So, let's say I have a bluff body in a moderate-speed wind environment, as in wind across the deck of a bridge. As the vortices form across its surface, do they apply alternating force to the structure? (Maybe I'm completely misunderstanding the nature of vortices) http://img9.imageshack.us/img9/2107/bridgevortices.jpg [Broken] Specifically, I'm putting a suspension bridge cross-section in a wind tunnel, and I'm hoping that if I attach a force gauge to the tail end, the graph will show distinct positive-negative peaks in force, in accordance with the Strouhal frequency. Is this what will happen? For reference, the force gauge I own graphs at 5000 samples/second, measured in nano-Newtons.