On the drag of two-dimensional flow about a circular cylinder

The drag force experienced by a circular cylinder in a two-dimensional (2D) flow is investigated experimentally. Both horizontal and vertical soap film tunnels are used to set up the 2D flow with Reynolds numbers Re ranging from 35 to 560 (based on the diameter of the circular cylinder). Momentum defect measurements are used to obtain the time averaged drag coefficients, via laser Doppler velocimetry. It is found that the drag curve is in good agreement with the 2D computations of Henderson [Phys. Fluids 7, 2102 (1995)]. Two separate three-dimensional instabilities of the natural wake at Re≅180 and 260 are not observed in the present data. Flow visualization of the characteristic wake patterns behind a circular cylinder, as Reynolds number increases, is also presented.