Flutter is a rather innocuous term for a potentially dangerous phenomenon that can occur for any flexible structure in a moving flow. Aeroelastic flutter occurs when aerodynamic forces and a structure’s natural modes of vibration get coupled: the surrounding flow causes the object to vibrate, which alters the nature of the aerodynamic forces on the object, which, in turn, feeds into the object’s vibration. In some cases, damping will contain the motion to a limit cycle, but under other conditions, flutter results in an uncontrollable self-exciting oscillation that persists until destruction, as in the famous Tacoma Narrows Bridge collapse.
Tag: flutter
Flutter and the Tacoma Narrows Bridge
Sixty years ago yesterday the original Tacoma Narrows Bridge (a.k.a. Galloping Gertie) collapsed as a result of aeroelastic flutter during 42 mph winds. Flutter is a phenomenon in which the fluid dynamics and structural dynamics of a system are closely coupled, in this case resulting in a dramatic failure. The high sustained winds provided an energy source for self-excitation of one of the bridge’s torsional modes; as the bridge contorted, the motion caused additional vortices to be shed from the bridge deck, causing further vibrational forces on the bridge. For an analysis of the bridge’s collapse and its common misrepresentations, see Billah and Scanlan. The bridge’s spectacular collapse prompted reconsideration and redesign of the decks of modern suspension bridges.
Langley’s Transonic Dynamics Tunnel
NASA Langley’s Transonic Dynamics Tunnel (TDT) recently celebrated 50 years of operation. It’s 16 x 16 ft test section has hosted models of many aircraft, including the Lockheed Electra, the C-141, the F-15, the F-16, and the FA-18 shown above. The tunnel is primarily utilized for aeroelastic studies of flutter, a potentially catastrophic phenomenon where aerodynamic forces couple to a structure’s natural modes of vibration. (via JediOliver and NASA_Langley)
