We employ passive flow control using two-dimensional hydrofoils to reduce vortex-induced vibrations (VIV) and drag on a cylinder of circular cross-section. We test the hypothesis that by using foils to bend the streamlines around the cylinder, and hence forcing the flow to approach potential flow-like patterns VIV and drag will be reduced. A systematic parametric search, first using groups of two and then four foils, shows that it is possible to completely eliminate vibrations and reduce the drag coefficient to about Cd=0.50 at sub-critical Reynolds numbers. This parametric search is conducted in conjunction with force measurement and particle image velocimetry on a fixed towed cylinder. The effectiveness of the foils in regards to VIV was further tested with an apparatus allowing free transverse vibrations of a towed cylinder.
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