How do I predict the mechanics of wind that has already passed through a wind turbine?

I am trying to study the double rotor HAWT :

and an issue that has appeared is the mathematical modelling of the motion of the wind[speed and direction] that has passed the first set of blades before it strikes the second set of blades. The reason I need to do that is so I can design the optimal sblade geometry for the second set of blades.

Information I have is :
- The speed and direction of the wind before hitting the first set of blades
- The Blade geometry of the first set of blades

Based on this, I want to deduce the speed and direction of the wind motion after passing through the first set of blades.

I don't expect there is an analytic way of dealing with the problem. I will probably need CFD but I don't know anything at all about this topic.

please help thanks