How can I increase Re or Velocity at each iteration run as input data ?
 

There is a 2-D tube. Water through a straight horizontal flat tube and heat flux is on the top wall. Reynolds number was assumed to be
increased at each iteration run as input data.

I need to compare different Re or Velocity of water, heating by a constant heat flux. It's like each section with different velocity shows in one figure but not a process(non continue heating from inlet to outlet).

For example, I can see a contour of Re 2000 at beginning and maybe Re 5000 at the end of the tube, so that I can calculate the heat transfer at each section.

How can I set increased velocity in fluent ?

you can use UDF or transient table
https://www.youtube.com/watch?v=s_YkmvFH8VQ