Wake Manipulation Using Control Cylinders in a Tandem Arrangement

The drag reduction phenomenon of a circular cylinder is investigated, using an X-wire probe, by placing a smaller diameter control cylinder of either circular or square cross-sectional upstream of the main circular cylinder. The separation between the two cylinders was chosen so as to minimise the overall drag of the main cylinder. Although both configurations resulted in drag reduction, the square control cylinder yielded a bigger reduction and had a greater impact on the mean velocity and turbulent velocity fluctuations in the wake. Both control cylinders led to a reduction in the wake half-width. Spectra in the near wake did not indicate any suppression in vortex shedding.