Fluidelastic behaviour of a normal triangular array subject to cross-flow

Abstract

The flow-induced vibratory response of a single flexible cylinder in an otherwise rigid normal triangular array, with a pitch-to-diameter ratio of 1·375, and subject to air cross-flow, has been investigated experimentally. Fluidelastic instability is obtained with the flexible cylinder in each of the seven rows of the array. The instability is predominantly in the cross-flow direction, although in rows 4, 5 and 6 an in-flow instability can also exist. For the_ seventh, and final, row of the array, the instability is purely in the in-flow direction. Stability boundaries for each of the seven rows are presented. Characteristics of the interstitial flow are discussed, including the existence of periodicities within the flow. The nature of flexible cylinder vibrational resonances and acoustic resonances with these flow periodicities are also considered. Finally, unconventional flow and vibrational behaviour are discussed, namely a nonuniformity and asymmetry of the flow downstream of the array, and a fluidelastic instability in the first row which is apparently triggered by an acoustic resonance.