Phase lag between vortex shedding from two tandem bluff bodies

This paper presents a work on the phase lag (φ) between vortex sheddings from two tandem cylinders of various shapes and its influence on fluctuating lift on the upstream cylinder. A differential equation of φ, dφ=[4πf_s/(2V_c-dV_c)] dx, is derived, where f_s is the vortex shedding frequency, V_c is the convective velocity of vortices, and x is the downstream distance from the upstream cylinder. Applying the condition φ=2π at L^* = L_c^*, as obtained from experimental data, the equation yields φ=2.44π St(L^* - L_c^*)+2π, where St is the Strouhal number, L^* is the normalized cylinder center-to-center spacing and L_c^* is the critical spacing defined as the minimum L^* at which the upstream cylinder could shed vortices in the gap between the cylinders. This relationship agrees well with experimental data previously reported as well as presently measured.