2009 Formula One Aerodynamics BMW Sauber F1.09 Fundamentally Different

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1 2009 Formula One Aerodynamics BMW Sauber F1.09 Fundamentally Different Torbjörn Larsson BMW Sauber F1 Team, Hinwil, Switzerland ABSTRACT To make Formula One more attractive to a broader audience, radical changes to the FIA technical regulations have been imposed for the 2009 season. Primarily, the lack of overtaking and exciting wheel-to-wheel racing is believed to be a direct consequence of the massive levels of aerodynamics down force generated by modern F1 cars. Therefore, these new regulations are targeting a significant reduction in achievable aero forces via specific restrictions to the shaping of the vehicle exterior. This should also lead to more aero performance retained on cars following in the wake of another car. Claiming back lost aero performance (to good levels) proved to be a true challenge for the aerodynamicists. Reliance exclusively on knowledge and insights gained from intensive engineering of concepts in the past was not going to be adequate to propel this project. New insights were essential, and a comprehensive CFD campaign became instrumental in devising the development path for a fundamentally different race car, BMW Sauber F BACKGROUND The winds of change are blowing through Formula One. The 2009 season sees arguably the most significant rewrite of the F1 technical rulebook in the history of the sport. New rules governing tires, aerodynamics and Kinetic Energy Recovery Systems (KERS), among others, are considered to be the biggest changes in the Formula One regulations for several decades. Driving forces behind these rule changes are the increasing needs for costcutting and improvements to the on-track spectacle. The aim of the new aerodynamic regulations, as well as the reintroduction of slick tyres, is to decrease reliance on aerodynamic down force and increase mechanical grip with the aim of making wheel-to-wheel racing easier, and hence, promote overtaking. These radical rule changes have literally brought the F1 engineers back to the drawing boards to start from a clean sheet of paper.

2 Figure 1: The BMW Sauber 2009 (left) vs (right) F1 racing cars. 2. AERODYNAMICS DEVELOPMENT PROCESS The development of the BMW Sauber 2009 F1 contender had to centre on the three key areas; tire utilization, aerodynamics and KERS integration. Addressed herein are exclusively the engineering challenges associated with the aerodynamics development of this brand new race car. Here one obvious design approach is to start from what you got, i.e. the existing race car, and convert it into a concept that complies with the new aero regulations. This is an ideal task for the CFD engineers, far more practical than building up any physical models for testing. By doing so, the very first CFD predictions revealed an overall down force reduction by more than 50%! Such a tremendous performance loss is not at all surprising, given that the existing race car is an evolution over many years of engineering and design (with relatively stable rules), whereas the 2009 spec car had to be something more of a revolution to meet the new standards. By nature and definition, revolution is disruptive to people, well-functioning organizations and processes. Hence, achieving revolutionary goals through an evolutionary process would be the desired path to the future. Still, taking such a path requires a process of adequate flexibility to allow for an efficient collection of new knowledge and insights. In this case, relying too much on experiences and know-how from the past might not necessarily bring enough leverage to propel the development forward at a sufficient rate, and it can even (in a worst case) be misleading. Hence, rather than building upon incremental refinements from a given design point, this requires several fundamentally different concepts to be analysed in order to populate a sufficiently broad design space. Computational Fluid Dynamics (CFD) and High Performance Computing (HPC) hold the keys to the success of such a design process.

3 2.1 CFD Methods and High Performance Computing The Hinwil based race team (before 2005 known as Sauber Petronas) has a long tradition in using CFD for aerodynamics research and development [1-5], and the CFD group has become an integral part of the aero department and its design processes. The launch of Albert3 in 2008, a state-of-the-art Intel based supercomputer tailored for large scale CFD applications, clearly underlines BMW Sauber s strong belief in, and commitment to, simulation technology. Rather than pursuing a second wind tunnel, the team took this pioneering approach with a future more focused around CFD and high performance computing. Figure 2: BMW Sauber Supercomputer Albert3. Frequently, BMW Sauber has been referred to as the benchmark in F1 regarding HPC and CFD. With a close to 10,000 fold increase in available compute capacity over the last decade, the team today performs simulation scenarios unheard of only a few years ago. Not only from building up such an outstanding compute facility, but also very much due to the team s strong commitment to CFD methods development, the overall aero process efficiency has taken a leap forward. Today, using advanced and tailor-made simulation methods, a broad design space can be explored in a relatively short period of time to devise directions for further and more extended research. And before committing to any physical parts production, many design concepts and ideas can be evaluated with good confidence on Albert3. 3. FLOW PHYSICS AND AERODYNAMICS The intricacy of the aerodynamics of a Formula One car is still one of the most fascinating aspects in the engineering of a competitive race car. In particular, the ability to control and stabilize flow patterns emanating from the exposed wheels is of fundamental importance in order to extract the ultimate aerodynamics performance from any open-wheel racing car.

4 EASC 2009 Fig gure 3: BMW W Sauber F1.09 F with CFD C stream mlines overla aid. 3.1 F1 Aerodynam A mics 2009 In essen nce the FIA techn nical regula ations have had the folllowing signiificant implications to the ve ehicle exterrior shaping g: 9 Narrower N and Taller Rear Wing pllaced Highe er Up 9 Wider and Lower L Fron nt Wing with h Unloaded Centre Secction arts Furtherr Back 9 Underbody Diffuser sta F Fewer Add-On A Airr-Control De evices (wing glets, barge-boards etcc.) 9 Far The prim me and imm mediate efffect of thesse rule chan nges was a dramatic reduction in n overall down fo orce (~50% %). To claim m back losst aero perfformance (down ( force e and efficiency) a comprehensive und derstanding g of the flow w physics is vital. Figure 4: exte erior (left) vs. v 2009 extterior (right)).

5 EASC 2009 Some noticeable n o observations s are: 9 R Rear wing becomes more of a stand-alon ne device and a flow in nteractions with the and diffuse u underbody er are much reduced 9 R Revised difffuser desig gn has a drramatic effe ect on unde erbody flow where mos st of the o overall dow wn force is being b genera rated 9 Exclusion E o auxiliary wings of w has a large direc ct and indire ect impact o on down forrce 9 Front F wing flow and itss interaction n with the re est of the ca ar is remarka ably differen nt As a co onsequence e of the ma ajor concep ptual chang ge to the frront wing design the front f tire wake flow has cha anged radically. This affects the e rest of the e car in a very differe ent way. Added to t this is the complete e ban of auxxiliary airflo ow control devices, d ma aking contro olling the tire wakke flow mucch more diffficult than before. b Tran nsient CFD simulationss on early concepts c also con nfirmed more flow flucttuations and d instabilitie es. Early co onceptual CFD C studie es to the 2009 aero regulations r revealed flow structures with underlying mechan nisms funda amentally different d to what w was believed b to be well und derstood ered concep pts, apparen nt on the previous yearr s race carss. and highly enginee Figure 5: Wake e flow patte erns behind 2008 and race ccars. ure 6: Frontt wing / tire flow f interacction concept c (lefft) vs concept (riight). Figu

6 Thus, to gain further insights into important underlying flow mechanisms, a large CFD research campaign was initiated, with main focus on front wing tire interaction. Being the foremost device the front wing design is of paramount importance for overall aerodynamics performance. In particular the wing interaction with the tire wake is crucial for the conditioning of the on-set flow to the underbody. Figure 7: Front wing flow pattern. Unloading the centre portion of the wing, via the mandatory FIA section, results in a distinct vortex being shed off the flap inboard tip as depicted in Figure 7 above. In addition, having a wider wing span pushes the outboard wing tip vortices outside of the front tire. Controlling these flow paths is of fundamental importance and one of the key considerations for finding aero performance. These dominating flow structures, how they interactt and influence the car, where initially not very well understood. Via a large DOE mapping in CFD of front wing shapess a new knowledge base could be built-up relatively quickly. This was achieved via coupling tailored methods for morphing, re-meshing and optimization to the FLUENT solver which allowed for an efficient scanning of a broad design space. A similar approach in the wind tunnel would not be feasible given time and cost constraints. 4. CONCLUSIONSS In the light of the present economic climate, efficiency in processes has become of utmost importance. More than ever before, advances in CFD / HPC methods, processes and infrastructure play an increasingly important role to stay competitive in any fast past industrial environment. Formula One is no different, and CFD has grown to be an integral part of the BMW Sauber team s aerodynamics research and development programme. Developing to the 2009 rule book has highlighted how CFD today is taking the lead in F1 aerodynamics research. In particular, the outcome of a front wing design study became instrumental in devising the development path for the 2009 F1 race car. By the time for the oral presentation at the EASC conferencee in Münich this summer, the 2009 F1 season is well underway and we should already have had a clear suggestion on how good of a job we did on finding aero performance given the highly revised and restricted technical regulations.

7 REFERENCES [1] Akanni S., Larsson T., Bienz C. Numerical Modelling of the Aerodynamic Flow Field about a Formula One Car, Fluent User Group Meeting, Germany [2] Bienz C., Larsson T., Sato T., Ullbrand B., In Front of the Grid CFD at SAUBER PETRONAS F1 Leading the Aerodynamic Development, 1 st European Automotive CFD Conference, Bingen, Germany, [3] Kremenetsky M., Larsson T., Numerical Studies on a ccnuma Computer Architecture for a Large Scale Race Car Aerodynamics Simulation, Parallel Computational Fluid Dynamics 2004, Elsevier Science, ISBN: [4] Larsson T., Sato T., Ullbrand B., Supercomputing in F1 Unlocking the Power of CFD, 2 nd European Automotive CFD Conference, Frankfurt, Germany, [5] Larsson T., High Performance Computing Shaping the Future of Formula One, Masterwork Session, 2007 International Supercomputing Conference, Reno, NV, USA.

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