A numerical study of geometric effects on vortex shedding from elongated bluff bodies

The flows around a series of flat plates with various leading- and trailing-edge shapes and a range of elongation ratios were simulated with a 2-D, high-resolution vortex method. The resultant map depicting the variation of chord-based Strouhal number, Stc, with elongation ratio, c/t, and leading/trailing edge angles reveals that there are upper and lower limits for Stc. The upper limit is characterized by linear variations of Stc with c/t, while the lower limit is characterized by constant Stc until a critical c/t ratio where Stc jumps to a new value. By changing the separation angle of the flow at the leading edge, the transition between these bounds is continuous. However, in contrast to the results for rectangular cylinders, Stc for plates with relatively small leading edge separation angles was observed to increase almost linearly with c/t after a jump, followed by a region where Stc is constant. Based on detailed analyses of the flow characteristics, the underlying mechanics leading to these behaviors were identified. It was found that it is the competition between the leading- and trailing-edge shedding for the control of the overall shedding process that leads to the observed linear and horizontal variations, as well as the abrupt jumps, of Stc.

► Flows around elongated bluff bodies are simulated with a vortex particle method.
► Geometric effects on the variation of chord-based Strouhal numbers are observed.
► The shedding frequency is influenced by both leading- and trailing-edge details.
► The underlying mechanics leading to these geometric effects are identified.