I read, did, searched and still not get the result, pls help me out my tidal turbine

altomos · March 26, 2011, 18:29

Dear CFX experts and everyone.

I finally end up helpless with my tidal turbine simulation though I've read, did and searched everywhere. So, I do hope some advices from your experience:

The problem is I used actuator disk method to simulate an one-meter-diameter turbine. It is sinked in a flow field contains both water and air (free surface model).

After many runs, I always got these results most:

1. No result due to Fatal overflow.

2. Result comes but: no change in water level near turbine position, no change in stream line direction (looks like they just go straightly from the turbine to the outlet)... Or very messy flow (looks like nothing!)

I tried with both tetra and hexa mesh, I hardly made the "floating disk" inside the flow field with no error. But until now, no desire result or my results are not correct with the real physical phenomenon.

So please give advices and help me out, here I attach my cfx file with. I do appreciate any help from you. Thank you very much.
http://www.mediafire.com/?thazui4xm4vi6li

altomos · March 28, 2011, 09:31

Please... Anyone can give me an advice?

ghorrocks · March 28, 2011, 19:29

Overflow means your simulation is diverging. Need to improve numerical stability. Read the doco or posts here about numerical stability.

altomos · March 28, 2011, 20:11

Thank you a lot Mr. Ghorrocks. Now, I fixed the fatal flow problem, the simulation runs well but it seems not correspond to actual flow.

Detailedly, there's just a very little water level drop right after turbine position. While in actual case, there's a significant drop of water level there.

How do you think about this? Thank you for your concern.

ghorrocks · March 30, 2011, 20:02

http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

altomos · March 30, 2011, 21:30

Thank you very much, Mr.Ghorrocks. By the way, here is my video for my simulation.
Would you mind having some comment for me please?
I'm so sorry for wasting your time, but since I'm a new learner, there are many things I still don't know and can not understand all at once. So I do need guidance from experts.
http://www.mediafire.com/?3zfsyf2kmncavzh

ghorrocks · March 31, 2011, 07:49

I do not understand what the video is showing. Can you explain your model better? What boundary conditions have you defined?

altomos · March 31, 2011, 11:08

Everything is defined in my *.cfx file I posted in this topic. I simulated a tidal turbine using actuator disc method. The flow field consists of water and air (free surface simulation), so I applied VOF model. Except inlet, outlet and the opening boundary on the top, the rest is wall. The video shows the variation of water level and movement of streamlines (before and after the turbine/actuator disc) during the flow of fluids from inlet to outlet. And what I want to see is the change of water level at turbine position, but it seems not to be true (in comparison to actual flow).

March 26, 2011, 18:29	I read, did, searched and still not get the result, pls help me out my tidal turbine	#1
altomos New Member Hoang Anh Dung Join Date: Jul 2010 Location: Korea Posts: 19 Rep Power: 16	Dear CFX experts and everyone. I finally end up helpless with my tidal turbine simulation though I've read, did and searched everywhere. So, I do hope some advices from your experience: The problem is I used actuator disk method to simulate an one-meter-diameter turbine. It is sinked in a flow field contains both water and air (free surface model). After many runs, I always got these results most: 1. No result due to Fatal overflow. 2. Result comes but: no change in water level near turbine position, no change in stream line direction (looks like they just go straightly from the turbine to the outlet)... Or very messy flow (looks like nothing!) I tried with both tetra and hexa mesh, I hardly made the "floating disk" inside the flow field with no error. But until now, no desire result or my results are not correct with the real physical phenomenon. So please give advices and help me out, here I attach my cfx file with. I do appreciate any help from you. Thank you very much. http://www.mediafire.com/?thazui4xm4vi6li

March 28, 2011, 09:31		#2
altomos New Member Hoang Anh Dung Join Date: Jul 2010 Location: Korea Posts: 19 Rep Power: 16	Please... Anyone can give me an advice?

March 28, 2011, 19:29		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Overflow means your simulation is diverging. Need to improve numerical stability. Read the doco or posts here about numerical stability.

March 28, 2011, 20:11		#4
altomos New Member Hoang Anh Dung Join Date: Jul 2010 Location: Korea Posts: 19 Rep Power: 16	Thank you a lot Mr. Ghorrocks. Now, I fixed the fatal flow problem, the simulation runs well but it seems not correspond to actual flow. Detailedly, there's just a very little water level drop right after turbine position. While in actual case, there's a significant drop of water level there. How do you think about this? Thank you for your concern.

March 30, 2011, 20:02		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

March 30, 2011, 21:30		#6
altomos New Member Hoang Anh Dung Join Date: Jul 2010 Location: Korea Posts: 19 Rep Power: 16	Thank you very much, Mr.Ghorrocks. By the way, here is my video for my simulation. Would you mind having some comment for me please? I'm so sorry for wasting your time, but since I'm a new learner, there are many things I still don't know and can not understand all at once. So I do need guidance from experts. http://www.mediafire.com/?3zfsyf2kmncavzh

March 31, 2011, 07:49		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	I do not understand what the video is showing. Can you explain your model better? What boundary conditions have you defined?

March 31, 2011, 11:08		#8
altomos New Member Hoang Anh Dung Join Date: Jul 2010 Location: Korea Posts: 19 Rep Power: 16	Everything is defined in my *.cfx file I posted in this topic. I simulated a tidal turbine using actuator disc method. The flow field consists of water and air (free surface simulation), so I applied VOF model. Except inlet, outlet and the opening boundary on the top, the rest is wall. The video shows the variation of water level and movement of streamlines (before and after the turbine/actuator disc) during the flow of fluids from inlet to outlet. And what I want to see is the change of water level at turbine position, but it seems not to be true (in comparison to actual flow).