The way you would have Flow Simulation find the Drag Coefficient of a model is by using an Equation Goal. Equation Goals in Flow Simulation would require that you setup other goals for the variables you would use within the Equation Goal. In this case it would be drag force and flow velocity. This video shows how this setup would be done in practice (GoEngineer - SOLIDWORKS Flow Simulation - Drag Coefficient) to find the Drag Coefficient.
Thanks for the video, it helped.