Multiscale-generated Turbulent Flows

Purpose and focus of SIG

After more than a century of exhaustive research on the aerodynamics and hydrodynamics of geometrically simple shapes, whether streamlined as in wings or bluff as in spheres and cylinders, it is blindingly natural to expect much of the future in fluid mechanics to lie in
the aerodynamics and hydrodynamics of geometrically complex, and thereby multiscale, shapes. There has of course been work over the past decades on how to model and simulate complex turbulent flows, but the emphasis here is on working out the rules for the design of multiscale objects so as to obtain desired flow effects beneficial
for particular applications.

The simplest cases of multiscale shapes are fractal shapes, which is why they have been a good start in this new research area. These are multiscale shapes with a complex appearance which can nevertheless be defined with only a small number of scaling parameters. However, the even simpler cases of interactions between pairs of flows (e.g. two wakes, two jets etc) is also part of this SIG and a foundation for more complex flows.

This is where well established research work starting in the 1970s on the importance and imprint of initial/boundary conditions on turbulent flows fits in and gives meaning to the endeavour. If turbulent flows keep a degree of memory of the conditions which generate them (through the existence of coherent structures, for examples, whether large or small) then the possibility exists of designing bespoke turbulent flows tailor-made for particular applications. This can be far better than turbulent flow control if it can be achieved.

Multiscale/fractal generation/design is about using multiscale/fractal objects (such as grids, fences, profilers etc) to shape the nature of the resulting turbulent flow over a broad range of scales for a broad range of applications. Examples of applications already pursued include fractal mixers, fractal combustors, fractal spoilers and fractal wind breakers/fences.