Characteristics of the Turbulent/Turbulent Interface Geometry in a Cylinder Wake

The spatial evolution of the geometrical properties of the turbulent/ turbulent interface (TTI) of a cylinder wake is examined in comparison to a turbulent/non-turbulent interface (TNTI). The cylinder is positioned at different downstream distances from a grid. Various grids are employed to generate background turbulence with varying turbulence intensities and integral length scales. A planar laser induced fluorescence experiment was carried out to capture the interface between the wake and the ambient flow, spanning from the near to the relatively far field, at a Reynods number of 3800 based on the inlet velocity and the cylinder diameter. A transition region of the interfaces' spreading towards the ambient flow is identified, beyond which the interfaces propagate at a slower rate than upstream and their mean positions scale with the local wake half-width. It is also found that the locations of both the TNTI and TTI have non-Gaussian probability density functions (PDFs) in the near wake because of the influence of the large-scale coherent motions. The length scale in the background turbulence significantly influences the TTI fractal dimension in the near wake, whilst the turbulence intensity only becomes important for the fractal dimension farther downstream.