Hi Nek Forum, Paul I am having temp = 1 and temp = 0 at the inner and outer boundaries. Gravity is pointing in the -ve z-direction along the axis of the annulus. The top and bottom planes have zero heat flux conditions. I have Coriolis force added as a body force. The Rayleigh number is around 10000. The resolution is 8, 25, 24 elements in the r, phi and z directions respectively with order 9. My initial condition is very low arbitrary velocity perturbation (~10^(-8)). The time resolution is set to 10^(-5) for param12. The CFL is set to 0.5. Please indicate how to control it. As you have rightly mentioned, I start the simulation with a very low value of the Rayleigh number and gradually increase it. Yet, the corner values only get large. Other regions of the domain are fine. Thank you Swarandeep On Thu, Jun 1, 2017 at 7:38 PM, <[email protected]> wrote:
Hi Swarandeep,
How large is your Rayleigh number and what is your resolution? What are your thermal bcs? What are your ICs?
There should be no particular issue with your configuration - but you do need to control spatial and temporal resolution.
For RB, you often have to start at low Ra and/or small dt because the nonlinear response can often drive the velocities to be quite high very rapidly before the CFL constraint kicks in. RB flows are one of the rare instances where I use variable time step size (param 12 > 0), but even then you have to keep the target CFL quite small until the flow is established.
hth,
Paul
________________________________________ From: [email protected] [[email protected]] on behalf of [email protected] [[email protected]] Sent: Thursday, June 01, 2017 7:27 AM To: [email protected] Subject: [Nek5000-users] Corner elements giving large values
Dear Nek forum,
I am simulating Rayleigh Benard flow in a 3D finite cylindrical annulus. I am getting spurious large values of velocity at the corner regions of the annulus i.e. the edges where the inner cylinder joins the top and bottom planes. The boundary condition is no-slip and no penetration for velocity at these edges. Can someone point out a plausible reason.
Thank you Swarandeep _______________________________________________ Nek5000-users mailing list [email protected] https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users _______________________________________________ Nek5000-users mailing list [email protected] https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users