Obtaining Force from Bt and Gh simulation around airfoil

Hello

I am trying to run a cfd simulation around a section of an airplane wing. I was able to calculate the velocity and pressure field around the free surface. Now I would like to extract the values at the surface and calculate the resultant force in order to get Lift and Drag forces. 

I was reading and found that OpenFOAM has a library that calculates this forces but not sure how to implement it within gh. 

The idea is to then run a gradient based optimization to iterate over changes in geometry to obtain (L/D)max

Thanks for your help and support.

Luca