Abstract
Large eddy simulations (LES) were performed to study the turbulent characteristics in the wake of a circular disk normal to the free air stream (the diameter of the disk is 40 mm, thickness is 8 mm). The Reynolds numbers are 1×104, 1×105and 2.5×105 respectively. It was found that when Re>1×104 , the distributions of mean velocity and Reynolds stress as well as drag coefficient vary little with Re. Drag coefficient is mainly contributed by the pressure difference between the front and rear of the disk. By means of power spectral density analysis, three most influential instability mechanisms are disclosed in the large scale structure of a disk’s near wake: a very low frequency (St≈0.028) corresponding to the recirculation bubble pulsation along an axis of symmetry; a natural frequency (St≈0.138～0.146) related to antisymmetric helical vortex shedding; and a high frequency (St≈1.437) associated with Kelvin-Helmholtz instability of the separated shear layer.
Abstract
Large eddy simulations (LES) were performed to study the turbulent characteristics in the wake of a circular disk normal to the free air stream (the diameter of the disk is 40 mm, thickness is 8 mm). The Reynolds numbers are 1×104, 1×105and 2.5×105 respectively. It was found that when Re>1×104 , the distributions of mean velocity and Reynolds stress as well as drag coefficient vary little with Re. Drag coefficient is mainly contributed by the pressure difference between the front and rear of the disk. By means of power spectral density analysis, three most influential instability mechanisms are disclosed in the large scale structure of a disk’s near wake: a very low frequency (St≈0.028) corresponding to the recirculation bubble pulsation along an axis of symmetry; a natural frequency (St≈0.138～0.146) related to antisymmetric helical vortex shedding; and a high frequency (St≈1.437) associated with Kelvin-Helmholtz instability of the separated shear layer.
Open Access
JUSTC
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