I will try to explain. What I am trying to accomplish is a simulation of a flow of fluid that is opposed by a gas flow. For example your average windshield sprinklers, when you spray the water, the flow is effected by the surrounding air flow caused by the motion of the vehicle.
This will be covered in our NX10 implementation of two-phase, immiscible flows.
The following approach could be used : The windshield would be a wall, the washer jet would be an inlet with area fraction of unity (assuming the washer fluid is the tracked constituent) and any arbitrary constant or time-varying velocity, the oncoming air would be an inlet with zero area fraction and the specified relative windspeed, and the other boundaries of the domain would be openings with area fraction of zero (i.e. any back flow entering the domain from the openings would be purely air).