Investigation of the Asymmetric Wake Mode of a Three-Dimensional Square-Back Bluff Body

This paper reports a detailed investigation of the asymmetric wake mode behind a three-dimensional square-back bluff body using both experimental measurement and numerical simulation at ReH = U0H/v = 9.2 × 104 (where U0 is free-stream velocity, H is the height of body and v viscosity). The analyses of the instantaneous back pressure, velocity field as well as the side aerodynamic force suggest that the near-wake is dominated by a random displacement of the wake between two preferred reflectional-symmetry-breaking (RSB) locations. Utilizing the proper orthogonal decomposition (POD), three dynamic modes of unsteady wake are identified: the bi-stable behavior or RSB characterized by a long time-scale, the global oscillation leading to vortex shedding at StH = 0.154 and the periodic pumping at StH = 0.07. The reconstruction of the velocity field is analyzed, revealing a mutual connection between different coherent structures.