Problem with Boundaries when simulatin a FAN

Alanum · September 17, 2016, 12:33

Hello CFD people! That's my first time writing, so hope that I will explain my case perfectly!

I am trying to simulate a FAN using CFX with the following setup (a pipe with a FAN in the middle)

First I have an inlet in a stationary disc

Second there is the FAN defined as a pressure jump + rotation of the domain with the RPMs of the fan (I know that this is not the perfect simulation, but just to give angular velocity to the fluid)

Finally, there is another stationary disc

I am defining the interference region as Frozen rotor and does not work properly.
I have tried also the "Rotational periodicity" and the fluid goes straight, when arrives to the rotational zone, the fluid moves with an angular velocity BUT when arrives to the latest stationary disc, the fluid goes straight again.

Could anyone help me with that??

Thanks in advance!!

flotus1 · September 17, 2016, 13:00

Your inner region may be rotating, but there is nothing that could transfer (angular) momentum to the fluid. Of course it will keep going straight. The angular velocity you see inside the rotating zone is probably just a post-processing error. In a stationary frame of reference, the fluid should go straight even in this zone. A very simplistic approach could be to add a source term for angular momentum in your rotating zone. Or to model the geometry of the fan blades explicitly. There quite a few ways to simulate this, each have their pros and cons.

Alanum · September 18, 2016, 17:06

Quote:

Originally Posted by flotus1

Your inner region may be rotating, but there is nothing that could transfer (angular) momentum to the fluid. Of course it will keep going straight. The angular velocity you see inside the rotating zone is probably just a post-processing error. In a stationary frame of reference, the fluid should go straight even in this zone. A very simplistic approach could be to add a source term for angular momentum in your rotating zone. Or to model the geometry of the fan blades explicitly. There quite a few ways to simulate this, each have their pros and cons.

Thanks! I will work on that!

September 17, 2016, 12:33	Problem with Boundaries when simulatin a FAN	#1
Alanum New Member Alanum Join Date: Sep 2016 Posts: 2 Rep Power: 0	Hello CFD people! That's my first time writing, so hope that I will explain my case perfectly! I am trying to simulate a FAN using CFX with the following setup (a pipe with a FAN in the middle) First I have an inlet in a stationary disc Second there is the FAN defined as a pressure jump + rotation of the domain with the RPMs of the fan (I know that this is not the perfect simulation, but just to give angular velocity to the fluid) Finally, there is another stationary disc I am defining the interference region as Frozen rotor and does not work properly. I have tried also the "Rotational periodicity" and the fluid goes straight, when arrives to the rotational zone, the fluid moves with an angular velocity BUT when arrives to the latest stationary disc, the fluid goes straight again. Could anyone help me with that?? Thanks in advance!!

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September 17, 2016, 13:00		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Your inner region may be rotating, but there is nothing that could transfer (angular) momentum to the fluid. Of course it will keep going straight. The angular velocity you see inside the rotating zone is probably just a post-processing error. In a stationary frame of reference, the fluid should go straight even in this zone. A very simplistic approach could be to add a source term for angular momentum in your rotating zone. Or to model the geometry of the fan blades explicitly. There quite a few ways to simulate this, each have their pros and cons.