Kingston University: Exploring Automotive Aerodynamics History

This research paper provides a comprehensive overview of the general principles and history of automotive aerodynamics. It begins by outlining the early approaches and shapes used in automotive design, followed by a discussion of wind tunnels and their role in streamlining cars. The report examines the change in drag coefficient over time and explores the key features of aerodynamic vehicles, including flow fields, flow improvement techniques, and the characteristics of flow. It also delves into the causes of drag force and the phenomenon of boundary layer separation. A comparison with aircraft aerodynamics is presented to highlight the differences and similarities. Finally, the report discusses various methods of studying aerodynamics, such as wind tunnel testing and computer modeling. This student contributed document is available on Desklib, a platform offering a wide range of study resources.

Automotive Aerodynamics 1
GENERAL AND HISTORY OF AUTOMOTIVE AERODYNAMICS
A Research Paper on Aerodynamics By
Rikash Mohamed
Kingston University

Automotive Aerodynamics 2
Contents
INTRODUCTION...........................................................................................................................................3
OBJECTIVES..............................................................................................................................................4
HISTORY.......................................................................................................................................................4
Approaches in Early Stages and Shapes...................................................................................................4
Wind Tunnels...........................................................................................................................................8
Car Streamlining......................................................................................................................................9
Change in Drag Coefficient of Cars........................................................................................................10
FEATURES OF AERODYNAMIC VEHICLES....................................................................................................12
Flow Field..............................................................................................................................................13
Improvement of flow.............................................................................................................................15
Characteristics of Flow...........................................................................................................................16
Causes of Drag Force.............................................................................................................................16
Boundary Layer Separation...................................................................................................................17
COMPARISON WITH AIRCRAFT AERODYNAMICS.......................................................................................18
METHODS OF STUDYING AERODYNAMICS................................................................................................20
Wind Tunnel Testing..............................................................................................................................20
Computer Modelling..............................................................................................................................22
CONCLUSION.............................................................................................................................................23
BIBLIOGRAPHY...........................................................................................................................................24

Automotive Aerodynamics 3
INTRODUCTION
This research paper is about the general and history of automotive aerodynamics and majorly
focuses of the approaches in early stages and shapes, wind tunnels, car streamlining, change of
drag coefficient of cars, features of aerodynamic vehicle such as boundary layer separation,
causes of drag force, characteristics of flow, improvement of flow, as well as flow field and also
comparison with aircraft aerodynamics. Aerodynamics involves the study of air motion,
specifically as interaction with a solid object like automotive. Automotive aerodynamics can be
defined as the study of the road vehicles aerodynamic. The major objectives of studying
aerodynamics of vehicles are to prevent aerodynamic instability at high speed and undesired lift
forced, minimize noise emission, wind noise, and reduce drag.
It first began as a way to determine methods of reducing the required power to move the
automotive at a specific speed on the roadways. In the year 1920s, engineers started considering
the shape of automobiles as a way of minimizing aerodynamic drag at a high velocity. In the
1950s, British and German automotive engineers were examining the impacts of automotive
friction for vehicles of high performance. They became conscious of the substantial increase in
the levels of sound produced by automotive at high speed by the late 1960s. Soon the highway
engineers started designing roadways to contemplate the speed effect of aerodynamic friction
generated levels of sound and the manufactures of these automobiles considered the same factors
in the design of the vehicles. Currently, numerous automakers have their own facilities for
testing wind tunnel, using it in developing and studying the aerodynamic features of any new
automotive (Ainegren & Jonsson, 2018).

Automotive Aerodynamics 4
OBJECTIVES
The main objectives of this research paper on the general and history of automotive
aerodynamics are:
 To analyze the approaches in the early stages and shapes of automotive
 To evaluate the features of aerodynamics
 To compare aerodynamics with aircraft aerodynamics
 To determine the method of studying aerodynamics (Alam, et al., 2012)
HISTORY
The aerodynamic drag caused by the frictional force significantly increases with the speed of the
vehicle. In the early 1920s, engineers stated considering the shape of an automobile so as to
minimize aerodynamic friction at high velocity. By the year 1950s, British and German
automotive engineers were examining systematically the impacts of automotive friction for the
vehicles of higher performance. Engineers also became conscious of the substantial increase in
the levels of sound produced at high speed by the vehicles by the late 1960s (Antanaitis, 2012).
Approaches in Early Stages and Shapes
The air presented the greatest obstacle to the economy and automotive speed and this was
intuitively and scientifically understood before the dawn of automotive. Entrepreneurs, racers,
engineers, and dreamers were lured by the potential for the aerodynamic offered and profound
gains. The efforts to do resulted in more remarkable vehicles even if they challenged the
aesthetic assumptions of their moments. The origins of streamlining go back to 200 years ago
and the ideal form of streamline was illustrated by Sir George Cayley in 1865. Racers,
specifically those chasing the coveted and Speed Record were normally the first to apply the aids

Automotive Aerodynamics 5
of aerodynamics (Antanaitis, 2016). The first automobile to break the 100km record in 1899 was
Jamais Contente shown in the figure below:
Figure 1: Jamais Contente of 1899 (Bansal & Sharma, 2014)
The position of the driver seems to reduce the aids of aerodynamics. The aerodynamic evolution
for the land speed record cars was rapidly remarkable as evidently shown in 1906 by Stanley
Rocket. The increased velocity was also even dramatic since the Rocket broke the barrier if
200km with a run of 205.44 kmh.
Figure 2: Stanley Rocket of 1906 (Buljac & Džijan, 2016)

Automotive Aerodynamics 6
The first known attempt at streamlining a passenger vehicle was in 1914 in the Alfa Romeo
which was built for the Italian Count Ricotti by the coachbuilder Castagna. This vehicle turned
out not to improve the maximum velocity of the open Alfa due to the very heavy bodywork it
possessed (Chandar & Damodaran, 2010).
Figure 3: Alfa streamliner of 1941 (Chen, 2014)
The actual success of aerodynamic passenger vehicle was the German Rumpler of 1921. Unlike
the heavy and impractical Castagna Alfa, this vehicle was influential and different dynamically
due to its complete integration and original engineering and design. This car had numerous
features such as a four-wheel independently suspended by the use of swing axles and also a mid-
engined W6 engine. The German Rumpler was tested in a wind tunnel of VW in 1979 and
attained a Coefficient of drag of .28 remarkably. This degree of Coefficient of drag was later
attained by the Passat in 1988. The Coefficient of drag of a body denotes the relative
aerodynamic slipperiness of the vehicle irrespective of its entire size. The cross-section of the
vehicle looking straight on is multiplied by the Coefficient of drag to attain the critical total
aerodynamic drag which determines efficiency and the power required. The German Rumpler
was very aerodynamic relatively, however, it was quite boxy and tall, which led to numerous of
such designs to be used basically as taxis (Dalessio & Duncan, 2017).

Automotive Aerodynamics 7
One of the most lasting and influential designers of this entire period was Hans Ledwinka of
Australia. After taking over the position of the chief design engineer in 1921 at Czech firm, he
came up with the primary series in 1921 of outstanding Tatra and ultimately streamliners with
frame platforms, rear air-cooled engines, and independent suspensions.
Figure 4: Tatra v570 of 1933 (Dong, et al., 2009)
The later series of Volkswagen after 1934 showed a very strong resemblance to the Tatra v570.
The introduction if streamlining in America had come in 1934, two years earlier with the
stunning Chrysler Airflow.
Wind Tunnels
Wind tunnels are huge tubes with air moving inside and this movement of air around the
automotive will make it seem like the vehicle is actually flying. The first enclosed wind tunnel
for the purposes of aerodynamics was operated and designed by Francis Herbert in 1871 from
the Aeronautical Society of Great Britain. Despite this early research, the testing of wind tunnel
was applied only to automobiles approximately one century later, after years of using simulations
by computer instead of the actual real-life. This delay was as a result of the fact that aircraft
aerodynamics differs from the automotive aerodynamics in numerous ways. This difference is

Automotive Aerodynamics 8
because vehicles do not run in free air and their motion is less affected by the forces of
aerodynamics while operating speed is also lower (Gatto, et al., 2010).
English mathematician and engineer Benjamin Robins first invented a whirling arm apparatus
which was used in determining drag and then used this apparatus to perform the first
experimentations on the theory of aviation. The whirling arm was also used by Sir George
Cayley to determine the lift and drag of numerous airfoils. His whirling arm attained top speed
between 20 and 10 feet per second and was 1.5m long. Nevertheless, the whirling arm does not
generate air flow that is reliable affecting the test shape at normal incidence. An Aeronautical
Society of Great Britain Council Member by the name Francis Herbert (1824-1908), addressed
this issue by operating, inventing, designing in 1871 the first enclosed wind tunnel. In 1897,
Konstantin Tsiolkovsky designed wind tunnel with an open-section as well as a centrifugal
blower and also determined spheres, cylinders, and flat plate’s coefficient of drag (Geyman, et
al., 2014).
In 1901, the Wright brothers used a sample wind tunnel to determine the impacts of airflow over
numerous shapes while establishing their Wright Flyer. In France 1909, Gustave Eiffel
constructed the first open-return wind tunnel at the base of the tower with his name written on it
which was powered by a 50kW electric motor. He performed wind tunnel tests equivalent to a
total of approximately 4000 tests, and his research set new aeronautical research standards
(Ghoreyshi, 2019).
Car Streamlining
While engineers have less or more conscious of what it takes to build aerodynamic designs for a
long duration, it took time for the principles of aerodynamics to be implemented in the designs of

Automotive Aerodynamics 9
automotive. Previously, there was no concept of aerodynamic in these vehicles such as Ford
Model T which resembled more like a carriage of horse and was characterized by boxy design.
In the early 1900s, some racing cars incorporated aerodynamic and tapering features to one
degree or another. Edmund Rumpler who was a German inventor built the Rumper-Tropfenauto
in 1921 with a Coefficient of drag of .27. One of the biggest leaps on the American side ahead in
aerodynamic design came in 1930 with the Chrysler Airflow. Chrysler Airflow was one of the
initial vehicles designed with the mindset of aerodynamics and was inspired by the birds in
flight. This car design used some unique techniques in construction and had a nearly had an
equal distribution of weight (Gnemmi, et al., 2012).
Between 1960s and 1950s, there were some of the major developments in automotive
aerodynamics, especially in racing cars. Initially, automotive engineers investigated with
different designs having known that shapes that are streamlined could assist their vehicle to
handle between higher speeds and go faster. This ultimately evolved the racing cars into a very
precise crafting science that majority of aerodynamic. On the side of consumers, companies such
as Porsche, Lotus, and Citroen established vehicle designs that are very streamlined, however,
these were majorly implemented in sports cars of high-performance and not in daily automotive
for ordinary drivers. The development vehicle streamlined design of ordinary vehicles started in
the 1980s with the Audi 100 which had a Cd of .30 (Han & Cai, 2013).

Automotive Aerodynamics 10
Figure 5: Ley racing car of 1923 (Hart, et al., 2016).
Change in Drag Coefficient of Cars
Automobile drag coefficient is a parameter used in automotive design to measure its
aerodynamics and also other performance characteristics. Cd is a quantity that is dimensionless
and is used to determine the resistance or drag of a body in an environment made of fluid, like
water or air. This quantity is applied in the equation of drag in which a lower coefficient of drag
shows that the object will have a hydrodynamic drag or aerodynamic (Hirz & Stadler, 2013).
Figure 6: Measure of Coefficient of drag (Hodson, 2014)

Automotive Aerodynamics 11
The drag coefficient affects the way in which the vehicle passes through the air surrounding
since it increases with the square of speed. The first cars were manufactured before the invention
of wind tunnel tests and before Wright brother's era. The wind tunnels were used extensively in
the design of aircraft, however, the designers of cars notice slowly the effect of aerodynamics in
the performance of cars (Howell, 2015).
The beginning of drag reduction was between 1890 and 1920 and was started by the first car ever
to cross 100 kmh barrier in 1899. This car was made by racer Camille Jenatzy and was known as
La Jamais Content shown in figure 1 above. The shape of the vehicle was like torpedo so the
body of the vehicle was streamlined but the wheels and driver lost some of the benefits of the
body shape of the vehicle. However, this was the first attempt at designing a vehicle to be
advantageous aerodynamically. The next vehicle that was designed was the Alpha Romea Ricotti
which was designs in 1914 as an aerodynamic prototype with a shape like a teardrop and a hap
impressive high speed of 140 kmph. As shown in figure 3 above. As the aerodynamic principles
were becoming available to the engineers, they started to experiment and design with the
vehicles. The water drop falling was considered to be a perfect aerodynamic, and after the First
World War, numerous aeronautical engineers from Germany began designing vehicles (Islam &
Gaylard, 2017).
Edmund Rumpler was one of the engineers who in 1922 designed Rumpler Tropfenwagen. He
was the first person to perform wind tunnel experiments on cars and this car had drag three times
compared to the previously manufactured cars. One of the influential designers during this period
was Paul Jaray who was initially a designer of Zeppelin fenders. He designed cars with cambered
windshields, integrated headlights and fenders, and smooth body surfaces as well as other
innovations. This design was later copied by VW, Audi, and BMW. Jaray car design reduced Cd

Automotive Aerodynamics 12
to 0.29 from the prevailing 0.64. The wind tunnel experiments by Klempered showed that the
lowest Cd with wheels close to earth for half body was just 0.15 and therefore the succeeding
streamlined vehicles were designed while keeping in mind the half body design (Islam &
Gaylard, 2017).
This trend changed however after the crisis of petrol of 1970 which made oil to be unaffordable.
The result is that detailed optimized car such as VW Scirocco of 1974 has a Cd of 0.41 compared
to 1969 Open GT streamlined design of Cd 0.42. After late 1970, the work of aerodynamic
design continued from where it had previously stopped due to lack of petrol which led to the
introduction of shape optimization. The first design car to apply the shape optimization was Audi
C3100 which had Cd of 0.3 and was made in 1983. Modern cars have Cd which ranges between
0.25 and 0.30 and the future target is expected o be lower than 0.25 (Jiang & Liu, 2011).
FEATURES OF AERODYNAMIC VEHICLES
An aerodynamic automotive integrates the lights and wheel arcs into the entire shape so as to
minimize resistance caused by friction in fluid. The vehicle will be streamlined such that there
are no sharp edges above the windshield crossing the wind stream and also possess a kind of tail
known as liftback or fastback or Kammback. Vehicles such as Volkswagen 1-litre, Lomero, and
Aotra 2s tend to minimize the back area. They have a smooth and flat floor to produce desirable
downwards aerodynamic forces and support the venturi effect. It is used for passengers, cooling
and combustion, then accelerated by a nozzle and then removed beneath the floor. For mid
engines and rear of the vehicle, air is pressurized and decelerated in a diffuser, depressurizes
when passing the engine bay, and then finally filling the slipstream. These vehicles require seals
amid the high pressure around the gearbox and low-pressure region around the wheels. The