Stockcar Engineering 2015

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

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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 www.racecar-engineering.com 5

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 6 www.racecar-engineering.com STOCKCAR ENGINEERING 12

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.

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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 8 www.racecar-engineering.com STOCKCAR ENGINEERING 12

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.

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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

10 www.racecar-engineering.com STOCKCAR ENGINEERING 12

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 OpenFOAMÂŽ, 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

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TECHNOLOGY – NASCAR

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.

12 www.racecar-engineering.com STOCKCAR ENGINEERING 12

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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TECHNOLOGY – NASCAR

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.

14 www.racecar-engineering.com STOCKCAR ENGINEERING 12

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 16 www.racecar-engineering.com STOCKCAR ENGINEERING 12

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) STOCKCAR ENGINEERING 12

www.racecar-engineering.com 17

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 18 www.racecar-engineering.com STOCKCAR ENGINEERING 12

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

STOCKCAR ENGINEERING 12

www.racecar-engineering.com 19

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.

20 www.racecar-engineering.com STOCKCAR ENGINEERING 12

‘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 STOCKCAR ENGINEERING 12

www.racecar-engineering.com 21

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 22 www.racecar-engineering.com STOCKCAR ENGINEERING 12

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 STOCKCAR ENGINEERING 12

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