Simulation of Axial Fan Flow using A Momentum Source Subdomain

klettmann · March 15, 2013, 07:01

Hello philflow,

have you written an FAQ or a short summary of your experience with an axial fan simulation? I'm working on the same problem. It would be very nice if you have something like an summary for me!

Best regards,

A.

ghorrocks · March 16, 2013, 05:59

The documentation describes source terms and source term coefficients pretty well.

klettmann · April 18, 2013, 05:00

Hello again,

I have problems to simulate an axial fan. In the image, the test case I am working with is shown. The green bar, is my subdomain.

I am able to set a momentum source to get the exact pressure rise. But this is only half the way I have to go.

I would like to set a specific pressure rise and a volumeflow rate.
My idea is to simulate different blades in my fan. the first blade has an pressure rise of 35[kPa] and a volume rate of 70 [m^3/s] the second one has a pressure rise of 35 [kPa] and a volumeflow rate of 50[m^3/s]. So in my opinion the subdomain is a "black box" for my blades. And I am able to simulate different blades.

I have tried a lot of possibilities.
1.I rotate the subdomain with the frame change model "stage" and give a axial momentum source
2.I try to give an axial and a theta momentum source
3. I give an axial momentum source and an energy sourc

I have no more real ideas how to simulate different blades in my nacelle.
I hope someone can help me.
Thanks a lot.

klettmann · April 18, 2013, 05:06

here is the image
http://www.flickr.com/photos/95041584@N02/8660319970/

ghorrocks · April 18, 2013, 07:29

I think you will find that specifying the pressure rise and flow rate is over-specifying the flow. You specify either the pressure rise or the flow rate but not both. You can even specify the pressure rise as a function of flow rate (or vice-versa) - in fact the is recommended if you are trying to find the operating point and you do not know the exact fan speed.

klettmann · April 23, 2013, 11:04

Is there no way to specify both parameters? In my thougths it is like I have two different Operating Points which I can define. Or like two different blades.
Blade 1: pressure difference 35 [kPa] with 70 [m^3 s^-1]
Blade 2: pressure difference 35 [kPa] with 60 [m^3 s^-1]

With only the Momentum Source I can give a pressure change and a result is a volumeflow rate.
The task of my simulation is to find solutions for my nacelle with different blades.

singer1812 · April 23, 2013, 17:37

Glenn is correct. You are overspecifying the problem. I assume your blades have more than one operating point. You should have a mdot vs Pdrop for each blade.

You can input this into your model, and your model will find the operating point using the Pdrop of your system.

p08tm007 · July 16, 2013, 08:11

In fluent there is only possibility of defining momentum source in either x,y & z directions. If we want to define momentum source over a cylinder, then how to do this in fluent. Hey guys please help me regarding this, as this option is not there in fluent.

Thanks in Advance...

singer1812 · July 16, 2013, 09:24

This is a CFX forum. Try Fluent Forum.

But with not much thought put into the answer, you could use a coordinate transform to put your source into cartesian coords.

July 16, 2013, 08:11	Momentum source for cylinder in FLUENT	#28
p08tm007 New Member Hanumanth Join Date: Aug 2009 Posts: 6 Rep Power: 17	In fluent there is only possibility of defining momentum source in either x,y & z directions. If we want to define momentum source over a cylinder, then how to do this in fluent. Hey guys please help me regarding this, as this option is not there in fluent. Thanks in Advance...

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March 15, 2013, 07:01		#21
klettmann New Member Join Date: Feb 2013 Posts: 4 Rep Power: 13	Hello philflow, have you written an FAQ or a short summary of your experience with an axial fan simulation? I'm working on the same problem. It would be very nice if you have something like an summary for me! Best regards, A.

March 16, 2013, 05:59		#22
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	The documentation describes source terms and source term coefficients pretty well.

April 18, 2013, 05:00		#23
klettmann New Member Join Date: Feb 2013 Posts: 4 Rep Power: 13	Hello again, I have problems to simulate an axial fan. In the image, the test case I am working with is shown. The green bar, is my subdomain. I am able to set a momentum source to get the exact pressure rise. But this is only half the way I have to go. I would like to set a specific pressure rise and a volumeflow rate. My idea is to simulate different blades in my fan. the first blade has an pressure rise of 35[kPa] and a volume rate of 70 [m^3/s] the second one has a pressure rise of 35 [kPa] and a volumeflow rate of 50[m^3/s]. So in my opinion the subdomain is a "black box" for my blades. And I am able to simulate different blades. I have tried a lot of possibilities. 1.I rotate the subdomain with the frame change model "stage" and give a axial momentum source 2.I try to give an axial and a theta momentum source 3. I give an axial momentum source and an energy sourc I have no more real ideas how to simulate different blades in my nacelle. I hope someone can help me. Thanks a lot.

April 18, 2013, 05:06		#24
klettmann New Member Join Date: Feb 2013 Posts: 4 Rep Power: 13	here is the image http://www.flickr.com/photos/95041584@N02/8660319970/

April 18, 2013, 07:29		#25
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	I think you will find that specifying the pressure rise and flow rate is over-specifying the flow. You specify either the pressure rise or the flow rate but not both. You can even specify the pressure rise as a function of flow rate (or vice-versa) - in fact the is recommended if you are trying to find the operating point and you do not know the exact fan speed.

April 23, 2013, 11:04		#26
klettmann New Member Join Date: Feb 2013 Posts: 4 Rep Power: 13	Is there no way to specify both parameters? In my thougths it is like I have two different Operating Points which I can define. Or like two different blades. Blade 1: pressure difference 35 [kPa] with 70 [m^3 s^-1] Blade 2: pressure difference 35 [kPa] with 60 [m^3 s^-1] With only the Momentum Source I can give a pressure change and a result is a volumeflow rate. The task of my simulation is to find solutions for my nacelle with different blades.

April 23, 2013, 17:37		#27
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	Glenn is correct. You are overspecifying the problem. I assume your blades have more than one operating point. You should have a mdot vs Pdrop for each blade. You can input this into your model, and your model will find the operating point using the Pdrop of your system.

July 16, 2013, 09:24		#29
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	This is a CFX forum. Try Fluent Forum. But with not much thought put into the answer, you could use a coordinate transform to put your source into cartesian coords.