It is a very interesting problem. When I extend the Y direction from 1m to 2m while keeping the mesh size the same, error 195 happens at the initial time. The case run well when operating with Y = 1m.45_2.zip (86.1 KB)
Please try with setting NORM_G=0.0 in mfix.dat (or in the GUI: Numerics>Residuals> Fluid normalization = 0.0) and see if it helps.