Numerical study on the flow over two circular disks in tandem arrangement

Abstract

The flows over the two circular disks in tandem arrangement at low Reynolds numbers are numerically studied using large-eddy simulations. Both disks have the same aspect ratio (χ = d/w = 5, where d and w are, respectively, the diameter and the thickness of the disk), while the upstream disk has a coaxial hole in D diameter. First, the effect of the Reynolds number on the near-wake evolution of the tandem disks with spacing of l/d = 0.1 is investigated. Compared with a single circular disk, it is found that the upstream apertured disk (D/d = 0.2) delays the wake transition. Four bifurcations, i.e., “Steady state,” “Zig-zig,” “Zig-Zag,” and “Weakly chaotic” modes, are captured at critical Reynolds numbers of 178, 207, 212, and 275, respectively. Second, the effect of disk spacing on near-wake evolution is studied for Re = 200 and D/d = 0.2. The wake is steady and planar-symmetric at l/d = 1, in which a totally new wake mode characterized by a three-thread wake is observed. The wake becomes unsteady but planar-symmetric at l/d = 1.5. At l/d = 2, however, the planar-symmetric wake structures are all broken. The upstream disk wake retains planar-symmetry, while the downstream disk wake is similar to the “Reflectional-symmetry-broken” mode in a single disk wake. The planar symmetry is recovered for both disks at l/d = 6. It is found that for l/d > 3, the interaction between the two disks becomes weaker as the spacing increases. Finally, the effect of disk spacing on the drag and lift coefficients for each disk is examined. When disk spacing is constant, the lift coefficient of the upstream disk is always lower than that of the downstream disk. The drag coefficient of each disk in tandem is smaller than that of a single disk. With the increase in disk spacing, the drag coefficient of the upstream disk changes little while the drag coefficient of the downstream disk increases rapidly.

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