how to change eq. variables?
 

I have to change velocity components after each time step:

u = u + rand(+-0.1u)

in every cell in domain. I tried to find the solution in Fluent's manual, but all I could find was how to change BCs, material properties etc, which is not satisfactory for me. How to access and modify flow variables using UDF? Any other way?

I need this for a flat channel flow simulation in LES, with very low given Re (Re_t=2000), which allows inflow velocity of only 1 m/s. Therefore I must force turbulent flow by modifying velocity, as shown above.

Thanks in advance.