Flow around three circular cylinders in equilateral-triangular arrangement

Abstract

A three-cylinder array arranged in equilateral-triangular configuration represents one of the most common, basic units of multi-cylinder systems in engineering practice. The present study investigates this flow configuration, focusing on the effects of the cylinders’ spacing ratio (P/d = 2.8–5.2) and the array orientation with reference to the oncoming flow (α = 0°–30°), under a fixed Reynolds number 8000 (based on the cylinder diameter d). The hydrodynamic forces (drag and lift) on each cylinder were directly measured using piezoelectric load cells, together with concurrent flow measurements using Particle Image Velocimetry (PIV) technique to quantitatively visualize the shear layer development, vortex formation and interaction process. The flow interference among the cylinders, which shares some similarities with that of two cylinders arranged in side-by-side, tandem or staggered configuration, is further complicated due to the presence of the third cylinder and exhibits many unique features. A number of different flow patterns, including shear layer reattachment, induced separation, synchronized or independent vortex shedding, etc., are identified over the (P/d, α) parameter space. The effects of flow interference are also quantified in terms of Reynolds shear stress distributions around the cylinder array, mean and root-mean-square (RMS) drag/lift coefficients and vortex shedding frequencies of each cylinder.