The question needs some clarification, but at first thought here's a sketch of an answer.
The aerodynamics of rotors of a quad rotor can be simplified as independent from each other. Just to give a glimpse, here's a simple introduction to rotor aerodynamics, including near field flow directions, and average air velocity near (down) the rotor: Helicopter momentum Analysis.
Keep in mind that this is a very simple (yet practically quite an accurate) representation of the real flow phenomena near the vehicle.
Things that should be considered for a more detailed approach:
existence and interaction of multi rotors
rotor - body interaction
unsteadiness (the propellers are in fact creating a periodic flow)
environmental changes (wind, pressure change)
control induced variations (even in perfect air conditions, if the quad rotor is moving a camera or weight, there will be control commands, changing the flow a bit)