AERODYNAMIC DRAG REDUCTION AND IMPROVING FUEL

ECONOMY

Bhaskar Thakur , Prof.Dr.S.B.Barve

School of Mechanical Engineering , MIT World Peace University, Pune

Abstract
Due of higher cost, restricted supply and negative effects on condition by petroleum
derivative, car enterprises have coordinated their concentration in diminishing the fuel utilization
of vehicles so as to accomplish the lower aerodynamic drag. As an outcome, various explores
have been completed all through the world for not just getting the ideal streamlined structure
with lower drag punishment and yet additionally different boundaries that expansion the fuel
utilization. In such manner, research and mathematical results on vehicle drag decrease
considering different methods, for example, active, passive and combined techniques so as to
defer or suppress stream seperation behind the vehicles have been considered. Besides, the
impacts of drag decrease and their appropriateness on the vehicles are additionally represented in
this paper. Hence, it is guessed that the drag decrease has been improved as much as 20%,
21.2%, and 30% by utilizing the dynamic, detached and consolidated control frameworks,
separately.
Introduction

Since the commencement of the engine vehicle there have been singular vehicles that have
exhibited solid streamlined impact upon their structure. Up to this point their streaming lines
were essentially an announcement of style and design with little respect for the monetary
advantages. It was just rising fuel costs, set off by the fuel emergency of the mid 1970s, that gave
a genuine drive towards eco-friendly streamlined plan. The three essential impacts upon eco-
friendliness are the mass of the vehicle, the productivity of the motor and the streamlined drag.
Just the streamlined structure will be considered in this segment however it is essential to
perceive the associations between every one of the three since it is their joined activities and
communications that impact the dynamic dependability and consequently the security of the
vehicle.

Aerodynamic forces

Streamlined exploration at first engaged upon drag decrease, yet it before long became obvious
that the lift and side powers were likewise of incredible essentialness regarding vehicle
soundness. A terrible symptom of a portion of the low drag shapes created during the mid 1980s
was decreased solidness particularly when driven in cross-wind conditions. Cross-wind impacts
are presently regularly considered by architects however our comprehension of the exceptionally
intricate and frequently flimsy streams that are related with the wind stream over traveler
vehicles stays scrappy. Test strategies and computational stream forecast techniques despite
everything require generous turn of events if an adequate comprehension of the stream material
science is to be accomplished.

“The force and second coefficients are characterized separately as,

where F is force (lift, drag or side), M is a moment, ρ is air density, v is velocity, A is reference
area and l is a reference length. Since the aerodynamic forces acting on a vehicle at any given
speed are proportional to both the appropriate coefficient and to the reference area (usually
frontal area) the product CfA is commonly used as the measure of aerodynamic performance,
particularly for drag.” [1]

Fig 1 : Lift, drag, side force and moment axes

Drag

The drag force is most effortlessly perceived in the event that it is separated into five constituent
components. The most noteworthy of the five according to street vehicles is the structure drag or
weight drag which is the segment that is most firmly related to the outside state of the vehicle.
As a vehicle pushes ahead the movement of the air around it offers ascend to pressures that
fluctuate over the whole body surface. If a small element of the surface area is considered then at
that point the force segment acting along the pivot of the vehicle, the drag power, relies on the
greatness of the weight, the zone of the component whereupon it acts and the tendency of that
surface component Figure (b). Consequently it is workable for two distinct plans, each having a
comparable frontal region, to have totally different estimations of structure drag.
(a) Static pressure coefficient distribution (b) Force acting on a surface element

As wind streams over the outside of the vehicle frictional powers are created offering ascend to
the second drag segment which is normally alluded to as surface drag or skin contact drag. On
the off chance that the consistency of air is viewed as practically steady the frictional powers
anytime on the body surface rely on the shear stresses produced in the limit layer. The limit layer
is that layer of liquid near the surface wherein the air speed changes from zero at the surface
(comparative with the vehicle) to its neighborhood most extreme some good ways from the
surface. That most extreme itself changes over the vehicle surface and it is legitimately identified
with the neighborhood pressure. Both the nearby speed and the thickness and character of the
limit layer rely generally on the size, shape and speed of the vehicle.

The remainder of the significant impacts upon vehicle drag is that emerging from the cooling of
the motor, the cooling of other mechanical parts, for example, the brakes and from lodge
ventilation streams. Together these inside drag sources may ordinarily contribute in
overabundance of 10% of the general drag (for example Emmelmann, 1982).
Literature Review

J Abinesh and J Arunkumar (04/10/2014) [1] The rising fuel price and strict government
regulations makes the road transport uneconomical now a days. The exterior styling and
aerodynamically efficient design for reduction of engine load which reflects in the reduction of
fuel consumption are the two essential factors for a successful operation in the competitive
world. The bus body building company’s precedence’s are outer surface and structure of the bus
and ignore the aerodynamic aspect. The present intercity buses have a poor aerodynamic exterior
design. This project aims to modify the outer surface and structure of the bus aerodynamically in
order to reduce the effect of drag force of the vehicle which in turn results in reduction of fuel
consumption of the vehicle. The Two prototype bus body has been modeled by using CFD to
reduce the drag force.

Mohammad Firdaus Mohammed Azmi, Mohammad Al Bukhari Marzuki and Mohd Arzo
Abu Bakar (07/04/2017) [2] The aerodynamics analysis on a vehicle has become a major
concern nowadays. This is due to its effect on vehicle driving characteristics, fuel consumption,
etc. This study will analyse the aerodynamics characteristics of a multi-purpose vehicle (MPV)
generic design using ANSYS Workbench. Fluent is utilised in this study in order to investigate
the aerodynamics of generic MPV design, attaining coefficient of drag and lift and observing the
airflow streamline across the body of the vehicle. The turbulence modelling selected is realizable
k-ε with enhanced wall treatment. Based from the result obtained, the coefficient of drag and lift
recorded for the car modelled is 0.28 and 0.05 respectively after the solution converged. This
study can be used as reference for car manufacturers and designers especially when designing a
multi- purpose vehicle (MPV) design.
Jaspinder Singh, Jagjit Singh Randhawa (2012) [3] Computational Fluid Dynamics
(CFD) is the numerical techniques to solve the equations of fluid flow. CFD tool is found very
useful in automobile industry ranging from system level (exterior aerodynamics, ventilation,
internal combustion engines) to component level (disk brake cooling).CFD simulations are
carried out by dividing the physical domain into small finite volume elements and numerically
solved the governing equations that describe the behaviour of the flow. The governing equation
(Navier Stokes equations) is very complex and almost impossible to solve analytically thus
requires numerical techniques. In the present paper, research work in the field of “CFD analysis
of aerodynamic drag reduction of automobile car” has been reviewed.

Ioannis Oxyzoglou (May 2017) [4] This Thesis describes the process of designing and
developing the aerodynamic package of the 2016 Formula Student race car (Thireus 277) of
Centaurus Racing Team with the use of CAD Tools and Computational Fluid Dynamics (CFD).
It further investigates the effects of aerodynamics on the vehicle's behavior and performance
with regard to the Formula Student competition regulations. The methods used during the
development are evaluated and put into context by investigating the correlation between the CFD
results of the car model and the lap-time simulated counterpart. The aerodynamic package
consists of a nosecone, two sidepods, an undertray, a front and a rear wing. The Thesis details all
the stages involved in designing and optimizing these components to achieve the desired results
and maximize the amount of performance enhancing aerodynamic downforce by the
aerodynamic package, while maintaining drag force at low levels.

Triya Nanalal Vadgama, Mr. Arpit Patel, Dr. Dipali Thakkar (04/04/2015) [5] A modern
Formula One (F1) Racing Car has almost as much in common with an aircraft as it does with an
ordinary road car. Aerodynamics has become a key to success in the sport and teams spend
millions of dollars on research and development in the field each year for improving
performance. In this project, a Formula One race car will be designed using the CAD software
CATIA V5R20. All the dimensions are based on the standards laid down by the FIA (Fédération
Internationale de l'Automobile). The car design will be enhanced to streamline the flow over the
car. Various parts that will be designed include the wheels, front and rear airfoils, front and rear
wings, car body chassis, among other subassemblies. A driver will also be placed in a typical
driving position inside the car.

A N M Mominul Islam Mukut and Mohammad Zoynal Abedin (04/01/2019) [6] Due to higher
price, limited supply and negative impacts on environment by fossil fuel, automobile industries
have directed their concentrations in reducing the fuel consumption of vehicles in order to
achieve the lower aerodynamic drag. As a consequence, numerous researches have been carried
out throughout the world for not only getting the optimum aerodynamic design with lower drag
penalty and but also other parameters that increase the fuel consumption. In this regard, relevant
experimental and numerical outcomes on vehicle drag reduction considering various techniques
such as active, passive and combined techniques in order to delay or suppress flow separation
behind the vehicles have been considered in this review paper. Furthermore, the effects of drag
reduction and their applicability on the vehicles are also illustrated in this paper.

Ram Bansal and R. B. Sharma (23/03/2014) [7] This work proposes an effective numerical
model using the Computational Fluid Dynamics (CFD) to obtain the flow structure around a
passenger car with different add-on devices. The computational/numerical model of the
passenger car and mesh was constructed using ANSYS Fluent which is the CFD solver and
employed in the present work. In this study, numerical iterations are completed, and then
aerodynamic data and detailed complicated flow structure are visualized. In the present work, a
model of generic passenger car was developed using solidworks, generated the wind tunnel, and
applied the boundary conditions in ANSYS workbench platform, and then testing and simulation
have been performed for the evaluation of drag coefficient for passenger car. In another case, the
aerodynamics of the most suitable design of vortex generator, spoiler, tail plates, and spoiler with
VGs are introduced and analysed for the evaluation of drag coefficient for passenger car. The
addition of these add-on devices are reduces the drag coefficient and lift coefficient in head-on
wind. Rounding the edges partially reduces drag in head-on wind but does not bring about the
significant improvements in the aerodynamic efficiency of the passenger car with add-on
devices, and it can be obtained. Hence, the drag force can be reduced by using add-on devices on
vehicle and fuel economy, stability of a passenger car can be improved.

Feasibility Study
 Analysis of vehicle aerodynamics such as rotating wheels and air flow under the bonnet
and cabin.

 Improving CFD technological advancement for a more precise and easier way to find
solution to problems associated with aerodynamics.
 To optimise the current additional components this would include lower the angle of the
outer diffuser channel to reduce the flow separation with these channels.
  The modification the wheel arches to allow air to flow more freely out of them which
would reduce the pressure within them, the way this could be done by the design of vents
to release and re-direct the air flow freely around the vehicle.
 To eliminate the flow distribution happening around the bottom of the wind screen and
down the rear window this could be done by lowering the angle of the windscreen, and
for the rear window it needs to have less of a recess and to make more flush with the
body of automobile.

Best Solution approach or outline

 Movable Underbody Diffuser

The portable underbody diffuser innovation is utilized for decreasing streamlined drag in
the vehicle by controlling back stream field. For example, it is broadly uncovered that the
back stream field of vehicle is impacted by the stream coming out under the vehicles
which suggests that the back stream field can be changed by controlling the stream under
the vehicles. Kang et al. built up a portable under body diffuser as appeared in Figure and
mathematically examined that the vehicle's streamlined drag could be diminished by a
normal of over 4%, which would assist with improving the steady speed eco-friendliness
by roughly 2% at a scope of driving velocities surpassing 70 km/h.

Figure : Basic concept of actively translating rear diffuser

 Steady Blowing
Vehicles streamlined attributes have been significantly impacted by the state of backside,
which likewise influences the steadiness and comfort. The impact of consistent blowing
has been examined tentatively on a practical vehicle model, at three distinctive position
specifically, (i) perpendicular top position air jet (ii) perpendicular bottom position air jet
(iii) tangential bottom position air jet which are shown in Figure.

Their outcomes indicated that back hub lift was decreased by about 5% with coefficient
of drag (CD) changes around 1%. Another examination has been done to assess the
adequacy of consistent blowing on the wake structure of a streamlined ¼ downsize
square vehicles at an assortment of points on the rooftop following edge. Its belongings
were assessed by actualizing different stream and weight estimation strategies and results
demonstrated that general increases were accomplished. Be that as it may, because of the
prerequisite for huge mass stream rate, this method has restricted appropriateness to street
vehicles.
The impact of consistent passing up both tentatively and mathematically on an Ahmed
body at 25° inclination edge and relying upon Reynolds' number, and the drag decrease
has been accomplished from 6 to 10.4% (at 90° slant angle). The impact of blowing point
has been researched mathematically and it is discovered that 11.1% drag decrease has
been acquired at a blowing edge 45°. A variety of blowing consistent 53 miniature flies
as appeared in Figure 4 were likewise discovered to be compelling on a model of a
nonexclusive vehicle shape, the Ahmed body with a 25° inclination in decreasing drag
coefficient (9-14%) and lift coefficient (up to 42%) contingent upon Reynolds Number.
These varieties of consistent miniature planes were situated at 6 mm downstream of the
detachment line between the rooftop and the inclined back window.
The utilization of little scope, consistent planes (miniature planes) in typical and
digressive infusion directions has been explored through trial parametric examinations
and contrasted and mathematical reenactments on Honda Simplified Body (HBS) and it
is discovered that drag experienced by HSB is decreased by almost 2.6% with net
decrease in power utilization.
 Figure : Positions of blowing jets

 Steady Suction
Car businesses look for better answer for decrease contamination and fuel utilization, in
such manner, dynamic stream control strategies have tremendous consideration as it
requires no shape adjustment of the vehicles. Consistent attractions is a functioning
stream method which adjust vertices that influences back wake of the vehicle. The work
capacity of consistent pull has been assessed by both exploratory and mathematical
methodologies on improved fastback vehicle calculation as appeared in Figure and this
procedure is competent to stifle back window partition and decrease drag over 17%. The
commitment of this technique towards isolated district has been dissected by stream
geography on an iso-surface of all out weight misfortune, which is appeared in Figure. It
is discovered that attractions is compelling to kill the isolated layer created and
reattachment of stream is gotten. The impact of pull around the horizontal edges of a
disentangled vehicle windshield has been tried tentatively in a water burrow, which gives
a drag decrease of 6%.

A Large Eddy Simulation (LES) has been completed on a 25° inclination point on an
Ahmed body, in a view to that the joined impact is favorable over single alone as net zero
mas motion. In their examinations, twelve cuts were orchestrated in six sets in which
each pair gives blowing and pull as appeared in Figure and a drag decrease of 9.5% has
been found. The consolidated control of pull and blowing apparently is successful on
 changing the back window wake structure, in which smoothes out of time normal stream
is isolated (without control) and re-joined (with joined control) as appeared in Figure.

Figure : (a) Schematic of the used geometry and (b) Implementation of the control system

Figure : Effects of suction on rear window (a) without control and (b) with control

 Body Modification
Body alteration is the aloof procedure to improve streamlined drag decrease which assists
with diminishing fuel utilization. Body change incorporates vehicle body blueprint, front
and back part; underbody calculation of the vehicle, now and then extra included surfaces
or diffusers which adjust the base math of vehicles. These diffusers really increment the
air speed beneath the vehicles which decrease the pneumatic force. Subsequently vehicles
security is improved as the descending powers are expanded. The base of a Sedan and
Wagon had been adjusted which has a point at the base back that demonstrations like an
underbody diffuser. The exhibition of underbody diffuser has been tried with differing
edges appeared in Figure. Results from this examination indicated a potential streamlined
drag decrease of the vehicle around 10%, and the cart vehicle by 2-3 %.
The impact of underbody diffuser with folds and vanes has been mathematically explored
on an equation SAE vehicle. The expansion of vanes with diffuser upgraded the
siphoning limit of diffuser just as increment up to 13% down power. The expansion of a
flap over the following edge of the diffuser additionally expanded down power by 25%.
A mathematical examination has been completed with various underbody drag decrease
gadgets like covert, underfine, and side air dam on the real state of a car type vehicle,
among these underbody can diminish the streamlined drag by 8.4 %.
Shape advancement has been done on a vehicle by Artificial Neural Network (ANN),
which center around back shape change. To accomplish the streamlined objective by
shape improvement, six nearby parts from the finish of car have been picked as plan
factors and an ANN estimation model was built up with 64 trial focuses produced by the
D-ideal approach. Because of these shape improvement, 5.639% lower coefficient of
drag has been gotten. Six boundaries in particular, (I) hood (ii) windshield (iii) back
window (iv) side window (v) backside shrinkage and (vi) trunk top have been changed to
advance body shape mathematically on a disentangled vehicle. A decrease of 13.23%
streamlined drag has been accomplished.
Mathematical examination has been done on an Ahmed body with non-smooth dimpled
surfaces on its inclination back. The math of non-smooth surfaces are appeared in Figure.
So as to augment the drag decrease execution of the dimpled non-smooth surface, a
streamlined improvement strategy dependent on a Kriging Surrogate model was utilized
to structure the dimpled non-smooth surface. Four structure boundaries had been chosen
as the plan factors, and a 16-level structure of trials technique dependent on symmetrical
exhibits had been utilized to examinations the sensitivities and the impacts of the factors
on the drag coefficient; a proxy model had been built from these. The outcomes
demonstrated that the ideal blend of plan factors can decrease the streamlined drag
coefficient by 5.20%.
 Figure : Details of AMD (a) attachment on Ahmed body and (b) AMD configuration

Figure : Comparison of drag coefficient for Sedan and Wagon

Figure : Non-smooth dimpled surfaces

Expected Improvement in the solution

Future work would incorporate attempting to improve the current extra segments this would
incorporate lower the edge of the external diffuser channel to lessen the stream detachment with
these channels.

Another region that would be remembered for future work would be adjustment the wheel curves
to permit air to stream all the more openly out of them which would lessen the weight inside
them, the manner in which this should be possible is by structuring vents to deliver and divert the
wind current easily around the vehicle.

One more suggestion would to attempt to take out the stream detachment occurring around the
base of the breeze screen and down the back window this should be possible by diminishing the
point of the windscreen, and for the back window it needs to have a to a lesser degree a break
and to be made all the more flush with the bodywork.

Take-away From paper

The vehicle streamlined drag is the principle supporter of increment the fuel utilization which
influences the world fuel holds as well as nature. Consequently, decreasing streamlined drag is
the best answer for the greener world just as for the fuel climb. Different stream control
strategies have been tried and approved mathematically and tentatively of whose, the vast
majority of the cases, improved has been picked. The significant discoveries from the current
survey investigation might be summed up as follows:

1. Latent stream control techniques utilize the extra shape on the vehicle body which influence
the stream field along these lines attractive effect on drag decrease. In any case, these strategies
are once in a while added additional drag because of its shape. Other than their connection on
vehicle body are a bit complex.

2. Then again, dynamic stream control frameworks come in real life just when it is important to
control the stream. Their connections are tad simpler than latent stream control. Fundamental
weakness of dynamic stream control is that these expect capacity to come in real life which
increment power utilization of vehicles.

3. The examination results about the drag decrease of vehicle from these control strategies have
been discussed . It is guessed that the drag decrease for dynamic, detached and consolidated
control frameworks could be as much as 20%, 21.2%, 30%, individually.

References

1. Jason Moffat , “Aerodynamic Vehicle Design and Analysis”,(2016)

2. Firdaus Azmi , Mohammad Al Bukhari Marzuki , “Vehicle aerodynamics analysis of
a multi purpose vehicle using CFD”, (2017)
3. Jaspinder Singh, Jagjit Singh Randhawa, “CFD Analysis of Aerodynamic Drag
Reduction of Automobile Car”, (2012)
4. J Abinesh and J Arunkumar, “ CFD analysis of aerodynamic drag reduction and
improve fuel economy”, (2014)
5. Ioannis Oxyzoglou, “Design & Development of an Aerodynamic Package for an FSAE
Race Car”, (2017)
6. Triya Nanalal Vadgama, Mr. Arpit Patel, Dr. Dipali Thakkar, “Design of Formula One
Racing Car”, (2015)
7. A N M Mominul Islam Mukut and Mohammad Zoynal Abedin, “Aerodynamic Drag
Reduction of Vehicles”, (2019)