Vortex-Excited Transverse Surface Waves in an Array of Randomly Placed Circular Cylinders

Abstract

The results of an experimental investigation on the generation of transverse surface waves inside an array of randomly placed circular glass cylinders are presented. The transverse waves are generated from the forces developed by periodic vortex shedding from the glass cylinders. A lock-on, or a coupling, can occur between the vortex-shedding frequency and the frequency of transverse water waves. In all the experimental runs, the amplitude of the periodic transverse waves initially increased with an increase in water depth but decreased rapidly after reaching a maximum value. The amplitude reached a maximum value at a critical value of the water depth. The maximum amplitude increased with an increase in cylinder diameter. For the lengths of all of the arrays, the maximum amplitude occurred at approximately one-fifth of the total length from the upstream edge of the array. The maximum amplitude across the array increased with increasing Reynolds number until a critical value of the Reynolds number is reached, for which surface waves form and the amplitude is at its maximum. This critical value of the Reynolds number and the range of flow velocity for which the surface waves exist are different for different cylinder diameters. A previous mathematical model developed for the prediction of amplitudes has been modified for random arrays, which agrees well with the present experimental data.