Can a grid cell be too small?

Danny

Dear Fellows,

I've been running lately simulations of a transient laminar 2D micro-jet flow field in response to a short period physical disturbance (about 2 msec). I tried to find a transient process convergence depended on time step (down to 1 micro-sec) and grid size (down to less than 1 micron x 1 micron cell size). It seemed like there can be found a process convergence but when the grid cell size was about 0.6 micron x 0.6 micron the result deviated from the general convergence direction. Can anyone explain this phenomenon? Is there a criterion for a grid cell size that may be too small? Is there a combination of cell size and time step that may cause increasing errors? Thank you in advance. Danny.