Thank you so much for answering my question so quick. I use an implicit solver and my model has a minimum edge length 3.81e-2 and has maximum velocity 10.67 m/s. So the fixed time step for this should be less than (1*3.81e-2)/10.67 in order to make sure that courant number in all of my domain will be less than 1 and achieve accurate solution am i doing it right?