  Numerical simulation results in recent years show that vortex-induced
vibration (VIV) can occur at a subcritical Reynolds number. And the VIV has
been observed numerically at Reynolds numbers as low as Re = 20. The current
study presents an experimental evidence for the subcritical VIV of a cylinder.
We designed and built a rotating channel that makes it possible to perform VIV
experiments at subcritical Reynolds numbers. Based on the rotating channel, two
sets of tests were carried out for fixed natural frequency with variable
incoming flow speed and fixed incoming flow speed with variable natural
frequency. In both sets of experiments, subcritical VIV were observed and the
VIV can be observed at a Reynolds number as low as 23, which is close to the
numerical results of Mittal.
