Decay of Turbulence in Axisymmetric Wakes

Abstract

Turbulent wakes formed downstream of flat, circular disks were surveyed with hot-wire anemometers in a low-speed wind tunnel. Three regions were discernible in the wake. Between the disk and x = 50 disk diameters D downstream, the turbulence was highly anisotropic and new turbulence was generated locally. An approximate similarity region (100 ≲ x/D ≲ 400) existed where isotropic turbulence relations were adequate for estimating decay. The far downstream wake (x/D ≳ 400) was highly intermittent throughout; the decay rate lessened in this final period. Over a 4-fold range of disk size and a 7 1/2-fold range of mean flow velocity, Taylor’s microscale was correlated by the mean residence time x/U∞; this relation was independent of disk size.