Discrete Vortex Simulation of Pulsating Flow Behind a Normal Plate

Abstract

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 + A0 cosfp t). 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, (fp ≤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 fp exceeds a threshold value. The modulation of vorticity shedding is also detected when fp 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 fp 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.