Vibrations and stability of a flexible disk rotating in a gas-filled enclosure—Part 2: Experimental study

The vibrations and acoustic oscillations of a rotating disk coupled to surrounding fluids in an air-filled enclosure are investigated experimentally. Aeroelastically excited disk transverse vibrations are measured in a specially designed enclosure on a high-speed test stand using different disk materials. In addition, acoustic modes are monitored as a function of disk rotating speed using microphones which are installed at the top and bottom covers of the enclosure. It is shown from the acoustic pressure measurements that acoustic modes can be classified as in-plane modes that decouple from disk vibration or out-of-phase modes that couple to disk vibration. Further, it is also shown that with disk rotation both these types of acoustic modes split into forward and backward traveling waves, offering direct evidence of a rotating core in the fluid flow in the enclosure. It is confirmed from measurements of the disk vibration that disk flutter does not occur by mode coalescence but by a damping-induced instability as described in the accompanying theoretical paper. Beyond the flutter speed, it is shown that acoustic pressures oscillate severely at the frequency of disk instability. These phenomena are, for the most part, predicted by accompanying theory. Other phenomena are observed that are not predicted by current theory including moderate amplitude 1/2 rotation speed subharmonics in the disk vibration spectrum. Put together these experiments confirm several theoretical predictions, but also reveal new phenomena that can occur in enclosed rotating disk systems such as in CD/DVD ROMs, hard disk drives, and micro-gas turbines.