A friend of mine (
whose dad made the streamlined aero model T in the 1930's) showed me a neat looking app on his ipod last week. The simulation looked really good.
There's a free and paid version, and I don't think you can place your own shape in the free version.
Details at:
algorizk.com/windtunnel/overview/
It probably won't run on my old Android, but if anyone tries it, let us know.