Performance of vortex shedding from a circular cylinder with a slit normal to the stream

Flow-field study was conducted concerning vortex shedding from a circular cylinder with a slit normal to the stream. Experiments were carried out in a low-speed wind tunnel and a water channel, respectively, with emphasis on the impact of the slit width on the quality of the vortex shedding signal measured. It is found that among the cases studied, whose slit widths ranging from 0 to 0.3 dd, where dd denotes the diameter of the circular cylinder, an optimal range of slit width, 0.1–0.15 dd, was identified, within which not only the vortex shedding signals show the best quality, but also the relation of the Strouhal numbers against the Reynolds numbers studied appears to be the most linear. By spanwise correlation measurements made in the wind tunnel, it is further found that among the cases of s/d=0s/d=0, 0.05, 0.15, 0.2, and 0.3 studied, the vortex shedding flow structures of s/d=0.15s/d=0.15 appear to be the most two-dimensional. Moreover, it is worthwhile to mention that for the slit circular cylinders, the signal quality of vortex shedding remains well acceptable for the Reynolds number as low as 2.4×103. Thus, the rangeability of flow measurement is increased significantly.

► For s/d=0.1s/d=0.1 to 0.15, the error of linearity in St   is the least.
► The signal quality is greatly improved with a slit in the circular cylinder.
► The two-dimensionality of vortex shedding flow structures is sensitive to s/ds/d.
► The vortex formation length is significantly shorter with a slit circular cylinder.