The "lock-in" phenomenon has been investigated experimentally by vibrating cylindrical bluff body surfaces locally using piezoelectric actuators. The maximum amplitude of oscillation is of the order of 20 pm (nearly 1.0 X 10-3 times the body thickness), and the excitation frequency covers below and above a natural vortex shedding frequency from the body. The Reynolds number renges from 5.25 X 103 to 2.31 x 104. Substantial entrainment of vortex shedding frequency has been observed by exciting the upstream surface of sidewalls, where a short laminar separation bubble exists. Vortex shedding becomes more periodical and the total pressure in the wake becomes high by the local excitation of body surfaces. Possibilities for application to the active control of vibration and noise due to vortex shedding, as well as to drag reduction are discussed.
