oscillations of residuals

- February 8, 2019 at 4:16 pm
  
  Andrea159357
  Subscriber
  
  Hi, i'm trying to simulate flow over a cylinder (von karman effect) with steady laminar flow. Residual do not converge but oscillating. I was wondering if the problem is a wrong setting in the solver, bad quality mesh or that i'm trying to capture an instant of an highly unsteady flow with a stetady solver.
  
  Can someone clear my doubts?
  
  thank you
- February 8, 2019 at 4:40 pm
  
  Rob
  Forum Moderator
  
  If the residuals dropped to around 0.01 or so and they're showing something like a sine curve you've probably picked up the transient.
  
  https://www.youtube.com/watch?v=nmvEyeOGgqI
  
  If you post images (please post using the icons in the editor rather than attaching) of the mesh, residuals & result we can give a more informed answer.
- February 9, 2019 at 5:50 pm
  
  Andrea159357
  Subscriber
  
  These are residuals. They are 1e-3 for mass and 2e-6 for momentum.
  
  I'm also monitoring velocity in a point in the domain.
  
  So, residuals and velocity keep oscillating because, even in steady simulation, i'm capturing the unsteadyness of the flow?
  
  Can i consider my solution converged?
- February 10, 2019 at 8:38 am
  
  DrAmine
  Ansys Employee
  
  With steady solver you are not capturing any unsteadiness but just a snapshot of the flow.
- February 10, 2019 at 12:16 pm
  
  Andrea159357
  Subscriber
  
  ok, i 'm capturing a snapshot at T = infinity. Since RANS are avg in time to remove oscillations. If the flow is symmetric i get a beaufiful resuls. ùbut in this case, flow behind the cylinder is not symmetric, what snapshot should i get?
- February 10, 2019 at 12:28 pm
  
  DrAmine
  Ansys Employee
  
  Something unreasonable from physical side in nutshell. It is per maths as the steady solver will just point to one of stable modi if the run.