# What is the difference between flutter and vortex induced vibration?

During flutter, the airfoil oscillates with a large amplitude, which generates vortices at the wake. In vortex induced vibration (VIV) the oscillations of the airfoil are caused by the shedding of vortices. Both flutter and VIV have airfoil oscillations and vortex shedding. How are they different other than the cause and effect relation? And also how to distinguish which one is the cause and which one is the effect for a case where we don't know beforehand whether it is flutter or VIV?

• You mean beyond the inverted cause and effect you lined out in your question? – AEhere supports Monica Apr 17 '19 at 6:46
• @ AEhere Yes. Is there any other reason than the cause and effect relation? And also how to distinguish which one is the cause and which one is the effect? – Upid Apr 17 '19 at 7:15
• Maybe add that bit about distinguishing cause and effect into the question then :) I hope somebody more versed in flutter can help, but from what I recall the answer is along the lines of vortex shedding being what stabilizes the flutter limit cycle oscillations (without the shed vortex the amplitude would diverge). Good question! – AEhere supports Monica Apr 17 '19 at 7:25
• @AEhere Thanks for the suggestion. I have updated the question. – Upid Apr 17 '19 at 7:32
• I would say that VIV is induced vibrations caused by shed vortices, usually in a control surface,whose energy is totally absorbed and damped by the stiffness of the primary wing or tail structure to which it's connected. It becomes flutter when the stiffness of the root structure is low so that the vibrating surface is able to displace it in torsion, so that it stores and returns energy, AND the harmonics of the two components align so that they magnify each other. One is just vibrations,"buzz" in other words, and the other induces oscillations in the entire structure that make it come apart. – John K Apr 17 '19 at 13:40