Complex flow dynamics for a static triple-box girder under various angles of attack

Due to the existence of the upstream and downstream gap, the flow dynamics around a separated triple-box girder becomes quite complex. This work explores the flow dynamics around a triple-box girder, i.e., multiple separation-reattachment effect, shear layers' impingement-rebound effect, separated- and double-shear-layer instability, etc. Three angles of attack (AOAs), i.e., 0 degrees, +5 degrees, and -5 degrees, were considered for investigating the vortex dynamics of a classical triple-box girder, and the Reynolds number (Re) was set at 1.05 x10(4). The time-averaged and instantaneous flow fields as well as the distribution of the fluctuating magnitude are discussed. The results show that, under 0 degrees AOA, the upstream gap flow (flow in the upstream gap) is characterized by the shear layer impingement while intermittent vortex-shedding appears in the downstream gap. Time-frequency analysis and instantaneous flow fields reveal that the spectral intermittency is caused by oscillations of the lower shear layer. The different flow dynamics are analyzed in detail by the spectral proper orthogonal decomposition analysis. Under +5 degrees AOA, the interactions of the shear layers in both gaps show weak periodicity, and the instability of the separated shear layer dominates the whole flow field. Under -5 degrees AOA, the double-shear-layer instability dominates both gap flows. The periodical shedding vortices are observed simultaneously in both gaps with varied dominant frequencies. The complex impacts of the impingement-rebound effect as well as the essence of the "multi-frequency" phenomenon are also revealed.