Reply To: HBLM for stokes drag force simulation
for tau too close to 0.5 the simulation gets unstable, but a too large tau (depending on the case of application, e.g. tau=1) can lead to deviations from the physical setup.
You can apply no-slip boundaries, however the best results will be optained with a domain large enough. You might have to test that.
In your case epsilon is two orders of magnitude below the cell size physDeltaX. It will probably have almost no effect.