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Modelling Tidal Turbine, general momentum source, body forces

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Old   August 29, 2012, 05:46
Default Modelling Tidal Turbine, general momentum source, body forces
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Susan Tully
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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.
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Last edited by st268; August 29, 2012 at 05:54. Reason: Equations did not show
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Old   August 29, 2012, 07:53
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Glenn Horrocks
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Are you intending replacing the whole turbine with a single momentum source to model the drag it imposes on the flow?
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Old   August 29, 2012, 08:28
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Susan Tully
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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 15:56. Reason: Update
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Old   August 29, 2012, 18:29
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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.
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Old   September 3, 2012, 14:37
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Wouldn't a interface do the job?
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Old   September 3, 2012, 18:36
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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.
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Old   September 3, 2012, 20:11
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You guys were discussing about doing a domain with a source of momentum... that's why I suggested an interface with this source term!

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