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MASSIVE Research Stories: Turbulence

Engineers are closer to understanding, and therefore manipulating, invisible aerodynamic drag forces, that cause an estimated 50 per cent of transportation fuel to be lost before we can use it.

Professor Julio Soria, Director of Monash University's Laboratory for Turbulence Research in Aerospace and Combustion (LTRAC), said the technology to visualise these forces, which by causing drag or wind resistance, waste energy, was now available. Understanding how these forces operate and controlling them could lead to significant financial and environmental savings.

Turbulence-subset2

The velocity field of the turbulent boundary area. The turbulent flow exhibits a variety of arch- and cane-like vortex structuresthat evolve in time and space. The color represents the distance of these structures away from the wall.

 

"We are trying to understand the turbulent boundary layer - the region right next to objects' surfaces that causes drag on aeroplanes, ships, trains, trucks - all vehicles, as well as the resistance to flow of water, oil and gas in pipes" Professor Soria said.

The LTRAC team is working on ways to manipulate this layer to control and reduce drag and increase aerodynamic efficiency.

"Based on Airbus estimates, even a 10% reduction of this drag would result in a fuel savings of about 100,000 Euros per aircraft per year, or 1 billion Euro savings over the world every year (the fuel bill of world air transport was 114 billion $ in 2009, corresponding to about 25% of the operational cost)," Professor Soria said.

"This isn't achieved by making the plane lighter - that won't reduce drag orfuel costs at all. A manipulation of the turbulent boundary layer is required to reduce aerodynamic drag."

The mechanics of turbulence of the boundary layer have remained a mystery because the structure of the boundary layer  change dramatically and unpredictably depending on the size of the object, its orientation  and its speed. As it is almost impossible to effectively measure and analyse the conditions on a large object like the wing of an aircraft in motion, Engineers have made use of computations to numerically simulate what they cannot measure.

Despite the challenges, Professor Soria and his team are making progress in understanding turbulence by taking advantage of the cutting-edge measuring and processing technology available at two facilities in Australia. The Multi-modal Australian Sciences Imaging and Visualisation Environment (MASSIVE) at Monash University and the National Computational Infrastructure (NCI) in Canberra, which allow the team to quickly process and visualise the flow data they collect, and run large numerical simulations.

The LTRAC team is also using the facilities to investigate ways to better combine data from experiments with numerical simulations for more accurate predictions.

MASSIVE is a supercomputer-powered facility that allows close to real-time visualisation of high-resolution 2D, 3D and time-resolved 3D data. 

Professor Soria said having access to NCI and MASSIVE allowed the team to study turbulent boundary layer air flows in great detail.

"We couldn't do these very large computations and visualisations without MASSIVE. To load and visualise this much data you need a supercomputer," Professor Soria said.

The facilities are revealing more details than ever about complex three-dimensional structure of  the turbulent boundary layer.

"Now we have better technology, we're seeing phenomena that we couldn't see before, and so didn't account for. The more research we do, the more we realise how little we understand. As we delve deeper into the structure of the turbulent boundary layer, we find effects that we didn’t even consider."

The team is making progress. Professor Soria said the turbulent  flows the team is visualising are unpredictable, but not random. They can see patterns and can observe the lifespan of clearly identifiable coherent structures in what seems to the naked eye to be a random flow.

"We need to understand what generates them, how they are born, how they live and transport energy and how they die due to the dissipation of energy," Professor Soria said.

"Once we understand this, we can design surface control strategies that manipulate the turbulent boundary layer to minimise drag which will result in more efficient aircraft, more efficient trains and ships, and less energy losses in the transport of water, oil and gas in pipes. This will also reduce the amount CO2 we produce, and the pain in our hip pockets."