Discrete Vortex Simulation of Pulsating Flow Behind a Normal Plate

A numerical study is made of the separated flow behind a flat plate. The plate is placed normal to the direction of the approach flow. The oncoming freestream velocity contains a pulsating part, U_∞ = U₀(1 + A₀cosf_pt). The temporal behavior of vortex shedding patterns is scrutinized over broad ranges of the two externally specified parameters, i.e., the pulsation amplitude (A₀≤ 0.6), and the dimensionless pulsation frequency, (f_p≤0.32). A version of the discrete vortex method is utilized. The variable-position nascent vortex technique is applied, and it proves to be adequate for pulsating approach flows. The numerical results clearly capture the existence of lock-on when f_p exceeds a threshold value. The modulation of vorticity shedding is also detected when f_p is reasonably low. The influence of A₀ on the flow characteristics is examined in detail. As A₀ increases to a moderate value (e.g., A₀≤0.6), an appreciable broadening is seen of the range of f_p for which lock-on occurs. Based on the numerical results, three characteristic flow modes in the wakes are identified. These findings are qualitatively consistent with the existing flow-visualization studies for a cylinder.