At Swansea University an aerodynamics team is using Computational Fluid Dynamics (CFD), to create and predict the airflow data that will and has shaped the car features.

"From the nose to the tail, anything that has any kind of aerodynamic influence we are modeling," says researcher Dr. Ben Evans. "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."

The predecessor of the BLOODHOUND SSC, “Thrust SSC” was a car capable of supersonic velocity as it crossed the sound barrier and was supersonic for a short time (seconds).

The difference between BLOODHOUND SSC and Thrust SSC is that the target velocity is 1,000mph or mach 1.4. The car will be traveling supersonic which is faster than mach one, for a longer duration. This velocity will generate supersonic shockwaves that will be far greater than Thrust SSC, and these forces will interact with the car and the desert floor track.

"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 shockwaves and are most identifiable when they reach the ground as a 'sonic boom'.

Evans points out that: "What we're trying to understand is what happens when this shockwave interacts with a solid surface which is a matter of centimeters away."
What the team has determined is that 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 another fluid drag component not accounted for in classic aerodynamic theory as applied to rolling vehicles or cars. "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 development team is looking at key engineered systems individually. Research and development has already changed the car engine configuration from twin to single air intake for enhance stability. Other improvements are that the car will utilize exotic materials, such as 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 minimizing 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 minimize 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."

Adapted from materials provided by National Physical Laboratory.