Modelling Tidal Turbine, general momentum source, body forces

st268 · August 29, 2012, 06:46

Hello,

I am trying to model a tidal turbine (HATT) in CFX via a subdomain containing a general momentum source. I am interested in a very specific case, I know the free stream velocity, the TSR and the lift and drag coefficients for iterative 2d sections of my blade. From these I have the equations attached

Where Theta rel is the angle of the relative velocity taking into account the rotation. Fazim is around the plane of rotation and the z axis is my rotation axis.

I am stuck trying to write the above in a form that will be accepted by the general momentum source options in CFX. If anybody could point me in the right direction your help would be greatly appreciated.

ghorrocks · August 29, 2012, 08:53

Are you intending replacing the whole turbine with a single momentum source to model the drag it imposes on the flow?

st268 · August 29, 2012, 09:28

Thank you for replying first off.

Yes, I have my body forces in terms of unit volume. I wished to apply this to a subdomain of my flow. I am now trying manually inputting my expressions from which I got the force equations above and letting ANSYS start from there. When I try and simple put in the above equations as they stand I of course get errors regarding the units.

Update:
So I have figured it out. I had done all my initial work in Matlab and tried to simply transfer my final x,y,z forces to CFX. ANSYS did not like that, so I built them up from scratch using user expressions and functions. Only thing I am pondering is whether I have to set my subdomain to rotating or whether I have described this aspect sufficiently in my body forces.

ghorrocks · August 29, 2012, 19:29

if you are replacing the turbine with a momentum source then no, do not put this in a rotating frame of reference. If the turbine puts a swirl in the flow coming off it then you should include this in the momentum source, but in a stationary frame of reference.

Felggv · September 3, 2012, 15:37

Wouldn't a interface do the job?

ghorrocks · September 3, 2012, 19:36

Do what job? This simulation can be done as a single domain so there should not be any need for an interface. However interfaces can sometimes be useful as they are 2D regions which you can apply source terms to.

Felggv · September 3, 2012, 21:11

You guys were discussing about doing a domain with a source of momentum... that's why I suggested an interface with this source term!

Bye!

August 29, 2012, 09:28		#3
st268 New Member Susan Tully Join Date: Jul 2012 Posts: 15 Rep Power: 14	Thank you for replying first off. Yes, I have my body forces in terms of unit volume. I wished to apply this to a subdomain of my flow. I am now trying manually inputting my expressions from which I got the force equations above and letting ANSYS start from there. When I try and simple put in the above equations as they stand I of course get errors regarding the units. Update: So I have figured it out. I had done all my initial work in Matlab and tried to simply transfer my final x,y,z forces to CFX. ANSYS did not like that, so I built them up from scratch using user expressions and functions. Only thing I am pondering is whether I have to set my subdomain to rotating or whether I have described this aspect sufficiently in my body forces. Last edited by st268; August 29, 2012 at 16:56. Reason: Update

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August 29, 2012, 08:53		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Are you intending replacing the whole turbine with a single momentum source to model the drag it imposes on the flow?

August 29, 2012, 19:29		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	if you are replacing the turbine with a momentum source then no, do not put this in a rotating frame of reference. If the turbine puts a swirl in the flow coming off it then you should include this in the momentum source, but in a stationary frame of reference.

September 3, 2012, 15:37		#5
Felggv Member Felipe Gobbi Join Date: Apr 2012 Location: Brazil Posts: 76 Rep Power: 14	Wouldn't a interface do the job?

September 3, 2012, 19:36		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Do what job? This simulation can be done as a single domain so there should not be any need for an interface. However interfaces can sometimes be useful as they are 2D regions which you can apply source terms to.

September 3, 2012, 21:11		#7
Felggv Member Felipe Gobbi Join Date: Apr 2012 Location: Brazil Posts: 76 Rep Power: 14	You guys were discussing about doing a domain with a source of momentum... that's why I suggested an interface with this source term! Bye!