METHOD OF PREVENTING KARMAN'S VORTEX SOUND

PROBLEM TO BE SOLVED: To reduce Karman's vortex and the vortex sound accompanying it with a simple method by arranging a second columnar body near a first columnar body set in a fluid. SOLUTION: To a first cylinder 11 placed vertically in a fluid, a short second cylinder 12 is arranged within the vertical plane to the flow direction in the upstream or downstream thereof. A high-speed air flow is blown out from a nozzle 13, for example, at a flow rate of about 20 m/s, and the vortex sound by the Karman' s vortex generated in a wake of the cylinders 11, 12 in the jet is measured. The nozzle has a dimension of about 100×200 mm, and the vortex sound measurement is performed by arranging a microphone in a place separated about 500 mm from the nozzle jet surface. When the cylinder 12 is arranged in the upstream, a sound reducing quantity of 10 dB or more is provided as the experimental result although the sound reducing effect is varied by changing the crossing angle θ. The best sound reducing effect can be provided when the ratio L/D of the length L of the cylinder 12 to the diameter D of the cylinder 11 is 2 or more, and the crossing angle θ is about 30 deg..