Post on 11-Jul-2015
August 2014
Josep Mª Carbonell Oyonarte
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a racing car
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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About the author
This project was performed in the CFD and
Race car aerodynamics course imparted by
Tecnica F1. The author is Josep Mª Carbonell,
aeronautical student at UPC in Terrassa
(Barcelona), and a race cars enthusiast.
That’s the reason behind this project, the
objective was to put all this knowledge into
designing a race winning car concept.
Contact Details
Mail: jmcarbonelloyonarte@gmail.com
Phone number: +0034687688061
Linkedin: Josep M Carbonell Oyonarte
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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Contents
Concept
1- Introduction ............................................................................................. 3
2- Reviewing the concept ........................................................................ 6
Preparation and results
3- Targets of the study .............................................................................. 9
4- Meshing ...................................................................................................... 9
5- Simulations and results .................................................................... 10
5.1- Downforce .................................................................................... 14
5.2- Drag ................................................................................................. 15
Resolutions
6- Conclusions ........................................................................................... 16
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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1- Introduction
In the world of motorsport, there have been a lot of developments benefiting maximum speed, resistance and speed cornering. This document deals with the later. Generally speaking there are 2 main ways to increase cornering speed:
· Increasing mechanical grip through improvements of shock absorbers, springs, anti-roll bars, camber and castor angles, etc.
· Increase the downforce of the car through aerodynamic work with spoilers, wings, air flow around and under the car, etc.
Since mid-60’s, the most popular way to obtain downforce have been the implementation and fine tuning of aileron, flaps and spoilers but there have been some others paths to create downforce from the air. One of these ways is creating a low pressure area under the car, as a high pressure are always try to move towards a low pressure area the car is effectively sucked towards the ground. The basic idea is to accelerate the air under the car, the first step is adding a rear diffuser which accelerates the air exiting the rear. Also, we have to ensure that as little air as possible enters the bottom of the car through the sides and that there is the least possible air under the car. There are two ways to make that:
· Putting skirts to the floor.
· Creating an aerodynamic wall along the car.
In 1970 a new concept was born. Jim Hall and his team created a new car, the Chaparral 2J. it was a pioneer of one of the most incredible
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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inventions and pieces of lateral thiniking in racing history: placing a fan at the rear of the car in order to suck the air from under the car increasing the pressure differences and effectively sucking the car to the tarmac. This development was quickly banned in the Can-Am category, due to the large performance advantage of this concept.
Eight years after, Gordon Murray and his Brabham team, run by Bernie
Ecclestone, resurrected this concept in Formula 1 with the BT46B,
famously remembered as the “Fan car”. The story of this car was the
same than Chaparral, it was banned after the first race because of the
overwhelming dominance.
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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Figure 1- Chaparral 2J
Figure 2- Brabham BT46B “Fan car”
The fan of the Brabham was
connected to the crankshaft
by a small gearbox, so the
velocity of the fan could be
modified.
The two 17-inch fans
were driven by a 45 hp
two strike twin
snowmobile engine.
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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2- Reviewing the concept
After so many years without any advances on this concept, a new car
has been developed. This car is different, because it’s a virtual car, the
Red Bull X1. The designer, Adrian Newey, used all the advances and
concepts possible to improve the car, even if they aren’t allowed in any
category of motorsport.
Our objective was to study a car similar to Red Bull X1, and quantify
the Fan Effect and it’s on the performance of the car.
This is the car used:
Figure 3- Car used renderized in Loews turn
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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And this is the fan placed behind:
Figure 4- Fan
As we can see, the car has wheel fairings and a close cockpit, two
improvements in terms of drag reduction banned in Formula 1. Also, it
counts with ground effect, because it is a so-called “wing car”. This
design allows increasing total downforce, and combined with the fan,
the magnitude of downforce can be stunning.
We can see the low
pressure around the fan
due to the high velocity of
the suctioned air.
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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The definitive improvement of the car is its skirts, closing the area for a
better suction.
Fan cars: What’s it all about? Aerodynamic study of the implementation of a fan to a race car
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3- Targets of the study
The main targets of the study are as follows:
Minimum fan speed in order to improve downforce.
Correlation between downforce and fan speed.
Correlation between drag and fan speed.
We are not looking for quantitative results, because the resources able
for this project don’t permit more precision on the data resulted, but
we are able to obtain a good qualitative results of the targets of this
study.
4- Meshing
We have configured a polyhedral mesh and a boundary layer around
the car to obtain more precisely the downforce and the drag induced
on the body. Before configure the boundary layer, we calculate first
layer thickness based on the air speed and the y+ desired. Also, we
added a block mesh on the entire region around the bottom of the car
and the diffuser. This block mesh has smaller mesh size than the rest of
the volume and gives us more control and precision around this area,
the most important of the car in this study.
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5- Simulations and results
The first step was to set up the basic parameters:
Air velocity: 220 Km/h
Rolling ground and wheels to make the simulation and its results
more realistic.
The next step was to identify the minimum fan speed which increases
downforce. After several simulations at different fan speeds, the
minimum speed was determined as 25000 rpm. Under this speed, the
fan decelerates air passing under the car and downforce falls.
This is the pressure distribution over the car:
Figure 5-Pression distribution over the car
These points have high
pressure because the air is
decelerated when hit the
car.
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And this is the pressure distribution under the car:
Figure 6-Pression distribution under the car
We can see the depression created by the diffuser and the fan, which
starts just at the front skirt of the car. This is the reason of the large
improvement in terms of downforce.
As we can see in this
picture, the low pressure at
the bottom of the car has
the meaning of a high speed
of air or the vacuum effect
created. In other words, we
can see how the ground
effect is working.
We can see how the front
wheels produce a large
increase in pressure and a
resulting large increase in drag.
The rear wheels produce much
less drag as they are better
protected by the car’s body.
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These are the streamlines over the car, and we can see how the air
interacts with the car:
Figure 7- Streamlines over the car
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Another interesting visualization is the velocity vectors on side plane
for a future upgrade of the aerodynamic design of the car:
Figure 8- Air speed vector side view
After this previous study, we proceeded to compare the drag and
downforce of different fan speeds and, of course, the base scenario
where there is no fan.
This picture proves turbulences
created by the fan.
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5.1- Downforce
When simulations had been made, we analyze the outcomes of
downforce of each speed, and compared them with the downforce of
the car without fan as we were looking the improvement made by
using a fan.
We can see now the effects of using a fan in terms of downforce
improvement. We can say that the magnitude of improvement is
remarkable in terms of speed through the corners, but before
definitive conclusions we must analyze what is the effect on the
maximum speed, since a large increase in drag would penalize us much
on the straights.
0
5000
10000
15000
20000
25000
30000
30000 35000 40000 45000 50000
Increased downforce (N)
Fan speed (Rpm)
Table 1- Increase of downforce related with fan speed
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5.2- Drag
Here we analyze the results of the drag in each fan speed. We did the
same as for the downforce, so we compared the drag with fan and
without it.
The study demonstrated an increase proportional to the fan speed, an
increase in downforce always causes more drag. Maybe the most
important fact is that the increase in drag is very small compared with
the gains in downforce.
80
90
100
110
120
130
140
150
160
170
30000 35000 40000 45000 50000
Increased drag (N)
Fan speed (Rpm) Table 2- Increase of drag related with fan speed
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6- Conclusions
The results show the very interesting use of a fan, it produces a large
gain in downforce but with only a small increase in drag. The use of the
fan is recommended in all circuits except very bumpy circuits where
large changes in distance of the floor to the ground could suddenly
produce an alarming loss of downforce, resulting in a potentially
uncontrollable and dangerous car. Moreover, the use of ground effect
needs stiffer suspensions as the distance of the floor to the ground has
to be the controlled as much as possible. This means a more difficult
work for the driver.
One of the possible ways to improve this concept is to design a system
which allows transmitting the best fan velocity, or the right grade of
blades, for each condition and positon of the car. The next step is to
stop the fan in the straights because its effect is detrimental for the
tires and it harms maximum speed.
As a conclusion, it’s clear that, with some investment and fine tuning of
the system, this concept can be very worthwhile.
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