I import basic 3d models of different cars into Unity. And want to be calculate how aerodynamic the shape is, which will influence its speed. Is there a way achieve this? It doesn’t have to be accurate or realtime. Just a way to estimate how aerodynamic a car shape is.
If an existing package can help that’d be cool.
The drag force on the vehicle (Fdrag) = 0.5 x p x v^2 x A x Cd where:
p = air density (1.225 kg/m^3)
v = velocity of the car (m/s)
A = frontal area (m^2), the area of the cross-section you would get if you cut the car in half at its ‘largest’ point
Cd = coefficient of drag for that vehicle
You may see a value online for CdA which just means that they have done the Cd x A calculation for you - be very careful that the A was in m^2 or you will need to apply a correction factor. It’s very important that you use a consistent unit system (I recommend SI).
Your maximum speed is limited by the amount of power available to match that drag force
power (w) = Fdrag(N) x velocity (m/s)
(for your information, 1 hp = 746 watts)
So this leaves you with one tricky problem: Getting the Cd value. To get the real value computationally is very involved, you would either have to plug-in or create your own CFD solver, which is way beyond the scope of anything any sane person would want to do for a computer game. So I suggest that you construct a lookup table from the data available online e.g.
https://ecomodder.com/wiki/Vehicle_Coefficient_of_Drag_List
Perhaps a simpler option is to identify 10-15 typical profiles and allow selection of the most similar.
If you wanted to get really fancy you could train a neural network on a sample set of side-profiles and use that to estimate a Cd for unknown profiles - if you have too much time on your hands 
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