Characteristics of distinct flow regimes in the wake of an infinite span normal thin flat plate

Abstract

The wake of an infinite, two-dimensional (2D), thin flat plate of height h was studied using Direct Numerical Simulation (DNS) for two Reynolds numbers, Re=1.2×103 and 2.4 × 103. The vortex shedding Strouhal number was 0.158. In addition to the high - and low - intensity shedding regimes (H and L) first reported by Najjar and Balachandar (1998), a distinct period of reorganization (M) is identified following regime H. The average flow characteristics for regime M are similar to those of the long-term mean flow. The regime-averaged recirculation length at Re=1.2×103 was 2.16h during H, 3.60h during L and 2.81h during M. Whereas the spanwise vortex rollers are well-organized during both regimes H and M, the arrangement of the streamwise ribs is much more regular and can be observed further downstream in regime H than M. The flow is highly three-dimensional during regime L, which includes less-coherent vortex rollers and spanwise randomly distributed ribs. The impact of this behavior on the roll-up, and thus the extension of the shear layer, is identified as a driving mechanism for generation and sustainability of the periodic wake behavior.