Copyright 2002 Fluent Inc. EX166 Page 1 of 2

A P P L I C A T I O N B R I E F S F R O M F L U E N T

The flow around a model of theRed Bull Sauber C-20 FormulaOne (F-1) racing car (Figure 1) isstudied in this example. ModernF-1 cars are capable of reachingspeeds in excess of 350 km/hr.Cornering in these conditions ispossible because of the largenegative lift, or downforce, gener-ated primarily by wing structuresat the front and rear of the vehicle.When combined with wind tunneltests, CFD can be used to under-stand the effect that these wingshave on the vehicle aerodynamics.

To explore the complex flowaround the F-1, a half-car modelof the Red Bull Sauber C-20 wassimulated. An unstructuredhybrid mesh was used for theturbulent, 3D, steady-statesimulation. A free stream velocityof 69.44 m/s (250 km/hr) was setat the inlet boundary of thesolution domain, as wereturbulence quantities based onlocal turbulence intensity andlength scale. The Spalart-Allmaras turbulence model wasused to facilitate closure of theNavier-Stokes equations. Thisone-equation turbulence modelperforms well in the prediction ofattached and separated flows,

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Development of the CFD modelbegan with a geometry file,created by the CAD packageCATIA. ANSA was then used tocreate a triangular surface mesh.This mesh was imported intoTGrid, where a hybrid mesh ofapproximately 20 millionprismatic and tetrahedral elementswas created. The surface mesh onthe driver's helmet and cockpitarea is shown in Figure 2. Thelower rear mainplane (wing) meshis shown in gray in Figure 3. Inthis figure, a planar surface with aquadrilateral mesh, used togenerate layers of prismaticelements, is shown in red.

Pressure contours on the surfaceof the car in Figure 4 show highpressure regions (red) at the uppersurfaces of the front and rear

typical of those in the vicinity ofthe front and rear wings of the car.The model is also capable ofresolving the salient features ofthe exterior and interior flowfields. To complete the simulationof the car motion, the groundplane was given a velocity equalto the free stream velocity, and thetires were assigned a corres-ponding rotational speed.

Formula 1 External AerodynamicsIn this example, FLUENT 5 is used to study the flow around a model of the Red Bull Sauber C-20Formula One (F-1) racing car in high speed, high downforce conditions. Pressure coefficients,computed at two locations on the rear wing and flap, are in very good agreement with experimentalmeasurements. Other results are helpful in understanding the interaction between the many complexcomponents of the car.

Figure 2: The surface mesh in the cockpit area

Figure 1: A model of theRed Bull Sauber C-20Formula One racing car

Figure 3: The surface mesh in the rear wing area,showing a planar surface of quadrilateral faces,used to create prism layers

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wings, indicative of the strongdownforce generated by thesecomponents. Low pressureregions (green) indicate areaswhere the air velocity is highest.

Path lines around the car body areshown in Figure 5. Of interest isthe interaction between the frontwing and wheels. The degree ofupwash generated by the frontwing is also important. The up-wash can have a deleterious effecton the cooling system and cancompromise the aerodynamicbehavior of some componentsimmediately downstream of thewing. At the rear of the car, astrong upward motion of air is inevidence, along with a pair oflarge, counter-rotating vortices.These effects are the result of thedownforce produced by the carunderbody and rear wing,respectively.

The upper rear wing of thevehicle consists of two compo-nents: the mainplane wing, and aflap. These are designed togenerate a strong downforce athigh speeds. To illustrate the

effectiveness of these compo-nents, the pressure coefficient, Cp,is plotted against the normalizedchordwise position, x/c in Figures6 and 7. In both cases, theFLUENT predictions arecompared to wind tunnel test data.In Figure 6, the results correspondto a position that is 100 m to theside of the vehicle centerline.There is very good agreementbetween the predicted pressuresand the experimentalmeasurements for both themainplane and flap.

In Figure 7, Cp is again plottedagainst the normalized chordwiseposition, only the results corres-pond to a position that is 400 mmfrom the vehicle centerline.Experimental measurements areagain in good agreement withFLUENT predictions. The smalldifferences that do exist can beattributed to differences in thefree stream conditions used in theexperiment and simulation,possible localized regions of

Figure 4: Contours of static pressureon the surface components

laminar flow in theexperiment (that are notin the CFD model), andthe presence of themain wind tunnel strutwhich is absent fromthe geometry used inthe numerical solution.In addition, thedifference between theresults in Figures 6 and

7 suggest that 2D simulations ofwing components will fail to ade-quately capture the full three-dimensional nature of the flow.

The results presented in thisexample demonstrate that it ispossible to use CFD to analyze thecomplex flow field about arealistic contemporary FormulaOne car model. The pressuredistribution and surface flowvisualization compare well withexperimental results, showing thatthere is significant merit in using aone-equation turbulence model forthis type of application, despitethe anisotropic nature of thehighly turbulent, separated flow.The results derived from thenumerical solutions havecomplemented the experimentalprogram at Sauber PetronasEngineering AG, allowing for amore rigorous approach to findingimprovements in car performance.

Courtesy of Sauber PetronasEngineering AG, Hinwil, Switzerland

Figure 7: Pressure coefficient 400 mm from thecenterline of the rear wing mainplane and flap

Figure 6: Pressure coefficient 100 mm from thecenterline of the rear wing mainplane and flap

Figure 5: Path lines around the vehicle