Explain me Expressions!!!
 

Ansys CFX EXPRESSIONS:
What is it really means?is it means that we can enter any consistent equations to find the unknown or to apply for Time Step properties..can we us those as input for other unknown phenomena at any time which is not included as a option in CFX..example we write expression for Diffusivity for any time and we pointing that expressions to Kinematic diffusivity in boubdry condition..can we do that for Cl or Cp

It is a mathematical expression of some sort, instead of just some single value. You can use it to define properties, boundary conditions, variables, other expressions, just about whatever you want.