drag reduction techniques

1. Department of Mechanical Engineering
P.E.S. MODERN COLLEGE OF
ENGINEERING, PUNE-411005.
A Seminar on
AIRCRAFT DRAG REDUCTION
TECHNIQUES
Prepared by:
Dhanashree .M. Waghmare
Under the guidance of:
Prof. V. A. Yevalikar

2. SUMMARY:
• Literature review
• Aims and objectives
• Introduction
• Basic principles of aerodynamics
• Airfoils and terminology
• Theory of flight
• Forces acting on an airplane in flight
• Forms of drags
• Factors affecting drag
• Reduction techniques
• Conclusion
• Future scope
• References

3. LITERATURE REVIEW
 FUNDAMENTALS OF AERODYNAMICS
AUTHOR: John D. Anderson,
University of Maryland
 FLUID MECHANICS
AUTHORS: YUNUS CENGEL
JOHN M. CIMBALA
 AIRCRAT DRAG REDUCTION- A REVIEW
AUTHOR: D M Bushnell
NASA Langley Research Center
 AIRCRAFT SURFACE COATINGS SUMMARY REPORT
Staff of Boeing commercial airplane company
Boeing commercial airplane company Seattle, Washington
 DRAG REDUCTION BY RIBLETS
AUTHOR: RICARDO GARCÍA-MAYORAL AND JAVIER JIMÉNEZ*
School of Aeronautics, Universidad Politécnica de Madrid, 28040 Madrid, Spain
 A REVIEW OF DRAG REDUCTION BY RIBLETS AND MICRO-TEXTURES IN THE
TURBULENT BOUNDARY LAYERS
Samira Sayad Saravi, PhD Kai Cheng, Prof School of Engineering and Design, Brunel
University, Uxbridge, London, UK

4. AIMS AND OBJECTIVES
• To study the basic fundamental principles of
aerodynamics.
• To study the nomenclature of an aircraft wing.
• To understand the various forces acting on an
aircraft and to study their effects.
• To research about the different types of drag, its
effects, factors affecting drag and numerous
methods to reduce it.
• To research about the recent trends and
technologies of drag reduction.

5. INTRODUCTION
• The study of moving air and the forces that it produces is
referred to as aerodynamics. For the design of any aerial
vehicle it is very essential to know the forces acting on it. One
such force is aerodynamic drag; it always acts parallel to the
direction of motion but opposes the motion of an aircraft.
• Since drag slows down an aircraft and also makes it less
efficient, it is always aimed to design planes that produce less
drag. Drag reduction for aircrafts has a wide range of positive
consequences viz. reduction in fuel consumption, larger
operational range, greater endurance, and higher achievable
speeds.
• The drag consequences has a wide effect on the configuration,
size, and cost, thus on the decision to proceed with the design.
• Various methods have been adopted since the drag effects
have been seriously felt

6. BASIC AERODYANAMIC PRINCIPLES
• Aerodynamics is the study of motion of air particularly in interaction with a
solid object.
• The most frequently used words in aerodynamics are: "pressure," "density,"
"temperature," and "flow velocity''.
• Pressure is the normal force per unit area exerted on a surface due to the
time rate of change of momentum of the gas molecules impacting on (or
crossing) that surface.
• Another important aerodynamic variable is density, defined as the mass per
unit volume.
• Temperature takes on an important role in high-speed aerodynamics. The
temperature T of a gas is directly proportional to the average kinetic energy
of the molecules of the fluid.
• The principal focus of aerodynamics is fluids in motion. Hence, flow
velocity is an extremely important consideration. The velocity of a flowing
gas at any fixed point in space is the velocity of an infinitesimally small fluid
element as it sweeps through the fixed point.

7. (contd)
• The aerodynamic forces and moments on the body are due to only two basic
sources; 1. Pressure distribution over the body surface 2. Shear stress
distribution over the body surface
• The net effect of the p and T distributions integrated over the complete body
surface is a resultant aerodynamic force R and moment M on the body. The
resultant R can be split into components. V∞ is the relative wind, defined as
the flow velocity far ahead of the body.
• L=lift component of R perpendicular to V∞
• D=drag component of R parallel to V∞

8. TERMINOLOGY OF AN AIRCRAFT WING:

9. THEORY OF FLIGHT
Bernoulli’s theory of flight:

10. Newton’s theory of flight:

11. FORCES ACTING ON AN AIRPLANE IN
FLIGHT
FORCES
LIFT:
created by
differences in
air pressure
DRAG:
force that acts
opposite to the
direction of
motion
WEIGHT:
the force of
gravity
THRUST:
force that
propels a
flying
machine

12. FORMS OF DRAG
INDUCED DRAG: drag
due to lift
PRESSURE OR FORM
DRAG: caused by the
air that is flowing over
the aircraft or airfoil
SKIN FRICTION
DRAG: caused by the
actual contact of the air
particles against the
surface of the aircraft
WAVE DRAG:
associated with the
formation of the shock
waves
PARSITE DRAG:
consists primarily of
the skin friction,
roughness, and
pressure drag

13. FACTORS AFFECTING DRAG:
ANGLE OF
ATTACK:
angle of attack
increases the
drag
MOTION OF AIR:
drag actually
varies with the
square of
the relative
velocity between
the object and the
air
OBJECT
GEOMETRY:
drag depends
linearly on the
size of the object
moving through
the air
PROPERTIES OF
AIR: depends
directly on
the mass of the
flow going past
the aircraft, also
depends on
viscosity
,compressibility

14. DRAG REDUCTION METHODS
• SKIN FRICTION DRAG
Turbulent drag reduction
i. Riblets
ii. Large eddy break-up devices
iii. Surface coatings
Laminar flow control
i. Boundary layer suction
ii. Hybrid laminar flow concept
iii. Boundary layer flow control
iv. Wing tip devices
v. Vortex generators

15. (contd…)
• LIFT INDUCED DRAG
i. Increase the aspect ratio of the wing
ii. Develop wing tip devices acting on the tip
vortex which is at the origin of the lift-induced
drag.
iii. Wing-tip mounted vortex generator method
iv. Non-planar vortex sheet approaches
v. Energy/thrust extraction from the tip vortex
vi. Alteration of tip boundary conditions

16. (contd)
• Wave drag
All of the wave drag reduction methods involve weakening
the shock.
i. The “usual” (linear theory) approaches to wave drag
reduction include wing sweep, area ruling and reduced
thickness as well as wing twist/camber/warp.
ii. non-linear wave drag reduction techniques include the
use of nose spikes (either physical or via forward
projection of energy, gases or particulates) to extend
effective body length, particularly useful on blunt
nosed bodies and base blunting, which reduces the
strength of the base recompression shock.

17. CONCLUSION:
 The hybrid laminar flow technology (about 10%) The
innovative wing-tip devices ( about 2%)
 The shock control and trailing edge devices which allow
to adapt the wing geometry to flight conditions
(variation of the lift coefficient or of the Mach number),
(about1%)
 The sub-layers vortex generators and MEMS technology
which can be used to control flow separation. These
technologies can be associated to maximize the drag
reduction.
 Future laminar flow aircraft can, for example, be fitted
with wing tip devices and equipped with riblets in the
rear part of the wing upper surface.

18. FUTURE SCOPE:
• The friction drag reduction concept is a world-first technical approach that obtains a
natural laminar flow wing with a subsonic leading edge at supersonic speed.
• Strut-bracing allows thinner, smaller chord, lower sweep and higher aspect ratio
wings. The smaller chord, leading edge radius and sweep have a favorable influence
upon HLFC, increasing the amount of wetted area laminarized and reducing suction
mass flow and roughness sensitivity as well as increasing attachment line stability
• Circulation control, powered by the auxiliary power unit, could be utilized on a
conventionally sized tail to work the engine-out problem. All these benefits produce
very large increases in the lift-drag ratio and range at cruise. Strut-bracing for the
SST allows very significant reductions in both vortex and wave drag due to the lift via
an extreme arrow configuration and could be favorable to LFC via reduced chord
Reynolds number.
• All of these advanced configurations, CTOL and SST, provide large potential drag
reductions, along with many other benefits. They deserve serious research effort
utilizing modern design optimization technology. Reduction of boundary layer
separation regions can also be obtained by an active system avoiding the drawbacks
of vortex generators which increase the drag coefficient at low lift coefficient.

19. REFERENCES:
• Bushnell, D. M., (2003) “Aircraft drag reduction―a review” Proc. Instn
Mech. Engrs Vol. 217 Part G: J. Aerospace Engineering.
• Bushnell, D. M., and Hefner, J. N., (1990) “Viscous Drag Reduction in
Boundary Layers” Progr. In Astron. and Aeron., Vol. 123, AIAA.
• Fundamentals of aerodynamics; Author: John D. Anderson; University of
Maryland
• Fluid mechanics, Authors: Yunus Cengel, John M. Cimbala
• Aircraft surface coatings summary report, Staff of Boeing commercial
airplane company, Boeing commercial airplane company Seattle,
Washington
• drag reduction by riblets, author: Ricardo García-Mayoral and Javier
Jiménez, School of Aeronautics, Universidad Politécnica de Madrid, 28040
Madrid, Spain
• A review of drag reduction by riblets and micro-textures in the turbulent
boundary layers ,Samira Sayad Saravi, PhD Kai Cheng, Prof School of
Engineering and Design, Brunel University, Uxbridge, London, UK

20. THANK YOU!!