Wake interaction experiments with two flexible circular cylinders in flowing water

An examination is made of wake interaction effects between two identical flexible circular cylinders in flowing water. The two vertical cylinders are separated by a variable distance G along a common centre-line in the direction of flow for the range 0·25 < G/d < 6. Oscillations in the fundamental and second normal modes in the flow direction and in the fundamental mode cross-flow are induced by coherent vortex shedding. Reynolds numbers of the individual cylinders are in the range 103 < Re < 2 × 104, and the two one-inch diameter cylinders were tested in depths of water varying from 22 diameters to 30 diameters. Results are presented from tests on the uncoupled cylinders and also from tests with the cylinders coupled by elastic or rigid members. The stability of the two cylinders is explained by reference to oscillatory mode shapes and from considerations of the two possible types of vortex shedding (symmetric and alternate). Where possible, comparisons are made with results from wind tunnel investigations.