i need to set the orthogonal coefficients to arbitrary but needed values in order to control the pressure loss. I would have assumed that setting those to high enough value would leave me with a flow at 45 degrees whose pressure loss is controlled by the porous coeficients in the direction 1. Apparently not.

What am i missing ? Is there a way to achieve what i want ? Namely making a flow in a given direction and controlling the pressure loss with this direction instead of setting it to 0 and manually changing the other two (irrelevant) directions coeficients to match the required pressure loss.

I didn't try porous jump and a udf to fix the velocities at 45 degrees and then adjusting the porous jump to match the required pressure loss.

I hope it's not too complicated a request and my explanations are clear enough. I'll try to clarify if so ! Thanks for your help

). I would love to undestand why it's behaving like this also, as in my understanding with orthogonal direction and the "main" direction orders of magnitude more "porous" the other two should not change the velocity field and pressure jump, but it does. It does not however if i set the angle to 0 or use the basic fluent options... Then indeed with the main direction a couple orders of magnitude more porous changing the other directions coeficients doesn't change anything as long as they are high enough compared to the dir 1 one...

veepee · July 26, 2019, 15:28

Have you calculated the inertial resistance using the values of pressure and velocity?

zog · July 29, 2019, 01:20

Yeah it's the first thing i did. It didn't work well even if idon't try not vertical holes due to flux not perpendicular to the sheet.

However it's not really related to why there is no threshold when increasing the perpendicular components of the porous tensor.

July 22, 2019, 14:46	Porous sheet with thin holes at a given angle	#1
zog New Member Jacques Join Date: Jul 2019 Posts: 11 Rep Power: 7	Hey there ! I am trying to set up porous media condition to compute the effects of a thin sheet with holes at (fe) 45 degrees. I have the data of the pressure loss for a given flux which i fitted to get the permeability and inertia lots coefficients. I then tried various method but none gave satisfying results. I tried source terms with a calculated new porosity matrix given by a rotation of 45 degrees. It worked but i had to use the porous jump in fluent and remove said jump in the udf along with the rotation to make it work. I also tried to use the direction vector, setting dir 1 to the 45 degrees direction of the holes and dir 2 to the orthognal vector in the sheet plane. It worked too. However both methods leave me puzzled as i need to set the orthogonal coefficients to arbitrary but needed values in order to control the pressure loss. I would have assumed that setting those to high enough value would leave me with a flow at 45 degrees whose pressure loss is controlled by the porous coeficients in the direction 1. Apparently not. What am i missing ? Is there a way to achieve what i want ? Namely making a flow in a given direction and controlling the pressure loss with this direction instead of setting it to 0 and manually changing the other two (irrelevant) directions coeficients to match the required pressure loss. I didn't try porous jump and a udf to fix the velocities at 45 degrees and then adjusting the porous jump to match the required pressure loss. I hope it's not too complicated a request and my explanations are clear enough. I'll try to clarify if so ! Thanks for your help ). I would love to undestand why it's behaving like this also, as in my understanding with orthogonal direction and the "main" direction orders of magnitude more "porous" the other two should not change the velocity field and pressure jump, but it does. It does not however if i set the angle to 0 or use the basic fluent options... Then indeed with the main direction a couple orders of magnitude more porous changing the other directions coeficients doesn't change anything as long as they are high enough compared to the dir 1 one...

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July 26, 2019, 15:28		#2
veepee New Member Veena Join Date: Jul 2019 Posts: 1 Rep Power: 0	Have you calculated the inertial resistance using the values of pressure and velocity?

July 29, 2019, 01:20		#3
zog New Member Jacques Join Date: Jul 2019 Posts: 11 Rep Power: 7	Yeah it's the first thing i did. It didn't work well even if idon't try not vertical holes due to flux not perpendicular to the sheet. However it's not really related to why there is no threshold when increasing the perpendicular components of the porous tensor.