Oscillation at the begin of the calculation

[Jundi He]

Hi:

I have two cases, one is a normal annulus fluid domain, another one is an annulus with a little distortion(bow). Both are inlet from the top surface and outlet from the bottom surface, and all the boundary condition setup are the same. I set a monitoring probe in the middle of the fluid domain. When I run the case, the temperature at the monitoring point of the normal annulus case is smooth and finally comes to a constant temperature (converge). But the distortion case, the temperature of the monitoring point has a big oscillation at the first 150 time steps, which shows some unreasonable temperature like 10e+12 degree C. The only different of the two case is the mesh, one is a normal annulus and another one is the annulus with a bow in the middle. The temperature variation at the monitoring point of the distortion case is attached. Could anyone explain why there is such an oscillation at the first 150 time step? Thank you.

Best Regards!
Jundi He

[Yvan Fournier]

Hello,

How does the flow itself behave ? Yes, mesh distortion might be the explanation, but with this little info,it is hard to tell.

Some code options may help here (adding sweeps, adding upwind, ...); check the best practice recommendations.

Regards,

Yvan

[Jundi He]

Yvan:

Thanks for the reply! I can't find out why the fluctuation happen and just limit the solution temperature in a certain range.

Best Regards!
Jundi He