An experimental study of flow past two rotating cylinders

Flow past two uniformly rotating cylinders in a side-by-side configuration is studied experimentally at Reynolds numbers, \textit{Re}, varying from 100 to 500 and the ratio of surface speed of cylinder to the free stream velocity, $\alpha $, varying from 0 to 5. The center-to-center spacing between the cylinders, $T$, normalized by the cylinder diameter, $D$ are 1.8, 2.5, 4.0, and 7.5. Two possibilities of rotations are considered with the cylinder surfaces in between the two cylinders moving upstream in one case (inward rotation case) and downstream in the other (outward rotation case). The diagnostics is done by flow visualization and particle-image-velocimetry. Vortex shedding is found to be suppressed in the inward rotation cases for \textit{Re} = 200 to 500 and all spacing ratios at $\alpha =\alpha _{s}\sim $2.0. The value of $\alpha _{s}$ for \textit{Re} of 100 in this case increases from 1.2 to1.7 as $T/D$ increases from 1.8 to 4.0 and does not increase further with $T/D$. For outward rotation cases, vortex shedding suppression is observed for \textit{Re} of 100 and for all values of $T/D$; however, for higher \textit{Re}, suppression is observed for $T/D$ of 4.0 and 7.5 only. The measurements of $\alpha _{s}$ in this case showed a decreasing trend with increasing $T/D$. Symmetry breaking in the wake is reported for inward rotation case near $\alpha _{s}$ = 1.35 for the case of $T/D$ = 2.5 at \textit{Re} of 200.