Originally Posted by zz4gta
I agree, everything does flex to some extent. However, I think that the finish on the foils itself and the trailing edges (non-laminar flow) will cause the hum before a "flex" or vibration hits it's natural harmonic frequency. Or am I looking at this completely wrong? Not trying to be a smart ass, just trying to learn.
The non-laminar flow is what is causing the flex. As the eddys exert a small amount of pressure on one side then the other, you get a small amount of flex either direction. As the frequency of the flex reaches the harmonic frequency, you get a hum. The water doesn't hum, just like the wind doesn't hum or whistle. The finish of the foil and the shape of the trailing edge (and the rest of the foil) will effect the laminar flow, and the resultant eddys.