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-   -   Negative cells in AutoGrid (http://www.cfd-online.com/Forums/numeca/92247-negative-cells-autogrid.html)

funmaker September 7, 2011 11:10

Negative cells in AutoGrid
 
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.


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