Influence of freestream turbulence on the near-field growth of a turbulent cylinder wake: Turbulent entrainment and wake meandering

The influence of freestream turbulence (FT) on near-field development of turbulent wakes is assessed with regards to both the entrainment rate of background fluid into the wake and the extent of wake meandering. It is shown that FT increases the entrainment rate into the near wake, and thereby the rate at which the wake spreads. The influence of FT on wake meandering is more complex, but it is shown that the integral length scale is the dominant property affecting meandering. In a novel control experiment, large-scale coherent motion in the wake is suppressed, and the far-wake results are recovered: that is, turbulent entrainment is reduced via the suppression of small-scale nibbling.