Groups of Vertical Cylinders Oscillating in Water

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Abstract
Drag, lift, and moment on twenty-four parallel vertical 1/2-in. cylinders oscillating with 13-in. amplitude in water were measured in a laboratory tank 5.5 ft by 16 ft. A comparison, Do, is defined as 24 times the calculated drag on one of the cylinders alone in a uniform stream flowing at the maximum velocity of the group oscillation. Drag increases from 0.3 Do, with cylinders in contact, to 0.9 Do at 4 diameter spacing, and to approximately Do at 8 diameters. At small spacings, lift decreases from approximately Do to 0.3 Do as Reynolds numbers increase from 5,000 to 15,000. At 2.8 to 8 diameters spacing, lift reaches the large value of 1.7 Do for the higher Reynolds numbers. Moments about the vertical axis of the group are 1 to 9 times the product of Do and the group radius. Vibration frequencies in all modes are at natural frequencies of the group in its corresponding modes. Staggered and square cylinder patterns give approximately the same results.

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