CFD analysis of flow-induced rotation of a circular cylinder with a detached rear splitter plate in laminar flow

Abstract

This paper numerically investigated the flow-induced rotation response of an elastically mounted circular cylinder fitted with a detached rear splitter plate in laminar flow. With the help of ANSYS-FLUENT, the fluid governing equations were solved with the finite volume method, and the fluid-structure interaction was achieved with user-defined functions. Three different gap ratios of G* = 0, 0.25, and 0.5 were examined in the computations that carried out for a reduced velocity range of Ur = 3–18. For the typical case of G* = 0.25, a symmetry-breaking bifurcation, i.e., the structure's equilibrium position deflects to a position which is not parallel to the free stream, occurs at Ur > 15. Before bifurcation, there is only one stable flapping motion. However, two extra rotary processes are observed when bifurcation appears, including a negatively-directional deflection and the 2nd flapping motion. For G* = 0, the bifurcation is found at Ur > 12, while it is absent for G* = 0.5. The varying tendencies of the root-mean-squared rotary angle for all considered cases show a VIV rotary response. The smaller gap distance leads to the larger rotary angles at Ur ≤ 12, while the opposite tendency is observed at Ur > 12. The hydrodynamic coefficients of the rotary cylinder-plate body are significantly reduced, as compared with a bare cylinder. The drag- and lift-reduction are mainly due to the recovery of base pressure behind the cylinder and the delayed vortex formation. The global vortex shedding is identified to be 2S mode for both cases with and without bifurcation, although the vortex formation and the shedding pattern in the near wake vary with gap distance and reduced velocity. Due to the deflection, reattachment behavior is more likely to appear and its position shifts from the plate surface or tail to the leading edge of the splitter plate with increasing gap ratio.