Wake analysis and regimes for flow around three side-by-side cylinders

Abstract

In this study, an analysis of flow field around three circular cylinders in side-by-side configuration at various gap ratios and Reynolds number has been carried out. This work is among the first experimental efforts in the low Reynolds number regime. The instantaneous and time averaged flow structures were obtained using the particle image velocimetry technique. The gap ratio utilized for the experiment is from 1.5 ≤ s/D ≤ 4.0 (where s is the distance between the cylinders and D is the diameter of the cylinder). The Reynolds number is in the range of 90 ≤ Re ≤ 560. Five different types of flow regimes were observed: three biased flow regimes namely, asymmetric biased flow, bi-stable biased flow and equal biased flow at lower gap ratios (s/D < 3); two unbiased flow regimes namely, equal unbiased flow and synchronous equal flow as the gap ratio increases. The biased flow regimes are produced because of the shear layer interaction. The flow regime characteristics are shown in the downstream distance of 1.5D–6D. When the gap ratios are small, the interaction of the inner shear layers formed between the cylinders are more compared to the interaction between the shear layers formed around a cylinder. The drag coefficient variation shows that the value of drag coefficient is comparatively higher for asymmetric biased flows. It is found that the variation in both Reynolds number and gap ratio affects the formation of flow regimes as well as variation in drag coefficient in the Reynolds number regime 90 < Re < 600.