Low frequency resonance effects in wake shedding from parallel plates

Abstract An experimental investigation was made of resonances excited by the wakes shed from cascades of flat plates mounted between side walls in a low-speed wind tunnel. Attention was concentrated on the lower frequencies at which the nodal spacings were greater than the plate spacing. The resonances occur in sequences where the lowest frequency of each sequence corresponds to wave propagation at a velocity close to the velocity of sound and the velocity of propagation falls progressively as the wavelength decreases. The sequence ends with the mode where there is a node in the plane of each plate. Amplitudes as high as 145 dB (re: 00002 dyne/cm 2 ) were recorded in several cases with relative air velocities less than 100 ft/sec.