I want to calculate mixing index of two fluids by giving input flow rate in a straight microchannel. Till flow rate value 270 ul/min (Re 20), results are OK, but I don't know why from flow rate 405 ul/min (at Re 30) onwards the concentration results in graphics is weird. Can you please check the simulation and let me know where I am going wrong, what is the solution for it. I have to solve it till flow rate 1350 ul/min (Re 100). The simulation is done using COMSOL v5.0