Article contents
Two tandem cylinders of different diameters in cross-flow: effect of an upstream cylinder on wake dynamics
Published online by Cambridge University Press: 11 December 2017
Abstract
This work aims to provide a systematic experimental study on the wake of two tandem cylinders of unequal diameters. The fluid dynamics around a circular cylinder of diameter $D$ placed in the wake of another circular cylinder with a smaller diameter of
$d$ is investigated, including the time-mean drag coefficient (
$C_{D}$), the fluctuating drag and lift coefficients (
$C_{D}^{\prime }$ and
$C_{L}^{\prime }$), the Strouhal number (
$St$) and the flow structures. The Reynolds number based on
$D$ is kept constant at
$4.27\times 10^{4}$. The ratios
$d/D$ and
$L/d$ vary from 0.2 to 1.0 and 1.0 to 8.0 respectively, where
$L$ is the distance from the upstream cylinder centre to the forward stagnation point of the downstream cylinder. The ratios
$d/D$ and
$L/d$ are found, based on extensive hotwire, particle imaging velocimetry, pressure and flow visualization measurements, to have a marked influence on the wake dynamics behind the cylinders. As such, the flow is classified into the reattachment and co-shedding flow regimes, the latter being further subdivided into the lock-in, subharmonic lock-in and no lock-in regions. It is found that the critical spacing that divides the two regimes is dictated by the upstream-cylinder vortex formation length and becomes larger for smaller
$d/D$. The characteristic flow properties are documented in each regime and subdivided region, including the flow structure,
$St$, wake width, vortex formation length and the lateral width between the two gap shear layers. The variations in
$C_{D}$,
$C_{D}^{\prime }$,
$C_{L}^{\prime }$ and the pressure distribution around the downstream cylinder are connected to the flow physics.
JFM classification
- Type
- JFM Papers
- Information
- Copyright
- © 2017 Cambridge University Press
References
- 83
- Cited by