negative volume and folded mash

wizards · November 7, 2017, 21:33

Hi, Im calculating the wing's fluid-structure interaction. Now I meet a error.My wing's length and width is 1m. When the velocity of inlet is 50m/s, I set the timesteps to 0.001s. then negative volume and folded mash appeared. If I ramp up the timesteps such as 0.01 0.1 , the solver show overflow. What can I do to fix it? Thanks to everyone.
When v=1m/s, timesteps=0.1s, it works nice.
negative sector volume, nagetive element volume, folded mesh has occurred. and the location of negative volume is in the domain of fluid, not at the wing. that's wierd. the location is far away the wing

ghorrocks · November 8, 2017, 04:21

This suggests to me you have a fundamental instability in your simulation which cannot be fixed by time step size alone.

This FAQ may help: https://www.cfd-online.com/Wiki/Ansy...do_about_it.3F

CFD should converge quickly and easily with small time steps. The fact your does not suggests something is very wrong.

Christophe · November 11, 2017, 16:17

I would try ramping up the velocity, as I believe with that high velocity it may be causing too much deformation and thus the elements fold inward on themselves causing the negative volume error. Also perhaps making your fluid domain larger will help with mesh deformation problems.

November 7, 2017, 21:33	negative volume and folded mash	#1
wizards New Member bradly wall Join Date: Oct 2017 Posts: 3 Rep Power: 8	Hi, Im calculating the wing's fluid-structure interaction. Now I meet a error.My wing's length and width is 1m. When the velocity of inlet is 50m/s, I set the timesteps to 0.001s. then negative volume and folded mash appeared. If I ramp up the timesteps such as 0.01 0.1 , the solver show overflow. What can I do to fix it? Thanks to everyone. When v=1m/s, timesteps=0.1s, it works nice. negative sector volume, nagetive element volume, folded mesh has occurred. and the location of negative volume is in the domain of fluid, not at the wing. that's wierd. the location is far away the wing

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November 8, 2017, 04:21		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,728 Rep Power: 143	This suggests to me you have a fundamental instability in your simulation which cannot be fixed by time step size alone. This FAQ may help: https://www.cfd-online.com/Wiki/Ansy...do_about_it.3F CFD should converge quickly and easily with small time steps. The fact your does not suggests something is very wrong.

November 11, 2017, 16:17		#3
Christophe Member Join Date: Jan 2015 Posts: 62 Rep Power: 11	I would try ramping up the velocity, as I believe with that high velocity it may be causing too much deformation and thus the elements fold inward on themselves causing the negative volume error. Also perhaps making your fluid domain larger will help with mesh deformation problems.