Large-eddy simulations of flow normal to a circular disk at Re=1.5×105

Numerical simulations of the flow normal to a circular disk have been carried out using the large-eddy simulation (LES) method with Smagorinsky subgrid scale model. The Reynolds number (Re) based on the free stream velocity and the diameter of the disk is 1.5 × 105. The thickness to diameter ratio of the disk is 0.02. The instantaneous vortical structures in wake of the disk are revealed. Toroidal vortices are formed along the disk edges due to Kelvin-Helmholtz instability. The toroidal vortices break up as the flow goes downstream and then hairpin-like vortices are formed. Worm-like vortices parallel to the axis of the disk are observed in the center region of the medium wake. Two distinct vortex spreading modes in the far wake are observed: one has a main shedding plane; the other has not. Three dominant frequencies at the Strouhal number St1=0.01,Stn=0.148 (corresponding to the natural frequency) and St3 ≈ 0.8-1.35, characterizing that the wake instability mechanisms are found through frequency analysis. The time and azimuth averaged statistics, e.g., streamlines, pressure, vorticity and profiles of velocity and kinetic energy, are also presented and discussed.