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The flow around a seal-vibrissa-shaped cylinder (SVSC) is numerically investigated using the large eddy simulation framework at a Reynolds number of 20 000. Compared with a circular cylinder (CC), the wake of the SVSC presents more stable three-dimensional separation, a longer vortex formation length, and a weaker vortex strength. The mean drag and fluctuation of the lift coefficient are 59.5% and 87.7% lower than those of the CC, respectively. Three-dimensional spectral proper orthogonal decomposition (SPOD) is used to investigate the turbulent flow around these two types of cylinders in terms of the spatial modes, mode energy, mode coefficients, and reconstructed flow by a reduced-order modeling. Four typical vortex shedding patterns are first extracted by SPOD for the SVSC, producing crescent-, twist-, branch-, and knot-shaped vortices. A concept model is proposed for the wake dynamics of the SVSC, allowing the formation and transformation of these modes to be elucidated. Detailed analysis of the impact of the flow pattern on the associated forces indicates that the dominant out-phase vortex shedding at the upper and lower saddle planes makes a significant contribution to the reduction in lift fluctuations. [ABSTRACT FROM AUTHOR]

The wake dynamics of a rectangular flat-backed bluff body is studied using both the wind tunnel experiment and Improved Delayed Detached Eddy Simulation (IDDES) at Re = 9.2 × 104. Both approaches are systematically investigated in order to provide a quantitative comparison. The wake barycenter deficit and base pressure gradient dynamics are first investigated to characterize the wake states. Second, the known global dynamics such as long-term bi-stability, vortex shedding, and wake pumping are analyzed using proper orthogonal decomposition. It is found that the wake dynamics is globally well captured by the IDDES, but with a more intense activity due to the absence of the fore-body separations observed in the experiment. The coupling of these global dynamics is explored by utilizing low-order modeling in cross planes and elaborating the evolution of the three-dimensional (3D) instantaneous wake flow from IDDES. The shedding of a large-scale hairpin vortex from the horizontal shear layer is closely associated with the pumping motion during wake switchings or switching attempts. A concept model is proposed for 3D bi-stable wake topology, which attempts to elucidate both asymmetric and symmetric wake configurations. [ABSTRACT FROM AUTHOR]