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siw October 2, 2009 02:57

Modelling an air filter

I need to model air flow through a pipe and then into a radial filter and finally out through an exit pipe. Luckly, CFX has a tutorial for a porous domain modelling, which I shall run next. However, my filter is not a catalytic converter so the numerical data in the tutorial would be different to my case.

Does anyone have experience in modelling air filters, my past CFD work has always been on external aerodynamics, so some pointers would be useful. I doubt relative data will be available from the filter manufacturer - such as volume ratio as mentioned in the CFX Solver Theory guide.


WalterW October 2, 2009 07:39

I do have some experience with flat filter panels.

Usually, we measure the pressure drop of the cartridge in a rectangular or circular duct as a function of mass flow. It is then relatively safe to assume a uniform velocity distribution on the filter, allowing us to convert the (pressure-drop/mass flow) curve into a (pressure drop / mm filter height / velocity) curve, which usually looks like a 2nd grade polynom: Voilá, there are your linear and quadratic isotropic loss coefficients.

Something similar should work for radial filter cartridges, too.

siw October 3, 2009 05:18

Great, thanks for the information. I have a few extra questions now that I have finished the Catalytic Converter tutorial.

Do you always set the Reference Pressure to the required value and keep the Relative Pressure zero? I found that for my external aerodynamics work this produced wrong answers and had to set the Ref. Press. to zero and the Rel. Press. to a value.

In the Porosity Settings Loss Model do you use the Superficial or the Tru Velocity Loss Velocity Type? The tutorial uses the Superficial but the guides don't say much about them.


WalterW October 5, 2009 07:54


Is the "Porous Domain" Domain type new to CFX 12?
I was taught to use subdomains to model a porous medium... and there is no option for superficial velocity and the like.

ckleanth October 5, 2009 09:21

No the feature was available in v11. if you use a momentum loss in a fluid domain you have to use superficial velocity, for full porous domain model you can chose the velocity (superficial or true velocity) that your experimental values are based on.

ljacobs12 September 13, 2011 12:48

I don't know if this is an OK place to post my question because I am not sure what modeling an air filter is. To be honest, I don't know anything about air filters and I have really dumb question to prove it. Let me start out by saying that I am a girl and I know nothing about cars. For the past month my husband has been talking about how his car needs a new air filter and I'm going to surprise him by buying one and installing it in his truck! Step one was to start searching for where to buy them. I looked online and found this website that sells discount filters. I have no idea if these filters are the same kind of filters that go in vehicles. Can someone tell me if there is a difference between house air filters and car air filters? Does that place have the car kind? My second question is how to install them into the truck? Seriously, thank you so much for any help! Try to hurry with your answers, I want to have this done by this weekend!

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