Effect of shear-layer thickness on the Strouhal–Reynolds number relationship for bluff-body wakes

In a previous paper, we provided a rationale for the empirically observed St–Re number relationship for vortex shedding in bluff-body wakes. This rationale derives from a mechanism of vortex formation observed in numerical simulations coupled with an estimate of the terms in the vorticity transport equation based on this mechanism. Adopting the typical size of the body D   as the characteristic length scale resulted in a rationale which matches the traditional 1/Re1/Re-fit. Here, we propose to adopt the thickness of the separated shear layers as the length scale which governs the diffusion of vorticity during the vortex-formation process instead of D  . Thus, providing a new rationale matching Williamson–Brown's 1/Re-fit, which has one order of magnitude less error than the traditional fits in terms of 1/Re1/Re.