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-   -   question about streamwise direction in the porosity (http://www.cfd-online.com/Forums/cfx/118882-question-about-streamwise-direction-porosity.html)

starhunter521 June 5, 2013 22:06

question about streamwise direction in the porosity
 
Hi, everyone!
I have encountered a question when I set the streamwise direction in the porosity domain. The porosity domain is of revolution, and consquently the streamwise direction varies with theta, which is shown in the pic. However, the option in setting porosity just provides a unquine direction, which can't vary with theta.
Is anyone helping me? :)

http://ww1.sinaimg.cn/bmiddle/65a92d...20v30ffn0a.jpg

cdegroot June 5, 2013 23:26

You can specify the direction in cylindrical coordinates rather than Cartesian. Looks like that would work for your case.

starhunter521 June 6, 2013 00:25

Quote:

Originally Posted by cdegroot (Post 432317)
You can specify the direction in cylindrical coordinates rather than Cartesian. Looks like that would work for your case.

Thank you for your suggestion.
I just specified the direction in cylindrical coordinates.
what confused me is the option only set one direction.
When theta=0 degree, the direction is 45 degree and in cylindrical coordinates r=1, z=1, which is shown in the left of the pic.
When theta=180 degree, the direction is 135 degree and in cylindrical coordinates r=1, z=1.
In the option , the theta is just a value, and I can't let it equal from 0 to 360.
What shall I do?
http://ww4.sinaimg.cn/bmiddle/65a92d...20g105hq3f.jpg

oj.bulmer June 6, 2013 07:52

Why do you insist on using a thicker porous model? Why not use the porous interface? Since the flow is normal to the inlet surface of your porous zone and proceeds (relatively) normally, interface makes sense.

You can deduce the pressure drop as a function of dot product of local surface normal of inlet surface and the local velocity.

OJ

cdegroot June 6, 2013 10:39

Quote:

Originally Posted by starhunter521 (Post 432327)
Thank you for your suggestion.
I just specified the direction in cylindrical coordinates.
what confused me is the option only set one direction.
When theta=0 degree, the direction is 45 degree and in cylindrical coordinates r=1, z=1, which is shown in the left of the pic.
When theta=180 degree, the direction is 135 degree and in cylindrical coordinates r=1, z=1.
In the option , the theta is just a value, and I can't let it equal from 0 to 360.
What shall I do?
http://ww4.sinaimg.cn/bmiddle/65a92d...20g105hq3f.jpg

The theta value you are entering would be the component of the direction vector in the theta direction (not a value of theta), which in your case is zero. The direction vector has only components in the r and z directions. Since the vector is pointing inwards (towards the rotation axis) it seems like your r component would be -1 and your z component would be z=1 to have a 45 degree angle from the horizontal. This assumes the rotation axis is at the centre of your volume of revolution.


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