Terascale Direct Numerical Simulations of Turbulence Generated by Fractal Grids

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Turbulence is of enormous importance in the enviroment, meteorologyand oceanography and also in many industries where fluid flow isinvolved such as in the chemical, mixing, car, aerospace and navalindustries. Just as an example, the cost of pumping oil throughpipelines is directly proportional to the frictional losses whichturbulence causes. As another example, worldwide ocean shippingconsumes about 2.1 billion barrels of oil per year. Understandingturbulence can lead to flow control schemes for reducing skin frictiondrag. At 75 US dollars per barrel (nowadays a very conservativeestimate), 10% such reduction would save 15 billion US dollars peryear, not to mention the consequent impressive reductions ofpollutants in ship emissions. Similar projections can be made forairline industries which consume about 2 billion barrels of jet fuelper year.Over the past 60 years or so the efforts in turbulence have beenmostly in ad hoc modelling of specific flows and the progress has beenlimited. An understanding of turbulence dynamics is needed, and forthis a particular experiment is needed where these turbulence dynamicscan be set out of joint so as to give us clues for understanding them.This is what has been achieved recently at Imperial College Londonwhere the first ever experiments of turbulence generated by fractalgrids in wind tunnels have been conducted with impressive results. Itis now necessary to develop computer simulations of these flows. Theseare very large simulations, in prticular because of the multiscalenature of the fractal turbulence generators, and require state-of-theart top-end parralel computing. The challenge is computational.Meeting this challenge presents us with an unprecedented opportunityto understand turbulence and how to manipulate it.