Computational Fluid Dynamics for BLOODHOUND SSC - Swansea ...

Computational Fluid Dynamics for BLOODHOUND SSC
By the College of Engineering at Swansea University
1,000mph
BLOODHOUND SSC is a car that hopes to reach
1,000 mph (Mach 1.3 or 1.3 times the speed of
sound) and set a new World Land Speed Record.
18 Dec 1898
July 21 1904
Apr 27 1926 Mar 19 1927 Sep 3 1935
Sept 5 1963 Nov 15 1965 Oct 23 1970 Oct 4 1983 Oct 15 1997
39.24 mph
The first official land speed record
was set by Chasseloup-Laubat of
France driving Jentaud Duc. It was
an electric powered car and the
record was set in Yvelines, France.
103.56 mph
The first car to go over 100 mph
was Gobron Brille; an internal
combustion engine powered car.
It was driven by Louis Rigolly; a
Frenchman at Ostend in Belgium.
168.07 mph 203.79 mph 301.12 mph 407.447 mph 600.601 mph 622.407 mph 633.468 mph 763.035 mph
J.G. Parry-Thomas drives Babs to a new
record at Pendine Sands, Wales. This was
bettered the next day (170.62 mph). Bluebird,
driven by Malcolm Campbell, reached
174.22 mph at Pendine the following year.
Sunbeam 1,000hp was the first car to
go over the 200 mph mark and was
the first car to set a record outside of
Europe. It was driven by Henry
Seagrave at Daytona Beach in the USA.
Malcolm Campbell drove
Bluebird past the 300 mph mark
at Bonneville Salt Flats, USA.
No record had been set for nearly 30
years and in 1963, the age of
jet and rocket propulsion began. Craig
Breedlove was the first man over 400
mph, driving Spirit of America
powered by a turbojet at Bonneville.
The duel between Green Monster,
built by Art Arfons, and Spirit of
America began. Eventually
Breedlove became the first man
to exceed the 600 mph mark.
The first rocket powered car to set a land
speed record was Blue Flame driven by the
American Gary Gabelich. It was the first
record over 1,000 km/h (621 mph).
Nearly 13 years later, Richard Noble
(now project director of BLOODHOUND
SSC) drove Thrust 2 to a new land
speed record. The record was set at
Black Rock Desert in the USA.
Noble, along with his team, then
developed Thrust SSC powered by a
turbofan. Andy Green, an RAF pilot,
drove the car. It was the first to go
over 700 mph and was the first to
exceed the speed of sound on land.

The Navier-Stokes Equations
The equations describing the compressible aerodynamic
flows around BLOODHOUND SSC are called the
Navier-Stokes equations (named after Claude-Louis
Navier and George Gabriel Stokes). They form a set of
five partial differential equations, derived by considering
the conservation of mass in equation (1), the conservation
of momentum (Newton’s 2nd law of motion:
Force=mass x acceleration) in equations (2) to (4),
and finally the conservation of energy in equation (5).
Mathematicians cannot prove that solutions to these
equations always exist in 3D models but CFD can yield
highly accurate approximated solutions to these equations.
The Clay Mathematics Institute has recognised that solving
the Navier-Stokes equations is one of the most important
problems in all of maths and if someone were to come up
with a proof, then a $1 million prize will be awarded.
Claude Navier
1785-1836
George Stokes
1819-1903
Spray Drag
As BLOODHOUND SSC travels at supersonic speed, the
shockwaves created around the body of the car, interact with
the surroundings disturbing the desert surface. This causes sand
and dust particles to rise from the ground under the influence of
pressure forces and these particles will then be moved up into the
air by resistive drag forces. If there are enough particles in the air,
then the air speed will be significantly affected. This could result in
additional resistive forces acting on the car which are not typically
accounted for in CFD analysis.
It is believed that this ‘spray drag’ phenomena will have a crucial
effect on the aerodynamic performance of BLOODHOUND SSC
and researchers at Swansea University are modelling the impact
that this may have on the car’s top speed.
High Performance Computing
CFD calculations could be done by hand,
but it would take an extremely long time.
Practically, a supercomputing cluster must
be used to solve them using parallel
processing. The procedure for CFD analysis
is as follows:
1. The definition of the vehicle surface to be examined is provided to
the team at Swansea University as a Computer Aided Design (CAD)
output from the engineers based in the design office in Bristol
2. This CAD output is analysed and a computational mesh is generated
using the FLITE computer system, developed at the College of
Engineering at Swansea University
3. The mesh is formatted using in-house pre-processing software in such
a way that the Swansea University supercomputing cluster can be
used to run the solver program
4. In-house fluid solver software containing the Navier-Stokes solution
algorithm is run on the supercomputing cluster
5. A ‘post-processing’ software package is used to convert the solutions
coming from the solver into meaningful flow visualisation plots and
force distributions
Imaging by Curventa
How is CFD used for BLOODHOUND SSC?
Visualisation of the airflow around BLOODHOUND SSC
aids the design team in understanding the behaviour of
the aerodynamics. Flow phenomena such as shock waves,
boundary layers and pressure distributions can be displayed.
The aim is to reduce drag forces which may prevent the car
from reaching its maximum speed and to control the lift of the
car. High pressure beneath the car at high speeds would be
extremely dangerous and CFD is used to alleviate this. Further
analysis and modifications are then applied to the next
configuration as the car design evolves.
Computational Fluid Dynamics
for BLOODHOUND SSC
By the College of Engineering at Swansea University
What is Computational Fluid Dynamics?
DRAG
REAR WHEELS
WEIGHT
LIFT
FRONT WHEELS
THRUST
BLOODHOUND SSC is a car that hopes to reach 1,000 mph
(Mach 1.3 or 1.3 times the speed of sound) and set a new
World Land Speed Record. Engineers based at Swansea
University will be using computational fluid dynamics (CFD) to
assist the aerodynamic design process. CFD is a branch of fluid
mechanics that models the movement of fluids over surfaces,
by using numerical methods such as the finite element method,
and sets of instructions, called algorithms. Traditionally, designs
would have been tested in a wind tunnel using an accurate
scale model of the car and a rolling road to simulate ground
effects. There are no rolling roads which can replicate
speeds of 1,000 mph, so this type of experimental testing is
inappropriate. CFD has no such limitations and, in addition,
it reduces the turnaround time between design modifications.
To analyse the airflow over the car, 3D meshes are generated in
the surrounding volume (domain). This domain is split into millions
of tiny pieces called elements, with each element representing
a volume of space. The elements are generally in the form of
tetrahedra, pyramids or prisms. It is possible to reach a very
accurate approximation of the fluid flow behaviour by solving
the Navier-Stokes Equations on each of these elements.
CFD was used in the design process of Thrust SSC, the current
Land Speed Record holder. The CFD process was validated
using rocket tests at Pendine Sands in South Wales. CFD is
used throughout the aerospace industry to model airflows for
commercial and military applications.