I am trying to repeat the NACA0021 test of Witherden, Jameson (2020) (https://arc.aiaa.org/doi/abs/10.2514/1.J058434), Sec D. Basically, starting with
order = 1 without antialiasing with
tend = 100.0 and with Re = 27000 (i.e.
mu = 0.000037), I attempted restarting from there with
order = 4 activating antialiasing for another 300 t (i.e.
tend = 400) and modifying the Re to 270000 (
mu = 0.0000037).
The first part of the simulation was completed without errors. However, the restarted simulation crashed after time 107.28, with the following error:
RuntimeError: Minimum sized time step rejected
From the forum, I already noticed that such kind of error can happen when restarting the simulation with a different order (see page https://pyfr.discourse.group/t/naca-0021-airfoil-in-deep-stall-minimum-sized-time-step-rejected/295).
I adopted the
p4_aa.ini config file as a template for my simulation, available within the supplemental material of Park, Witherden, and Vincent (2017) (see https://arc.aiaa.org/doi/full/10.2514/1.J055304). The relevant differences between the warmup and restart phase are as follows:
[constants] ... mu = 0.000037 ... [solver] ... order = 1 #anti-alias = flux, surf-flux ... [solver-time-integrator] ... tend = 100.0 ...
[constants] ... mu = 0.0000037 ... [solver] ... order = 4 anti-alias = flux, surf-flux ... [solver-time-integrator] ... tend = 400.0 ...
I kept the rest of the file unchanged, therefore the filtering section for both config files is:
[soln-filter] freq = 0 cutoff = 0 order = 16 alpha = 36
Can someone give me some hints on how to heal/monitor the instability that is making the code crashing?
For sake of clarity, I adopted the mesh
naca0021_p4_4c.msh for this test, that is available within the supplemental material of the paper Park, Witherden, and Vincent (2017).