Probing the shape of inertial subrange eddies in boundary layer turbulence*

The inertial subrange of turbulent scales – whose signature is a power law in scale-dependent statistics – is widely studied in both theory and experiments. Yet the shape of these motions in physical space is often described in vague, ill-defined terms such as eddies or blobs. This presentation builds upon previous studies on the topic of fractal geometries to provide a more detailed picture of the instantaneous flow features that underpin the inertial subrange power law signature. Wind tunnel boundary layer measurements are used to assess the geometric properties of streamwise velocity isosurfaces. The size of "wrinkles" along each isosurface is statistically self-similar only within the inertial subrange. Simplified velocity signals are used to demonstrate that these wrinkles yield power laws in one-dimensional (point) statistics including the longitudinal structure function. The findings suggest that the presence of inertial subrange turbulent motions is reflected by the self-similar wrinkles of isosurfaces that are persistent throughout the flow field.