Flow measurements regarding the timing of vortices during flutter

Although the aerodynamic cause of the collapse of the Tacoma Narrows Bridge is known to be flutter, there is still little known about the fluid mechanics of this phenomenon. Wind tunnel testing ensures that other bridges should not fail due to this instability, but flow field measurements, other than point measurements, are rare. Recent hypotheses have attributed the cause of the instability to the timing of vortices moving around the deck; however, there is minimal flow data to support this notion. In the current work, measurements were performed using the section model technique on a rectangular cross-section (chord/thickness=7) at different points during the build-up of flutter. These measurements include displacement measurements and high-speed PIV measurements. Experiments were also performed on a static body. The results confirm that the shedding frequency and frequency of the body motion are indeed distinct and both can be observed throughout the build-up of flutter. Moreover, it is shown that the vortex shedding activity changes minimally from that of a static body to one that is experiencing bluff body flutter. These results indicate that the timing of leading edge vortices cannot be the cause of the flutter instability.