Problem with viscosity

ivanfb95 · July 2, 2017, 14:57

Hi,

I'm trying to run Ahmed body 2D case. I have a 3 million Reynolds number and I have used simpleFoam and pimpleFoam solver.

I need a viscosity of 15e-6 and when I use it I get this error: mpirun noticed that process rank 4 with PID 26165 on node ivan-Lenovo-G510 exited on signal 8 (Floating point exception).

When I use a lower viscosity there isn't any error.

Anybody can help me?

Thanks.

piu58 · July 3, 2017, 00:38

If you increase the Reynolds number wth the viscosity (which is normally the case) I would first try to lower the time step with increasing Re.

ivanfb95 · July 3, 2017, 05:11

You are right but I tried with very low times step and the error continues.

Can be a mesh problem?

piu58 · July 3, 2017, 08:16

It is always a good idea to have a look at the mesh. Another problem may rise form incorrect boundary conditions.

I would check it the following way:
- Let OF calculate a simulation with a quite high Re, which doesn't crash
- Look at the result (p and U) with paraFoam. Look whether you find regions which look strange
- Think what may be the reason, mesh or b.c.

July 2, 2017, 14:57	Problem with viscosity	#1
ivanfb95 New Member IvánFB Join Date: Mar 2017 Location: Spain Posts: 10 Rep Power: 10	Hi, I'm trying to run Ahmed body 2D case. I have a 3 million Reynolds number and I have used simpleFoam and pimpleFoam solver. I need a viscosity of 15e-6 and when I use it I get this error: mpirun noticed that process rank 4 with PID 26165 on node ivan-Lenovo-G510 exited on signal 8 (Floating point exception). When I use a lower viscosity there isn't any error. Anybody can help me? Thanks.

July 3, 2017, 00:38		#2
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 16	If you increase the Reynolds number wth the viscosity (which is normally the case) I would first try to lower the time step with increasing Re. ivanfb95 likes this. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

July 3, 2017, 08:16		#4
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 16	It is always a good idea to have a look at the mesh. Another problem may rise form incorrect boundary conditions. I would check it the following way: - Let OF calculate a simulation with a quite high Re, which doesn't crash - Look at the result (p and U) with paraFoam. Look whether you find regions which look strange - Think what may be the reason, mesh or b.c. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

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July 3, 2017, 05:11		#3
ivanfb95 New Member IvánFB Join Date: Mar 2017 Location: Spain Posts: 10 Rep Power: 10	You are right but I tried with very low times step and the error continues. Can be a mesh problem?