Experimental and numerical analysis of the bi-stable turbulent wake of a rectangular flat-backed bluff body

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 x 10(4). 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.