Turbulent entrainment into a cylinder wake from a turbulent background

The effect of free-stream turbulence (FST) on entrainment into a cylinder wake is investigated through simultaneous particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) experiments. Previous studies have indicated the individual importance of the turbulence intensity, length scale and dissipation rate on turbulent/turbulent entrainment (TTE), however a complete study considering all three parameters is lacking. Space filling fractal grids are used to generate FST and allow us to conduct a parametric study by independently varying all three parameters, whilst commenting on the influence of each. The wake behavior in both the near and far field is measured. It is found that the incoming FST inherently affects the shedding mechanism of the cylinder. There is an observed difference in the shedding Strouhal number when FST is introduced, with a marked increase in the vortex formation length. FST is also seen to promote increased spreading of the wake by encouraging vortex centers to drift further away from the centerline. Furthermore, phase hiccups in the vortex shedding, which are intermittent events that lead to a complete loss of wake structure, come into existence when FST is introduced.