Effect of Pressure and Temperature on Flow near a Cylinder with a Hydrophobic Surface at Large Reynolds Numbers

I have studied the effect of the Reynolds number, static pressure, and flow temperature on vortex structures in the turbulent wake behind a circular Teflon cylinder. Velocity fields have been measured by the PIV method in a water channel at Reynolds numbers from 1.75 × 10⁵ through 2.84 × 10⁵. The drag coefficient of the cylinder, as well as average wake characteristics, has been found to point to an earlier drag crisis, corresponding to rough nonhydrophobic surfaces. Reducing the oncoming flow pressure has been shown to cause an increase in the wake behind the cylinder and drag. In spite of the large wake characteristics, raising the flow temperature leads to a decrease in cylinder drag, which is attributable to the decrease in Reynolds stress on the cylinder surface and, accordingly, in friction drag.