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Issue 12 • Spring 2015 • www.racecar-engineering.com/stockcar
NASCAR 2015
The start of a simulated revolution?
FROM THE PUBLISHERS OF
STOCKCAR ENGINEERING – SPRING 2015
E
ver since NASCAR introduced its fifth
Generation Cup car, the so called Car of
Tomorrow, there have been cries that a
revolution would come to stockcar racing. But
since then, right through the introduction of the
Generation 6 cars, the long-awaited opening of
the technological floodgates has not happened.
Yet. Sure there have been lots of small changes –
laser scanning cars to help the panel beaters and
to catch the cheats, RFID tags to keep track of
chassis, a rather archaic form of fuel injection and
an underutilised ECU.
CFD is becoming more and more prevalent
as you will see in this edition of SCE, but many
areas of stockcar racing are still decidedly oldfashioned. But it seems as though all that is finally
starting to change and it is not the teams that are
bringing that change, it is NASCAR.
In 2015 NASCAR is for the first time issuing the
rule book for Cup electronically, and while this
may seem like a very small step, and something
that other regulatory bodies like the FIA have
been doing for years, it is a sign of a gigantic
shift in attitudes for the sanctioning body and
the wider sport. It has, I suspect, after years of
resistance finally given in to the inevitable wave
of technology – gone now are the 43 white-suited
officials that once kept an eagle eye looking for
pit road infractions, replaced by a set of digital
video cameras and lasers. It makes you wonder
who will intervene the next time Brad Keselowski
and Jeff Gordon decide to have a conversation?
The ramifications of the changes are more
widespread than a few loose fists though and
the cars will slowly and surely sprout more and
more sensors and data acquisition equipment,
although I really hope that the teams are never
given access to that information, as some
anachronisms are beautiful. The dashboards of
the cars no longer have to be old 1950s style
gauges encased in the best lightweight housings
Fibreworks can create, instead teams can now
adopt a digital dashboard if they choose to do so.
Soon enough all teams will have them and the
flagman’s job will become more ceremonial than
anything else as race control beams messages to
the drivers via the digital dashes.
All of these changes show that NASCAR R&D
has adopted a forward thinking attitude towards
the sport and where it is heading. The same is
also true of NASCAR’s commercial operation in
Daytona, which has been uploading races, in full,
to YouTube, something that F1 would never ever
consider (possibly one of the reasons behind its
dwindling fan involvement).
What will this new broom sweep into the
sport? Downsized engines have openly been
talked about and direct injection must be on
the radar too. Smaller cars could offer similar
performance on track to what we have now with
more relevance to what is seen in the showroom,
although one hopes that they don’t get too small
– who does not like a muscle car?
The 2015 Daytona 500, or more likely the
2015 All Star race in Charlotte, will mark the final
opening of those technological floodgates and
I say that with great conviction, though perhaps
not great confidence!
SAM COLLINS
Editor
CONTENTS
4 NEWS
Haas gets ready for Formula 1, plus
the new look K&N series cars, and
News Shorts
6 TOYOTA AND THE 2015
REGULATIONS
How the Japanese company
re-homologated its underperforming
Camry ahead of the introduction of
new rules
10 UNDERSTANDING AERO N
SPRINT CUP
NASCAR R&D gives us an exclusive
look at how it is modelling airflow
around the car in an attempt to spice
up the racing
16 SIMULATING A LACK OF
SYMMETRY
How conventional software
developed for understanding how
cars perform on road courses has
been adapted to run on ovals
22 THE SECRET OF ECR ENGINES
How a piece of software inspired by
F1 allows one NASCAR engine tuner
to develop much faster than its rivals
NASCAR R&D has adopted a forward thinking attitude
towards the sport and where it is heading
STOCKCAR ENGINEERING 12
www.racecar-engineering.com 3
STOCKCAR – NEWS
Haas ready for F1 & NASCAR double duty
The Haas F1 team is rapidly taking shape with
new facilities in North Carolina and Banbury,
England. Shortly before Christmas it acquired
the Marussia Formula 1 team facility along
with some of its computer equipment. ‘We took
possession of the facility in Banbury a couple of
weeks ago,’ Gene Haas told Racecar Engineering
recently. ‘We are reconfiguring that to meet our
needs at the moment and we have just finished
the place at Kannapolis,’ he continued.
He went onto reveal that
aerodynamic development of the
teams 2016 Grand Prix car is already
underway using a 60 per cent scale
model at the Ferrari wind tunnel in
Maranello, Italy.
‘Our model is in Ferrari’s wind
tunnel. We are working in collaboration
with Dallara and they are making some
parts for the model in Italy,’ Haas said.
‘Right now we are looking at
buying our haulers and getting the
equipment in place and getting
organised,’ he explained. ‘The final
car probably won’t get built until
December, and we won’t start final
production until late summer.’
Haas F1 will make its race debut in
the 2016 using Ferrari power, and has
already taken on around 50 full time
staff split between Kannapolis, Banbury
and Italy. Stewart-Haas vice president
of engineering Matt Borland is heading
up the technical team and will manage
knowledge transfer between the
organisations NASCAR and Formula 1
projects, while Günther Steiner, CEO
of Fibreworks Composites based in
Mooresville, North Carolina, will act as
the team’s principal.
Haas F1 has taken over this former
Formula 1 team facility in England
NASCAR manufacturers praise selling-power of Gen-6
The motorsport bosses of the three
manufacturers involved in the
NASCAR Sprint Cup have said the
change to the Gen-6 car has had a
positive impact on forecourt sales.
The Gen-6 formula was introduced
in 2013 at the behest of Ford, Chevrolet
and Toyota as a way of giving the
racecars product greater relevance
by making them look more like their
street car cousins.
Now each manufacturer has
reported it is seeing positive signs in
terms of general interest and sales
NASCAR’s manufacturers havew enjoyed increased sales on the back of the Gen-6 cars
4 www.racecar-engineering.com STOCKCAR ENGINEERING 12
which can be tracked to their NASCAR
Sprint Cup programmes.
Jamie Alison, director of Ford
Racing, said: ‘We generate a lot of leads
for our dealers. We have generated
570,000 leads this year, which is up
60 per cent from a year ago. We track
sales, match leads generated from
on-track activation, and our sales are
up 90 per cent versus a year ago. These
are gigantic swings in engagement,
gigantic swings in fan affinity, and it
translates all the way down to intention
to buy. Success on the track translates
directly into fan consideration and
purchase intention.’
Jim Campbell, US vice president,
performance vehicles and motorsports
at Chevrolet, agreed. He said: ‘We like
that genuine connection from track
to the showroom and we see it in the
numbers. The research numbers show
that fans are relating to the car and
we’re making it more relevant to what
they see on the track to what they see
in the showroom and on the street.
We love that, and really that’s one of
the reasons why we race – we want to
make that connection of relevance.’
David Wilson, president and
general manager of Toyota Racing
Development USA, which has recently
launched its new Sprint Cup Camry, as
featured elsewhere in this supplement,
added that it was important that the
manufacturers continued to keep
the racecars aesthetically in line with
the street cars. He said: ‘This is about
relevancy. When we undertook the
project to bring the Gen-6 to the
racetrack, we all knew that we were
going to continue to evolve our
production cars and that with that
comes the need to evolve our racecars.’
BRIEFLY
SEEN: New NASCAR K&N Pro Series body
Mike Helton who has been NASCAR since
president since 2000, has been named
vice chairman of NASCAR and chief
operating officer Brent Dewar has been
named to the NASCAR board of directors.
Helton will remain the senior NASCAR
official at all national races overseeing
competition and reporting to Chairman
Brian France. In its competition
department, Chad Little has moved
to the new role of managing director
of technical inspection and officiating,
while Elton Sawyer has replaced Little
as managing director of the NASCAR
Camping World Truck Series. Both are
former drivers, Sawyer most recently team
manager at Action Express the 2014 Rolex
Daytona 24hr championship winning
team. Chad Seigler is now vice president
of business development within NASCAR.
A new body for NASCAR’s top
developmental championship, the K&N
Pro Series, was unveiled at the SEMA Show
in Las Vegas in November. It’s made from
a state-of-the-art composite laminate
blend and was developed by NASCAR in
partnership with Five Star Race Car Bodies.
NASCAR says its modular design allows
teams to easily install and repair damaged
panels, while it is expected to cut labour
costs associated with body maintenance by
up to 50 per cent. The body is eligible for
competition at the start of the 2015 season
and is mandated as the only approved body
in the series from 2017. It will be available
in all three manufacturer models: Chevrolet
SS, Ford Fusion and Toyota Camry.
The final season for steel bodies in
K&N is 2015, and the current one-piece
composite body will be phased out after
the 2016 season. The new body will also be
eligible for competition in the ARCA Racing
Series from 2015 onwards.
Jay Guy has joined H Scott Motorsports as
crew chief for a second full-time NASCAR
Sprint Cup team announced at the end
of January and will serve as crew chief for
the new team. Furthermore the two-car
South Carolina based operation that has
a partnership with Hendrick Motorsports
to supply cars and engines, will also work
closely with Stewart Hass Racing for 2015.
Ford restructures high performance division
The ‘Blue Oval’ has restructured its
high performance and motorsport
divisions and created a single
new corporate entity called ‘Ford
Performance’. It combines Ford
Racing, Ford SVT and Team RS to
serve as an innovation laboratory
and test bed to create performance
vehicles, parts, accessories and
experiences for customers. This
includes developing innovation and
technology in aerodynamics, lightweighting, electronics, powertrain
performance and fuel efficiency
that can be applied more broadly to
Ford’s product portfolio.
Ford hopes technology created by
its Performance division will filter
In addition to using racetracks
around the world, the team will
develop new vehicles and technology
at Ford’s engineering centres globally
and at the new state-of-the-art
technical centre in Concord, North
Carolina. This cutting edge facility
will help the team deliver racing
innovation, as well as advance tools for
use in performance vehicles and daily
drivers alike. It is already equipped with
a comprehensive range of high end
simulation tools. The Ford Performance
organisation is led by Dave Pericak,
who has been appointed director of
Global Ford Performance.
Over the next five years the new
organisation will create and deliver a
new range of at least 12 models, most
of which will also have competition
variants, though many details have yet
to be announced.
‘Ford still races for the same reasons
Henry Ford did in 1901 – to prove out
our products and technologies against
the very best in the world,’ said Nair.
‘The Ford Performance organisation
will continue to pursue performance
innovation, ensuring we can deliver
even more coveted performance cars,
utility vehicles and trucks to customers
around the world.’
Longtime ECR Engine chief operating
officer Richie Gilmore has been
promoted to the position of President.
The former head of DEI Engines joined
ECR in 2007 when RCR Engines merged
with DEI and ECR was formed.
A race fan hit by an overhead remote TV
‘CamCat’ camera cable at the 2014
Coca-Cola 600 is suing Fox Sports and
Charlotte Motor Speedway for $10,000
plus. Fox has not used the technology
since, and the fan, one of 10 people
injured, is the only one to take legal
action. The cable was hit by 19 cars
after it fell on the track, results of the
investigation into the failure remain
private due to the legal suit.
The Motorsports Group who moved
from the NASCAR Xfinity Series to the
Sprint Cup Series this year has named
Pat Tryson as crew chief for the new
Chevrolet powered team that is taking on
the monumental task of building its own
race engines.
Richard Childress Racing settled a
lawsuit in February with former NASCAR
Sprint Cup team engineer Matt McCall
who left the organisation at the end of
2014 to take a crew chief position with
Ganassi Racing. RCR lost its request for
a temporary restraining order in North
Carolina Superior Court in December.
Bray Pemberton has joined Tommy
Baldwin Racing as the newly named
general manager and chief legal counsel,
while Danielle Randall has been named
director of business development,
while Mark Gutekunst’s moves into the
position of lead engineer.
down to its road cars of the future
TOYOTA – CAMRY SPRINT CUP
Racecar reboot
How Toyota used the 2015 rulebook to give
its Camry Cup car a dramatic overhaul
By SAM COLLINS
I
n late 2014 Toyota took the wraps off its
new NASCAR Sprint Cup car, with a new
body shape loosely based on its 2015
Camry model. The Japanese marque
needed to make a move after an appalling 2014
season saw it take only two wins. ‘Yes we came
12 miles from winning our first championship,
but setting all that aside, it was extremely
disappointing,’ says Dave Wilson, president and
general manager, Toyota Racing Development,
USA. ‘It was the worst season since our debut
in 2007 when we won zero races. Any way you
slice it, it was disappointing. We collectively did
The biggest challenge
of creating the new
machine was taking into
account feedback from
the Toyota driver stable
not perform well through the season. It just was
not a year that we can feel good about.’
It was time for the manufacturer to take
action and it introduced an all-new body for its
cars with a completely different nose shape. As it
is the first time during the Generation 6 era that
one of the designs has been re-homologated
there is much interest in how the new Camrys
perform on track.
‘A lot of hard work has gone into
redesigning the 2015 Camry race car for
NASCAR competition,’ explains David Wilson,
TRD’s president and general manager. ‘It was a
challenging process balancing performance and
design, but working closely with Calty Design,
NASCAR and our race team partners, we were
able to develop a racecar that looks similar
to its production counterpart and provide a
performance upgrade on the track.’
TRD, Toyota’s north American motorsport
department, started work on the 2015 Camry
project well before the debacle of the 2014
season. Andy Graves, a former Cup crew chief
and now TRD’s technical director, headed up the
project. ‘It had been on our radar screen for two
years and we’ve been working on it every day
for the last 18 months,’ he explained at the cars
roll out in Charlotte. ‘Turning the Calty Design
shape into a competition car is a balancing act.
We’re trying to keep as much character as we
can in the Gen-6 platform,but also we want to
try and eke out every bit of performance that we
can within the parameters that the OEM group
has given us to work in. We’ve looked at some
CFD simulations to make sure that we’re trying
to capture everything that we can, not just from
the standpoint that the car will run good by
itself, but also to ensure it runs good in traffic.
We’ve tried to understand that and tweak the
design accordingly, based on those parameters.’
As well as the new nose the car also features
a revised hood and tail. The quarter windows
have also been reshaped. All of this has had a
significant aerodynamic impact and NASCAR
has made steps to ensure the new Toyota does
not gain a substantial advantage over its rivals.
‘Ultimately we had two critical wind tunnel
tests,’ Wilson adds. ‘Those were the tests where
The new look Camry features a new nose, hood, rear quarter windows and tail. At the first attempt to get the changes
approdved by NASCAR the design was reportedly too effective and got rejected. In 2015 Cup teams will no longer be
allowed to distort the side skirts of the car to gain an aerodynamic advantage
not only does NASCAR come to evaluate, but
our colleagues from Ford and Chevy were also
there. That’s part of our deal, transparency,
because we need everybody to buy into this
and believe it’s inherently fair.’
The reason that Toyota had two tests is
that after the first test the new Camry was
reportedly found to be a bit too good, and the
TRD engineers were told to go away and make
it less good before coming back to retest.
‘Everyone wants to be as close to the line
as possible from a competitive standpoint.
We pushed it as far as we could but we were
sweating bullets at the test. We passed; we were
within in the box so here we go,’ Wilson reveals.
‘But the reworked car for the wind tunnel
test was not just about the data that came out
of the computers next to the working section.
It’s the things that can’t be measured in the
wind tunnel, that’s where we worked. The
biggest challenge of creating the new machine
was taking into account feedback from the
Toyota driver stable,’ Graves continues, ‘that’s
the way the car handles in traffic, the transient
conditions, the transient aspects of the vehicle
on the track and trying to understand how to
measure and do a better job of refining that.’
Greater adjustability
The changes are more than skin deep and
behind the new Toyota body panels teams such
as Joe Gibbs Racing have been developing
ducting and underbody layout solutions to
improve the cars performance on track.
‘It provided us with a lot of opportunity in
the cooling area with the brake duct packaging.
Even though the area is the same, it’s allowed us
to grow in that area and do some things better
than maybe we did several years ago when
we came out with the old nose,’ claims Jason
Ratcliff, one of the crew chiefs at Gibbs. ‘There’s
a lot of engineering that goes into the area
behind the grille opening, not just for cooling,
but for many other things too.’
Toyota is in for a busy 2015. Not only do the
teams have to contend with a new car, they also,
in common with all teams, have to deal with
a significantly updated rule book introduced
after the homologation of the new Camry was
completed. And in a first for the series, that rule
book has been issued electronically.
It contains almost 60 changes covering
adjustments to the powertrain, aerodynamics
and chassis that are designed to work in
concert to deliver more flexibility to drivers
and more adjustability to teams. ‘We have had
fantastic racing so far in 2014,’ explains Gene
Stefanyshyn, NASCAR senior vice president of
innovation and racing development. ‘We remain
committed and constantly looking to improve.
Our fans deserve it and our industry is pushing
for it. That will not stop with the 2015 package;
the development will continue over many
years to come.’ The headline changes include
a shorter rear spoiler (from eight inches down
to six), something experimented with in 2014,
along with a reduction of engine power, lower
rear differential gear ratios and an optional
driver adjustable track bar. Additionally a wider
radiator pan has been introduced (see P10) and
the weight of the cars has been reduced by
23kg, by cutting ballast.
CAMRY SPRINT CUP
The new Camry won first time out, with a Joe Gibbs run car taking the spoils in the Sprint Unlimited at Daytona
There have been significant changes under
the hood too, as the power output of the cars
has been cut significantly. In 2014 the 5.7-litre
naturally aspirated V8 Cup engines produced
between 860-900bhp, but this has been cut to
around 725bhp via the use of a tapered spacer
in the inlet, similar to those used in the Truck
series and Xfinity championship. The change
to the lower rear differential gear ratios should
see the maximum revs fall to around 9000rpm,
while roller valve lifters replace flat valve lifters.
‘The engine configuration as we know it
is going to change considerably, and what it
means is a different camshaft,’ says Ford engine
builder Doug Yates. ‘Going from flat tappet to
roller lifter is a step in the right direction for
longevity, but as far as the cam design, the
cylinder head, intake manifold and exhaust
system, all of those things that are related to
airflow have to change. It’s not a total tear-up by
any means. Gene Stefanyschyn and the guys at
NASCAR have done a good job of talking to the
engine builders and trying to get our input and
feedback on how we would like to go about.
That process explored many different ways of
reducing power, but at the end of the day I think
we as a sport have made a good and a costeffective decision going forward. It’s good for
the engine shops, it’s good for the teams and it’s
good for the sport. There are a lot of ways you
can do it, but this makes sense for the current
All private testing has
been outlawed with teams
being instead invited to
participate in official tests
throughout the season
engine we have today.’
Major changes such as cutting engine
capacity down to 5.0-litres were on the table at
one point but that change was rejected, for now,
although major changes such as using direct
injection and more substantial downsizing
could be on the horizon. The new engines will
not be introduced until the second race of the
year, held at Atlanta, and the engine rules for
the super speedways at Talladega and Daytona
carry over from 2014.
‘It’s not fully appreciated, but the fact of
the matter is that we’ve had the same engine
for basically 25 or 30 years and it’s at 850 or
860 horsepower, where it used to be 500,’
Pemberton said in explanation of the new rules.
“And we are at the same race tracks where we
used to run 160 (miles per hour). We’re now
qualifying at 190 and running 213 going into
the corners. There’s been a lot of engineering
and gains made across the board.’
Compounding the impact of the changes
to the cars themselves is another rule change
aimed at cutting costs which will make it
much harder for teams to evaluate their
developments. All private testing has been
outlawed with race teams being instead invited
to participate in NASCAR / Goodyear tests
throughout the season. If a team is caught
conducting private tests in secret then it will
be hit with a 150 point penalty, a six week
suspension for the crew chief and other team
members and a minimum $150,000 fine.
One thing that many of the teams would
like to test will be tyre pressures, as NASCAR will
no longer enforce a minimum tyre pressure for
the 2015 campaign. This gives crew chiefs more
control of how little they put in their tyres but
also increases the risk of a blowout. Goodyear
will continue to provide teams with a minimum
tyre pressure recommendation, but teams
do not have to abide by it. ‘With Goodyear
constantly working on its communications with
the teams on tyre durability, it’s putting it in
the team’s hands for different strategies,’ Robin
Pemberton explains. Pemberton went on to
say that officials are working on having a tyre
pressure monitoring system on the dashboard
to give drivers a warning when tyre pressure is
too low although it is still ‘a fair old way away’
from happening anytime in the near future.
But one change that will be immediately
apparent when watching the races is the
reduction of the number of officials in their
distinctive white fire suits on pit road – NASCAR
has cut their number from 43 down to just 10.
Replacing them on pit road are HD cameras
which will be constantly monitored by NASCAR
officials sitting in the tech trailer. 45 of these
cameras will cover all of pit road and monitor
two pit stalls each, and in addition to this the pit
stalls will be laser measured.
One thing that they will be looking for is
team members yanking on the side skirts of
the cars. These panels on the lower part of
the bodyworks are officially known as vertical
rocker panel extensions and engineers in the
teams found that if the panels were deliberately
distorted during a pitstop by mechanics then an
aerodynamic gain could be derived.
Safety compromised?
Now teams who make unapproved adjustments
under caution will have to come back in under
caution, fix the car, restart at the rear of the
field and then do a pass-through on pit road
at pit-road speed under green. Teams who
make unapproved adjustments under green
will have to come in under green and fix
the car to NASCAR’s satisfaction. If NASCAR
identifies a crew member who makes the illegal
adjustment, it will issue that person a warning
for the first offence and subsequently increase
the sanctions for additional offences.
Another change is that the cameras and the
few remaining officials will no longer monitor
the teams wheel changing in great detail.
NASCAR will not penalise teams for missing
lug nuts out on the car and this opens up the
possibility of crew chiefs to gamble more with
strategy, possibly making a late race stop and
only using three or four lug nuts on the wheel
rather than all five in order to get a faster stop
and gain track position. It also allows wheel
changers to take more risks as losing a lug nut in
is now far less of a penalty, but NASCAR will still
penalise teams who lose wheels on track.
Even with all of the new rules, which were
introduced after the homologation of the 2015
Camry, the new car seems to work as it won its
debut race, the Sprint Unlimited at Daytona.
Toyota may once again be back on the pace and
closer to its first ever title, but its work is far from
finished as NASCAR has already declared that it
will release the 2016 rulebook in the Spring or
early summer and SCE understands that it will
contain some substantial changes.
18 0 m p h w i t h o u t m o v i n g a n i n c h
Take cutting-edge wind tunnel technology. Add a 180 mph rolling road.
And build in the best in precision data acquisition capabilities. When we
created the world’s first and finest commercially available full-scale testing
environment of its kind, we did much more than create a new wind tunnel.
We created a new standard in aerodynamics.
+1 704 788 9463
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w i n d s h e a r i n c .c o m
TECHNOLOGY – NASCAR
Taking
stock
From short tracks to
super speedways,
NASCAR has
always recognised
the importance of
aerodynamic research
By ERIC JACUZZI
T
he National Association
for Stock Car Auto Racing,
or NASCAR as it is more
commonly known, is the
sanctioning body for the premier
stock car racing series in the world.
Since it was founded in the late 1940s,
the emphasis has been on the quality
of the racing for fans. This continuous
drive to make racing as exciting as
possible, while ensuring fair and
equitable competition among drivers
and teams, is at the fore of the work
done by the team at the NASCAR
Research and Development Center in
Concord, North Carolina.
While Formula 1 is viewed by
many as the pinnacle of aerodynamic
development, regulations in NASCAR
have permitted such development
within a narrower technical window
utilising scale wind tunnels, full scale
wind tunnels, and Computational
Fluid Dynamics (CFD).
The region around the Charlotte
area features two racecar-specific full
scale tunnels, the 130mph Aerodyn
wind tunnel and the 180mph rolling
road tunnel of Windshear Inc. Teams
build specific cars for superspeedway
tracks that emphasise low drag,
while intermediate cars are built for
maximum downforce and side force.
NASCAR has always realised
the importance of aerodynamics,
with specific sets of rules for the
various tracks that the series runs
on. Short tracks are typically defined
as those tracks less than one mile in
length, with more emphasis on the
mechanical grip due to lower speeds.
Superspeedways, such as Daytona
and Talladega, utilise restrictor plates
to limit horsepower, resulting in
pack racing that emphasises drag
and drafting as the key performance
differentiators. Intermediate tracks
(1-2.5 miles) make up the majority
of the schedule, consisting of tracks
such as Charlotte Motor Speedway,
which is 1.5 miles in length and
features banking of 24 degrees in
the corners. The unique aspect of
intermediate tracks is that they are
essentially maximum handling tracks
that are heavily dependent on both
mechanical and aerodynamic grip.
Apex speeds can range from
160-190mph, with top speeds from
195-220mph. Understanding the
aerodynamic behaviour of the cars in
traffic is crucial to ensuring the cars do
not become overly aero sensitive and
limit the racing quality.
Intermediate car aerodynamics
The aerodynamics of an intermediate
track NASCAR Sprint Cup Series car
are dominated by three primary
forces: downforce, sideforce and, to a
lesser extent, drag. The magnitudes
of these forces are shown for the
baseline 2014 CFD model. It should
be noted that the reliance on an older
chassis and the lack of development
on the outer body means the CFD
model is 15-25 per cent lower in
downforce than a current race car
in optimum attitude. However, the
performance mechanism and flow
structures are more than adequate to
study vehicle performance in traffic
conditions. See Table 1.
Downforce is primarily generated
by the underbody of the car. The
front splitter and 43-inch wide
radiator pan are the largest single
downforce generating system on the
car, accounting for 700-1,000lb of
downforce depending on setup.
The angles of attack of the splitter
and radiator pan are adjustable for
the teams. Typical aerodynamic
downforce balance is between 45-50
per cent front downforce, due to the
extended/near steady-state cornering
the cars experience on typical
intermediate track corners.
The splitter and radiator pan
form a diffuser surface that works to
accelerate and concentrate the air
coming under the splitter nose into
a strong central jet. The attachment
effectiveness of this jet and its
expansion is heavily dictated by the
pressure conditions under the centre
and rear of the car. These areas are
maintained at as low pressures as
Table 1: Downforce, sideforce and drag
Description
2014 CFD Baseline
Lift Total
[lbf]
Outerbody
Lift [lbf]
Underbody
Lift [lbf]
Lift Front
[lbf]
Lift Rear
[lbf]
Sideforce
Total [lbf]
Front
Sideforce
[lbf]
Rear
Sideforce
[lbf]
Yaw
Moment
[lb-ft]
% Front
L/D
-2,367
+1,416
-3,817
-1,092
-1,275
-524
-209
-315
115
46.1%
-2.05
Figure 1: Splitter and radiator pan with streamlines
Figure 2: Underbody flow structures. Purple represents free stream conditions, while
the red of the central jet indicates faster-than-free-stream
Figure 3: Overhead view of CFD model with tail offset visible
possible via the low base pressure
created by the spoiler and maintained
by the side skirts. This is why typical
optimum ride height in mid-corner
is around 0.5in splitter gap and the
skirts of the car as low to the track as
possible. See Figures 1 and 2.
Sideforce is dominated by the
asymmetrical body shape of the car.
Not immediately apparent to the
untrained eye, the right side of the car
is straight from the front wheel back,
while the left rear quarter panel is
cambered towards the right by 4in.
This gives the top view of the car
a subtle aerofoil shape. The ratio of
front and rear sideforce is the main
driver of the overall yaw moment of
the car. As expected, the rear sideforce
is greater than the front to allow the
driver to confidently yaw the car
in the range of 3-5 degrees. While
sideforce forms a lesser component
of overall cornering force than the
downforce magnitude, sideforce acts
directly on the car without acting
through the tyres. This means that the
500lb of sideforce is directly translated
into lateral acceleration, while 500lb
of downforce is at the mercy of
the chassis setup and tire friction
coefficient at that particular track.
CFD results, as well as driver feedback,
indicate that sideforce variation
may be more critical than any loss in
downforce. See Figure 3.
Drag is the least important
factor for present power levels on
an intermediate track. The pursuit
of downforce and sideforce allows
drivers to apply throttle incrementally
earlier on corner exit. With power
levels approaching 900 horsepower,
this vastly outweighs the narrow
band of drag gains that teams can
achieve. And while the iconic images
of NASCAR races are the large drafting
packs of cars at superspeedways like
Daytona and Talladega, the reality is
that the 100-150lb drag advantage
of a trailing car at an intermediate
track is not enough to outweigh any
on-throttle disadvantage due to car
mishandling in traffic.
A sample of telemetry from a
lap demonstrating this is shown in
Figure 4. In this case, the number
4 car of Kevin Harvick (red traces) is
trailing the number 48 car of Jimmie
Johnson (blue traces). The 4 car drops
in behind the 48 car on corner entry,
trailing behind by 2-3 car lengths.
On corner exit, the 4 car attempts to
apply throttle as usual but the car
understeers up the track and Harvick
is forced to modulate the throttle
heavily. He is then at approximately 50
per cent throttle for several hundred
feet of the lap, while the leading 48
car is at full throttle. The 4 car is then
slower at every point on the track
until the next corner, losing 0.2 to 0.3
seconds from this incident alone.
The largest drag item on the car
is the 8in spoiler. The relationship
between drag and spoiler height
is almost perfectly linear, with 1in
of spoiler accounting for 40 drag
Figure 4: Lap 157 telemetry from number 4 of Kevin Harvick and number 48 of Jimmie
Johnson. Throttle traces are shown by dashed lines while speed is indicated by solid
lines. The lap is divided by fraction (0.00-1.00) with 0.01 of a lap equating to 0.015 miles
horsepower at 200mph. Drag
horsepower is the industry standard
measurement for aerodynamic drag.
Aerodynamics programme
In 2012, NASCAR embarked on its first
CFD study of the problem. Previously,
the sanctioning body had relied on
occasional team support for one or
two car runs, but with the scale of
the problem requiring substantial
personnel and computational
resources, the assistance was valuable
but limited in scope and timeliness.
The need for a well-funded CFD study
was too great to ignore any longer. To
help facilitate this, NASCAR turned to
TotalSim, a US-based company that
provides software and engineering
solutions to the motorsport,
automotive and aerospace industries.
TotalSim support and develop
OpenFOAM®, an open source CFD
software package, and has experience
in applying it in every professional
racing series in motorsports. NASCAR
was able to leverage this expertise
and within a few weeks was able
to have a fully functioning CFD
capability of its own running out of
its Concord R&D center.
Baseline model
The R&D centre in Concord owns
several older cars with bodies
representative of the current field
in the Sprint Cup Series. Complete
scans were made of both the outer
and underbody and pre-processed
in Beta-CAE’s ANSA. Since ANSA
converts native CAD and scan
data into the Standard Tesselation
Language (STL) format, it saves
substantial time in CAD cleanup
by allowing quick corrections and
rebuilds of poor surfaces into quick,
watertight CFD geometry. The car
is broken into approximately 30
Figure 5: CFD model underbody. The various colours represent the force patches as
they are reported
Figure 6: XY plane velocity slice approximately 5ft behind the lead car, with the
black region representing airspeeds of less than 50 per cent of the red free stream
velocity. The large ground wake region is evident, as well as the ‘Snoopy nose’
feature at the left, caused by the rear window and decklid fins
Figure 7: Drag percentage delta of trailing car compared to the lead car
Figure 8: Downforce delta in lbf of trail car compared to the lead car
Figure 9: Underbody downforce of trailing car compared with itself alone in free air
separate regions that separate the
outer and inner components and
regions into reporting patches of
interest. See Figure 5.
The solution is carried out by
OpenFOAM, featuring customised
wall functions and using the K-Omega
SST turbulence model. Typical grid
sizes for a single car run are on the
order of 50 million polyhedral cells,
while two car runs are on the order
of 110-120 million depending on
proximity. Several transient Detached
Eddy Simulation (DES) runs have also
been performed to validate certain
critical results and wake structures
behind the car, but have not yielded
any substantial changes that would
necessitate running in this condition.
For comparison, a 144-core steady
state single car run can be completed
from ANSA STL to results in 10 hours,
while a transient DES run starting
from a resolved steady state run
can take upwards of four days to
run three seconds of flow time on
similar hardware. Given this, runs
are performed in an incompressible
steady-state manner, which yielded a
good compromise of run time versus
accuracy. See Figure 6.
Aero performance mapping
After establishing the baseline
model performance and validating
at a variety of ride heights and yaw
conditions, two car traffic simulations
were performed. These consist of
a lead car that remains stationary,
while a series of 46 simulations are
performed with the trailing car in
a variety of positions laterally and
longitudinally behind the lead car.
Both cars are at the same ride height
and yaw angle. The 46 CFD runs
generate 500Gb of data that includes
force patch reporting and automatic
pressure and velocity imaging.
The next question is how to
best handle the volume of data and
visualise the aerodynamic behaviour
effectively. This is done by plotting the
aerodynamic characteristic of interest
using a contour plot that interpolates
that characteristic spatially between
the discrete simulation points. Using
a simple two colour common scale
creates effective imagery to convey
car performance. The black dots
indicate where the centre of the
trail car’s splitter was on the run that
generated data for that point.
The drag delta plot shows that
while the trailing car has a drag
advantage of around 5-10 per cent
from one car length and further back,
at closer range its drag increases
markedly. This is a two-fold change:
the trailing car is helping the lead
car by forming a more aerodynamic
two car body, which is at the same
time shielding the usually very low
pressure A-pillars of the trailing car,
increasing its drag. See Figure 7.
The downforce delta plot of the
trailing car vs. the lead car begins
to show regions where cornering
performance is compromised, even
at substantial lengths behind the lead
car. There is a region to the left side
of the lead car where the trailing car
is at a downforce advantage. Drivers
are aware of this region and will work
to prevent a trailing car from being in
that area. What is the reason for this?
Since the body of the car makes lift,
when any region of it is in the wake
of the lead car, the body makes less
lift – and hence downforce. In a sense,
the maximum downforce the outer
body of the car makes is when it’s
stationary. The opposite is true of the
underbody of the car, particularly the
splitter and radiator pan system which
require faster moving air to make
maximum downforce. Plotting the
underbody downforce of the trailing
car in traffic compared to in free air
reveals the underbody downforce
deficit caused by the slow moving air
near the track. See Figure 8.
The underbody downforce plot
of the trailing car compared to itself
in clean air paints a clear picture of
where downforce losses are coming
from. The underside of the trailing
car, from the splitter to the very tail of
the car is running in the large ground
wake formed by the lead car. The
majority of the component level loss
here is from the splitter-radiator pan
system, followed by the underhood
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Figure 10: Skewing the car (pre-yawing it with the rear axle). This makes the car faster
by itself but can make for poor handling in traffic
Figure 11: CFD results indicate that the hood and fender region contacting a small part
of the slow moving wake causes an increase in front downforce
Figure 12: The trailing car is forced to run in the loss region in order to run
its optimum line
Figure 13: Sideforce and traffic-handling issues: the proportion of the total cornering
force the sideforce makes up at various positions
and central underbody regions.
See Figure 9.
The sideforce delta plot reveals
a dramatic loss in sideforce of over
300lb, which is well over 50 per
cent of the car’s total sideforce
performance. Interestingly enough,
across the various series that NASCAR
operates (NASCAR Camping World
Truck Series, NASCAR K&N Series and
so on), drivers’ comments and setup
decisions by teams seem to indicate
that over-reliance on sideforce is
a negative characteristic. This was
particularly noticeable in the K&N
The change of the trail car
illustrated here is dictated entirely by
the downforce of the car and excludes
sideforce. In the regions where the car
tends toward understeer, the splitter
and radiator pan (and subsequently
the underhood region) take a
substantial loss in downforce due
to reduced airspeed and mass flow
rate. The opposite effect occurs in the
oversteer regions; a small portion of
the high lift hood and fender areas
enter into the car’s wake, reducing
lift and causing the balance to tend
toward oversteer.
Many people attribute the
oversteer handling characteristic
in traffic to a loss in downforce at
the rear of the car – an obvious
conclusion to draw. But the data
shows that in most situations the
spoiler and its effect on the lifting
greenhouse of the car vary only by
10-20lb, nowhere near the magnitude
required to substantially influence
car performance. The CFD results
indicate that the hood and fender
region contacting a small part of the
slow moving wake causes an increase
in front downforce (by mitigating lift),
leading to the forward balance shift.
See Figure 11.
The cornering force plot
highlights the difficult situation
Series, which featured two separate
car bodies: a composite car body
based on an older superspeedway car,
and a steel bodied car that was built
more similarly to a current Sprint Cup
car in sideforce levels. The composite
car crew chiefs would state that they
knew they could generate more
sideforce, and hence performance,
by ‘skewing’ the car (pre-yawing the
car with the rear axle). This made
the car faster by itself, but made
the car handle poorly in traffic
when sideforce was more highly
compromised. See Figure 10.
Future steps
N
ASCAR recently invested in
a 128-channel Scanivalve
pressure scanning system,
with a 128 Kiel probe modular
array to begin verifying CFD
prediction of the wake structures.
Long commonplace in F1, this
aerodynamic testing methodology is
slowly making its way into the sport.
NASCAR will continue to work on
improving car aerodynamics, while
considering what magnitudes of
forces work best at specific tracks and
for tyre supplier Goodyear.
Ultimately, bringing solutions
from CFD to the wind tunnel can be
challenging enough. But bringing
solutions that improve racing quality
is an even further abstraction,
involving simulated races on track
with test drivers who may or may
not prefer to be on leave between
races rather than pounding
around the track.
So the answer is not always
clear. But continuing on the path of
scientific analysis and attacking the
problem analytically will ultimately
yield the best result for fans, drivers,
and the series as a whole.
the trailing finds itself in, and how
position dependent that plight is.
Cornering force is the combination
of both downforce and sideforce
(both converted to positive numbers).
Behind the lead car and to the right
can put the trailing car at a 500lbforce disadvantage to the leading car,
while positioning the trailing
car toward the left quarter-panel of
the lead car can lead to a cornering
force advantage.
It should be noted that on many
ovals, the trailing car would be forced
to run in the loss region to run the
optimum line. See Figure 12.
A final interesting plot is using the
cornering force metric, but adjusting
downforce by an average tyre friction
coefficient value of 0.8 to reflect how
much downforce is converted to
lateral force. We then can look at what
proportion of the total cornering force
the sideforce makes up at various
positions. Alone, the sideforce usually
accounts for around 40 per cent of the
total cornering force, but in the wake
region of the lead car, this drops to
only 10 per cent or less. This reaffirms
more recent thinking that making
sideforce with the car body may be
a large contributor to traffic
handling issues that drivers report.
See Figure 13.
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TECHNOLOGY – ASYMMETRIC DATA GATHERING
Asymmetric
correlation techniques
When it comes to gathering useful data,
the devil is in the detail
By DANNY NOWLAN
Asymmetric data gathering plays a
crucial role in car setup on oval tracks
Figure1: Beam pogo stick
visualisation of the race car
R
ecently I have been doing a lot of
asymmetric modelling work. In
particularly I have been working
closely with a stock car racing
organisation. In the past when ChassisSim
has been used on ovals I’ve simply turned it
over to the customer and left them to their
own devices. This time though I’ve had to be
more involved, which is actually a good thing
because in terms of correlating the model there
are some nuances you need to be aware of.
Let me state from the beginning of this
article that I will not be discussing data directly.
Suffice to say I have had access to very sensitive
information which I have been sworn to secrecy
on. I don’t take stuff like this lightly and never
will. That being said I realise that particularly
in North America there is a large body of circle
In an asymmetric car the four springs have much more of a role to play.
The big thing here is the pitch and role modes are now coupled
track and oval racers who have expressed an
interest in ChassisSim. Consequently, while I
can’t talk quantitatively, I can tell you what I did
and this is going to make your life a lot easier
when you come to do this for yourself.
Also to keep things simple I’ll assume linear
motion ratios. While this isn’t accurate I’m using
this as a teaching tool. If you understand how
to do it for the linear case the non-linear case
becomes an extension of the former.
A review of the beam pogo stick model
will tell you the key differences between a
symmetric and an asymmetric car. This is
presented in Figure 1.
Figure 2a: Front left load vs damper displacement
Figure 2b: Front right load vs damper displacement
Figure 2c: Rear left load vs damper displacement
Spring rates
The thing to pay attention to is the four main
springs. In a symmetric car the front and the rear
spring rates are the same. This makes your life
a lot easier because you have less to play with.
In an asymmetric car all of a sudden the four
springs have much more of a role to play. The
big thing here is the pitch and roll modes are
now coupled. For example, in a symmetric car if
the rear roll isn’t matching up you can typically
double the bar rate and you can fix it easily. In an
asymmetric case it’s no longer just the bar. We
now have different spring rates side to side that
will make their presence felt. Not surprisingly it
is very easy to get lost in the analysis. The good
news is that there are ways we can tackle this
that will make your life a lot easier.
Our first port of call is to fit a good data
system to the car and plot load vs damper
displacement for all four corners of the car. At
first this might seem a little strange but this will
tell you a wealth of information. The reason we
are looking at this first is it will tell us a lot about
what the loads are doing so we can then focus
on other bits of the model. The load vs damper
displacements are shown in Figures 2a – 2d.
The first things to look at are the two graphs
of the rear springs. Looking at them they are
both linear. What this means is that we don’t
have a rear roll bar. This makes correlating the
rear really easy but we have to quantify the
different spring rates which tie in the pitch and
roll correlation. In terms of calculating the spring
rates this is what we are looking at in Equation 1.
Effectively the spring rate is the slope of
Figures 2a - 2d. This is really important data. In
EQUATIONS
Equation 1
ks =
Figure 2d: Rear right load vs damper displacement
ΔLoad / MR
Δdamper
Here we have
ks
= Spring rate
δLoad
= Change in Load
δdamper = Change in Damper movement
MR
= Motion ration of the spring (damper/wheel)
TECHNOLOGY – ASYMMETRIC DATA GATHERING
Table 1
Parameter
Load Front Left
Load Front Right
Load Rear Left
Load Rear Right
Speed
Value
50 kgf
100 kgf
150 kgf
200 kgf
250 km/h
Table 2: Sanity checking numbers
Figure 3: Looking at roll data
EQUATIONS
Equation 2
CL A =
=
Equation 3
Load FL + Load FR + Load RL + Load RR
0.5 ⋅ ρ ⋅ V 2
9.8 ⋅ (50 + 100 + 150 + 200)
LDAMP = MR ⋅ k ⋅ md
= 0.6 ⋅ 1000 ⋅ 20
= 12000 N
2
0.5 ∗ 1.225 ∗ (250 / 3.6)
= 1.66
= 1225.5kgf
particular Figure 2c and 2d give you the rear
spring rates of the car. This is one less variable
you need to worry about.
The reason the data looks like a blob as
opposed to a line is the effect of bumps and
damping. What you are looking for here is
trends. Once you have the trends you can get
cute with the details later. Don’t do it the other
way around as you’ll drive yourself nuts.
this then calculating the bar rate is easy. This
should be your procedure:
• Calculate the main spring rate using the
data to the left bifurcation point.
• Calculate the spring point post the
bifurcation point.
• The bar rate is simply the difference
between the two.
Bar rates
I prefer to calculate the bar rates from the
most linear of the curves, which in this case is as
shown in Figure 2a.
Now we have our spring rates the next step
is to calculate the downforce, if there is any
present on the vehicle. As per the symmetric car
you are using exactly the same techniques to
get yourself into the ballpark – that is choose a
point on the straight or low lateral acceleration
and confirm with a hand calculation. Let me
give you a quick example. Let’s say we have our
loads zeroed on the ground and we have this
data set, as demonstrated in Table 1.
Calculating the CLA we see Equation 2.
This is a bit of a Mickey mouse example but
it illustrates the point.
Also at this point in the game let me offer
some reflections about resolving load and
damper channels. In my experience load cells
are a bit like fish and chips or romantic movies.
They are either really good or really bad and
there is no inbetween. Consequently you must
always sanity check them. The first port of call
is Figure 2a – 2d. If it’s not consistent then that
is your first alarm bell. Fortunately in this case it
was consistent, so that is the first pass mark.
Where things get really interesting is the front.
Looking at both Figure 2a and 2b there is a
distinct bifurcation point. Just a note on data
analysis. If you ever see something like Figure
2a and 2b print it off and hold it up next to a
light. If there are any non-linearities it will show
up as plain as day. It’s a rule of thumb taught
to me by one of my physics professors. In both
Figure 2a and 2b there is a distinct bifurcation
point where the gradient has changed slope.
Typically if you see something like this we
have hit a roll bar. What we need to do now is to
cross reference this with the data. The thing to
pay attention to is quantifying the bifurcation
point to when the roll kicks in. You are looking
for a situation like the one in Figure 3.
You’ll notice I have placed the cursor on
the bifurcation point of the front left damper.
Firstly you’ll notice the bottom trace which is the
front roll. Then you’ll notice how the front roll
has increased from zero at this point. If you see
something similar to this you know the shape of
Figure 2a is being influenced by the roll bar.
The good news is that if you have data like
Quantity
Spring Rate
Damper Value
Load
Motion Ratio (damper/wheel)
Value
1000 N/mm
20mm
700 kgf
0.6
The next step is to sanity check that the
dampers and loads are telling you the same
thing. To illustrate this lets consider an example,
as illustrated in Table 2.
For the sake of this discussion all motion
ratios are linear and springs are linear. From the
data the load on the tyre from the damper data
is shown in Equation 3.
As you can tell there is a discrepancy here
that needs to be addressed. In order to resolve
this tools such as wind tunnels, CFD and on track
experience will be your best friends.
Now that we have spring rates and some
idea of downforce we are now in a position to
do correlation. Where things get a bit trickier
than in the symmetric case is that separating the
pitch and roll isn’t as straightforward as it is with
the symmetric case. So for correlation this will
be our game plan:
• Correlate on the loaded side.
• Look at the unloaded side.
• Then check pitch and roll channels.
Working through this process the loaded
side looks pretty good and this correlation is
shown in Figure 4.
For reference I have used the lap time
simulation, but the reality is that the track replay
simulation is just as good. Also the actual data
is coloured and the simulated data is black.
Looking at the right side the damper correlation
is very good. Going down the straight there
are some things we need to tidy up with the
aeromap, but this is a good start.
Also let me state that particularly for the lap
time simulation trace you are not looking for
perfect correlation. At this stage you are looking
for something that is in the ballpark so you can
get basic validation done. Once reach this point
you can concentrate on getting an accurate model.
However, things need tidying up somewhat
on the unloaded side. The correlation is as
shown in Figure 5.
Load cells are a bit like fish and chips. They are either really good or really
bad and there is no inbetween. You must always sanity check them
Again coloured is actual and black is
simulated. Looking at the rears in mid-corner
and we are actually pretty close to where we
want to be. However, there is a discrepancy in
the middle of the circuit, but chances are we
might need to refine the aeromap at that point.
Looking at the data for the front left and it
becomes apparent that it’s down everywhere.
This would indicate we need to slightly soften
the front spring. However, the big area that
needs to be worked on is on turn entry where
the damper movement unloads everywhere.
This indicates two things – we either need
to increase rebound on the dampers or the
aeromap needs attention.
Applying these changes yielded very
interesting results, as shown in Figure 6.
Again actual is coloured and simulated is
black. The rear damper results have definitely
improved, particularly in the area that the inside
rear has unloaded. This is especially apparent
in Turn 2. Turn 1 needs work but this is being
exaggerated by the speed difference. However,
at a first pass it would appear the front dampers
overall are worse, but as always the devil is in
the detail. The raw front damper data would
indicate we have gone backwards yet the pitch
and the roll channels tell a very different story.
Looking at the roll channel the correlation is
very good. Given the linear nature of the springs
and motion ratios it would indicate we have the
front mechanically sorted.
Figure 4: Loaded side correlation
Figure 5: Unloaded side correlation
Pitch values
The real giveaway that we’re where we want to
be is the pitch channel. Going down the straight
the correlation is good. However, as we get into
the corner the front pitch falls away and this is
telling us is we need to increase the downforce
in this section of the aeromap. Remember on an
oval the normal loading of the car will increase,
the car will compress on its springs and the ride
height will go down due to the banking. You can
see this on data as clear as a bell in places such
as Daytona. Consequently we need to adjust the
aeromap to suit the conditions.
Once we are at this point and the necessary
modifications have been made we can start
running tyre force optimisation and begin work
on setting the car up.
In summary achieving correlation for an
asymmetric car isn’t significantly different to
it’s symmetric counterpart – it’s just a bit more
in depth. Our process starts by making sure we
have good data on the racecar. We then plot
load vs dampers for each corner of the car to
quantify what the springing of the car is doing.
We then sanity check the data and as per the
symmetric car we then double check the aero
results. We then move on to comparing both the
loaded and unloaded dampers. We then make
modifications and then tie this together using
pitch and roll data. Once you arrive at this point
you finally have a model you can use as the
basis to get results.
Figure 6: Effect of applying a softer front left spring and increasing rebound everywhere
Achieving correlation for an
asymmetric car isn’t significantly
different to its symmetric counterpart
– it’s just a bit more in depth
TECHNOLOGY – COMPUTATIONAL FLUID DYNAMICS
Power tool
How state-of-the-art software is
revolutionising engine tuning
By NICK BAILEY
W
hen an engine specialist as
experienced as Brian Kurn is
excited about a technology,
others in the field tend to take
notice. If they don’t, they should.
Kurn is currently working at ECR Engines,
a division of Richard Childress Racing and is in
charge of valvetrain development together with
all virtual prototyping technologies, including
engine and valvetrain simulation, as well as
computational fluid dynamics (CFD). In a
career spanning 25 years he has worked
for some of the biggest names in the sport,
including Roush, Hendrick and Bill Davis
Racing. Kurn started his craft building and
improving V8 engines for the small dirt tracks
and worked his way up to the elite series in
NASCAR. He was highly-regarded for his work
on cylinder heads and his ability to extract
more power while retaining reliability. Today,
he’s a highly-respected engine developer who
has plied his trade, successfully, across many
racing championships – Tudor United Sportscar
Championship, NHRA Pro Stock, American
Le Mans Series (ALMS), Touring Cars in Brazil
and Argentina, Truck-pulling, Supercross and,
of course, NASCAR.
‘In the good old days, so-called tuners
determined the biggest valves that could be
used and then they simply began to hand-port
the head, believing that the more air that would
flow, the more power it should make,’ says Kurn.
‘After spending a lot of time doing this,
you took the parts to the dyno and only then
did you find out if you had found a solution or
just scrapped another cylinder head. It was an
expensive and time-consuming way to see if
your idea gained a few more horses or not. And
each time you got a new head design, you really
had to start again!’ It was this inefficiency which
drove the forward-thinking Kurn to investigate
simulation technologies.
As an experienced CFD user, primarily to
analyse internal flows in the engine, both standalone and coupled with engine simulation, Kurn
is at home with state-of-the-art technology.
But, in those early days just over a decade ago,
CFD posed problems. ‘The run-times to do the
Using trusted valvetrain simulation, we can now optimise the
design to work in the real world, even in a NASCAR application
Richard Childress Racing’s Austin Dillon put
the engine tweaks to good use on the track
simulations took too long and when we had
to create our own mesh, we really suffered
with the variability between users,’ claims
Kurn. ‘It can affect your results and introduce
inconsistency, which ultimately means your
trust in the data can go out of the window.’
Mix and mesh
Even today, creating a good mesh is crucial
to resolve the flow. But the quest for an
automatically-generated mesh never quite
delivered the accuracy needed to move
away from user-generated data. For years,
engineers simply accepted the challenges
and did what little they could to minimise
the variations.
For Kurn, it was a frustration. ‘I never believed
that an effective automatic meshing tool would
happen in my lifetime. I thought we would
be stuck with the longer run-times forever,’ he
explains. But after learning that Converge had
collaborated with engine simulation provider
Gamma Technologies, everything changed.
It was there that Kurn first encountered
an innovative automatic meshing solution
called Converge™ CFD Software. Developed
by Wisconsin firm Convergent Science Inc.,
it automates the meshing at run time with
a perfectly orthogonal Cartesian mesh that
eliminates the need for a user-defined mesh.
‘To be honest, I’d heard it all before and I
was sceptical,’ says Kurn. ‘Automatic meshing
had been around for long time but none of
the solutions I tried lived up to their claims of
a completely automatic mesh that produced
accurate results. But if the guys at Gamma
were convinced Converge was different then I
thought maybe it was worth a look. I’d always
struggled with meshing, and longed for the day
when I wouldn’t have to predict the outcome in
order to define the mesh, and I didn’t want my
meshing to affect the result. I ended up taking a
look – the rest is history.’
Time saver
Written by engine simulation experts to address
the deficiencies of other CFD codes, Converge
offers run-time grid generation and refinement
TECHNOLOGY – COMPUTATIONAL FLUID DYNAMICS
RCR’s engines have benefited
from increased reliability
so users such as Kurn no longer need to spend
their time creating meshes.
Instead, the user supplies a triangulated
surface and a series of guidelines from which the
Converge proprietary code creates the grid at
run-time. ‘They had hit on my objective; reduce
the run-time while retaining the accuracy of the
simulation, removing assumptions,’ says Kurn.
‘Testing would become more fruitful as with
consistent meshing and we could test more
solutions in the same time frame. Once you
have the model you can keep re-running the
job without recreating the case.’
For race teams, the software achieves the
one thing that is hard to buy – more time – and
Kurn has been astounded with the amount
he’s saved. ‘We gained literally weeks on some
developments in 2014,’ says Kurn. ‘On our
Daytona prototype engine we got ahead of the
development schedule and we were able to
start testing different trumpet lengths before
the engine was even ready to run on the dyno,
or got anywhere near the car. This saved not
only time but also the number of prototype
parts produced. Knowing the exact parameters
of key items such as combustion chamber,
intake and exhaust ports means now when we
make changes, we can accurately measure just
those changes and have complete control over
them. We now run a number of simulations and
with the accurate data generated can select the
best one or two to try on the car.’
Predictable combustion
CFD comes into its own for in-cylinder propagation as it’s far more accurate than using a larger mesh
Trumpet design is just one of the areas that Kurn
is trusting to the new software. Others include
the very challenging modelling of combustion,
and Kurn can see the potential for using it for
optimising future fuel efficiency.
Rob Kaczmarek, marketing director from
Convergent Science, explains: ‘Our genetic
algorithm optimisation can run cases depending
on design parameters such as fuel efficiency or
power and is capable of thinking outside the
box. Our founders came from engine simulation
and struggled with CFD meshing in the early
years so they focused on creating a tool that
would simplify meshing and increase accuracy.
To achieve this they allowed the program to
automate the mesh at run-time and refine when
and where it is needed through adaptive mesh
refinement (AMR).’
A common area of interest where this
approach works particularly well for is
in-cylinder flame propagation. Kaczmarek
believes non-Converge users really struggle with
hard-to-define areas such as this.
‘It leads them to either go to a larger-sized
mesh, maybe up to 1mm, in order to save time.
But doing this loses accuracy. Going to a smaller
mesh increases accuracy but also leads to an
increase in run-times,’ explains Kaczmarek.
The good news is Converge can take care
of this, allowing the programme to refine when
and where it is needed at run-time for
Richard Childress Racing has profited from adopting CFD – the perfomance and reliability gains took the team to second in the Sprint Cup Series Championships
more accuracy – while keeping run times
manageable. In addition, the software comes
equipped with detailed chemistry and physical
models to help engineers make gains.
‘For example, measuring turbulence
of a flame in microseconds and how it changes
is very hard to do but it’s crucial for efficiency,’
adds Kaczmarek. ‘Converge can help. It’s
great for transients and we saw, for example,
with the use of direct injection in Daytona
prototypes and other high pressure scenarios,
that Converge is very effective. Even though
NASCAR engines have been around for a
long time, well over 40 years, some of the
best tuners who think they have understood
them can now really see and truly understand
what is actually happening for the first time,’
explains Kaczmarek.
Working at the track rather than in the
garage is another area where fast and accurate
simulation is helping. Kurn believes that a
NASCAR pushrod engine is one of the worst
case scenarios for different behaviours when
fired up. ‘The actual exhaust valve opening can
be delayed as much as 10-15 crank degrees as
a result of the cylinder pressure acting on the
valves,’ he explains. ‘Using trusted valvetrain
simulation, we can now optimise the design of
the valvetrain components to work in the real
world, even in a NASCAR application.’
Simplicity and support
Virtual testing is currently unrestricted in
NASCAR and is becoming more and more
popular as teams look for the edge over the
competition. As Kurn points out: ‘Track testing,
save for the odd tyre test, is zero!’ Despite
half the teams having simulation tools, he
is unsure how many are actually using them
NASCAR has no regulations governing virtual testing – pretty soon most of the paddock will be following RCR’s lead
effectively. The simplicity of Converge leads
him to believe anybody with CFD experience
could use it – and within 10 minutes they’d
have a surface modelled.
‘I have found Converge to be one of the
simplest and most powerful simulation tools
available. And if there are any issues, there’s
usually a solution to hand. All we have to do
is pick up the phone with any questions and
together we’ve provided answers to many
issues. I can’t fault the team’s support.’
Tracking the results
It is results on track that define success and
2014 was a very successful year for Converge,
as demonstrated by the significant gains in
power achieved in 2014.
These leaps in performance helped Richard
Childress Racing (RCR) secure second overall in
the Sprint Cup Series Championship standings
with Ryan Newman, while more than 23 top
10 finishes resulted in Brian Scott snatching
4th in the Xfinity championship with Ty Dillon
gaining a rookie victory at Indianapolis and
5th overall in the final standings. Team mate
Brendan Gaughan showed the versatility
of the team’s development, winning on the
traditional Road America circuit. ECR’s engines
proved crucial in the TUSCC, helping Chevrolet
to win both titles. The Action Express Daytona
Prototype, with an ECR engine, scored eight
podiums including three victories, most
notably the Daytona 24 hours. The ECR engine
was reliable; the car completed every lap of
competition last season. ‘It was a special year
for Kurn and the ECR team,’ adds Kaczmarek.
‘We are so proud to have been involved with
the team and Brian.’
Even though NASCAR engines have been around for a long time, some
of the best tuners can now really understand what is happening
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