Issue 12 • Spring 2015 • www.racecar-engineering.com/stockcar

NASCAR 2015 The start of a simulated revolution?

FROM THE PUBLISHERS OF FA_Ad_210x297_WF_2015_out.indd 1 2/18/15 12:25 PM STOCKCAR ENGINEERING – SPRING 2015

ver since NASCAR introduced its fifth more sensors and data acquisition equipment, Generation Cup car, the so called Car of although I really hope that the teams are never CONTENTS ETomorrow, there have been cries that a given access to that information, as some 4 NEWS revolution would come to stockcar racing. But anachronisms are beautiful. The dashboards of Haas gets ready for Formula 1, plus since then, right through the introduction of the the cars no longer have to be old 1950s style the new look K&N series cars, and Generation 6 cars, the long-awaited opening of gauges encased in the best lightweight housings News Shorts the technological floodgates has not happened. Fibreworks can create, instead teams can now Yet. Sure there have been lots of small changes – adopt a digital dashboard if they choose to do so. 6 TOYOTA AND THE 2015 laser scanning cars to help the panel beaters and Soon enough all teams will have them and the REGULATIONS to catch the cheats, RFID tags to keep track of flagman’s job will become more ceremonial than How the Japanese company chassis, a rather archaic form of fuel injection and anything else as race control beams messages to re-homologated its underperforming an underutilised ECU. the drivers via the digital dashes. Camry ahead of the introduction of CFD is becoming more and more prevalent All of these changes show that NASCAR R&D new rules as you will see in this edition of SCE, but many has adopted a forward thinking attitude towards areas of stockcar racing are still decidedly old- the sport and where it is heading. The same is 10 UNDERSTANDING AERO N fashioned. But it seems as though all that is finally also true of NASCAR’s commercial operation in SPRINT CUP starting to change and it is not the teams that are Daytona, which has been uploading races, in full, NASCAR R&D gives us an exclusive bringing that change, it is NASCAR. to YouTube, something that F1 would never ever look at how it is modelling airflow In 2015 NASCAR is for the first time issuing the consider (possibly one of the reasons behind its around the car in an attempt to spice rule book for Cup electronically, and while this dwindling fan involvement). up the racing may seem like a very small step, and something What will this new broom sweep into the that other regulatory bodies like the FIA have sport? Downsized engines have openly been 16 SIMULATING A LACK OF been doing for years, it is a sign of a gigantic talked about and direct injection must be on SYMMETRY shift in attitudes for the sanctioning body and the radar too. Smaller cars could offer similar How conventional software the wider sport. It has, I suspect, after years of performance on track to what we have now with developed for understanding how resistance finally given in to the inevitable wave more relevance to what is seen in the showroom, cars perform on road courses has of technology – gone now are the 43 white-suited although one hopes that they don’t get too small been adapted to run on ovals officials that once kept an eagle eye looking for – who does not like a muscle car? pit road infractions, replaced by a set of digital The 2015 , or more likely the 22 THE SECRET OF ECR ENGINES video cameras and lasers. It makes you wonder 2015 All Star race in Charlotte, will mark the final How a piece of software inspired by who will intervene the next time opening of those technological floodgates and F1 allows one NASCAR engine tuner and Jeff Gordon decide to have a conversation? I say that with great conviction, though perhaps to develop much faster than its rivals The ramifications of the changes are more not great confidence! widespread than a few loose fists though and SAM COLLINS the cars will slowly and surely sprout more and Editor 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 He went onto reveal that ‘Right now we are looking at staff split between Kannapolis, Banbury new facilities in North Carolina and Banbury, aerodynamic development of the buying our haulers and getting the and Italy. Stewart-Haas vice president England. Shortly before Christmas it acquired teams 2016 Grand Prix car is already equipment in place and getting of engineering Matt Borland is heading the Marussia Formula 1 team facility along underway using a 60 per cent scale organised,’ he explained. ‘The final up the technical team and will manage with some of its computer equipment. ‘We took model at the Ferrari wind tunnel in car probably won’t get built until knowledge transfer between the possession of the facility in Banbury a couple of Maranello, Italy. December, and we won’t start final organisations NASCAR and Formula 1 weeks ago,’ Gene Haas told Racecar Engineering ‘Our model is in Ferrari’s wind production until late summer.’ projects, while Günther Steiner, CEO recently. ‘We are reconfiguring that to meet our tunnel. We are working in collaboration Haas F1 will make its race debut in of Fibreworks Composites based in needs at the moment and we have just finished with Dallara and they are making some the 2016 using Ferrari power, and has Mooresville, North Carolina, will act as the place at Kannapolis,’ he continued. parts for the model in Italy,’ Haas said. already taken on around 50 full time 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 and Toyota as a way of giving the which can be tracked to their NASCAR that fans are relating to the car and manufacturers involved in the racecars product greater relevance Sprint Cup programmes. we’re making it more relevant to what NASCAR Sprint Cup have said the by making them look more like their Jamie Alison, director of Ford they see on the track to what they see change to the Gen-6 car has had a street car cousins. Racing, said: ‘We generate a lot of leads in the showroom and on the street. positive impact on forecourt sales. Now each manufacturer has for our dealers. We have generated We love that, and really that’s one of The Gen-6 formula was introduced reported it is seeing positive signs in 570,000 leads this year, which is up the reasons why we race – we want to in 2013 at the behest of Ford, terms of general interest and sales 60 per cent from a year ago. We track make that connection of relevance.’ sales, match leads generated from David Wilson, president and on-track activation, and our sales are general manager of Toyota Racing up 90 per cent versus a year ago. These Development USA, which has recently are gigantic swings in engagement, launched its new Sprint Cup Camry, as gigantic swings in fan affinity, and it featured elsewhere in this supplement, translates all the way down to intention added that it was important that the to buy. Success on the track translates manufacturers continued to keep directly into fan consideration and the racecars aesthetically in line with purchase intention.’ the street cars. He said: ‘This is about Jim Campbell, US vice president, relevancy. When we undertook the performance vehicles and motorsports project to bring the Gen-6 to the at Chevrolet, agreed. He said: ‘We like racetrack, we all knew that we were that genuine connection from track going to continue to evolve our to the showroom and we see it in the production cars and that with that NASCAR’s manufacturers havew enjoyed increased sales on the back of the Gen-6 cars numbers. The research numbers show comes the need to evolve our racecars.’

4 www.racecar-engineering.com STOCKCAR ENGINEERING 12 SEEN: New NASCAR K&N Pro Series body BRIEFLY

Mike Helton who has been NASCAR since A new body for NASCAR’s top president since 2000, has been named developmental championship, the K&N vice chairman of NASCAR and chief Pro Series, was unveiled at the SEMA Show operating officer Brent Dewar has been named to the NASCAR board of directors. in Las Vegas in November. It’s made from Helton will remain the senior NASCAR a state-of-the-art composite laminate official at all national races overseeing blend and was developed by NASCAR in competition and reporting to Chairman partnership with Five Star Race Car Bodies. . In its competition NASCAR says its modular design allows department, has moved to the new role of managing director teams to easily install and repair damaged of technical inspection and officiating, panels, while it is expected to cut labour while Elton Sawyer has replaced Little costs associated with body maintenance by as managing director of the NASCAR up to 50 per cent. The body is eligible for Camping World Truck Series. Both are competition at the start of the 2015 season former drivers, Sawyer most recently team manager at Action Express the 2014 Rolex and is mandated as the only approved body Daytona 24hr championship winning in the series from 2017. It will be available team. Chad Seigler is now vice president in all three manufacturer models: Chevrolet of business development within NASCAR. SS, Ford Fusion and Toyota Camry. Jay Guy has joined H Scott Motorsports as The final season for steel bodies in crew chief for a second full-time NASCAR K&N is 2015, and the current one-piece Sprint Cup team announced at the end composite body will be phased out after of January and will serve as crew chief for the 2016 season. The new body will also be the new team. Furthermore the two-car eligible for competition in the ARCA Racing South Carolina based operation that has a partnership with Series from 2015 onwards. to supply cars and engines, will also work closely with Stewart Hass Racing for 2015.

Longtime ECR Engine chief operating officerRichie Gilmore has been Ford restructures high performance division promoted to the position of President. The former head of DEI Engines joined The ‘Blue Oval’ has restructured its In addition to using racetracks Over the next five years the new ECR in 2007 when RCR Engines merged high performance and motorsport around the world, the team will organisation will create and deliver a with DEI and ECR was formed. divisions and created a single develop new vehicles and technology new range of at least 12 models, most new corporate entity called ‘Ford at Ford’s engineering centres globally of which will also have competition A race fan hit by an overhead remote TV ‘CamCat’ camera cable at the 2014 Performance’. It combines Ford and at the new state-of-the-art variants, though many details have yet Coca-Cola 600 is suing Fox Sports and Racing, Ford SVT and Team RS to technical centre in Concord, North to be announced. for $10,000 serve as an innovation laboratory Carolina. This cutting edge facility ‘Ford still races for the same reasons plus. Fox has not used the technology and test bed to create performance will help the team deliver racing Henry Ford did in 1901 – to prove out since, and the fan, one of 10 people injured, is the only one to take legal vehicles, parts, accessories and innovation, as well as advance tools for our products and technologies against action. The cable was hit by 19 cars experiences for customers. This use in performance vehicles and daily the very best in the world,’ said Nair. after it fell on the track, results of the includes developing innovation and drivers alike. It is already equipped with ‘The Ford Performance organisation investigation into the failure remain technology in aerodynamics, light- a comprehensive range of high end will continue to pursue performance private due to the legal suit. weighting, electronics, powertrain simulation tools. The Ford Performance innovation, ensuring we can deliver who moved performance and fuel efficiency organisation is led by Dave Pericak, even more coveted performance cars, from the NASCAR Xfinity Series to the that can be applied more broadly to who has been appointed director of utility vehicles and trucks to customers Sprint Cup Series this year has named Ford’s product portfolio. Global Ford Performance. around the world.’ 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 as the newly named general manager and chief legal counsel, while Danielle Randall has been named director of business development, Ford hopes technology created by while Mark Gutekunst’s moves into the its Performance division will filter 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

n late 2014 Toyota took the wraps o its not perform well through the season. It just was project. ‘It had been on our radar screen for two new NASCAR Sprint Cup car, with a new not a year that we can feel good about.’ years and we’ve been working on it every day body shape loosely based on its 2015 It was time for the manufacturer to take for the last 18 months,’ he explained at the cars Camry model. The Japanese marque action and it introduced an all-new body for its roll out in Charlotte. ‘Turning the Calty Design Ineeded to make a move after an appalling 2014 cars with a completely di erent nose shape. As it shape into a competition car is a balancing act. season saw it take only two wins. ‘Yes we came is the  rst time during the Generation 6 era that We’re trying to keep as much character as we 12 miles from winning our  rst championship, one of the designs has been re-homologated can in the Gen-6 platform,but also we want to but setting all that aside, it was extremely there is much interest in how the new Camrys try and eke out every bit of performance that we disappointing,’ says Dave Wilson, president and perform on track. can within the parameters that the OEM group general manager, Toyota Racing Development, ‘A lot of hard work has gone into has given us to work in. We’ve looked at some USA. ‘It was the worst season since our debut redesigning the 2015 Camry race car for CFD simulations to make sure that we’re trying in 2007 when we won zero races. Any way you NASCAR competition,’ explains David Wilson, to capture everything that we can, not just from slice it, it was disappointing. We collectively did TRD’s president and general manager. ‘It was a the standpoint that the car will run good by challenging process balancing performance and itself, but also to ensure it runs good in tra c. design, but working closely with Calty Design, We’ve tried to understand that and tweak the The biggest challenge NASCAR and our race team partners, we were design accordingly, based on those parameters.’ able to develop a racecar that looks similar As well as the new nose the car also features of creating the new to its production counterpart and provide a a revised hood and tail. The quarter windows performance upgrade on the track.’ have also been reshaped. All of this has had a machine was taking into TRD, Toyota’s north American motorsport signi cant aerodynamic impact and NASCAR department, started work on the 2015 Camry has made steps to ensure the new Toyota does account feedback from project well before the debacle of the 2014 not gain a substantial advantage over its rivals. season. Andy Graves, a former Cup crew chief ‘Ultimately we had two critical wind tunnel the Toyota driver stable and now TRD’s technical director, headed up the tests,’ Wilson adds. ‘Those were the tests where

6 www.racecar-engineering.com STOCKCAR ENGINEERING 12 The new look Camry features a new nose, hood, rear quarter windows and tail. At the fi rst 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 Racecar reboot

not only does NASCAR come to evaluate, but conditions, the transient aspects of the vehicle after the homologation of the new Camry was our colleagues from Ford and Chevy were also on the track and trying to understand how to completed. And in a rst for the series, that rule there. That’s part of our deal, transparency, measure and do a better job of re ning that.’ book has been issued electronically. because we need everybody to buy into this It contains almost 60 changes covering and believe it’s inherently fair.’ Greater adjustability adjustments to the powertrain, aerodynamics The reason that Toyota had two tests is The changes are more than skin deep and and chassis that are designed to work in that after the rst test the new Camry was behind the new Toyota body panels teams such concert to deliver more  exibility to drivers reportedly found to be a bit too good, and the as have been developing and more adjustability to teams. ‘We have had TRD engineers were told to go away and make ducting and underbody layout solutions to fantastic racing so far in 2014,’ explains Gene it less good before coming back to retest. improve the cars performance on track. Stefanyshyn, NASCAR senior vice president of ‘Everyone wants to be as close to the line ‘It provided us with a lot of opportunity in innovation and racing development. ‘We remain as possible from a competitive standpoint. the cooling area with the brake duct packaging. committed and constantly looking to improve. We pushed it as far as we could but we were Even though the area is the same, it’s allowed us Our fans deserve it and our industry is pushing sweating bullets at the test. We passed; we were to grow in that area and do some things better for it. That will not stop with the 2015 package; within in the box so here we go,’ Wilson reveals. than maybe we did several years ago when the development will continue over many ‘But the reworked car for the wind tunnel we came out with the old nose,’ claims Jason years to come.’ The headline changes include test was not just about the data that came out Ratcli , one of the crew chiefs at Gibbs. ‘There’s a shorter rear spoiler (from eight inches down of the computers next to the working section. a lot of engineering that goes into the area to six), something experimented with in 2014, It’s the things that can’t be measured in the behind the grille opening, not just for cooling, along with a reduction of engine power, lower wind tunnel, that’s where we worked. The but for many other things too.’ rear di erential gear ratios and an optional biggest challenge of creating the new machine Toyota is in for a busy 2015. Not only do the driver adjustable track bar. Additionally a wider was taking into account feedback from the teams have to contend with a new car, they also, radiator pan has been introduced (see P10) and Toyota driver stable,’ Graves continues, ‘that’s in common with all teams, have to deal with the weight of the cars has been reduced by the way the car handles in tra c, the transient a signi cantly updated rule book introduced 23kg, by cutting ballast.

STOCKCAR ENGINEERING 12 www.racecar-engineering.com 7 CAMRY SPRINT CUP

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 The new Camry won first time out, with a Joe Gibbs run car taking the spoils in the Sprint Unlimited at Daytona team members yanking on the side skirts of the cars. These panels on the lower part of There have been significant changes under engine we have today.’ the bodyworks are officially known as vertical the hood too, as the power output of the cars Major changes such as cutting engine rocker panel extensions and engineers in the has been cut significantly. In 2014 the 5.7-litre capacity down to 5.0-litres were on the table at teams found that if the panels were deliberately naturally aspirated V8 Cup engines produced one point but that change was rejected, for now, distorted during a pitstop by mechanics then an between 860-900bhp, but this has been cut to although major changes such as using direct aerodynamic gain could be derived. around 725bhp via the use of a tapered spacer injection and more substantial downsizing in the inlet, similar to those used in the Truck could be on the horizon. The new engines will Safety compromised? series and Xfinity championship. The change not be introduced until the second race of the Now teams who make unapproved adjustments to the lower rear differential gear ratios should year, held at Atlanta, and the engine rules for under caution will have to come back in under see the maximum revs fall to around 9000rpm, the super speedways at Talladega and Daytona caution, fix the car, restart at the rear of the while roller valve lifters replace flat valve lifters. carry over from 2014. field and then do a pass-through on pit road ‘The engine configuration as we know it ‘It’s not fully appreciated, but the fact of at pit-road under green. Teams who is going to change considerably, and what it the matter is that we’ve had the same engine make unapproved adjustments under green means is a different camshaft,’ says Ford engine for basically 25 or 30 years and it’s at 850 or will have to come in under green and fix builder Doug Yates. ‘Going from flat tappet to 860 horsepower, where it used to be 500,’ the car to NASCAR’s satisfaction. If NASCAR roller lifter is a step in the right direction for Pemberton said in explanation of the new rules. identifies a crew member who makes the illegal longevity, but as far as the cam design, the “And we are at the same race tracks where we adjustment, it will issue that person a warning cylinder head, intake manifold and exhaust used to run 160 (miles per hour). We’re now for the first offence and subsequently increase system, all of those things that are related to qualifying at 190 and running 213 going into the sanctions for additional offences. airflow have to change. It’s not a total tear-up by the corners. There’s been a lot of engineering Another change is that the cameras and the any means. Gene Stefanyschyn and the guys at and gains made across the board.’ few remaining officials will no longer monitor NASCAR have done a good job of talking to the Compounding the impact of the changes the teams wheel changing in great detail. engine builders and trying to get our input and to the cars themselves is another rule change NASCAR will not penalise teams for missing feedback on how we would like to go about. aimed at cutting costs which will make it lug nuts out on the car and this opens up the That process explored many different ways of much harder for teams to evaluate their possibility of crew chiefs to gamble more with reducing power, but at the end of the day I think developments. All private testing has been strategy, possibly making a late race stop and we as a sport have made a good and a cost- outlawed with race teams being instead invited only using three or four lug nuts on the wheel effective decision going forward. It’s good for to participate in NASCAR / Goodyear tests rather than all five in order to get a faster stop the engine shops, it’s good for the teams and it’s throughout the season. If a team is caught and gain track position. It also allows wheel good for the sport. There are a lot of ways you conducting private tests in secret then it will changers to take more risks as losing a lug nut in can do it, but this makes sense for the current be hit with a 150 point penalty, a six week is now far less of a penalty, but NASCAR will still suspension for the crew chief and other team penalise teams who lose wheels on track. members and a minimum $150,000 fine. Even with all of the new rules, which were All private testing has One thing that many of the teams would introduced after the homologation of the 2015 like to test will be tyre pressures, as NASCAR will Camry, the new car seems to work as it won its been outlawed with teams no longer enforce a minimum tyre pressure for debut race, the Sprint Unlimited at Daytona. the 2015 campaign. This gives crew chiefs more Toyota may once again be back on the pace and being instead invited to control of how little they put in their tyres but closer to its first ever title, but its work is far from also increases the risk of a blowout. Goodyear finished as NASCAR has already declared that it participate in official tests will continue to provide teams with a minimum will release the 2016 rulebook in the Spring or tyre pressure recommendation, but teams early summer and SCE understands that it will throughout the season do not have to abide by it. ‘With Goodyear contain some substantial changes.

8 www.racecar-engineering.com STOCKCAR ENGINEERING 12 180 mph without moving an inch

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+1 704 788 9463 [email protected] windshearinc.com TECHNOLOGY – NASCAR Taking stock From short tracks to super speedways, NASCAR has always recognised the importance of aerodynamic research By ERIC JACUZZI

he National Association wind tunnel and the 180mph rolling essentially maximum handling tracks study vehicle performance in traffic for Stock Car Auto Racing, road tunnel of Windshear Inc. Teams that are heavily dependent on both conditions. See Table 1. or NASCAR as it is more build specific cars for superspeedway mechanical and aerodynamic grip. Downforce is primarily generated commonly known, is the tracks that emphasise low drag, Apex speeds can range from by the underbody of the car. The Tsanctioning body for the premier while intermediate cars are built for 160-190mph, with top speeds from front splitter and 43-inch wide series in the world. maximum downforce and side force. 195-220mph. Understanding the radiator pan are the largest single Since it was founded in the late 1940s, NASCAR has always realised aerodynamic behaviour of the cars in downforce generating system on the the emphasis has been on the quality the importance of aerodynamics, traffic is crucial to ensuring the cars do car, accounting for 700-1,000lb of of the racing for fans. This continuous with specific sets of rules for the not become overly aero sensitive and downforce depending on setup. drive to make racing as exciting as various tracks that the series runs limit the racing quality. The angles of attack of the splitter possible, while ensuring fair and on. Short tracks are typically defined and radiator pan are adjustable for equitable competition among drivers as those tracks less than one mile in Intermediate car aerodynamics the teams. Typical aerodynamic and teams, is at the fore of the work length, with more emphasis on the The aerodynamics of an intermediate downforce balance is between 45-50 done by the team at the NASCAR mechanical grip due to lower speeds. track NASCAR Sprint Cup Series car per cent front downforce, due to the Research and Development Center in Superspeedways, such as Daytona are dominated by three primary extended/near steady-state cornering Concord, North Carolina. and Talladega, utilise restrictor plates forces: downforce, sideforce and, to a the cars experience on typical While Formula 1 is viewed by to limit horsepower, resulting in lesser extent, drag. The magnitudes intermediate track corners. many as the pinnacle of aerodynamic pack racing that emphasises drag of these forces are shown for the The splitter and radiator pan development, regulations in NASCAR and drafting as the key performance baseline 2014 CFD model. It should form a diffuser surface that works to have permitted such development differentiators. Intermediate tracks be noted that the reliance on an older accelerate and concentrate the air within a narrower technical window (1-2.5 miles) make up the majority chassis and the lack of development coming under the splitter nose into utilising scale wind tunnels, full scale of the schedule, consisting of tracks on the outer body means the CFD a strong central jet. The attachment wind tunnels, and Computational such as Charlotte Motor Speedway, model is 15-25 per cent lower in effectiveness of this jet and its Fluid Dynamics (CFD). which is 1.5 miles in length and downforce than a current race car expansion is heavily dictated by the The region around the Charlotte features banking of 24 degrees in in optimum attitude. However, the pressure conditions under the centre area features two racecar-specific full the corners. The unique aspect of performance mechanism and flow and rear of the car. These areas are scale tunnels, the 130mph Aerodyn intermediate tracks is that they are structures are more than adequate to maintained at as low pressures as

10 www.racecar-engineering.com STOCKCAR ENGINEERING 12 Table 1: Downforce, sideforce and drag Description Lift Total Outerbody Underbody Lift Front Lift Rear Sideforce Front Rear Yaw % Front L/D [lbf] Lift [lbf] Lift [lbf] [lbf] [lbf] Total [lbf] Sideforce Sideforce Moment [lbf] [lbf] [lb-ft] 2014 CFD Baseline -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 fl ow 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 of downforce and sideforce allows created by the spoiler and maintained drivers to apply throttle incrementally by the side skirts. This is why typical earlier on corner exit. With power optimum ride height in mid-corner levels approaching 900 horsepower, is around 0.5in splitter gap and the this vastly outweighs the narrow skirts of the car as low to the track as band of drag gains that teams can possible. See Figures 1 and 2. achieve. And while the iconic images Sideforce is dominated by the of NASCAR races are the large drafting asymmetrical body shape of the car. packs of cars at superspeedways like Not immediately apparent to the Daytona and Talladega, the reality is untrained eye, the right side of the car that the 100-150lb drag advantage is straight from the front wheel back, of a trailing car at an intermediate Figure 4: Lap 157 telemetry from number 4 of Kevin Harvick and number 48 of Jimmie while the left rear quarter panel is track is not enough to outweigh any Johnson. Throttle traces are shown by dashed lines while speed is indicated by solid cambered towards the right by 4in. on-throttle disadvantage due to car lines. The lap is divided by fraction (0.00-1.00) with 0.01 of a lap equating to 0.015 miles This gives the top view of the car mishandling in tra c. a subtle aerofoil shape. The ratio of A sample of telemetry from a horsepower at 200mph. Drag in applying it in every professional front and rear sideforce is the main lap demonstrating this is shown in horsepower is the industry standard racing series in motorsports. NASCAR driver of the overall yaw moment of Figure 4. In this case, the number measurement for aerodynamic drag. was able to leverage this expertise the car. As expected, the rear sideforce 4 car of Kevin Harvick (red traces) is and within a few weeks was able is greater than the front to allow the trailing the number 48 car of Jimmie Aerodynamics programme to have a fully functioning CFD driver to con dently yaw the car Johnson (blue traces). The 4 car drops In 2012, NASCAR embarked on its rst capability of its own running out of in the range of 3-5 degrees. While in behind the 48 car on corner entry, CFD study of the problem. Previously, its Concord R&D center. sideforce forms a lesser component trailing behind by 2-3 car lengths. the sanctioning body had relied on of overall cornering force than the On corner exit, the 4 car attempts to occasional team support for one or Baseline model downforce magnitude, sideforce acts apply throttle as usual but the car two car runs, but with the scale of The R&D centre in Concord owns directly on the car without acting understeers up the track and Harvick the problem requiring substantial several older cars with bodies through the tyres. This means that the is forced to modulate the throttle personnel and computational representative of the current eld 500lb of sideforce is directly translated heavily. He is then at approximately 50 resources, the assistance was valuable in the Sprint Cup Series. Complete into lateral acceleration, while 500lb per cent throttle for several hundred but limited in scope and timeliness. scans were made of both the outer of downforce is at the mercy of feet of the lap, while the leading 48 The need for a well-funded CFD study and underbody and pre-processed the chassis setup and tire friction car is at full throttle. The 4 car is then was too great to ignore any longer. To in Beta-CAE’s ANSA. Since ANSA coe cient at that particular track. slower at every point on the track help facilitate this, NASCAR turned to converts native CAD and scan CFD results, as well as driver feedback, until the next corner, losing 0.2 to 0.3 TotalSim, a US-based company that data into the Standard Tesselation indicate that sideforce variation seconds from this incident alone. provides software and engineering Language (STL) format, it saves may be more critical than any loss in The largest drag item on the car solutions to the motorsport, substantial time in CAD cleanup downforce. See Figure 3. is the 8in spoiler. The relationship automotive and aerospace industries. by allowing quick corrections and Drag is the least important between drag and spoiler height TotalSim support and develop rebuilds of poor surfaces into quick, factor for present power levels on is almost perfectly linear, with 1in OpenFOAM®, an open source CFD watertight CFD geometry. The car an intermediate track. The pursuit of spoiler accounting for 40 drag software package, and has experience is broken into approximately 30

STOCKCAR ENGINEERING 12 www.racecar-engineering.com 11 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 fi ns

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

The next question is how to of the lead car where the trailing car best handle the volume of data and is at a downforce advantage. Drivers visualise the aerodynamic behaviour are aware of this region and will work e ectively. This is done by plotting the to prevent a trailing car from being in aerodynamic characteristic of interest that area. What is the reason for this? using a contour plot that interpolates Since the body of the car makes lift, Figure 9: Underbody downforce of trailing car compared with itself alone in free air that characteristic spatially between when any region of it is in the wake the discrete simulation points. Using of the lead car, the body makes less separate regions that separate the can take upwards of four days to a simple two colour common scale lift – and hence downforce. In a sense, outer and inner components and run three seconds of ow time on creates e ective imagery to convey the maximum downforce the outer regions into reporting patches of similar hardware. Given this, runs car performance. The black dots body of the car makes is when it’s interest. See Figure 5. are performed in an incompressible indicate where the centre of the stationary. The opposite is true of the The solution is carried out by steady-state manner, which yielded a trail car’s splitter was on the run that underbody of the car, particularly the OpenFOAM, featuring customised good compromise of run time versus generated data for that point. splitter and radiator pan system which wall functions and using the K-Omega accuracy. See Figure 6. The drag delta plot shows that require faster moving air to make SST turbulence model. Typical grid while the trailing car has a drag maximum downforce. Plotting the sizes for a single car run are on the Aero performance mapping advantage of around 5-10 per cent underbody downforce of the trailing order of 50 million polyhedral cells, After establishing the baseline from one car length and further back, car in tra c compared to in free air while two car runs are on the order model performance and validating at closer range its drag increases reveals the underbody downforce of 110-120 million depending on at a variety of ride heights and yaw markedly. This is a two-fold change: de cit caused by the slow moving air proximity. Several transient Detached conditions, two car tra c simulations the trailing car is helping the lead near the track. See Figure 8. Eddy Simulation (DES) runs have also were performed. These consist of car by forming a more aerodynamic The underbody downforce plot been performed to validate certain a lead car that remains stationary, two car body, which is at the same of the trailing car compared to itself critical results and wake structures while a series of 46 simulations are time shielding the usually very low in clean air paints a clear picture of behind the car, but have not yielded performed with the trailing car in pressure A-pillars of the trailing car, where downforce losses are coming any substantial changes that would a variety of positions laterally and increasing its drag. See Figure 7. from. The underside of the trailing necessitate running in this condition. longitudinally behind the lead car. The downforce delta plot of the car, from the splitter to the very tail of For comparison, a 144-core steady Both cars are at the same ride height trailing car vs. the lead car begins the car is running in the large ground state single car run can be completed and yaw angle. The 46 CFD runs to show regions where cornering wake formed by the lead car. The from ANSA STL to results in 10 hours, generate 500Gb of data that includes performance is compromised, even majority of the component level loss while a transient DES run starting force patch reporting and automatic at substantial lengths behind the lead here is from the splitter-radiator pan from a resolved steady state run pressure and velocity imaging. car. There is a region to the left side 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 Figure 11: CFD results indicate that the hood and fender region contacting a small part by itself but can make for poor handling in traffi c 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 Figure 13: Sideforce and traffi c-handling issues: the proportion of the total cornering its optimum line force the sideforce makes up at various positions and central underbody regions. Series, which featured two separate The change of the trail car the trailing  nds itself in, and how See Figure 9. car bodies: a composite car body illustrated here is dictated entirely by position dependent that plight is. The sideforce delta plot reveals based on an older superspeedway car, the downforce of the car and excludes Cornering force is the combination a dramatic loss in sideforce of over and a steel bodied car that was built sideforce. In the regions where the car of both downforce and sideforce 300lb, which is well over 50 per more similarly to a current Sprint Cup tends toward understeer, the splitter (both converted to positive numbers). cent of the car’s total sideforce car in sideforce levels. The composite and radiator pan (and subsequently Behind the lead car and to the right performance. Interestingly enough, car crew chiefs would state that they the underhood region) take a can put the trailing car at a 500lb- across the various series that NASCAR knew they could generate more substantial loss in downforce due force disadvantage to the leading car, operates (NASCAR Camping World sideforce, and hence performance, to reduced airspeed and mass  ow while positioning the trailing Truck Series, NASCAR K&N Series and by ‘skewing’ the car (pre-yawing the rate. The opposite e ect occurs in the car toward the left quarter-panel of so on), drivers’ comments and setup car with the rear axle). This made oversteer regions; a small portion of the lead car can lead to a cornering decisions by teams seem to indicate the car faster by itself, but made the high lift hood and fender areas force advantage. that over-reliance on sideforce is the car handle poorly in tra c enter into the car’s wake, reducing It should be noted that on many a negative characteristic. This was when sideforce was more highly lift and causing the balance to tend ovals, the trailing car would be forced particularly noticeable in the K&N compromised. See Figure 10. toward oversteer. to run in the loss region to run the Many people attribute the optimum line. See Figure 12. Future steps oversteer handling characteristic A  nal interesting plot is using the in tra c to a loss in downforce at cornering force metric, but adjusting the rear of the car – an obvious downforce by an average tyre friction ASCAR recently invested in from CFD to the wind tunnel can be conclusion to draw. But the data coe cient value of 0.8 to re ect how a 128-channel Scanivalve challenging enough. But bringing shows that in most situations the much downforce is converted to Npressure scanning system, solutions that improve racing quality spoiler and its e ect on the lifting lateral force. We then can look at what with a 128 Kiel probe modular is an even further abstraction, greenhouse of the car vary only by proportion of the total cornering force array to begin verifying CFD involving simulated races on track 10-20lb, nowhere near the magnitude the sideforce makes up at various prediction of the wake structures. with test drivers who may or may required to substantially in uence positions. Alone, the sideforce usually Long commonplace in F1, this not prefer to be on leave between car performance. The CFD results accounts for around 40 per cent of the aerodynamic testing methodology is races rather than pounding indicate that the hood and fender total cornering force, but in the wake slowly making its way into the sport. around the track. region contacting a small part of the region of the lead car, this drops to NASCAR will continue to work on So the answer is not always slow moving wake causes an increase only 10 per cent or less. This rea rms improving car aerodynamics, while clear. But continuing on the path of in front downforce (by mitigating lift), more recent thinking that making considering what magnitudes of scienti c analysis and attacking the leading to the forward balance shift. sideforce with the car body may be forces work best at speci c tracks and problem analytically will ultimately See Figure 11. a large contributor to tra c for tyre supplier Goodyear. yield the best result for fans, drivers, The cornering force plot handling issues that drivers report. Ultimately, bringing solutions and the series as a whole. highlights the di cult situation See Figure 13.

14 www.racecar-engineering.com STOCKCAR ENGINEERING 12 DC AD Racecar Oct14 AWF.pdf 1 16/10/2014 07:41

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“...let us run with endurance the race that is set before us...” Hebrews 12:1 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

ecently I have been doing a lot of Figure1: Beam pogo stick asymmetric modelling work. In visualisation of the race car particularly I have been working closely with a stock car racing Rorganisation. 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 Asymmetric 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 correlation techniques 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. Spring rates Figure 2a: Front left load vs damper displacement 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. Figure 2b: Front right load vs damper displacement 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 Figure 2c: Rear left load vs damper displacement 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 ΔLoad / MR ks = Δdamper Here we have ks = Spring rate δLoad = Change in Load Figure 2d: Rear right load vs damper displacement 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 Value Load Front Left 50 kgf Load Front Right 100 kgf Load Rear Left 150 kgf Load Rear Right 200 kgf Speed 250 km/h

Table 2: Sanity checking numbers Quantity Value Figure 3: Looking at roll data Spring Rate 1000 N/mm Damper Value 20mm EQUATIONS Load 700 kgf Motion Ratio (damper/wheel) 0.6 Equation 2 Equation 3

Load FL + Load FR + Load RL + Load RR The next step is to sanity check that the C A = LDAMP = MR ⋅ k ⋅ md L 0.5⋅ ρ ⋅V 2 dampers and loads are telling you the same = 0.6 ⋅1000 ⋅ 20 thing. To illustrate this lets consider an example, 9.8⋅ (50 +100 +150 + 200) = = 12000N as illustrated in Table 2. 0.5∗1.225∗ (250 / 3.6)2 For the sake of this discussion all motion = 1225.5kgf ratios are linear and springs are linear. From the = 1.66 data the load on the tyre from the damper data is shown in Equation 3. particular Figure 2c and 2d give you the rear this then calculating the bar rate is easy. This As you can tell there is a discrepancy here spring rates of the car. This is one less variable should be your procedure: that needs to be addressed. In order to resolve you need to worry about. • Calculate the main spring rate using the this tools such as wind tunnels, CFD and on track The reason the data looks like a blob as data to the left bifurcation point. experience will be your best friends. opposed to a line is the effect of bumps and • Calculate the spring point post the Now that we have spring rates and some damping. What you are looking for here is bifurcation point. idea of downforce we are now in a position to trends. Once you have the trends you can get • The bar rate is simply the difference do correlation. Where things get a bit trickier cute with the details later. Don’t do it the other between the two. than in the symmetric case is that separating the way around as you’ll drive yourself nuts. pitch and roll isn’t as straightforward as it is with I prefer to calculate the bar rates from the the symmetric case. So for correlation this will Bar rates most linear of the curves, which in this case is as be our game plan: Where things get really interesting is the front. shown in Figure 2a. • Correlate on the loaded side. Looking at both Figure 2a and 2b there is a Now we have our spring rates the next step • Look at the unloaded side. distinct bifurcation point. Just a note on data is to calculate the downforce, if there is any • Then check pitch and roll channels. analysis. If you ever see something like Figure present on the vehicle. As per the symmetric car 2a and 2b print it off and hold it up next to a you are using exactly the same techniques to Working through this process the loaded light. If there are any non-linearities it will show get yourself into the ballpark – that is choose a side looks pretty good and this correlation is up as plain as day. It’s a rule of thumb taught point on the straight or low lateral acceleration shown in Figure 4. to me by one of my physics professors. In both and confirm with a hand calculation. Let me For reference I have used the lap time Figure 2a and 2b there is a distinct bifurcation give you a quick example. Let’s say we have our simulation, but the reality is that the track replay point where the gradient has changed slope. loads zeroed on the ground and we have this simulation is just as good. Also the actual data Typically if you see something like this we data set, as demonstrated in Table 1. is coloured and the simulated data is black.

have hit a roll bar. What we need to do now is to Calculating the CLA we see Equation 2. Looking at the right side the damper correlation cross reference this with the data. The thing to This is a bit of a Mickey mouse example but is very good. Going down the straight there pay attention to is quantifying the bifurcation it illustrates the point. are some things we need to tidy up with the point to when the roll kicks in. You are looking Also at this point in the game let me offer aeromap, but this is a good start. for a situation like the one in Figure 3. some reflections about resolving load and Also let me state that particularly for the lap You’ll notice I have placed the cursor on damper channels. In my experience load cells time simulation trace you are not looking for the bifurcation point of the front left damper. are a bit like fish and chips or romantic movies. perfect correlation. At this stage you are looking Firstly you’ll notice the bottom trace which is the They are either really good or really bad and for something that is in the ballpark so you can front roll. Then you’ll notice how the front roll there is no inbetween. Consequently you must get basic validation done. Once reach this point has increased from zero at this point. If you see always sanity check them. The first port of call you can concentrate on getting an accurate model. something similar to this you know the shape of is Figure 2a – 2d. If it’s not consistent then that However, things need tidying up somewhat Figure 2a is being influenced by the roll bar. is your first alarm bell. Fortunately in this case it on the unloaded side. The correlation is as The good news is that if you have data like was consistent, so that is the first pass mark. 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 Figure 4: Loaded side correlation 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 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 Figure 6: Effect of applying a softer front left spring and increasing rebound everywhere running tyre force optimisation and begin work on setting the car up. In summary achieving correlation for an Achieving correlation for an asymmetric car isn’t significantly different to it’s symmetric counterpart – it’s just a bit more asymmetric car isn’t significantly in depth. Our process starts by making sure we have good data on the racecar. We then plot different to its symmetric counterpart load vs dampers for each corner of the car to quantify what the springing of the car is doing. – it’s just a bit more in depth 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.

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

hen an engine specialist as and worked his way up to the elite series in ‘After spending a lot of time doing this, experienced as Brian Kurn is NASCAR. He was highly-regarded for his work you took the parts to the dyno and only then excited about a technology, on cylinder heads and his ability to extract did you nd out if you had found a solution or others in the eld tend to take more power while retaining reliability. Today, just scrapped another cylinder head. It was an notice.W If they don’t, they should. he’s a highly-respected engine developer who expensive and time-consuming way to see if Kurn is currently working at ECR Engines, has plied his trade, successfully, across many your idea gained a few more horses or not. And a division of Racing and is in racing championships – Tudor United Sportscar each time you got a new head design, you really charge of valvetrain development together with Championship, NHRA Pro Stock, American had to start again!’ It was this ine ciency which all virtual prototyping technologies, including Le Mans Series (ALMS), Touring Cars in Brazil drove the forward-thinking Kurn to investigate engine and valvetrain simulation, as well as and Argentina, Truck-pulling, Supercross and, simulation technologies. computational  uid dynamics (CFD). In a of course, NASCAR. As an experienced CFD user, primarily to career spanning 25 years he has worked ‘In the good old days, so-called tuners analyse internal  ows in the engine, both stand- for some of the biggest names in the sport, determined the biggest valves that could be alone and coupled with engine simulation, Kurn including Roush, Hendrick and Bill Davis used and then they simply began to hand-port is at home with state-of-the-art technology. Racing. Kurn started his craft building and the head, believing that the more air that would But, in those early days just over a decade ago, improving V8 engines for the small dirt tracks  ow, the more power it should make,’ says Kurn. CFD posed problems. ‘The run-times to do the

20 www.racecar-engineering.com STOCKCAR ENGINEERING 12 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 put the engine tweaks to good use on the track

simulations took too long and when we had For Kurn, it was a frustration. ‘I never believed had been around for long time but none of to create our own mesh, we really suffered that an effective automatic meshing tool would the solutions I tried lived up to their claims of with the variability between users,’ claims happen in my lifetime. I thought we would a completely automatic mesh that produced Kurn. ‘It can affect your results and introduce be stuck with the longer run-times forever,’ he accurate results. But if the guys at Gamma inconsistency, which ultimately means your explains. But after learning that Converge had were convinced Converge was different then I trust in the data can go out of the window.’ collaborated with engine simulation provider thought maybe it was worth a look. I’d always Gamma Technologies, everything changed. struggled with meshing, and longed for the day Mix and mesh It was there that Kurn first encountered when I wouldn’t have to predict the outcome in Even today, creating a good mesh is crucial an innovative automatic meshing solution order to define the mesh, and I didn’t want my to resolve the flow. But the quest for an called Converge™ CFD Software. Developed meshing to affect the result. I ended up taking a automatically-generated mesh never quite by Wisconsin firm Convergent Science Inc., look – the rest is history.’ delivered the accuracy needed to move it automates the meshing at run time with away from user-generated data. For years, a perfectly orthogonal Cartesian mesh that Time saver engineers simply accepted the challenges eliminates the need for a user-defined mesh. Written by engine simulation experts to address and did what little they could to minimise ‘To be honest, I’d heard it all before and I the deficiencies of other CFD codes, Converge the variations. was sceptical,’ says Kurn. ‘Automatic meshing offers run-time grid generation and refinement

STOCKCAR ENGINEERING 12 www.racecar-engineering.com 21 TECHNOLOGY – COMPUTATIONAL FLUID DYNAMICS

so users such as Kurn no longer need to spend RCR’s engines have benefited their time creating meshes. from increased reliability 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 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 CFD comes into its own for in-cylinder propagation as it’s far more accurate than using a larger mesh and where it is needed at run-time for

22 www.racecar-engineering.com STOCKCAR ENGINEERING 12 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 NASCAR has no regulations governing virtual testing – pretty soon most of the paddock will be following RCR’s lead garage is another area where fast and accurate simulation is helping. Kurn believes that a effectively. The simplicity of Converge leads the Sprint Cup Series Championship standings NASCAR pushrod engine is one of the worst him to believe anybody with CFD experience with Ryan Newman, while more than 23 top case scenarios for different behaviours when could use it – and within 10 minutes they’d 10 finishes resulted in Brian Scott snatching fired up. ‘The actual exhaust valve opening can have a surface modelled. 4th in the Xfinity championship with be delayed as much as 10-15 crank degrees as ‘I have found Converge to be one of the gaining a rookie victory at Indianapolis and a result of the cylinder pressure acting on the simplest and most powerful simulation tools 5th overall in the final standings. Team mate valves,’ he explains. ‘Using trusted valvetrain available. And if there are any issues, there’s showed the versatility simulation, we can now optimise the design of usually a solution to hand. All we have to do of the team’s development, winning on the the valvetrain components to work in the real is pick up the phone with any questions and traditional Road America circuit. ECR’s engines world, even in a NASCAR application.’ together we’ve provided answers to many proved crucial in the TUSCC, helping Chevrolet issues. I can’t fault the team’s support.’ to win both titles. The Action Express Daytona Simplicity and support Prototype, with an ECR engine, scored eight Virtual testing is currently unrestricted in Tracking the results podiums including three victories, most NASCAR and is becoming more and more It is results on track that define success and notably the Daytona 24 hours. The ECR engine popular as teams look for the edge over the 2014 was a very successful year for Converge, was reliable; the car completed every lap of competition. As Kurn points out: ‘Track testing, as demonstrated by the significant gains in competition last season. ‘It was a special year save for the odd tyre test, is zero!’ Despite power achieved in 2014. for Kurn and the ECR team,’ adds Kaczmarek. half the teams having simulation tools, he These leaps in performance helped Richard ‘We are so proud to have been involved with is unsure how many are actually using them Childress Racing (RCR) secure second overall in 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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