ggulgulia 
May 19, 2013 08:19 
Hey Zhang
I am not giving you a software custom method to calculate the vehicle lift. What I am about to mention in the foregoing discussion is a standard method for calculating the lift/drag forces at any region of the body
The region of interest has to be explicitly defined in the code. For lift coefficient calculation you need to have the area (Vector) of the region normal to the longitudinal direction of the vehicle, say A, and the density of the fluid flowing over the surface of the vehicle, say d, The force has to be calculated by the expression in the code you will be using (all of the softwares nowadays have an inbuilt expression to calculate the force on the surface of interest. This force, say F, is fund out by running the simulation. Then you can create a custom expression to get the force coefficient and running the same in iteration. The following formula has to be used for calculating the force coefficient:
C= F/(0.5*d*A)
For drag coefficient F is along the direction opposite to the fluid flow or along the direction of the area vector, and for lift coefficient F is along the direction aligned with the vertical of the local coordinate system
