Hi, I was wondering if there are certain techniques to simulate a boundary layer between water and air. I would like to determine drag and lift forces of the hull of an amphibian aircraft planing on the water, just before lift-off. I placed the model of the aircraft in an assembly file where the top plane represents the surface of the water. I used the assembly cut extrude feature to remove everything above the top plane so that only the portion of the hull in the water remains. I set Analysis Type to External, Fluids to Water, Velocity in Z direction to 88 ft/s, Global Goals to Y and Z Component of Force, and Computational Domain Y max to 0 ft to represent the surface of the water.
After some investigation I realized the horizontal forces seemed far too high, the vertical forces were negative and that the water flow seemed to be crossing the top plane.
I then created a simple extrusion to represent the air and specified the bottom face as an ideal boundary wall condition. This corrected the flow lines of the water but the forces still do not make sense.
What else needs to be set up for a proper determination of drag force?

Thanks,
Peter Ferreira