Rotational flow mid-domain

ld1305 · March 20, 2019, 07:18

I'm looking to try and add a rotational flow in the middle of a domain if possible.

Essentially, I have a CFD model with a turbine in the middle from which I can know the angle of the flow through a specified cross section, however I'm looking to try to have a relatively quick look at the effects of some of the upstream geometry without having to introduce modelling of the blades themselves as an initial study.

I realise I can set rotational properties at a boundary but I'd like to have the boundary a little further away from where the blades would be, ideally.

I'm historically a Fluent user and have only just transitioned to CFX after moving jobs, so any additional info is much appreciated.

ghorrocks · March 20, 2019, 07:22

Sounds like a momentum source term. You will have to derive the desired thrust and flow rotational components, and you can apply them as a momentum source term on a subdomain.

ld1305 · March 20, 2019, 07:44

Quote:

Originally Posted by ghorrocks

Sounds like a momentum source term. You will have to derive the desired thrust and flow rotational components, and you can apply them as a momentum source term on a subdomain.

So it'd be possible to apply the subdomain to just one face? Had a quick look at them and it seems to only let me select whole volumes, rather than one face/plane. Possible I set the geometry up wrong to be honest, as I said I'm pretty new to CFX.

ghorrocks · March 20, 2019, 17:36

If you are trying to put a device to move the flow in the middle of your domain then you don't want a boundary face there. The momentum source approach is applied to a subdomain inside your domain and does not require boundary faces.

If this is not what you are looking for please post an image of what you want to do so I can understand your application.

ld1305 · March 25, 2019, 08:32

I realise that I don't want a boundary in the middle of my domain, I was just hoping to be able to impose a rotation on a plane rather than a volume (which subdomains seem to be) but a volume could work.

I've attempted the subdomain method but am unable to upload images due to a workplace IT policy, unfortunately.

What I notice is that the swirl in flow is only imposed downstream of the impeller volume subdomain, whereas I'm expecting that there should be some kind of entrainment realistically.

ghorrocks · March 25, 2019, 17:24

Quote:

What I notice is that the swirl in flow is only imposed downstream of the impeller volume subdomain,

I do not understand this comment. The momentum source term approach would not generate swirl downstream of the source term volume, it is generated at the volume. Please post an image of what you are getting to explain it better.

Quote:

whereas I'm expecting that there should be some kind of entrainment realistically.

I don't understand that comment either. Can you post an image to explain what you mean?

March 20, 2019, 07:18	Rotational flow mid-domain	#1
ld1305 Member Lauren Dransfield Join Date: Jan 2012 Posts: 50 Rep Power: 14	I'm looking to try and add a rotational flow in the middle of a domain if possible. Essentially, I have a CFD model with a turbine in the middle from which I can know the angle of the flow through a specified cross section, however I'm looking to try to have a relatively quick look at the effects of some of the upstream geometry without having to introduce modelling of the blades themselves as an initial study. I realise I can set rotational properties at a boundary but I'd like to have the boundary a little further away from where the blades would be, ideally. I'm historically a Fluent user and have only just transitioned to CFX after moving jobs, so any additional info is much appreciated.

March 20, 2019, 07:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Sounds like a momentum source term. You will have to derive the desired thrust and flow rotational components, and you can apply them as a momentum source term on a subdomain. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 20, 2019, 17:36		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	If you are trying to put a device to move the flow in the middle of your domain then you don't want a boundary face there. The momentum source approach is applied to a subdomain inside your domain and does not require boundary faces. If this is not what you are looking for please post an image of what you want to do so I can understand your application. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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March 25, 2019, 08:32		#5
ld1305 Member Lauren Dransfield Join Date: Jan 2012 Posts: 50 Rep Power: 14	I realise that I don't want a boundary in the middle of my domain, I was just hoping to be able to impose a rotation on a plane rather than a volume (which subdomains seem to be) but a volume could work. I've attempted the subdomain method but am unable to upload images due to a workplace IT policy, unfortunately. What I notice is that the swirl in flow is only imposed downstream of the impeller volume subdomain, whereas I'm expecting that there should be some kind of entrainment realistically.