Two- and three-dimensional wake transitions of a circular cylinder with a rear-attached splitter plate
Hongyi Jiang
Abstract
This study investigates the strong influence of a splitter plate on two- and three-dimensional wake transitions of a circular cylinder. Direct numerical simulations and Floquet analyses are conducted over a parameter space including Reynolds numbers ( Re ) of 10–480 and non-dimensional plate lengths ( L / D ) of 0–6. With the increase in L / D , the critical Re for the onset of vortex shedding ( Re cr 2D ) increases monotonically. The delayed onset of vortex shedding with elongation of the body is physically explained. The critical Re for the onset of three-dimensionality ( Re cr 3D ) and the three-dimensional wake instability modes and structures are also significantly altered by the splitter plate. Compared with an isolated cylinder, the Re cr 3D for L / D = 1 is significantly reduced via a long wavelength mode, whereas the Re cr 3D for L / D = 2–6 is significantly increased via other modes. For each L / D , with increasing Re over the wake transition process, the spanwise wavelength of the wake structure gradually decreases, and the wake structure becomes increasingly chaotic. The strong influence of the splitter plate on the formation of the primary vortices and three-dimensional wake structures alter the hydrodynamic characteristics strongly. In particular, optimal lift reduction is achieved at L / D ∼ 1. In addition, the existence/absence of a hysteresis effect at the onset of three-dimensionality is identified by three methods. Among which, the method involving the Landau equation may be contaminated by initial transients induced by stable Floquet modes and may thus lead to a false conclusion on the existence/absence of hysteresis.