How do i evaluate the CD values obtained from fluent software?

Is there any theoritical method to find the CD, given frontal area, freestream velocity, density of air?

There's a ton of data on drag for different objects. Drag depends heavily on the shape of an object (compare the drag of a sphere and an airfoil with the same frontal area... radically different). Search google for your shape, or try Hoerner's "Aerodynamic Drag" (great reference for drag for many different shapes). If it's an airfoil, look at books like Abbott and Von Doenhoff's Theory of Wing Sections.

Good luck, Jason