The word flutter is used in 4 very different settings: Science, Medicine, Music and Literature in general, with quite very different meanings.
- In Medicine it is one of the four (4) types of palpitations of the heart: pounding, too fast, skipping a beat and fluttering.
In Music it is used to describe a technique for rolling the tongue (or the throat) while playing wind instruments, as explained here on YouTube.
In Science it is a phenomenon encountered in flexible structures subjected to aerodynamic forces. The easiest example, here (YouTube).
It is this last meaning that I am looking for in Portuguese.
It is fairly obvious to see that the word is NOT synonymous with oscillation, reverberation, or resonance - and it is a very specific case (or type) of a vibration - so none of these should be a translation.