Control of the flow past a circular cylinder using a single tripwire on its surface has been studied experimentally as a function of the wire angular location for different wire-to-cylinder diameter ratios (0.029 ≤ d/D ≤ 0.059) and Reynolds numbers (5,000 ≤ Re_D ≤ 30,000). The use of an endplate with a sharp leading edge on each end of the cylinder yields adequate level of quasi twodimensionality in the near wake.

For each Reynolds number and wire size considered, two types of critical angular locations for the implementation of the large-scale wire on the cylinder surface were shown to exist based on the changes in the flow features in accord with the existing literature. At the first critical wire angle, the vortex shedding ceases for the majority of the time during which the vortex formation length extends, and there exists short time intervals where regular shedding resumes similar to the smooth cylinder. The second critical wire angle is found to encompass a range of angles (50° to 70°) where significant increase in spectral amplitude of Karman frequency is observed together with contraction of the near-wake. The angular location of the first critical wire angle decreases with the wire size, and increases with Reynolds number up to Re_D = 15,000, after which it remains unaffected by the Reynolds number.

Furthermore, the variations of the Strouhal number and the coherency of Karman vortex shedding are found to be, roughly, inversely related with each other. This investigation explains the relationship between different sets of critical wire angles previously defined by other researchers. Finally, a model is established for the estimation of the Strouhal number as a function of the wire angle. This model requires only the wire size (d), cylinder diameter (D), and Reynolds number (Re_D) as inputs, and, therefore, is applicable without any prior knowledge on the flow structures. It yields a low average error (<​6.2%) when compared with the experimental data.