Free surface waves induced by vortex shedding in cylinder arrays

The paper presents and discusses the results of an accurate and extensive experimental investigation on the waves that originate when an array of cylinders is placed in an otherwise uniform open channel flow. The study was originally aimed at providing new and more accurate data to calibrate and validate a theoretical model recently proposed in the literature. However, two interesting characteristics of the phenomenon at hand, never reported in the literature, also emerged from the experimental study, i.e. (i) the wave produced by the cylinders is actually a metachronal wave rather than a pure transverse seiche; (ii) two different resonant conditions exist for each single wave mode, i.e. two typical Strouhal numbers characterize the resonance frequency of vortex shedding from the cylinders in an array. Evidence of the metachronal wave, as well as some preliminary data on the longitudinal component of this wave, are given in the paper. Also, the double resonance condition is experimentally demonstrated and discussed.