Flow past two rotating cylinders

Abstract

Flow past two uniformly rotating cylinders with the same rotation rates in a side-by-side configuration is studied experimentally. The experiments are carried out at Reynolds numbers, Re, of 100, 200, 300, 400, and 500 and nondimensional rotation rates, α, varying from 0 to 5. The spacing ratios, T/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 using hydrogen bubble technique and quantitative measurements using particle image velocimetry (PIV). We present, using extensive flow visualization, the global view of the wake structure at Re of 200 for various rotation rates, and two senses. Vortex shedding suppression is studied through flow visualization and/or PIV at various Re’s, T/D’s, and two senses. Vortex shedding is found to be suppressed in the inward rotation cases at all Re and T/D’s. The value of α corresponding to vortex shedding suppression, αs, in the inward rotation case is ∼2.0 for Re of 200–500 at all T/D’s. The value of αs for Re of 100 in the case of inward rotation shows an increasing trend with T/D from T/D=1.8 to 4.0 with αs changing from 1.2 to 1.7; further increase of T/D does not change αs. For outward rotation cases, vortex shedding suppression is clearly observed for Re of 100 and for all values of T/D; however, for higher Re, vortex shedding suppression is observed for T/D of 4.0 and 7.5 only. The measurements of αs in this case showed a decreasing trend with increasing T/D. Symmetry breaking is reported for inward rotation case near α=1.35 for T/D=2.5 at Re of 200 where the wake pattern changes from in-phase to antiphase mode.