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A report on
CFD ANALYSIS OF DUEL ELEMENT REAR WING OF A F1 CAR
Lekhnath Gyawali1
1 Student at Kathmandu University, Department of Mechanical Engineering, Nepal
*bbekgyawali7@gmail.com
INTRODUCTION
A Formula One car also known as an F1 car is a single-seat, open-cockpit, open-wheel
formula racing car with substantial front and rear wings, and an engine positioned behind
the driver, intended to be used in competition at Formula One racing events[1]. Formula
One cars are the fastest cars in the world around a race track, owing to very high cornering
speeds achieved through the generation of large amounts of aerodynamic downforce[2].
Figure 1 Mercedes F1 car[3]
Downforce is a downwards lift force created by the aerodynamic features of a vehicle. In
case of a F1 car, the purpose of downforce is to allow the car to travel faster by increasing
the vertical force on the tires thus creating more grip. This effect is referred to as
"aerodynamic grip" which is a function of the car's mass, tires, and suspension. The
downforce is mainly governed by two main components in a F1 car and these are[4]:
a. Shape of the body resembling the shape of an airplane with some extra add-ons
like wings, spoilers and ducts to improve efficiency.
b. Airfoils, contributing much of the downforce in a F1 car i.e., one being front wing
and another a rear wing.
The downforce exerted by a wing is usually expressed as a function of its lift coefficient
which is given by:
where:
F is downforce (N), CL is the lift coefficient,
ρ is air density (SI unit: kg/m^3), v is velocity (SI unit: m/s),
A is the area of the wing, frontal area (SI unit: meters squared).
REAR WINGS
Rear wings of a F1 car uses two or more elements for larger downforce creation and each
of these elements can be adjusted at any moment of time. Rear wing has to produce more
than twice as much downforce as the front wing in order to balance the car. It contributes
about 25% of total downforce generated by a car[5].
In this case study we are going to examine the
duel NACA 2408 profiles at speed ranging from
50 to 320 km/h to examine the streamlines,
vortices produced, coefficient of drag and
pressure distribution. Also, in this study the
effect of DRS (Drag Reduction System) is
analyzed.
F =
Angle of Attack
The Angle of Attack is the angle at which relative wind
meets an airfoil. It is the angle formed by the Chord of
the airfoil and the direction of the relative wind or the
vector representing the relative motion between the
aircraft and the atmosphere.
LITERATURE REVIEW
The various results obtained by different researchers are enlisted below in term of rear
wings, its profile and downforce generated.
S.N.
Description
1
This paper[6], uses NACA 2408, 2412, and 2415 for the flap wing and BE50
for the main plane. Each case being simulated with a gap between the airfoil of
10 mm and 50 mm when the DRS is activated. Simulations were performed by
using k-kl-omega model and results show that the short flap wing generate lower
downforce than the big flap wing, but the drag force can be significantly reduced
as the short flap wing has more change in angle of attack when it is activated.
2
Here[7] each case is simulated with a gap between the airfoil of 15 mm and 45
mm when the DRS is activated. It interprets the connection of the coefficients
of drag and downforce changing with respect to the AOA (Angle of Attack).
3
This article[8] shows how poor design of the end plates and positioning of the
wing elements can led to large vortex production, the effects of these vortices
resulting in reduced negative lift
4
This article[9] shows the upwash effect and wake produced in a F1 rear wing at
boundary conditions of inlet velocity of 50 m/s, reference length of 0.4 m, slip
type boundary condition and by using k- turbulence model.
5
This paper[10], revealed that a 12° angle of attack is the optimal angle for
designing the spoiler. Twelve degrees angle of attack provided the highest
downforce. This downforce can improve the stability of high-speed sports car
without increasing much drag.
6
In this paper[11], a double-element rear wing was studied for varying angle of
attack using MSES code with Spalart-Allmarus model for turbulence at 3 106
to 4 106 Reynolds number. It concluded; the angle of attack had the same effect
as that of the single element wing with higher levels of downforce generation.
7
This paper[12], uses NACA 2312, NACA 2308 and NACA 2104 for the rear
wing analysis and finds the drag coefficient in range 0.01697 to 0.04340 and lift
coefficient in range -0.26427 to -0.35808.
8
This paper[13], shows the upwash generated at variable vertical distance and
states that the reduction of the camber of the tips in order to reduce the load
could expected to reduce pressure drag and increase the lift-drag ratio.
9
This paper[14], shows the most efficient ground clearance point moves from 22
percent to 25 percent of the chord length at a distance of 30, respectively 50
percent of a car length. The flow structure analysis clearly showed a positive
impact of the wing tip vortices coming from the bluff body.
10
This paper[15], states:
a. For an inverted NACA 8516 rear wing, the highest L/D ratio appears
when the Angle of Attack is 5o, the Stall Angle is around 15o, the
maximum negative force appears when the Angle of Attack is 15o.
b. Multi-Wing combination can generate more negative lift force, but
assembling too many wings will enhance the drag force and reduce the
l/d ratio.
PROBLEM STATEMENT
For the study of aerodynamic effect on F1 rear wing, spoiler profile of NACA 2408 having
the chord length of 2.26 mm was taken with DRS spoiler having length parameters 30%
of main spoiler. The simulation domain is taken as 15 mm by 8 mm. Three different
simulation setups were set with the main spoiler having angle of attack -12o with DRS
spoiler having angle of attack of -40o for corners & normal track position and at 0o for
straights. Here, the density of air is taken as 1.225 kg/m3.
Parameters
Values
Free stream velocity
13.889 m/s
Dynamic viscosity
0.000017894 kg/m s
Y+
1
Wall spacing
0.0000246 m
Reynolds number
950815.2
Table 1 Parameters for car at corners
Parameters
Values
Free stream velocity
44.44 m/s
Dynamic viscosity
0.000017894 kg/m s
Y+
1
Wall spacing
0.0000084 m
Reynolds number
3042304.68
Table 2 Parameters for car at normal track position
Parameters
Values
Free stream velocity
88.889 m/s
Dynamic viscosity
0.000017894 kg/m s
Y+
1
Wall spacing
0.0000043988 m
Reynolds number
6085225.49
Table 3 Parameters for car at straights
NUMERICAL MODEL
Numerical modeling of the problem is done using ANSYS Workbench 19.2 software but
the design of airfoil was done using SOLIDWORKS.
a. Modeling
As mentioned above, the model was prepared in Solidworks and saved in. IGS format
and imported in ANSYS for further procedures. The thickness of surface was kept 10
mm with chord length of spoiler as 2.26 mm and chord length of DRS airfoil of 0.70
mm.
b. Meshing
Meshing was done using ANSYS meshing having Nodes 588183 and Elements
561890. While meshing linear element order was kept having growth rate of 1.2.
Figure 2 Meshing with ANSYS CFX
c. Pre-processing
In pre-processing steady state analysis was carried out with k- turbulence modeling.
Working fluid was air and no slip wall condition was applied.
d. Post-processing
In post-processing various streamlines, contour plots and graphs were plotted
mentioning the effect of velocity, pressure and so on.
RESULTS
Various contours, graphs and streamlines shows the relation between velocity and
pressure at different angle of attack of spoiler and DRS encountering different inlet
velocity. Velocity and pressure distribution are plotted for the inlet velocity of 50 kmph,
160 kmph and 320 kmph respectively and are shown below.
a. For inlet velocity 50 km/h with DRS angle of attack at -40o
From the results shown, it can be observed
that at a low velocity and higher angle of
attack of DRS, the DRS acts accordingly to
its design by pushing air upward and
creating high velocity streams to lower side
of spoiler than that of upper which can be
observed in adjoined streamline. Here, in
the lower side of spoiler airfoil the streamlines get squeezed and thus according to
venturi effect its velocity increases resulting low pressure zone. The increase in
velocity and decrease in pressure can be observed in contour figure below. The graph
below also depicts the inverse relation of pressure and velocity for example the blue
line in graph represents the line through trailing edge of spoiler and taking data in
reference to that line it has seen that when velocity increases after inlet simultaneous
decrease in pressure is observed in adjoining pressure graph. Due to this relation, a
significant downforce is developed in the rear wing section of the car.
With frontal area of airfoil being 8.76 , inlet velocity of 13.88 m/s, downforce
of N and drag force of N, the coefficient of downforce
(negative lift) was found to be 0.0121 and coefficient of drag is found to be 0.05.
Figure 3 Streamline, velocity contour and pressure contour
b. For inlet velocity 160 km/h with DRS angle of attack at -40o
160 km/ h is normal racing speed having
quick turns and short straight in which
the DRS remains closed. The effect of
closed DRS can be observed from
contour plot below where it maintains the
downforce for tire grip but also traveling
in much faster speed with DRS closed
invited an unwanted factor called drag.
With frontal area of airfoil being 8.76 ,inlet velocity of 44.44 m/s, downforce
of N and drag force of 6.25 N the coefficient of downforce
(negative lift) was found to be 0.0176 and coefficient of drag is found as 0.059.
Figure 4 Streamlines, Contour plots and graph for car at speed 160km / h
c. For inlet velocity 320 km/h with DRS angle of attack at 0o
F1 cars of this time have maximum
speed of 320 kmph having DRS open
in straights. In this case, there is
minimum drag exerted on the car in the
expense of downforce which makes car
faster but loses tire grips. The same
pressure velocity relation can be seen
in this case as above.
With frontal area of airfoil being 8.76 ,inlet velocity of 88.88 m/s, lift force of
N and drag force of -3.689 N the coefficient of downforce
(negative lift) was found to be 0.012 and coefficient of drag is found as -0.0872.
Figure 5 Streamlines, velocity and pressure contour plots for inlet velocity of 320km/h
VALIDATION
As stated in paper [6], the result of this paper resembles the fact that the flap wing at an
angle produces more downforce while wing parallel to spoiler produces less downforce.
This can also be proven from the fact that the coefficient of downforce at an angle of -40o
found to be greater than that of at 0o even that at 0o the lift coefficient becomes greater
than 0 i.e., instead of producing downforce it produces lift.
In paper[12], having a different airfoil profile shape the drag coefficient in range 0.01697
to 0.04340 and lift coefficient in range -0.26427 to -0.35808 was found which is similar
to this study i.e., lift coefficient in range -0.0121 to -0.0176 and drag coefficient in range
-0.0872 to 0.05.
CONCLUSION
From this simulation it was proved that, increase in camber line increases the downforce
(i.e., coefficient of lift was found to be in range -0.0121 to -0.0176 which indicates the
downforce rather than lift) by increasing air flow in lower part of the airfoil and
subsequently decreasing the pressure which can be seen in pressure contour plot in figure
4, 5 and 6 with a bit more drag production i.e., at around 0.05 for angled DRS while when
the DRS airfoil is kept horizontal, less drag is created in expense of downforce with the
creation of lift (in case of car at speed 320 kmph where lift coefficient was found to be
0.0109). So, this shows that while taking corners the DRS wing should be at maximum
angle so as to increase the tire grip but while travelling in straights DRS wing should be
horizontal to the ground for maximum speed. All these data were calculated using ANSYS
CFX and verified with previous literature.
REFERENCES
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