The effects of shear and roughness on vortex shedding patterns behind a circular cylinder at critical Reynolds numbers

Wind tunnel tests were conducted in an effort to understand the vortex shedding patterns to be experienced by the OTEC cold water pipe. Test procedures are described for obtaining the velocity and distribution profiles, the surface pressure measurements, and the eddy characteristics. Results discussed include the surface pressure distribution for both uniform and sheared flow cases, the vortex shedding pattern for smooth and rough cylinders in sheared and uniform flow, and the effect of shear on cell length. A rather wide range of values of supercritical Strouhal numbers was observed. Newly documented phenomena associated with shear flow vortex shedding are: (1) any linear shear, however slight, in the upstream velocity profile, triggers a cellular vortex shedding pattern; (2) at a given supercritical Reynolds number, the range in shedding frequencies is greater on a smooth cylinder than on a rough cylinder; (3) the average cell length for a rough cylinder is greater than for a smooth cylinder in tests for which endplates effects are not predominant; (4) a general trend toward decreasing cell length with increasing shear.