Negative cells in AutoGrid

funmaker · September 7, 2011, 11:10

Hello everybody,

i have created a wind turbine geometry in IGG and try to generated a mesh in AutoGrid using the wind turbine wizzard. Everything is working fine. I import and link the geometry in AutoGrid by defining a suction and pressure side, leading and trailing edge and also shroud and hub.
In the B2B view i got sharp edges on the leading and trailing edge position because opened airfoil profiles. To get rounded edges i use the option blend the blade at leading/trailing edge. All this works great.
But by generating the 3D mesh for the blade and far field i get negative cells.
Thy reach from the center of blade tip into the far field.

Maybe one of you could give me and advice.
Kind regards Matthew

totti9090212 · September 17, 2011, 11:15

Hi, i think your geometry( bad geometry ) and poor gird distributed may lead negtive cells. see the b2b view of the position which have negtive cells. from it , you could find which cause negtive cells. if your geometry is good, you can adjust the gird points, cell width and expansion ratio to improve your grid quality.

venkat_aero2007 · July 17, 2012, 04:58

Hi,
Have you solved the problem of negative cells in farfield. I have the same problem. Could you please help me to solve this problem. I tried to change span wise distribution and expansion ration but all these didn't work.

funmaker · July 17, 2012, 05:17

Hi venkat_aero2007,

sorry for my late answere.
Yes, i solved the problem with the negative cells.
In my case i had to create the virtuell shroud-line above the blade. So that there is no intersection between the shroud-line and the blade. This sounds confusing but it worked.
I hope i could help you.

venkat_aero2007 · July 17, 2012, 05:34

Hi funmaker,
Thanks for your reply. Could you please tell me, What do you mean by "virtuell shroud-line". Does it mean you created a shroud line at the end of the far field and defined that has shroud. Could you please explain a bit more. And how long was your field?. Do you created two shroud line and define one has a shroud and other as what??

Actually my blade have a shroud gap of 0.25mm. I have a good quality mesh in the region of blade. But I get negative cells only in the far field. the negative cells are located in the blade tip block just above the shroud and continues till the far field.

Thanks in advance for your information. waiting for your reply.

September 7, 2011, 11:10	Negative cells in AutoGrid	#1
funmaker New Member Matthias Join Date: Sep 2011 Posts: 12 Rep Power: 14	Hello everybody, i have created a wind turbine geometry in IGG and try to generated a mesh in AutoGrid using the wind turbine wizzard. Everything is working fine. I import and link the geometry in AutoGrid by defining a suction and pressure side, leading and trailing edge and also shroud and hub. In the B2B view i got sharp edges on the leading and trailing edge position because opened airfoil profiles. To get rounded edges i use the option blend the blade at leading/trailing edge. All this works great. But by generating the 3D mesh for the blade and far field i get negative cells. Thy reach from the center of blade tip into the far field. Maybe one of you could give me and advice. Kind regards Matthew

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September 17, 2011, 11:15		#2
totti9090212 New Member totti Join Date: Feb 2010 Posts: 3 Rep Power: 16	Hi, i think your geometry( bad geometry ) and poor gird distributed may lead negtive cells. see the b2b view of the position which have negtive cells. from it , you could find which cause negtive cells. if your geometry is good, you can adjust the gird points, cell width and expansion ratio to improve your grid quality.

July 17, 2012, 04:58		#3
venkat_aero2007 Member venkatesh Join Date: May 2012 Posts: 93 Rep Power: 13	Hi, Have you solved the problem of negative cells in farfield. I have the same problem. Could you please help me to solve this problem. I tried to change span wise distribution and expansion ration but all these didn't work.

July 17, 2012, 05:17		#4
funmaker New Member Matthias Join Date: Sep 2011 Posts: 12 Rep Power: 14	Hi venkat_aero2007, sorry for my late answere. Yes, i solved the problem with the negative cells. In my case i had to create the virtuell shroud-line above the blade. So that there is no intersection between the shroud-line and the blade. This sounds confusing but it worked. I hope i could help you.

July 17, 2012, 05:34		#5
venkat_aero2007 Member venkatesh Join Date: May 2012 Posts: 93 Rep Power: 13	Hi funmaker, Thanks for your reply. Could you please tell me, What do you mean by "virtuell shroud-line". Does it mean you created a shroud line at the end of the far field and defined that has shroud. Could you please explain a bit more. And how long was your field?. Do you created two shroud line and define one has a shroud and other as what?? Actually my blade have a shroud gap of 0.25mm. I have a good quality mesh in the region of blade. But I get negative cells only in the far field. the negative cells are located in the blade tip block just above the shroud and continues till the far field. Thanks in advance for your information. waiting for your reply.