By definition, the drag coefficient is a function of several parameters like shape of the body. Being the symmetry condition a ‘mirror’ of the shape of the body, it will not affect de Cd.
In other words, that is what I said before: let’s imagine 3 different bodies with the same frontal area:
- a box
- a drop of water
- a sphere
Now, looking to the equation:
Cd = (2 Fd) / (ρ v2 A)
We can see that essentially is the ‘dynamic pressure multiplying the frontal area’ scaled by the ‘drag coefficient’ that is specific to the shape of the body, in our case a box, a drop of water and a sphere has the same value. A box and a sphere and a drop of water all with the same frontal area will have different Cd in the same flow.
You can visualize it better in THIS table, when some objects with the same frontal area do not have the same Cd.
To conclude our example, a drop of water clearly would cut through the flow easier than a box or sphere. So yes, the body along a plane of symmetry would reduce its frontal area by half, but the efficiency of the shape isn’t necessarily doubled (Cd cut in half) by cutting the body in half.
About the Freestream velocity in Result Control,: Yes, you should provide this magnitude as an input of the velocity.