flow-induced vibration

flow-induced vibration [¦flō in‚düst vī′brā·shən]

(fluid mechanics)

Structural and mechanical oscillations of structures immersed in or conveying fluid flow as a result of an interaction between the fluid-dynamic forces and the inertia, damping, and elastic forces in the structures.

---

Flow-induced vibration

The dynamic response of structures immersed in or conveying fluid flow. Fluid flow is a source of energy that can induce structural and mechanical oscillations. Flow-induced vibrations best describe the interaction that occurs between the fluid's dynamic forces and a structure's inertial, damping, and elastic forces. See Fluid mechanics, Vibration

The study of flow-induced vibrations has rapidly developed in aeronautical and nonaeronautical engineering. In aeronautics, flow-induced vibration is often referred to as flutter, a topic of aeroelasticity concerning the mutual interactions of aerodynamic, elastic, and inertial forces in a flying object, its components, or its propulsion systems. Flow-induced vibration also covers classical flutter of an airfoil in a low-speed flow, stall flutter associated with a separated flow, and buffeting flutter related to turbulent wakes. Nonaeronautical flow-induced vibrations are often found in blood vessels, smokestacks, suspension bridges, oil pipe lines, power transmission lines, telephone wires, television antennas, heat exchanger tubes, nuclear fuel assemblies, and submarine periscopes and hulls. All nonaeronautical structures are unstreamlined and susceptible to both stall flutter and buffeting flutter caused by flow separation. The interaction of these structures with a fluid stream usually is more complicated than that of aeronautical structures and offers more possibilities for the flow to trigger unstable oscillations in the structures.

Aircraft wing flutter

The fluid-elastic instability of an airplane wing or its control surfaces in a smooth flow without shock waves is called classical flutter. Flight tests show that the lift on an airfoil increases with increasing Mach number for a fixed angle of attack. This lifting force reaches a maximum at a critical Mach number, then drops sharply, and never increases no matter how high the flight speed is. This drop is due to flow separation or shock wave formation. Either of these two flow mechanisms can cause the airfoil to stall or can damage it. In these cases, the airfoil is said to be stall-fluttered or shock-stalled, depending on the flow process. See Shock wave

When a flow separates from an airplane wing, the flow behind the wing is turbulent and random in nature. The airplane's tail is therefore subject to random excitations from the wing's turbulent wake. The wings and tails that oscillate randomly can lose stability. This type of dynamic aeroelastic instability is called buffeting flutter because the oscillations are random. See Boundary-layer flow, Turbulent flow, Wake flow

Vibrations of cylinder arrays

Among the topics of flow-induced vibration, cylindrical structures play very important and vital roles. For instance, the slender bodies of aircraft fuselages, missiles, and rockets, and the main bodies of industrial smokestacks, power transmission cables, telephone wires, oil pipelines, reactor fuel rods, heat-exchanger tubes, and offshore structures, as well as the blood vessels are primarily made up of cylindrical structures. These structures, when in operation, are subject to unsteady fluid-dynamic forces and prone to vibrations. Such vibrations can be classified as axial-flow-induced or cross-flow-induced vibrations, depending on the incident angle of the incoming flow with respect to the cylinders' axes. Stall and buffeting flutter, also called fluid-elastic instabilities, including fluid-damping- and fluid-stiffness-controlled instabilities, as well as vortex shedding are all possible during flow-induced vibration.