Active-wall device for the generation of small traveling surface waves

Abstract

An all solid-state electromechanical device has been developed which produces short-wavelength traveling surface waves. The active wall was nominally designed for the cancellation of Tollmien–Schlichting waves in a laminar boundary layer in water. The primary purpose of the device was determination of traveling surface wave characteristics which are important for drag reduction with compliant coatings. Wave form, wave speed, frequency, and amplitude are independently selectable. Sinusoidal wall motion, measured in air with an electro-optical displacement sensor, ranged from 0.6–13 μm over a frequency span of 10–150 Hz. Roll-off frequency at the −3 dB point was 120 Hz, while the maximum phase speed was 166 cm/s. The electronic subsystem is a hybrid analog/digital device, and the active wall employs piezoelectric ceramic elements to produce surface motion.