Rotor_Stator_Turbine issue

AS_Aero · May 17, 2018, 10:43

Hi

I am trying to run a simulation for Horizontal Axis wind turbine and here I am taking only a symmetry of the geometry and in this I have an interface which is hitting upto a wall on the opposite side of the symmetry plane. And as per some previous information I got to know that I can give that side on the rotor part as a counter rotating wall as its the part of stator casing. But now the problem is there is a small surface created by the interface on that wall, which I am not sure what I can do with it. Kindly have look on the geometry if you want to understand what I am talking about.

https://wetransfer.com/downloads/2e3...7133441/0a02a3

ghorrocks · May 17, 2018, 19:55

Please show an image of the surface created and the interface.

AS_Aero · May 18, 2018, 04:11

Here there is few things to consider why this happend, As we had a previous discussion, the rotor interface is extended upto the surface of internal wall of a casing (which is the stator part), So when I did this and subtracted the rotor part from the stator to get the meshing domain of the stator, that circular surface was deleted from the stator casing wall, but since the stator casing is smaller compared to the rotor diameter, this small portion which doesnt has the stator casing created a small surface there. But now the problem is that internal wall on the stator is not there and am not sure what to do with this small surface. I have attached the images as well.
Thanks in advance.

ghorrocks · May 18, 2018, 08:07

why isn't there an interface at the end of the rotor? And why not a matching interface on the stationary part adjacent to the end face? Why does the interface extend beyond the radios of the rotor?

AS_Aero · May 18, 2018, 09:44

Thats the problem, the support from Ansys told me to extend the rotor interface upto the wall of the stator casing and hence I just have one cylindrical interface and the other one is the one marked on the image , but its a counter rotating wall as its sharing that face with the stator wall which is not rotating. And the radius of the interface is bigger than the radius of the rotor which I just got to know from the tutorial or the videos. But the problem is that since the surface of the rotor interface is hitting till the stator casing and hence the wall on the casing got deleted and a small surface was created in the stator as well.
It would be better if you can load the rotor and stator on spaceclaim to know exactly what I am trying to explain.

ghorrocks · May 19, 2018, 07:58

I try to avoid spaceclaim as much as possible. I think I am a CFD dinosaur.

It might be better to show us what you are trying to model, without all your blocks and interfaces. Do you have a photograph of it, or a screen shot of the solid model?

AS_Aero · May 22, 2018, 05:42

Hi Glenn

Sorry for the delay. Kindly have a look on the link where I have uploaded the real images of the stuff. The arrow in the image shows the flow direction. And I am only considering the symmetry of this part.

https://wetransfer.com/downloads/0dd...2083942/65e9ec

Gert-Jan · May 22, 2018, 06:47

You can only get away with a single cylindrical interface if the interfaces at the top end would completely be covered with a wall (BC: Counter rotating wall).

With the current setup you cannot get away with only a single cylindrical interface since your top end interfaces partly cover the stator wall partly float in the air.
So you have to go back to the previous setup (a month ago or so) where you placed 3 interfaces: 1 cylindrical and 2 at the top ends in the small gap between the rotor and the wall (Do a symmetric simulation, that would save you 50% of the work, and you only need 2 interfaces).

Alternatively, increase the stator wall such that it just covers your top end interface. But then you are somewhat violating your geometry and might miss some crucial effects........

Cheers, Gert-Jan

AS_Aero · May 22, 2018, 07:00

I doubt if I understood you correctly ! What if I extend my interface upto the wall of the stator frame ? And the other problem is that the stator frame is kind of bit offset from the rotor blade diameter, so when I extend the surface till the stator frame a small part of the circle diameter is generated. which is why I am not sure if I can get done with it. And the surface on the stator is also gone.

So two months back, what I did was creating 3 interfaces, top and bottom was in between the rotor and the stator and the cylindrical interface of little bigger diameter than the rotor. Then took the symmetry of it. (I think I should follow the same here right ?)

Gert-Jan · May 22, 2018, 07:17

Yes, you should follow the approach from 2 months ago.

As you mentioned, if you extend the surface to the stator frame, a small part of the circle diameter is generated. This is what I called 'floating in the air'. You have to do something with it. Therefore you have to follow the approach from 2 months ago.

AS_Aero · May 23, 2018, 05:32

Hi Gert
Thanks a lot for your reply !! Now I was told by the customer support to extend the interface only upto the end of the rotor disc or center of the rotor disc so that I will have 3 interfaces and the wall of the disc can be given as rotating wall, by doing so I can avoid that small section which hangs in air.

Then they also mentioned to do a 2D computation than a 3D, but here is my doubt, will the power prediction for the relevant RPM be the same as what we get for 3D 1m long turbine ? Can you give me some insight about it ? I have to find the optimum RPM for a constant wind velocity. So what I thought was to do for 3 different RPM for one Wind Velocity and draw the power curve and see where I have the maximum power and take that RPM as optimum. is this approach a correct way ?

Gert-Jan · May 23, 2018, 06:21

I am not sure if the result at 2D will be the same as 3D. But for optimizations studies, it is of course much faster. And it will give you a first impression. So I would go for it as well.
I think your approach is ok. Maybe 3 simulations is somewhat to little. Make it 5 for a better curve. That is what I use for pump curves.

I wonder what the TSR will be in the optimum you'll find. Can you share the curve?

AS_Aero · May 23, 2018, 08:39

Dear Gert

I havent tried to get the TSR, nor am not sure how I can calculate that. but if I find a way to calculate that I will surely share it with you.

May 17, 2018, 19:55		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Please show an image of the surface created and the interface. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

May 18, 2018, 08:07		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	why isn't there an interface at the end of the rotor? And why not a matching interface on the stationary part adjacent to the end face? Why does the interface extend beyond the radios of the rotor? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

May 19, 2018, 07:58		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	I try to avoid spaceclaim as much as possible. I think I am a CFD dinosaur. It might be better to show us what you are trying to model, without all your blocks and interfaces. Do you have a photograph of it, or a screen shot of the solid model? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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May 22, 2018, 05:42		#7
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 14	Hi Glenn Sorry for the delay. Kindly have a look on the link where I have uploaded the real images of the stuff. The arrow in the image shows the flow direction. And I am only considering the symmetry of this part. https://wetransfer.com/downloads/0dd...2083942/65e9ec

May 22, 2018, 06:47		#8
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,928 Rep Power: 28	You can only get away with a single cylindrical interface if the interfaces at the top end would completely be covered with a wall (BC: Counter rotating wall). With the current setup you cannot get away with only a single cylindrical interface since your top end interfaces partly cover the stator wall partly float in the air. So you have to go back to the previous setup (a month ago or so) where you placed 3 interfaces: 1 cylindrical and 2 at the top ends in the small gap between the rotor and the wall (Do a symmetric simulation, that would save you 50% of the work, and you only need 2 interfaces). Alternatively, increase the stator wall such that it just covers your top end interface. But then you are somewhat violating your geometry and might miss some crucial effects........ Cheers, Gert-Jan

May 22, 2018, 07:00		#9
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 14	I doubt if I understood you correctly ! What if I extend my interface upto the wall of the stator frame ? And the other problem is that the stator frame is kind of bit offset from the rotor blade diameter, so when I extend the surface till the stator frame a small part of the circle diameter is generated. which is why I am not sure if I can get done with it. And the surface on the stator is also gone. So two months back, what I did was creating 3 interfaces, top and bottom was in between the rotor and the stator and the cylindrical interface of little bigger diameter than the rotor. Then took the symmetry of it. (I think I should follow the same here right ?)

May 22, 2018, 07:17		#10
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,928 Rep Power: 28	Yes, you should follow the approach from 2 months ago. As you mentioned, if you extend the surface to the stator frame, a small part of the circle diameter is generated. This is what I called 'floating in the air'. You have to do something with it. Therefore you have to follow the approach from 2 months ago.

May 23, 2018, 05:32		#11
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 14	Hi Gert Thanks a lot for your reply !! Now I was told by the customer support to extend the interface only upto the end of the rotor disc or center of the rotor disc so that I will have 3 interfaces and the wall of the disc can be given as rotating wall, by doing so I can avoid that small section which hangs in air. Then they also mentioned to do a 2D computation than a 3D, but here is my doubt, will the power prediction for the relevant RPM be the same as what we get for 3D 1m long turbine ? Can you give me some insight about it ? I have to find the optimum RPM for a constant wind velocity. So what I thought was to do for 3 different RPM for one Wind Velocity and draw the power curve and see where I have the maximum power and take that RPM as optimum. is this approach a correct way ?

May 23, 2018, 06:21		#12
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,928 Rep Power: 28	I am not sure if the result at 2D will be the same as 3D. But for optimizations studies, it is of course much faster. And it will give you a first impression. So I would go for it as well. I think your approach is ok. Maybe 3 simulations is somewhat to little. Make it 5 for a better curve. That is what I use for pump curves. I wonder what the TSR will be in the optimum you'll find. Can you share the curve?

May 23, 2018, 08:39		#13
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 14	Dear Gert I havent tried to get the TSR, nor am not sure how I can calculate that. but if I find a way to calculate that I will surely share it with you.