CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

Linear & quadratic resistance coefficient - Fishing net as membrane/porous media

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   November 13, 2017, 08:17
Default Linear & quadratic resistance coefficient - Fishing net as membrane/porous media
  #1
New Member
 
Johan Björk
Join Date: Nov 2017
Posts: 2
Rep Power: 0
Burken is on a distinguished road
Hello!

I am doing a school project together with two other course participants, where we are supposed to simulate the water flow in a channel to analyse the behavior (deformation, drag, reaction forces etc.) of a net in the channel. To simulate this problem, we consider the net as a membrane/porous medium.

We use three domains, where the middle domain is the membrane/porous medium, but to simulate the behavior of the membrane, we need to know either the permeability and loss coefficient or the linear and quadratic resistance coefficient.

For alternative 1, the permeability should be determined by:

Q = - \frac{\kappa A}{\mu}\frac{dp}{dx},
but since we haven't done any experiments yet, a pressure difference in the channel isn't possible to determine.

We are therefore considering the use of the linear and quadratic resistance coefficients instead in alternative 2, and from Ansys help, we have found the expressions:

C_{R1} = \frac{\mu}{K_{perm}}, (Linear resistance coefficient)
and
C_{R2}=K_{loss}\frac{\rho}{2} (Quadratic resistance coefficient),

where K_{perm} is the permeability and K_{loss} the quadratic loss coefficient.

So once again we have the problem with determining the permeability without having any experimental data to evaluate, so the problem we need to find the answer to is: Is it possible to determine the permeability and/or the linear and quadratic resistance coefficients without experimental data? We were supposed to evaluate the results from the CFD analysis with experimental data, but the water pump is broken in the lab so we have started with the CFD in advance.

If we have to find the permeability via experiment, do you set arbitrary values for the coefficients, run the simulations and take the pressure difference to calculate a new value for the constants? In that case, is it possible to take the average pressure at the whole surface before and after the membrane, instead of looking at pressure differences in just points? If this isn't the supposed way to do, please give me some leadings.

Regards, Burken
Burken is offline   Reply With Quote

Old   November 13, 2017, 10:14
Default
  #2
Senior Member
 
JuPa's Avatar
 
Mr CFD
Join Date: Jun 2012
Location: Britain
Posts: 339
Rep Power: 8
JuPa is on a distinguished road
Hi Burken,

Interesting project!

The obvious question to ask is the pressure difference or the coefficients available in the literature? Has someone already done the experiment or CFD and published the data?

Could you get the answer by simplifying? E.g.
1. Simulate a very small pipe with the net in the middle (physically draw the net, include it in your geometry, and grid it up and run the CFD)
2. Set the Re number in the pipe to be the same order of magnitude as the Re in the channel
3. Get the pressure loss or coefficients across the net
4. Use the results from point 3 to do a full channel simulation with the net as the porous media
JuPa is offline   Reply With Quote

Old   November 14, 2017, 07:12
Default
  #3
New Member
 
Johan Björk
Join Date: Nov 2017
Posts: 2
Rep Power: 0
Burken is on a distinguished road
Quote:
Originally Posted by JuPa View Post
Hi Burken,

Interesting project!

The obvious question to ask is the pressure difference or the coefficients available in the literature? Has someone already done the experiment or CFD and published the data?

Could you get the answer by simplifying? E.g.
1. Simulate a very small pipe with the net in the middle (physically draw the net, include it in your geometry, and grid it up and run the CFD)
2. Set the Re number in the pipe to be the same order of magnitude as the Re in the channel
3. Get the pressure loss or coefficients across the net
4. Use the results from point 3 to do a full channel simulation with the net as the porous media
Thank you for your input JuPa!

We are trying to design a net now instead to simulate our problem. We decided that it would be easier to just ignore the idea of using membrane and just go with a drawn net instead.
Burken is offline   Reply With Quote

Reply

Tags
cfx, coefficients., membrane, permeability, resistance

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Quadratic resistance Coefficient Ramana CFX 4 November 26, 2012 17:25
Porous Media Inertial and Resistance giogio FLUENT 3 June 21, 2011 18:09
Viscous resistance coefficient in physical v-model AL FLUENT 0 December 15, 2008 15:52
Quadratic Resistance Coefficient Ramana CFX 0 January 2, 2006 04:43
Flow resistance of porous media Desheng Kong Main CFD Forum 3 December 19, 2000 12:07


All times are GMT -4. The time now is 08:14.