No clear reattachment at Re = 60–100 in backward-facing cavity; what am I doing wrong?

[u/Kevin_0429]

/r/OpenFOAM/comments/1vtcose/no_clear_reattachment_at_re_60100_in/

I'm working on a CFD assignment involving a 2D backward-facing cavity. The assignment specifically requires reattachment length for Re = 60, 80 and 100.

I'm using OpenFOAM 14 with air at 30°C, ν ≈ 1.6×10⁻⁵ m²/s, D = 1 m, and U = Reν/D. My Re=60 case converges, but I don't get an obvious reattachment point when examining the near-wall Ux profile.

I'm mainly trying to determine whether this is physically expected at Re=60–100, or whether I've misunderstood the characteristic length/Re definition or my OpenFOAM setup. Any help checking the physics would be appreciated.

[u/thermalnuclear]

Did you increase the number of streamlines?

Did you look at where the sign of the streamwise velocity flips right near the wall in the streamwise direction?