change operating temperature

Mahyar

Dear all i want to solve unsteady natural convection by Bossinesq method. in this method i should set operating temperature as a function of time. according to "Operating Condition Panel" in Fluent i can set only one value for all time step. but in my case,operation temperature(T0) varies with time marching physically. according to "Y" momentum equation, i think i should add a source term in "Y" momentum in order to cancel "TO" and add T0(t) instead by UDF. i read "UDF manual" completelly. but i don't know how i should use it. could anybody help me solve my problem.

thank you mahyar