Phase transition between pure modes A and B in a circular cylinder’s wake. Part I: analysis of fluid forces

Through direct numerical simulations, the transition from pure mode A to mode B in the near wake of a circular cylinder is studied with no effect of vortex dislocations. The Reynolds number is computed from 100 to 330 with the computational spanwise length of 4 diameters. In the present part, fluid forces are analyzed. The results show that mode swapping still exists in the range of Reynolds numbers from 230 to 240. In this range, fluid forces with low and high levels occur intermittently. Moreover, when the critical Reynolds number of 193 ( ± 0.5) is exceeded, with the increase of the Reynolds number, the vortex-shedding frequency gradually shifts from a single low frequency, high and low frequency coexistence to a single high frequency.