I'm trying to code a simple physics simulator in C++ but I'm stuck on the air resistance issue. Surfing the Internet I only find a drag coefficient for very basical area shapes when the air is perpendicular to the area. However, even when simulating a falling parallelepiped, I found this not sufficient to describe the motion of the falling body, as the air is not always perpendicular to each face. More precisely, I'm able to calculate the air drag on each face of the object, obtaining a 3D vector which describes the force acting on the body.
However it's obvious that when such an object falls through the air, even an angular momentum is induced to the body. I'm not able to determine it.
I was thinking about describing the air flow as a matrix of parallels vectors, thus obtaining a resultant force as a weighted sum of the effect of each vector hitting the body. However in this case I'm not able to determine the force of each single wind vector hitting the surfaces of the body.
What is the simplest way to obtain object rotation due to air resistance? And what is the finest way?