An experimental study of the flow around a cylinder with rms a single straight perturbation was conducted in a wind tunnel. With this bluff body, positioned in a uniform crossfiow, the vortex shed-S ding frequency and other flow characteristics could be manipulated, Smax The Strouhal number has been shown to be a function of the perturbation angular position, 0p, as well as the perturbation size Smi, t and Reynolds number. As much as a 50% change in Strouhal Uc number could be achieved, simply by changing 0p by 1 ~ The perturbation size compared to the local boundary layer thickness, 6, Umax was varied from approximately 1 6 to about 206. The Reynolds U~ number was varied from 10,000 to 40,000. For perturbation sizes U~c approximately 5 6 to 20 fi and Reynolds numbers of 20,000 to 40,000, x a consistent Strouhai number variation with 0 r was observed.A detailed investigation of the characteristic Strouhal number z variation has shown that varying 0p had a significant influence on the boundary layer separation and transition to turbulence. These Ax significant changes occurring in the boundary layer have been A~ shown to cause variations in the spacing between the shear layers, base pressure, drag, lift, and the longitudinal spacing between the vortices in the vortex street.

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Abstract. The development of a steady lift force on a stranded cable, which is yawed with respect to a flow, is a unique characteristic of a cable when compared to a circular cylinder. Comparisons of lift and normal drag coefficients and wake characteristics were made between stranded cable models and the cylinder. These were based upon surface pressure and hot-wire measurements and flow visualization studies conducted in a low speed wind tunnel on rigid cables and cylinders. The models were yawed to four different yaw angles and tested within the Reynolds number range of 5,000 and 50,000. Pressure profiles for the yawed cables indicated that the lift force is directed towards the side where the primary strands are more nearly aligned with the flow. The pressure profiles also indicated that the lift force is generated by asymmetric separation. The small scale irregularities associated with wires within individual strands also appeared to have an effect on the cable's lift and drag characteristics. Results show that cables have significantly different shedding characteristics and near-wake shear layer structure when compared to the circular cylinder. For the flow regime tested, the Strouhal number showed no dependence on Reynolds number nor spanwise position along the cable. List of symbols

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