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30 November 2008

Science Of Speed: Building The Fastest Car In The World

Science Of Speed: Building The Fastest Car In The World

ScienceDaily (Oct. 24, 2008) — World class UK research is helping to build the fastest car in the world thanks to the Engineering and Physical Sciences Research Council (EPSRC).

Computer-generated image of the BLOODHOUND SSC (super sonic car). If the vehicle achieves its target of 1,000mph (Mach 1.4), it will mark the greatest incremental increase in the history of the World Land Speed Record. (Credit: BLOODHOUND SSC image by CURVENTA)

The BLOODHOUND SSC Project, led by Richard Noble OBE, is aiming to set a new world land speed record of a thousand miles per hour by 2011.

The challenge at the heart of the project is to create a car capable of 1,000mph – a car 30% faster than any car that has gone before.

An aerodynamics team at Swansea University – funded by EPSRC – is playing a vital role. Using Computational Fluid Dynamics (CFD), the team has spent the last year creating the predictive airflow data that has shaped the car.

In time, the research could lead to better vehicle or aircraft design, improved fuel efficiencies, and even new medical techniques.

"From the nose to the tail, anything that has any kind of aerodynamic influence we are modelling," says researcher Dr. Ben Evans – who as a school boy watched the Thrust SSC record on TV.

"It's the kind of thing aerospace engineers would have traditionally done in a wind tunnel, but we're doing it on a computer, a big multi-processor super computer. Wind tunnels have massive limitations. BLOODHOUND SSC is a car, so it's rolling on the ground and there are no wind tunnels in existence where you can simulate a rolling ground with a car travelling faster than mach one, faster than the speed of sound."

This 'mach factor' is the major difference between this vehicle and its predecessor Thrust SSC. Thrust SSC was a supersonic car in that it crossed the sound barrier and was supersonic for a matter of seconds.

But with BLOODHOUND, the target speed is 1,000mph - mach 1.4. It will be going supersonic way beyond mach one, and for a much longer time period, which means the supersonic shockwaves it creates will be far stronger than Thrust SSC, and they will interact with the car and the desert floor for much longer.

"Once you start approaching, and go beyond the speed of sound, you can no longer send a pressure wave forward to tell the air ahead of you you're coming," explains Evans. "What happens is a big pressure wall builds up in front of you. Rather than air slowly and smoothly getting out of the way, at supersonic speeds these changes happen very suddenly in a shockwave."

Supersonic aircraft create these shockwaves and they dissipate in the surrounding atmosphere but still reach the ground as a 'sonic boom'.

Evans adds: "What we're trying to understand is what happens when this shockwave interacts with a solid surface which is a matter of centimetres away."

What the team do know is this 'interaction' creates a phenomenon known as 'spray drag' – a term first coined by BLOODHOUND team member and aerodynamicist Ron Ayers during the Thrust SSC attempts.

Spray drag is an additional drag component not accounted for in aerodynamic or rolling resistance theory.

"As the car interacts with the desert, and the shockwaves interact with the desert, they actually eat up the desert floor," says Evans.

"That introduces sand particles into the aerodynamic flow around the car and this interaction is not accounted for in standard CFD work. We plan to look at this spray drag phenomena, what happens and when, and how the sand particles impinge on the car."

The Swansea team are also looking at key systems in isolation. Work has already changed the car from twin to single air intake for stability.

The car will also sport solid titanium wheels with twin 'keels': "That was fundamentally an aerodynamic design decision," says Evans. "We studied different design options, a single keel running down the centre of the wheel, a design that had three keels and finally the one we went for with two keels. It was chosen as a compromise between lift and drag patterns and minimising the pressure disturbance around the wheel on the desert surface.

"Another thing we have been looking at closely is the exact nose shape. We want a nose that constantly generates a small down force on the front to help keep the car on the ground. But we're also constantly looking a how we can minimise spray drag and if we can constantly achieve a positive pressure on the desert surface leading up to the front wheels then hopefully the surface will remain intact until the front wheels roll over it."

But Evans and the team also remain focussed on the wider aims of the project and the application of their research in other areas.

"The whole point of doing this is not just to create a fast car. We live in a carbon economy and lots of the issues we face will require engineers and scientists to solve them – part of this project is to inspire young people."

And sat at his desk in Swansea he has a constant reminder of the potential of CFD.

"Some of my university colleagues are working on blood flow monitoring through the arterial system and trying to predict when aneurysms will explode through pressure loadings.

"On one side of the office we have pictures of Bloodhound and on the other we have pictures of blood flow through the heart.

"There are the obvious applications in aerospace, but any application you can think of that involves fluid flow can be modelled using CFD. Biomechanical systems seems to be one of the areas CFD is being applied to now."

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