# Formula 1 External Aerodynamics by skini.se

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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
EX166

Formula 1 External Aerodynamics
In this example, FLUENT 5 is used to study the flow around a model of the Red Bull Sauber C-20
Formula 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 experimental
measurements. Other results are helpful in understanding the interaction between the many complex
components of the car.

The flow around a model of the                                                                        Development of the CFD model
Red Bull Sauber C-20 Formula                                                                          began with a geometry file,
One (F-1) racing car (Figure 1) is                                                                    created by the CAD package
studied in this example. Modern                                                                       CATIA. ANSA was then used to
F-1 cars are capable of reaching                                                                      create a triangular surface mesh.
speeds in excess of 350 km/hr.                                                                        This mesh was imported into
Cornering in these conditions is                                                                      TGrid, where a hybrid mesh of
possible because of the large                                                                         approximately 20 million
negative lift, or downforce, gener-                                        Figure 1: A model of the   prismatic and tetrahedral elements
Red Bull Sauber C-20
ated primarily by wing structures                                          Formula One racing car     was created. The surface mesh on
at the front and rear of the vehicle.                                                                 the driver's helmet and cockpit
When combined with wind tunnel                   typical of those in the vicinity of                  area is shown in Figure 2. The
tests, CFD can be used to under-                 the front and rear wings of the car.                 lower rear mainplane (wing) mesh
stand the effect that these wings                The model is also capable of                         is shown in gray in Figure 3. In
have on the vehicle aerodynamics.                resolving the salient features of                    this figure, a planar surface with a
the exterior and interior flow                       quadrilateral mesh, used to
To explore the complex flow                      fields. To complete the simulation                   generate layers of prismatic
around the F-1, a half-car model                 of the car motion, the ground                        elements, is shown in red.
of the Red Bull Sauber C-20 was                  plane was given a velocity equal
simulated. An unstructured                       to the free stream velocity, and the                 Pressure contours on the surface
hybrid mesh was used for the                     tires were assigned a corres-                        of the car in Figure 4 show high
turbulent, 3D, steady-state                      ponding rotational speed.                            pressure regions (red) at the upper
simulation. A free stream velocity                                                                    surfaces of the front and rear
of 69.44 m/s (250 km/hr) was set
at the inlet boundary of the
solution domain, as were
turbulence quantities based on
local turbulence intensity and
length scale. The Spalart-
Allmaras turbulence model was
used to facilitate closure of the
Navier-Stokes equations. This
one-equation turbulence model
performs well in the prediction of                                                                    Figure 3: The surface mesh in the rear wing area,
Figure 2: The surface mesh in the cockpit area       showing a planar surface of quadrilateral faces,
attached and separated flows,                                                                         used to create prism layers

laminar flow in the
experiment (that are not
in the CFD model), and
the presence of the
main wind tunnel strut
which is absent from
the geometry used in
the numerical solution.
difference between the
Figure 5: Path lines around the vehicle
results in Figures 6 and
effectiveness of these compo-                         7 suggest that 2D simulations of
nents, the pressure coefficient, C p,                 wing components will fail to ade-
is plotted against the normalized                     quately capture the full three-
chordwise position, x/c in Figures                    dimensional nature of the flow.
6 and 7. In both cases, the
Figure 4: Contours of static pressure
on the surface components               FLUENT predictions are                                The results presented in this
wings, indicative of the strong                compared to wind tunnel test data.                    example demonstrate that it is
downforce generated by these                   In Figure 6, the results correspond                   possible to use CFD to analyze the
components. Low pressure                       to a position that is 100 m to the                    complex flow field about a
regions (green) indicate areas                 side of the vehicle centerline.                       realistic contemporary Formula
where the air velocity is highest.             There is very good agreement                          One car model. The pressure
between the predicted pressures                       distribution and surface flow
Path lines around the car body are             and the experimental                                  visualization compare well with
shown in Figure 5. Of interest is              measurements for both the                             experimental results, showing that
the interaction between the front              mainplane and flap.                                   there is significant merit in using a
wing and wheels. The degree of                                                                       one-equation turbulence model for
upwash generated by the front                  In Figure 7, Cp is again plotted                      this type of application, despite
wing is also important. The up-                against the normalized chordwise                      the anisotropic nature of the
wash can have a deleterious effect             position, only the results corres-                    highly turbulent, separated flow.
on the cooling system and can                  pond to a position that is 400 mm                     The results derived from the
compromise the aerodynamic                     from the vehicle centerline.                          numerical solutions have
behavior of some components                    Experimental measurements are                         complemented the experimental
immediately downstream of the                  again in good agreement with                          program at Sauber Petronas
wing. At the rear of the car, a                FLUENT predictions. The small                         Engineering AG, allowing for a
strong upward motion of air is in              differences that do exist can be                      more rigorous approach to finding
evidence, along with a pair of                 attributed to differences in the                      improvements in car performance.
large, counter-rotating vortices.              free stream conditions used in the
These effects are the result of the            experiment and simulation,                            Courtesy of Sauber Petronas
downforce produced by the car                  possible localized regions of                         Engineering AG, Hinwil, Switzerland
underbody and rear wing,
respectively.

The upper rear wing of the
vehicle consists of two compo-
nents: the mainplane wing, and a
flap. These are designed to
generate a strong downforce at
Figure 6: Pressure coefficient 100 mm from the        Figure 7: Pressure coefficient 400 mm from the
high speeds. To illustrate the                 centerline of the rear wing mainplane and flap        centerline of the rear wing mainplane and flap