FLOW VISUALIZATION OF THE INTERSTITIAL CROSS-FLOW THROUGH PARALLEL TRIANGULAR AND ROTATED SQUARE ARRAYS OF CYLINDERS

Flow visualization experiments are reported for the interstitial flow of a parallel triangular array of cylinders with pitch-to-diameter ratio, P/D, of 1.375, and a rotated square array of cylinders with P/D = 1.5, subject to water cross-flow with Reynolds numbers (Re) in the range of 80-1300. Most experiments were conducted with rigid arrays but, for the parallel triangular array, some were done with a flexibly mounted cylinder. At low Re, symmetric attached vortices are observed behind cylinders in all rows of the rotated square array. At a critical Re, the dividing line between these symmetric vortices becomes unstable and folds up on itself, resulting in alternate vortex shedding. On the other hand, for the parallel triangular array no vortex shedding was observed behind cylinders in any row of the rigid array, although attached eddies of recirculating flow did form behind the cylinders; when one of the third or fifth row rigid cylinders was replaced by a flexible cylinder, it exhibited large amplitude vibrations which caused the bound vortices to be shed and swept downstream in an antisymmetric manner.