SPHERE WAKES AT MODERATE REYNOLDS-NUMBERS IN A TURBULENT ENVIRONMENT

The structure of sphere wakes in a turbulent environment was measured over the following test range: sphere Reynolds numbers from 135 to 1560, ambient turbulence intensities of roughly 4%, ratios of streamwise spatial integral scales to sphere diameters of 11-59, and ratios of Kolmogorov length scales to sphere diameters of 0.08-0.80. At these conditions, some phenomena observed for sphere wakes at comparable Reynolds numbers in non-turbulent environments were suppressed, like the fast-decaying and self-preserving turbulent wake regions; instead, while the wakes were turbulent, their mean streamwise velocities scaled like self-preserving laminar wakes but with enhanced viscosities due to turbulence. Effective turbulent viscosities were relatively independent of position and ratios of integral length scales and Kolmogorov microscales to sphere diameters; however, they progressively increased with sphere Reynolds numbers. Low and high Reynolds number regimes were observed, separated by a transition regime involving sphere Reynolds numbers in the range from 300 to 600, which was associated with conditions where effects of vortex shedding were prominent in the temporal power spectra measured in the near-wake region.