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Direction-1 and Direction-2 in porous zone

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Old   October 19, 2014, 15:39
Default Direction-1 and Direction-2 in porous zone
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Hello,

I am having a hard time trying to figure out what Direction-1 and Direction-2 mean exactly. Could you please give me examples?

In addition, why are there differences in orders of magnitudes between components of viscous resistance and inertial resistance at different directions despite the isotropic media? I have seen this in some of the tutorials prepared for flow in porous media. For example, direction-1 component of viscous resistance has a value with order 10^7 whereas the other two have 10^9. Doesn't it matter even if I know those parameters for a certain porous medium? Where is the accuracy if I can manipulate the order of magnitude?

Thank you
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Old   October 19, 2014, 18:26
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Hello,

I am having a hard time trying to figure out what Direction-1 and Direction-2 mean exactly. Could you please give me examples?

In addition, why are there differences in orders of magnitudes between components of viscous resistance and inertial resistance at different directions despite the isotropic media? I have seen this in some of the tutorials prepared for flow in porous media. For example, direction-1 component of viscous resistance has a value with order 10^7 whereas the other two have 10^9. Doesn't it matter even if I know those parameters for a certain porous medium? Where is the accuracy if I can manipulate the order of magnitude?

Thank you
Viscose resistance is actually the inverse of permeability and its value is different in different materials. This parameter in fact shows the magnitude of flow permeation in each direction. Of course, in isotropic material, this value is the same in all directions (say, x,y,z) but in some others, anisotropic permeability dominates and permeation is usually several order magnitude lower in one direction compared to the two others. So, based on your problem and model, you can takes it into account or just ignore it. the same definition is for gas diffusivity and thermal conductivity as well.
Hope it helps
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Old   October 20, 2014, 04:44
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Thank you for your answer but I still do not know the influence of the directions. If the porous medium is isotropic, are the direction vectors supposed to be the same and non-zero?
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Old   October 20, 2014, 17:47
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Thank you for your answer but I still do not know the influence of the directions. If the porous medium is isotropic, are the direction vectors supposed to be the same and non-zero?
I don't understand what exactly you mean. But if the porous media is isotropic, the values of the permeability are the same for all three directions.
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Old   October 21, 2014, 02:41
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highhopes, Direction 1 and 2 are defined in the same panel in which you enter the inertial loss factors. Usually Direction 1 is 1,0,0 (x axis) and Direction 2 is 0,1,0 (y axis). If the media is isotropic then the direction vectors should still be different. You will just specify the same loss coefficient for each direction.
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Old   October 21, 2014, 15:57
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Thank you for your answers,

The only information regarding the directions is the one written under title "Defining the Viscous and Inertial Resistance Coefficients" in Fluent user guide. Is there any source clearly explaining how the direction vectors are used and what they are for? Is it basically about how they lie in the coordinate system? Or does it have something to do with the main flow direction? If so, doesn't any transverse velocity component die out even in porous media with very high porosities?

My medium is simply a porous cylinder whose axis is on x. Are the direction-1 and direction-2 vectors supposed to be (1,0,0) and (0,1,0), respectively?

Thank you again
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Old   October 22, 2014, 03:34
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Please refer to equations 6-1 and 6-2 in the Fluent Theory Guide 6.2.3.2 Momentum Equations for Porous Media. All of your questions are answered in the formulae. As you can see it will be a vector sum. For a porous cylinder then use the Conical option in the porous zone. Here you enter 1,0,0 as the axis vector, 0,0,0 for the cone axis (assuming that your cylinder has it central axis on the x axis) and then enter Direction 1, 2 and 3. For a cylinder the cone angle is 0. For the Conical option Direction 1 is tangential (i.e. along its length), 2 is normal to the cone surface (which is radial for a cylinder) and 3 is circumferential.
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Old   October 23, 2014, 02:36
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Thank you very much David.
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Old   June 28, 2017, 02:23
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Originally Posted by swiftaircraft View Post
Please refer to equations 6-1 and 6-2 in the Fluent Theory Guide 6.2.3.2 Momentum Equations for Porous Media. All of your questions are answered in the formulae. As you can see it will be a vector sum. For a porous cylinder then use the Conical option in the porous zone. Here you enter 1,0,0 as the axis vector, 0,0,0 for the cone axis (assuming that your cylinder has it central axis on the x axis) and then enter Direction 1, 2 and 3. For a cylinder the cone angle is 0. For the Conical option Direction 1 is tangential (i.e. along its length), 2 is normal to the cone surface (which is radial for a cylinder) and 3 is circumferential.
The porous zone is sphere .How should I set the direction vector?
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Old   June 28, 2017, 02:32
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You will need to have a custom UDF for this in order to define the relevant vectors around the sphere.
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Old   June 28, 2017, 07:21
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You will need to have a custom UDF for this in order to define the relevant vectors around the sphere.
Thank you for your answers,

I'm a little confused.
How do I define the relevant vectors around the sphere by udf?
Hope you can give me more suggestions
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Old   September 28, 2017, 14:08
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i am trying to simulate the 2d solar chimney in fluent.
i want to simulate solar storage layer as porous medium.

what should i put for direction-1 vector X & Y?

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Old   September 28, 2017, 19:00
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For defining porous media, you You definitely need the porosity and permeability of your of your model. For the permeability you can use experimental data or you can use start with fluent default values. If the porous media is homogeneous, Of course the baggies for pime ability in exam Y direction would be the same but if it's anisotropic, the values would be different. You need to consider it as well.

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Old   September 29, 2017, 09:54
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For defining porous media, you You definitely need the porosity and permeability of your of your model. For the permeability you can use experimental data or you can use start with fluent default values. If the porous media is homogeneous, Of course the baggies for pime ability in exam Y direction would be the same but if it's anisotropic, the values would be different. You need to consider it as well.

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thanks for your quick respons
for viscoue resistance and inertia resistance i use the same value in both direction , but i dont know what is the value for X&Y direction for storage medium ,llll.JPG
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