Dear all,
I have been trying to set up a time-dependent 2D external flow incompressible Navier-Stokes computation in the transitional regime (separated flow around airfoil at Re~5000, aoa=12) but I get unphysical pressure oscillations across the domain.
The main features of the flow, vortex shedding frequency, aerodynamic forces mean value and oscillation amplitude are captured with reasonable resolution. There appear, however, high frequency pressure oscillations whose amplitude is reduced by an increase in resolution without ever completely disappearing. The velocity field seems to be little affected by this pressure oscillations, but they are however quite annoying.
I have tried, but doesn't seem to have any effect whatsoever:
- many different meshes
- usual outlet boundary conditions (Neumann for velocity, Dirichlet for pressure) and HOutflow BC.
- nodal and modal expansions. (btw, what is the difference between GLL_Lagrange and GLL_Lagrange_SEM?)
- convective and skew-symmetric forms for the advection term
- 1st 2nd and 3rd order time integration with the IMEX time-stepper
- Reducing the timestep
Dealiasing with SpectralHPDealiasing has some effect, but not much. What seems to work quite well in smoothing the pressure oscillations is using SmoothAdvection (I am not sure of what this does), except that the computation eventually destabilises and produces NaNs.
I also wanted to try the inf-sup condition and use different expansion orders for pressure and velocity, but this does not seem to be possible other than with the direct solver, which cannot be used for fully nonlinear transient computations. Another option I considered was using the unconditionally stable rotational velocity-correction scheme of Dong & Shen (JCP 2010) but I think it is not implemented in the IncNavierStokesSolver.
Please find attached the files to run one of the many tests I have performed. Any help will be welcome. Many thanks in advance.
Cheers,
Fer
<naca0012A12Re5300.c07.N.0.xml><naca0012A12.c07.msh.xml>_______________________________________________
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