Wind turbine domains and boundaries

siardica · July 20, 2009, 17:36

Hi all -
Trying to set up a transient simulation in CFX for a 2D slice of a rotating vertical-axis wind turbine (just interested in the airflow features). This particular turbine is designed to operate at a very low rotational speed, with alot of empty space between one blade and the next (3 blades total). The simulation needs to run at least 3 full revolutions in order to capture the details we want.

I have read somewhat conflicting suggestions as to how one should divide the domains, assign boundary conditions, etc. All of these begin with a rectangular outer domain and a circular inner domain (with airfoils/hub cut out); however, from there, I've found instructions to just give the inner domain a rotational velocity, create a subdomain, use a mesh deformation, use a rotating wall, and various combinations of all of these. I've played around with several configurations and intuitively none of the results look correct yet...

Does anyone have sufficient experience with this sort of problem to offer advice as to which set-up is preferable?

ghorrocks · July 20, 2009, 19:54

Hi,

If the device purely rotates then stick the rotating component in a rotating frame of reference and put an outside domain in a stationary frame of reference. Join them with a GGI, probably in your case in Transient rotor-stator mode.

For wind turbines you need some idea of the atmospheric boundary layer and wind conditions. Your outer boundary must create a wind flow which represents the atmospheric boundary layer. I am not completely sure how to do this, it is not in my field of expertise.

Glenn Horrocks

siardica · July 20, 2009, 20:52

Glenn -
That was my initial set-up as well. However, someone on the ANSYS side seemed to think a much more complex arrangement with two stationary domains, a subdomain, and a mesh deformation specifying rotation was a better approach -- why, I'm not quite sure (unfortunately I have that info secondhand, so can't hit reply and ask!). I'm wondering whether their recommendation was based on an assumption that one would want to include pitch changes, if there isn't any more obvious reason to do it.

ghorrocks · July 20, 2009, 23:34

Use the simplest available model the capture the effect you are looking for. If you are not worried about pitch changes or blade flutter or those sort of details then use the rotating frame of reference approach.

Glenn

July 20, 2009, 17:36	Wind turbine domains and boundaries	#1
siardica New Member Join Date: Jul 2009 Posts: 4 Rep Power: 17	Hi all - Trying to set up a transient simulation in CFX for a 2D slice of a rotating vertical-axis wind turbine (just interested in the airflow features). This particular turbine is designed to operate at a very low rotational speed, with alot of empty space between one blade and the next (3 blades total). The simulation needs to run at least 3 full revolutions in order to capture the details we want. I have read somewhat conflicting suggestions as to how one should divide the domains, assign boundary conditions, etc. All of these begin with a rectangular outer domain and a circular inner domain (with airfoils/hub cut out); however, from there, I've found instructions to just give the inner domain a rotational velocity, create a subdomain, use a mesh deformation, use a rotating wall, and various combinations of all of these. I've played around with several configurations and intuitively none of the results look correct yet... Does anyone have sufficient experience with this sort of problem to offer advice as to which set-up is preferable?

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July 20, 2009, 19:54		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	Hi, If the device purely rotates then stick the rotating component in a rotating frame of reference and put an outside domain in a stationary frame of reference. Join them with a GGI, probably in your case in Transient rotor-stator mode. For wind turbines you need some idea of the atmospheric boundary layer and wind conditions. Your outer boundary must create a wind flow which represents the atmospheric boundary layer. I am not completely sure how to do this, it is not in my field of expertise. Glenn Horrocks

July 20, 2009, 20:52		#3
siardica New Member Join Date: Jul 2009 Posts: 4 Rep Power: 17	Glenn - That was my initial set-up as well. However, someone on the ANSYS side seemed to think a much more complex arrangement with two stationary domains, a subdomain, and a mesh deformation specifying rotation was a better approach -- why, I'm not quite sure (unfortunately I have that info secondhand, so can't hit reply and ask!). I'm wondering whether their recommendation was based on an assumption that one would want to include pitch changes, if there isn't any more obvious reason to do it.

July 20, 2009, 23:34		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	Use the simplest available model the capture the effect you are looking for. If you are not worried about pitch changes or blade flutter or those sort of details then use the rotating frame of reference approach. Glenn