Below is a link that explains how to run a flow simulation in SolidWorks:
http://personal.stevens.edu/~ffisher...oefficient.pdf
You need to input parameters that will influence the drag of the part to run this simulation, or just use the default values and simulate based on the shape of the part.
This simulation can give you an output as a drag force in a direction or a drag coefficient (among other variables that you ask it to solve for).
The data that you obtain from this simulation can be applied as a force in the motion study. The motion study would be separate than the flow simulation and you would need to first run the flow simulation before running the motion study. The results you obtain from the flow simulation is what you could use as an input to the motion study.
At this point this becomes a complicated and time consuming series of simulations and motion studies. I admit that the process would be easier if you could input data as a function of velocity (or at least i am not aware of how to do this for a motion study). Maybe there is a way by adding an equation driven linear motor in the motion study. However, I think it would be a better use of time to optimize the simple projectile motion rather than go through multiple simulations to accurately account for drag.