Car drafting

Hi,

While trying to learn flow simulation, I came across this page

http://www.solidworks.com/sw/products/cfd-flow-analysis-software.htm

on this page, there is a video of stock car drafting in which the author has plotted graphs of drag of the two cars as a function of distance between them. I wanted to try and do it for my CFD project. I have already modeled the car and the road. I am also able to run simulation and get cut plots of pressure and velocity but I have no idea how to get the drag vs distance plot.

Also, for flow trajectories, I am not able to get the proper trajectories and I think I am selecting the wrong surface. If you look in the video, there is something like a wall in front of the cars, I am using that as a surface for flow trajectories and all I get is straight arrows, no effect of the two cars.

Any Ideas ??

Thanks in advance

Umang

SolidworksFlow Simulation