Fractal-generated turbulence and mixing: flow physics and some industrial implications

Lead Research Organisation: Imperial College London
Department Name: Dept of Aeronautics


New industrial flow solutions based on new flow concepts are urgentlyneeded to meet the unprecedented requirements set by the dramaticallyevolving energy, environmental and climatic constraints. What isneeded is not just improvements to existing solutions, but radical newdevelopments that can dramatically increase energy savings and reduceadverse environmental impacts. The development of new flow concepts onwhich such solutions will eventually be based requires unprecedentedfully resolved simulations and laboratory experiments because existingturbulence models cannot be applied indiscriminately on radically newflow concepts.One very recent example of a new flow concept originating from the UKis turbulent flows generated by fractal grids (figure 1). As attestedby recent patent applications by Imperial Innovations,proof-of-concept studies at Imperial and reports in various popularscience and engineering periodicals (Food Manufacture, June 2008; TheChemical Engineer, July 2008; Process Engineering, 18 July 2008;Speciality Chemicals, September 2008; Scientific Computing World,August 2008; see this classof new flow concepts offers alternative solutions for industrialmixers, silent airbrakes and spoilers, natural ventilation, sun-roofsand combustion. In this proposal, we focus on new industrial staticinline mixers.These new flow concepts also pose unexpected challenges to turbulenceresearch and modelling. Over the past 60 years, efforts in turbulencehave been mostly in ad-hoc modelling of specific turbulent flows andthe progress has been limited. A fundamental understanding ofturbulence dynamics is needed if we want the development of an entireraft of new flow concepts to become a realistic possibility. For this,a well-designed and well-targeted experiment is required where theseturbulence dynamics can be set out of joint so as to give us clues forhow to understand and, if possible, control them. This is the otherfocus of this research proposal and it directly relates to the firstbecause both relate to the same new flow concept: turbulence generatedby fractal grids.

Planned Impact

As the two industrial letters of support attest to, there is an industrial view that fractal grids are very promising stirrers or mixing elements for various mixing applications. They generate turbulence which can be decoupled from the pressure drop across them and a range of turbulence scales which is also decoupled from the mean flow rate. These are unique properties with much potential for efficient mixing with and without chemical reactions. In fact, the potential applications go beyond the mixing industry and also include novel ventilation devices, airbrakes, combustors, etc. Hence, the potential beneficiaries are not only the mixing industry but also other industries. The PI will be in constant touch with Imperial Innovations for the purpose of involving other industries when the opportunities arise with clear applications. Fractal-generated turbulence, fractal mixing and fractal flow management offer a platofrm technology from which many applications may result. The industrial partners, ARi, Sasol and Sulzer will benefit from direct contact with developments. In particular, the research will aim at improved, perhaps even fully optimised, designs of fractal mixing elements which will directly benefit the industrial partners and the mixing indusry as a whole. The benefits of the research will be provided in international conferences, regular meetings and contacts with the industrial partners and perhaps also other industrial partners that Imperial Innovations might find on the basis of the two fractal-grid patents. The conference to be organised by the PI and the co-I with support from Imperial Innovations and the Institute for Mathematical Sciences at the end of the project will bring together industrial and academic delegates and benefits can be expected to result from these interactions. The Turbulence Research Programme at the Insittute for Mathematical Sciences will offer a very supportive context for this research with various courses, seminars, workhsops, national and foreign academic and industrial visitors as well as other PhD students and PDRAs, not to mention the potential for cross-ferilisation with the other research programmes in the same building. All this will greatly benefit the educational side of the project on all fronts: the PhD student, the PDRA as well as the industrial partners. In particular, the PhD student, the PDRA, the PI and the co-PI will also learn from industry their needs, constraints and existing solutions.


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Gomes-Fernandes R (2014) Evolution of the velocity-gradient tensor in a spatially developing turbulent flow in Journal of Fluid Mechanics

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Gomes-Fernandes R (2015) The energy cascade in near-field non-homogeneous non-isotropic turbulence in Journal of Fluid Mechanics

Description 1. Highly efficient mixing configurations involving fractal grids

2. Interscale energy balances in the very near field of a turbulent flow, where near field point at the proximity to the generator of the turbulent flow, in
this case a fractal grid. There is very little known that may be general concerning the way kinetic energy in the turbulence can be transfered from one
scale to another in the very near field of the flow which depends so much on its generator. This research has revealed the presence of an important
and simple interscale energy balance in the very near field in spite of the proximity.
Exploitation Route New ways to mix fluids
Sectors Aerospace, Defence and Marine,Agriculture, Food and Drink,Chemicals,Construction,Energy,Environment,Pharmaceuticals and Medical Biotechnology,Transport