full report

1
SUBSONIC FLOW ANALYSIS OF A TAILLESS
AIRCRAFT BY USING CFD
A PROJECT REPORT
Submitted by,
RAKESH M (80510141051)
SOORAJ JANARDHANAN (80510141061)
VISHNU V K (80510141064)
In partial fulfillment for the award of the degree
Of
BACHELOR OF ENGINEERING
IN
AERONAUTICAL ENGINEERING
DHANALAKSHMI SRINIVASAN ENGINEERING COLLEGE,
PERAMBALUR - 621 212
ANNA UNIVERSITY: CHENNAI - 600 025
APRIL 2014

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BONAFIDE CERTIFICATE
Certified that this project report “SUBSONIC FLOW ANALYSIS
OF A TAILLESS AIRCRAFT BY USING CFD” is the confide work of
“RAKESH M (80510141051), SOORAJ JANARDHANAN
(80510141061), VISHNU.V.K (80510141064)” who carried out the
project work under my supervision.
SIGNATURE SIGNATURE
Dr. K. ASHOK. Dr. K. ASHOK.
HEAD OF THE DEPARTMENT. HEAD OF THE DEPARTMENT.
Dept. Of Aeronautical Engg. Dept. Of Aeronautical Engg.
Dhanalakshmi Srinivasan Engg. Dhanalakshmi Srinivasan Engg.
College, Perambalur. College, perambalur.
Submitted this project for viva voce on……………………………
INTERNAL EXAMINER EXTERNAL EXAMINER

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DECLARATION
We hereby declare that the work entitled “SUBSONIC FLOW
ANALYSIS OF TAILLESS AIRCRAFT BY USING CFD” is submitted
in partial fulfillment of requirement for the award of the B.E. degree in
Anna University Chennai, is a record for our own work carried out by
us during the academic year 2013-2014 under the supervision and
guidance of Dr. K. ASHOK, Head of the department of Aeronautical
Engineering, Dhanalakshmi Srinivasan Engineering College,
Perambalur-621212. The extent and source of information are
derived from the existing literature and have been indicated through
dissertation at the appropriate places. The matter embodied in this
work is original and has not been submitted for the award of any
other degree or diploma, either in this or any other university.
RAKESH .M (80510141051)
SOORAJ JANARDHANAN (80510141061)
VISHNU .V .K (80510141064)
I Certify that the declaration made above by the candidate is
true,
Dr. K. ASHOK
Head of the department,
Department of Aeronautical
Engineering, Dhanalakshmi Srinivasan
Engineering College,
Perambalur – 621 212.

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ACKNOWLEDGMENT
We convey our sincere thanks to our beloved chairman of our
college, Shri. A. SRINIVASAN for giving us the inspiration and providing
all facilities for execution of this Project. We convey our heartiest thanks to
the principal of our college, Dr. C. NATARAJAN for providing us the
necessary infrastructure for completion of our Project. We extend our
sincere thanks to head of department, Dr. K. ASHOK for his valuable
guidance and advice to complete this project work easily and successfully.
We convey our heartiest thanks to our guide, Dr. K. ASHOK, for his
valuable guidance and advice to complete this project work easily and
successfully. We also thank our STAFF MEMBERS and all of our
FRIENDS making this project a successful one.

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ABSTRACT
This project aims to compare the aerodynamic characteristics
of conventional and blended wing body aircraft. The conventional
aircraft having disadvantage of increased drag and weight due to the
tail section, so by using tailless configurations we can reduce this to
an extent. Based on the same requirement two different
configurations, conventional and blended wing body options are
provided to make direct comparison. The two configurations are
designed using CATIA. Further the designed bodies are imported to
hyper mesh. The subsonic flow analysis is done by using FLUENT. It
is observed that tailless configuration is having reduced drag and
improved lift.
Keywords: CATIA, FLUENT, Subsonic flow, Blended Wing Body

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TABLE OF CONTENT
CHAPTER
NO:
TITTLE
PAGE
NO:
I ABSTRACT v
II LIST OF TABLES ix
III LIST OF FIGURES x
IV LIST OF SYMBOLS AND ABBREVIATIONS xi
1 INTRODUCTION 1
1.1 Tailless aircraft 2
1.1.1 History 2
1.1.2 Review of history of Tailless aircraft 4
1.1.3 Aerodynamic studies of Tailless aircraft 5
1.1.4 Stability studies of tailless aircraft 6
1.1.4.1 Longitudinal stability 6
1.1.4.2 Lateral-directional stability 6
1.2 Introduction to the software‟s 7
1.2.1 Computational Fluid Dynamics 7
1.2.1.1Why use CFD? 8
1.2.1.2 Mathematical model 9
1.2.1.3 Discretization process 10
1.2.1.4 Iterative solution strategy 10
1.2.1.5 CFD simulations 11
1.2.1.6 Post processing and analysis 12
1.2.1.7 Uncertainty and error 12

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1.2.1.8 Classification of errors 13
1.2.1.9 Verification of CFD codes 13
1.2.1.10 Validation of CFD models 14
1.2.1.11 Available CFD software 14
1.2.2 CATIA 15
1.2.2.1 History 15
1.2.2.2 Scope of application 17
1.2.2.3 Systems engineering 17
1.2.2.4 Aerospace applications 18
1.2.3 Hyper mesh 18
1.2.3.1 Benefits 19
1.2.3.2 Capabilities 19
1.2.3.3 High Fidelity Meshing 19
1.2.4 FLUENT 19
2 LITERATURE REVIEW 22
3 METHODOLOGY 29
3.1 Designing 31
3.2 Meshing 32
3.3 Solver 34
4 RESULT AND DISCUSSION 40
4.1 Lift 42
4.2 Drag 44
4.3 L/D ratio 46
4.4 Pressure 47
4.5 Velocity 50

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4.6 Conclusion 53
5 FUTURE WORK 55
5.1 Suggestions for future work 56
6 REFERENCES 57

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LIST OF TABLES
TABLE
NO:
TITLE
PAGE
NO:
1.1 Different configurations of aircraft 4
3.1 Material properties 35
3.2 Inlet conditions for Mach no: 0.4 37
4.1 Lift obtained for Mach 0.4(BWB) 42
4.4 Lift obtained for Mach 0.4(CB) 43
4.7 Lift force 44
4.8 Drag obtained for Mach 0.4(BWB) 44
4.11 Drag obtained for Mach 0.4(CB) 45
4.14 Drag force 46
4.15 L/D ratio 47

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LIST OF FIGURES
FIGURE
NO:
TITLE
PAGE
NO:
1.1 BWB design 4
1.2 Real experiment 8
1.3 CFD simulation 8
3.1 BWB aircraft three view 30
3.2 CATIA design of BWB 31
3.3 Conventional body aircraft (Boeing777) three view 32
3.4 Boeing 777 CATIA model 32
3.5 Meshed BWB 33
4.1 BWB with reference lines 47
4.2 Pressure variation 48
4.3 Pressure distribution through bottom surface of BWB 49
4.4 Pressure distribution over BWB 49
4.5 Velocity variation 50
4.6 Velocity distribution through bottom surface of BWB 51
4.7 Velocity distribution over BWB 52
4.8 Path lines colored by velocity magnitude 53

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LIST OF SYMBOLS AND ABBREVIATIONS
Ρ - Density
µ - Viscosity
T - Temperature
P - Pressure
L - Lift
D - Drag
K - Thermal conductivity
Cp - Specific heat
BWB - Blended wing body
CB - Conventional body
CFD - Computational fluid dynamics
CATIA
- Computer aided three dimensional interactive
application

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1. INTRODUCTION
1.1 Tailless aircraft
1.1.1 History
Over the past 100 years, although most aircraft have been designed
with a wing(as the primary lifting surface) and an aft tail (for stability and
trim), there have been several unconventional configurations. Tailless
aircraft are examples of unconventional configurations. Throughout this
thesis, the term “tailless aircraft" will be used to describe those aircraft that
are designed with only one main lifting surface, that being the wing, which
is responsible for producing the aircraft's lift and also contains all control
surfaces providing static and dynamic stability. These aircraft are sometimes
referred to as, blended-wing bodies or all-wing aircraft. The more
conventional two horizontal element designs, as indicated by the vast
majority of commercial aircraft, will be referred to as tailed aircraft."
However modest, tailless aircraft configurations have found
popularity alongside tailed configurations in particular applications. These
applications include sailplanes and gliders, light airplanes, unmanned aerial
vehicles (UAV), high-speed military planes, supersonic airliners, and
hypersonic re-entry vehicles. One need not look any further than the
Northrop B-2 stealth"-bomber in order to get a sense of the potential that
future tailless designs hold. And because only one lifting surface is used, it
has often been proposed that drag benefits should be realized and design
costs kept lower when implementing a tailless design versus a comparable
tailed design. Despite these positives, tailless configurations have seen
limited use in general aviation and commercial aircraft design, most likely
due to inherent complexity in the aerodynamic design of tailless aircraft and

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perhaps also due to the overwhelming history of tailed-aircraft use, giving
indication of the need for the advancement in tailless design technology.
One hindrance to the development of tailless aircraft is the idea that
these aircraft present difficulty for achieving longitudinal stability and trim,
as pointed out by Kroo. With seemingly limitless parameters used in modern
aircraft design, including wing and tail geometry variables, engine size, and
operational parameters for several flight conditions, it is understandable that
the conservative tailed design has stood the test of time as it satisfies trim
with little optimization necessary. However, analysis by Kroo has shown
that the removal of an aircraft's tail can result in aircraft gross weight, fuel
consumption, and direct operating cost reduction when compared to similar
tailed configurations. And further, by employing the design philosophy of
Reimar and Walter Horten of Germany that has the lift at the wing tips
nearly zero and utilizes twist to push much of the lift inboard, a tailless
aircraft that is very stable longitudinally is possible. In fact, this method
describes the classic bell-shaped lift distribution that is typical of successful
designs employed on modern tailless aircraft. Although tailless aircraft have
found most favor with UAV and military applications, there is evidence that
such a configuration may one day be utilized by the commercial airline
industry. The Boeing Company, in a joint venture with NASA, has recently
been exploring a blended-wing-body" (BWB) concept that has shown
preliminary improvements in airliner efficiency. Boeing studies have shown
15% reduction in sized take-off weight, 20% improvement in L/D,
27%reduction in fuel usage, 27% lower thrust, and 12% lower operating
empty weight when compared to a similar tailed design. The design has a
large delta-shaped wing/fuselage center section which accommodates a two-
storey passenger cabin.

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A conceptual sketch of this vehicle is provided in Fig. 1.1. Such a
design leads to reductions in root bending moment‟s stresses, as the fuselage
is largely incorporated in the wing section. It seems that this a design most
suited for a very large airliner, however negatives such as a large,
windowless cabin may lead to passenger discomfort, and need to be
addressed.
Figure: 1.1 BWB design
1.1.2 Review of history of tailless aircraft
Lippisch suggested that the aircraft could be classified by its plan
form shape. The conventional aircraft have wing, fuselage and tail. For the
aircraft without tail could be classified to tailless aircraft.
Table 1.1 Different configurations of aircraft

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According to the description of Castro the flying wing configuration is
no obvious boundary between central body and wing. The blended wing
body is the configuration with thick central body integrated on the wing.
There is a quite long history since engineers started the research and develop
the flying wing and blended wing body. Sponsored by NASA, Boeing has
been continuously improving its BWB concept. Lie beck systematically
introduces Blended-Wing-Body airplane concept development in Boeing.
The aim of the design is taking about 800 passengers flying across 7,000
nautical miles. They found that the amount of fuel used by a BWB is
expected to be 27% less than for a conventional configuration. The BWB in
that study had a take-off gross weight (TOGW) of 823000 lb (373000 kg)
and a wingspan of 280 ft (85 m). Based on the same requirements,
comparisons have been made between the BWB configuration and
conventional configuration.
1.1.3 Aerodynamic studies of tailless aircraft
Tjoek Eko Pambag mentioned there are at least two main benefits
from tailless configuration:
For the cruise condition, the most significant advantage of blended
wing body aircraft is its high lift to drag ratio. This is achieved by two
aspects. Firstly, the body of blended wing body generates lift; secondly, the
blended wing body has less wetted area than the conventional, which means
the reduction of drag.
For the take-off and landing condition, because of its comparatively
low wing loading, only simple high lift devices are needed. That will reduce
the design complexity as well as manufacture difficulty of the high lift
devices.

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At the first glance, the aerodynamic design of a blended wing body
aircraft seems to be an easy task. However, several difficulties will emerge
when studying this issue in-depth.
D.Roman et al mentioned a host of challenges faced by the designers
who want to develop a blended wing body aircraft. The first question is
higher thickness to chord ratio beyond the normal transonic airfoil due to the
volume requirement for containing the cabin, cargo and system. The second
tricky is trim at cruise condition should minimize the nose-down pitching
moment. The buffet and stall character should also be well considered. The
location and function of control surfaces are really hard issue. Besides, some
other important points such as the propulsion/airframe integration, landing
attitude and speed, and manufacture are discussed. Since the challenges have
been presented, solutions of some problems can be provided.
1.1.4 Stability studies of tailless aircraft
1.1.4.1 Longitudinal stability
Some previous work has been done for the stability of tailless aircraft.
In terms of longitudinal dynamics of tailless aircraft, for the phugoid mode,
Northrop found that the flying wing aircraft seems to have less damping than
the conventional aircraft because of relatively low drag. For the short period
mode, Northrop commented that the flying wing seems highly damped than
conventional one. However, Wilkinson et al mentioned that flying wing
seems to have less damping than the conventional configuration.
1.1.4.2 Lateral-directional stability
In terms of lateral-directional static stability tailless aircraft, Castro
pointed out that the main problem is its low directional static stability,
𝐶𝑛𝛽.For lateral –directional dynamic stability, Northrop mentioned out that
the two factors- low weather stability and low value of damping yaw

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coefficient contributing the Dutch roll mode is a long period comparatively.
The relative lower damping coefficient in yaw contributes less damping in
Dutch roll mode.
The blended wing body (BWB) is a tailless aircraft with the potential
to use 27% less fuel than a conventional aircraft with the same passenger
capacity and range. The primary purpose of the current study was to
determine the handling qualities of the BWB, using piloted-handling trials in
a moving-base simulator. The secondary purpose was to determine the effect
of simulator motion on handling-quality ratings.
BWB modeled in the current research is a “hybrid” BWB, because
parts of the model are drawn from various data sources. The aerodynamic
model, ground-force model, engine model, and wind and turbulence model
have all been modified from de Castro's model.
1.2. Introduction to software’s
1.2.1 Computational Fluid Dynamics
Fluid (gas and liquid) flows are governed by partial differential
equations which represent conservation laws for the mass, momentum, and
energy. Computational Fluid Dynamics (CFD) is the art of replacing such
PDE systems by a set of algebraic equations which can be solved using
digital computers.
Computational Fluid Dynamics (CFD) provides a qualitative (and
sometimes even quantitative) prediction of fluid flows by means of
• Mathematical modeling (partial differential equations)
• Numerical methods (discretization and solution techniques)

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• Software tools (solvers, pre- and post-processing utilities)
CFD enables scientists and engineers to perform „numerical
experiments‟ (i.e. computer simulations) in a „virtual flow laboratory‟
Figure:1.2 Real experiment
Figure 1.3 CFD simulation

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1.2.1.1Why use CFD?
Numerical simulations of fluid flow (will) enable
• Architects to design comfortable and safe living environments
• Designers of vehicles to improve the aerodynamic characteristics
• Chemical engineers to maximize the yield from their equipment
• Petroleum engineers to devise optimal oil recovery strategies
• Surgeons to cure arterial diseases (computational hemodynamics)
• Meteorologists to forecast the weather and warn of natural disasters
• Safety experts to reduce health risks from radiation and other hazards
• Military organizations to develop weapons and estimate the damage
• CFD practitioners to make big bucks by selling colorful pictures
1.2.1.2 Mathematical model
1. Choose a suitable flow model (viewpoint) and reference frame.
2. Identify the forces which cause and influence the fluid motion.
3. Define the computational domain in which to solve the problem.
4. Formulate conservation laws for the mass, momentum, and energy.
5. Simplify the governing equations to reduce the computational effort:
• Use available information about the prevailing flow regime
• Check for symmetries and predominant flow directions (1D/2D)
• Neglect the terms which have little or no influence on the results

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• Model the effect of small-scale fluctuations that cannot be captured
• incorporate a priori knowledge (measurement data, CFD results)
6. Add constitutive relations and specify initial/boundary conditions.
1.2.1.3 Discretization process
The PDE system is transformed into a set of algebraic equations
1. Mesh generation (decomposition into cells/elements)
• Structured or unstructured, triangular or quadrilateral?
• CAD tools + grid generators (Delaunay, advancing front)
• Mesh size, adaptive refinement in „interesting‟ flow regions
2. Space discretization (approximation of spatial derivatives)
• Finite differences/volumes/elements
• High- vs. low-order approximations
3. Time discretization (approximation of temporal derivatives)
• Explicit vs. Implicite, schèmes, stabilité, contraints
• Local time-stepping, adaptive time step control
1.2.1.4 Iterative solution strategy
The coupled nonlinear algebraic equations must be solved iteratively
• Outer iterations: the coefficients of the discrete problem are updated using
the solution values from the previous iteration so as to

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 get rid of the nonlinearities by a Newton-like method
 solve the governing equations in a segregated fashion
• Inner iterations: the resulting sequence of linear subproblems is typically
solved by an iterative method (conjugate gradients, multigrid) because direct
solvers (Gaussian elimination) are prohibitively expensive
• Convergence criteria: it is necessary to check the residuals, relative
solution changes and other indicators to make sure that the iterations
converge.
As a rule, the algebraic systems to be solved are very large (millions of
unknowns) but sparse, i.e., most of the matrix coefficients are equal to zero.
1.2.1.5 CFD simulations
The computing times for a flow simulation depend on
• The choice of numerical algorithms and data structures
• Linear algebra tools, stopping criteria for iterative solvers
• Discretization parameters (mesh quality, mesh size, time step)
• Cost per time step and convergence rates for outer iterations
• Programming language (most CFD codes are written in Fortran)
• Many other things (hardware, vectorization, parallelization etc.)
The quality of simulation results depends on
• The mathematical model and underlying assumptions
• Approximation type, stability of the numerical scheme

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• Mesh, time step, error indicators, stopping criteria . . .
1.2.1.6 Post processing and analysis
Post processing of the simulation results is performed in order to extract the
desired information from the computed flow field
• Calculation of derived quantities (stream function, vorticity)
• Calculation of integral parameters (lift, drag, total mass)
• Visualization (representation of numbers as images)
 1D data: function values connected by straight lines
 2D data: streamlines, contour levels, color diagrams
 3D data: cut lines, cut planes, iso-surfaces, iso-volumes
 Arrow plots, particle tracing, animations . . .
• Systematic data analysis by means of statistical tools
• Debugging, verification, and validation of the CFD model
1.2.1.7 Uncertainty and error
Whether or not the results of a CFD simulation can be trusted depends on
the
Degree of uncertainty and on the cumulative effect of various errors
• Uncertainty is defined as a potential deficiency due to the lack of
knowledge
(Turbulence modeling is a classic example)
• Error is defined as a recognizable deficiency due to other reasons

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 Acknowledged errors have certain mechanisms for identifying,
estimating and possibly eliminating or at least alleviating them
 Unacknowledged errors have no standard procedures for detecting
them and may remain undiscovered causing a lot of harm
 Local errors refer to solution errors at a single grid point or cell
 Global errors refer to solution errors over the entire flow domain
Local errors contribute to the global error and may move throughout the
grid.
1.2.1.8 Classification of errors
Acknowledged errors
• Physical modeling error due to uncertainty and deliberate simplifications
• Discretization error approximation of PDEs by algebraic equations
 Spatial discretization error due to a finite grid resolution
 Temporal discretization error due to a finite time step size
• Iterative convergence error which depends on the stopping criteria
• Round-off errors due to the finite precision of computer arithmetic
unacknowledged errors
• Computer programming error: “bugs” in coding and logical mistakes
• Usage error: wrong parameter values, models or boundary conditions
1.2.1.9 Verification of CFD codes
Verification amounts to looking for errors in the implementation of the
models (loosely speaking, the question is: “are we solving the equations
right”?)

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• Examine the computer programming by visually checking the source code,
documenting it and testing the underlying subprograms individually
• Examine iterative convergence by monitoring the residuals, relative
changes of integral quantities and checking if the prescribed tolerance is
attained
• Examine consistency (check if relevant conservation principles are
satisfied)
• Examine grid convergence: as the mesh and/or and the time step are
refined, the spatial and temporal discretization errors, respectively, should
asymptotically approach zero (in the absence of round-off errors)
• Compare the computational results with analytical and numerical solutions
for standard benchmark configurations (representative test cases)
1.2.1.10 Validation of CFD models
Validation amounts to checking if the model itself is adequate for practical
purposes (loosely speaking, the question is: “are we solving the right
equations”?)
• Verify the code to make sure that the numerical solutions are correct.
• Compare the results with available experimental data (making a provision
for measurement errors) to check if the reality is represented accurately
enough.
• Perform sensitivity analysis and a parametric study to assess the inherent
uncertainty due to the insufficient understanding of physical processes.
• Try using different models, geometry, and initial/boundary conditions.

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• Report the findings, document model limitations and parameter settings.
The goal of verification and validation is to ensure that the CFD code
produces reasonable results for a certain range of flow problems.
1.2.1.11 Available CFD software
ANSYS CFX
FLUENT
STAR-CD
FEMLAB
FEATFLOW
• As of now, CFD software is not yet at the level where it can be blindly
used by designers or analysts without a basic knowledge of the underlying
numerics.
• Experience with numerical solution of simple „toy problems‟ makes it
easier to analyze strange looking simulation results and identify the source
of troubles.
• New mathematical models (e.g., population balance equations for disperse
systems) require modification of existing / development of new CFD tools.
1.2.2 CATIA
CATIA (Computer Aided Three-dimensional Interactive
Application) is a multi-platform CAD/CAM/CAE commercial software
suite developed by the French company Dassault Systèmes. Written in the

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C++ programming language, CATIA is the cornerstone of the Dassault
Systèmes product lifecycle management software suite.
1.2.2.1 History
CATIA (Computer Aided Three-Dimensional Interactive Application)
started as an in-house development in 1977 by French aircraft manufacturer
Avions Marcel Dassault, at that time customer of the CAD/CAM CAD
software to develop Dassault's Mirage fighter jet. It was later adopted in the
aerospace, automotive, shipbuilding, and other industries.
Initially named CATI (Conception Assistée Tridimensionnelle
Interactive – French for Interactive Aided Three-dimensional Design ), it
was renamed CATIA in 1981 when Dassault created a subsidiary to develop
and sell the software and signed a non-exclusive distribution agreement with
IBM.
In 1984, the Boeing Company chose CATIA V3 as its main 3D CAD
tool, becoming its largest customer.
In 1988, CATIA V3 was ported from mainframe computers to UNIX.
In 1990, General Dynamics Electric Boat Corp chose CATIA as its
main 3D CAD tool to design the U.S. Navy's Virginia class submarine. Also,
Boeing was selling its CADAM CAD system worldwide through the
channel of IBM since 1978.
In 1992, CADAM was purchased from IBM, and the next year
CATIA CADAM V4 was published.

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In 1996, it was ported from one to four Unix operating systems,
including IBM AIX, Silicon Graphics IRIX, Sun Microsystems SunOS, and
Hewlett-Packard HP-UX.
In 1998, V5 was released and was an entirely rewritten version of
CATIA with support for UNIX, Windows NT and Windows XP (since
2001).
In 2008, Dassault released CATIA V6. While the server can run on
Microsoft Windows, Linux or AIX, client support for any operating system
other than Microsoft Windows was dropped.
In November 2010, Dassault launched CATIA V6R2011x, the latest
release of its PLM2.0 platform, while continuing to support and improve its
CATIA V5 software.
In June 2011, Dassault launched V6 R2012.
1.2.2.2 Scope of application
Commonly referred to as a 3D Product Lifecycle Management
software suite, CATIA supports multiple stages of product development
(CAx), including conceptualization, design (CAD), manufacturing (CAM),
and engineering (CAE). CATIA facilitates collaborative engineering across
disciplines, including surfacing & shape design, mechanical engineering,
and equipment and systems engineering.
CATIA provides a suite of surfacing, reverse engineering, and
visualization solutions to create, modify, and validate complex innovative

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shapes, from subdivision, styling, and Class A surfaces to mechanical
functional surfaces.
CATIA enables the creation of 3D parts, from 3D sketches, sheet
metal, composites, molded, forged or tooling parts up to the definition of
mechanical assemblies. It provides tools to complete product definition,
including functional tolerances as well as kinematics definition.
CATIA facilitates the design of electronic, electrical, and distributed
systems such as fluid and HVAC systems, all the way to the production of
documentation for manufacturing.
1.2.2.3 Systems engineering
CATIA offers a solution to model complex and intelligent products
through the systems engineering approach. It covers the requirements
definition, the systems architecture, the behavior modeling and the virtual
product or embedded software generation. CATIA can be customized via
application programming interfaces (API). CATIA V5 and V6 can be
adapted using Visual Basic for Applications and C++ programming
languages via CAA (Component Application Architecture), a component
object model (COM)-like interface.
Although later versions of CATIA V4 implemented NURBS, V4
principally used piecewise polynomial surfaces. CATIA V4 uses a non-
manifold solid engine.

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CATIA V5 features a parametric solid/surface-based package that
uses NURBS as the core surface representation and has several workbenches
that provide KBE support.
V5 can work with other applications, including Enovia, Smarteam,
and various CAE Analysis applications.
1.2.2.4 Aerospace applications
The Boeing Company used CATIA V3 to develop its 777 airliner and
used CATIA V5 for the 787 series aircraft. They have employed the full
range of Dassault Systèmes' 3D PLM products – CATIA, DELMIA, and
ENOVIA LCA – supplemented by Boeing-developed applications.
The development of the Indian Light Combat Aircraft has used
CATIA V5.
European aerospace Airbus has used CATIA since 2001.
1.2.3 Hyper mesh
Hyper Mesh is a high-performance finite element pre-processor to
prepare even the largest models, starting from import of CAD geometry to
exporting an analysis run for various disciplines.
Hyper Mesh enables engineers to receive high quality meshes with
maximum accuracy in the shortest time possible. A complete set of
geometry editing tools helps to efficiently prepare CAD models for the
meshing process. Meshing algorithms for shell and solid elements provide
full level of control, or can be used in automatic mode. Altair‟s Batch
Meshing technology meshes hundreds of files precisely in the background to

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match user-defined standards. HyperMesh offers the biggest variety of solid
meshing capabilities in the market.
With a focus on engineering productivity, HyperMesh is the user-preferred
environment for:
• Solid Geometry Modeling
•Shell Meshing
• Model Morphing
• Detailed Model Setup
• Surface Geometry Modeling
• Solid Mesh Generation
• Automatic Mid-surface Generation
• Batch Meshing
1.2.3.1 Benefits
With automatic and semi-automatic shell, tetra, and hexa meshing
capabilities, Hyper Mesh simplifies the modeling process of complex
geometries. Hyper Mesh provides a robust, common FEA modeling
framework across the corporation - minimizing niche modeling tool
investments and training costs.
1.2.3.2 Capabilities
Hyper Mesh presents users with an advanced suite of easy-to-use tools
to build and edit CAE models. For 2D and 3D model creation, users have
access to a variety of mesh-generation capabilities, as well as HyperMesh‟s
powerful auto-meshing module.
1.2.3.3 High Fidelity Meshing
 Surface meshing
 Solid map hexa-meshing
 Tetra meshing

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 CFD meshing
 SPH meshing
1.2.4 FLUENT
FLUENT is general-purpose CFD software ideally suited for
incompressible and mildly compressible flows. Fluent" is the general name
for the collection of computational fluid dynamics(CFD) programs sold by
Fluent, Inc. of Lebanon, NH.
 Gambit is the program used to generate the grid or mesh for the CFD
solver.
 Fluent is the CFD solver which can handle both structured grids, i.e.
rectangular grids with clearly defined node indices, and unstructured
grids. Unstructured grids are generally of triangular nature, but can
also be rectangular. In 3-D problems, unstructured grids can consist of
tetrahedrals (pyramid shape), rectangular boxes, prisms, etc.
Note: Since version 5.0, Fluent can solve both incompressible and
compressible flows.
 The normal procedure in any CFD problem is to first generate the grid
(with Gambit), and then to run Fluent.
Fluent Inc. General-purpose computational fluid dynamics (CFD)
software ideally suited for incompressible and mildly compressible flows.
Utilizing a pressure-based segregated finite-volume method solver,
FLUENT contains physical models for a wide range of applications
including turbulent flows, heat transfer, reacting flows, chemical mixing,
combustion, and multiphase flows. FLUENT provides physical models on

33
unstructured meshes, bringing you the benefits of easier problem setup and
greater accuracy using solution-adaptation of the mesh.
FLUENT remains the preeminent tool for fluid flow analysis. With
the most powerful model building tools available, a fully interactive
interface that makes you more productive, and reliable physical models,
FLUENT lets you visualize and achieve design excellence.

34
CHAPTER 2
LITERATURE REVIEW

35
2. LITERATURE REVIEW
William R. Sear stated that since there is no fuselage or tail assembly
on flying wing, the weight and inertia distribution is along the entire wing,
and the bending moments are much smaller. Surprisingly, maximum loads
on the flying wing may occur during landing rather than during in-flight
maneuvering or gusts. If an airplane is to always land and takeoff at the
same speed, then its weight can increase only with the square of its size. The
bending moments, however, increase by size cubed, as doe‟s weight. You
can thus build a bigger airplane, and obtain the effects of increased Reynolds
number and greater payload, by going to an all wing design. Any fuselage
should be eliminated, if at all possible, to both reduce drag and take full
advantage of span loading. All the above mentioned properties are obtained
from the comparison of YB-35/49.
R. W. Guiler and W. W. Huebsch [8]
has developed an adaptive
washout morphing mechanism for the control of a swept wing tailless
aircraft. The adaptive washout morphing mechanism was able to provide
effective roll, yaw and pitch control for a swept wing tailless aircraft. This
new control technique was experimentally and numerically compared to an
existing elevon equipped tailless aircraft and has shown the potential for
significant improvements over that system in terms of efficiency and
improved lift/drag. The feasibility of this mechanism was also validated by
designing, fabricating and testing a flight weight version which performed in
much the same way of a conventional elevon system.
According to Li Wen Qiang [11]
eliminating the vertical tails can
reduce airframe weight and the radar cross section, improve the aircraft

36
lift to drag ratio, and hence improve the aircraft agility .On the other hand,
the tailless configuration presents a main challenge from a stability and
control perspective. Absence of a vertical tail reduces directional stability
and directional control power.
Faliang Wang [5]
states at the cruise condition, the most significant
advantage of blended wing body aircraft is its high lift to drag ratio. This is
achieved by two aspects. Firstly, the body of blended wing body generates
lift; secondly, the blended wing body has less wetted area than the
conventional, which means the reduction of drag. For the take-off and
landing condition, because of its comparatively low wing loading, only
simple high lift devices are needed. That will reduce the design complexity
as well as manufacture difficulty of the high lift devices. The author also
summarizes some points like, The BWB configuration seems to be better
balanced in aerodynamic and stability. According to the present
configuration and internal mass arrangement, the aft CG of BWB is
unstable. Except this particular condition, the BWB configuration has
extended static margin than the FW configuration in other conditions.
According to the classical theory, the elliptic span wise lift distribution is
best for minimize the induced drag. This could be achieved by arranging the
suitable twist on several control sections. However, that twist arrangement
may lead to too much nose down pitching moment, which will cause more
difficulty for trim. Since trim is quite a big issue for tailless configuration,
therefore, it is of vital importance to find the balance point to take both the
lift distribution and pitching moment into consideration. The increasing of
the sweep angle will make the neutral point moves backward. At the same
time, the center of gravity will also have the same trend. Therefore, whether

37
the static margin could be improved depends on which moves faster.
Meanwhile, the lift curve slopes will inevitable be decreased as the increase
of sweep angle. The blended wing body configuration is really very sensitive
to changing geometry parameter. Several parameters are closely linked
together. Even one parameter changes will lead to a chain reaction. This
feature makes the design and optimization of Blended Wing Body a quite
complicated work.
Gary B. Cosentino [7]
has described and given examples of successful
CFD application to the design process of three true X-planes. The process of
conceptual design, CAD modeling and refinement, followed by CFD
methods application and further refinement has been described. Specifically,
how CFD can aid in the design of a wind tunnel model to yield few if any
surprises during wind tunnel testing was explained. Once in the wind tunnel,
data can then be directly correlated to the computed CFD database, thus
calibrating the CFD methodology and in some cases ensuring that the wind
tunnel data reduction is being performed correctly. CFD can be and has been
an enabling technology on the path to getting a new aircraft shape to flight.
Controlling an inherently unstable configuration is critically dependent on
determination of its aerodynamics and stability derivatives; CFD can provide
preliminary estimates of these quantities accurately enough for the
development of early control laws and a flyable simulation. Configuration
assessments and incremental redesign can then be accomplished in a
deliberate fashion, with the goal of arriving at a final configuration to be
committed to more detailed (and expensive) analysis leading toward a flight
model, with greatly improved chances of success.
According to Bras and Suleiman [2]
of University of Victoria, Tail
planes can either have movable elevator surfaces or be single combined

38
(stabilizer or flying tail). There can also be alternative approaches as V and
X tails and the case of tailless aircraft (flying wing) having all its horizontal
and vertical control surfaces on its main wing surface. Despite these
different tail configurations, they all serve the purpose of providing an
aircraft with pitch and yaw stability and control. The purpose of such a
component in an aircraft mimics the one of a tail in birds. In fact, birds seem
to adjust their tail to optimize their flight rather than just using them
uniquely as a stabilizing and control surface. They also studied the influence
of bird tails on profile and induced drag. He concluded that by using the tail
to generate lift, birds can have the small wings needed for fast flight (with
the tail closed) and still have good performance in slow flight (with the tail
spread), during turns, or when accelerating . Evans et al. conducted wind
tunnel tests on barn swallows and compared the results with delta wing
theory (slender-wing theory). He observed that at low speeds, the tail was
spread and held at a high angle of attack, and wingspan was maximized. At
high airspeeds, the tail was furled; held parallel to the airflow and wingspan
was reduced. However, their empirical observations failed to provide robust
support for the variable-geometry application of delta-wing theory. Birds
don‟t have a vertical tail stabilizer and yet they are capable of controlling
yaw motion
A study carried by Sachs [13]
revealed that, on one hand, bodies of
birds are aerodynamically well integrated in the wing. The integration of the
body is supported by its smaller size relative to the wing. As a consequence,
the effect of the integrated body on the tendency to sideslip when yawing
may be reduced when compared with a case where the body is considered
alone without a wing. On the other hand, birds have a fast restoring
capability in the yaw axis in terms of dynamic stiffness. This is due to the

39
fact that the yawing moment of inertia is more reduced with a size decrease
than the restoring aerodynamic moment, leading to a reduction in the
required aerodynamic yawing moment in birds. This suggests that in such a
case birds do not need a vertical tail as the wing alone can provide the
required aerodynamic yawing moment. A later study carried out by the same
author regarding the specific tail effects on yaw stability in birds with
different tail shapes revealed that elongated delta shaped tails can produce
yawing moment in case of sideslip. This is due to the asymmetry in the
airflow at the tail, because of the delta shape. This asymmetry leads to an
asymmetrical lift distribution which also causes a correspondingly
asymmetrical induced drag distribution forming a couple that yields a
yawing moment. The case of birds with forked tails was also studied and
such tails showed drag forces at the elongated elements. By controlling the
spread angle of each half tail, birds with such tails are able to control yaw
due to the drag forces with different lever arms, forming a couple and hence
a yawing moment. A further ability for producing stabilizing yawing
moments is due to the legs and feet, according to Sachs. Depending on their
length, they can stretch out in rearward direction to a considerably larger
extent than the tail to control the couple produced by the asymmetry in drag
produced by both feet. Sachs also suggests that as what happens with an
aircraft flying at low speeds (take-off and landing situations), where flaps
are used to increase drag, birds also lower their feet so that they are exposed
to the airflow and generate drag for low speed flight conditions, while
keeping them in a streamlined position for high speed flight, producing little
drag.
Ideal Lift Distributions and Flap Settings for Adaptive Tailless
Aircraft by Aaron Anthony Cusher [1]
(Under the direction of Dr. Ashok

40
Gopalarathnam) explored tailless aircraft configurations which utilize
multiple trailing-edge flaps for the purpose of wing adaptation and drag
reduction. Throughout this thesis, the term “tailless aircraft” will be used to
describe those aircraft that are designed with only one main lifting surface,
that being the wing, which is responsible for producing the aircraft‟s lift and
also contains all control surfaces providing static and dynamic stability.
These aircraft are sometimes referred to as flying wings, blended-wing
bodies, or all-wing aircraft. The more conventional two horizontal element
designs, as indicated by the vast majority of commercial aircraft, will be
referred to as “tailed aircraft. However modest, tailless aircraft
configurations have found popularity alongside tailed configurations in
particular applications. These applications include sailplanes and gliders,
light airplanes, unmanned aerial vehicles (UAV), high-speed military planes,
supersonic airliners, and hypersonic re-entry vehicles and because only one
lifting surface is used, it has often been proposed that drag benefits should be
realized and design costs kept lower when implementing a tailless design
verses a comparable tailed design. Despite these positives, tailless
configurations have seen limited use in general aviation and commercial
aircraft design, most likely due to inherent complexity in the aerodynamic
design of tailless aircraft and perhaps also due to the overwhelming history
of tailed-aircraft use, giving indication of the need for the advancement in
tailless design technology.
Tjoek Eko Pambag [15]
mentioned there are at least two main benefits
from tailless configuration: For the cruise condition, the most significant
advantage of blended wing body aircraft is its high lift to drag ratio. This is
achieved by two aspects. Firstly, the body of blended wing body generates
lift; secondly, the blended wing body has less wetted area than the

41
conventional, which means the reduction of drag. For the take-off and
landing condition, because of its comparatively low wing loading, only
simple high lift devices are needed. That will reduce the design complexity
as well as manufacture difficulty of the high lift devices. At the first glance,
the aerodynamic design of a blended wing body aircraft seems to be an easy
task. However, several difficulties will emerge when studying this issue in-
depth.

43
3. METHODOLOGY
The first step involved in this project is the selection of an appropriate
tailless aircraft model for analysis. The chosen designs are,
Figure: 3.1 BWB aircraft model.

44
3.1 Designing
The two configurations are designed by using CATIA. The
reason behind using this particular software because of its advanced tools
which supports 3D modeling and which allows export to multiple software
languages.
Figure: 3.2 CATIA design of BWB
The designing is done with the basic design configuration values that
we got from the internet as shown in the figure. The basic values may
include the span, chord, height, etc.. Since the blended wing body having the
airfoil shape, an airfoil will be designed for fuselage section and also for the
wing section. Each will be connected to each other in order to get the entire
body. According to the overall body an engine dimension is selected, and
designed in CATIA and each body will be merged together.

45
The same procedure is followed for designing the conventional body.
The design selected for the conventional body is Boeing 777 as shown in
figure. According to the basic design values it is designed in CATIA.
Figure: 3.3 Conventional body, Boeing 777
Figure: 3.4 Boeing777 CATIA model

46
3.2 Meshing
Followed by designing, selected design is meshed using hyper mesh
since Hyper Mesh enables us to achieve high quality meshes with maximum
accuracy in the shortest time possible. In addition we have created an
environment called domain where it includes an inlet and outlet
distinguished by distinctive colors. The purpose of the domain is to analyze
the flow around the body. Actually the domain defines the atmosphere, so
we need to define this atmosphere as large as possible compared with the
object. After defining the domain dimensions we need to define the inlet,
and outlet. It is shown with different colors on rendering. This
differentiation is done in order to understand the model in a simpler manner.
The meshed model is as shown in the figure below.
Figure: 3.5 Meshed BWB
The domain configurations are six times the dimension of the body
which is analyzed.

47
Length: 250m
Breadth: 240m
Height: 85m
After defining the domain, the model and domain have been meshed.
The Faces are meshed first. The face meshing will be done with tri sub map
on the domain faces, and tri pave on the model. With the reference of that
meshed faces, the volume is meshed with tetra hybrid elements with cooper
type. The meshing is done with unstructured mesh since the model has to be
structured separately with high concentration meshing over its boundary in
order to get accurate result.
The complete meshed domain and the model will be defined in this
part. In the domain, the air inlet is defined as Velocity inlet, and the outlet is
defined as Out flow. The whole model will be defined as wall. So that while
exporting the file the code will automatically write the defined parts into the
required model.
The meshing Quality can be analyzed by using the tool which is given
by the hyper mesh software. By using that we could analyze each meshed
element in the whole body. There by increasing the accuracy of mesh and
also the result given by the solver.
After defining, the whole body is exported to FLUENT software,
which will convert the file format into FLUENT software readable format.
The file will be saved as an .msh file.

48
3.3 Solver
The FLUENT software is used as the solver. The reason behind using
this software is because of its ease of use and different kind of equations
available in it. The model is already exported to FLUENT software. So the
next step is to read the particular .msh file. On reading the file that we
exported to FLUENT, it automatically defines the wall, inlet and outlet. That
could be seen by the tool called grid display. Inlet, outlet and wall will be
shown with different colors.
Property Units Method Value(s)
Air properties
Density (ρ) kg/m3
constant 1.225
Cp (Specific Heat) J/kg-k constant 1006.43
Thermal
Conductivity (K)
W/m-k constant 0.0242
Viscosity(µ) kg/m-s constant 1.7894e-05
Molecular Weight kg/kg-mol constant 28.966
L-J Characteristic
Length
Angstrom constant 3.711
L-J Energy
Parameter
K constant 78.6
Thermal
Expansion
Coefficient
1/k constant 0

49
Degrees of
Freedom
No unit constant 0
Speed of Sound m/s none 330
Aluminium properties
Density kg/m3
constant 2719
Cp (Specific Heat) J/kg-k constant 871
Thermal
Conductivity(K)
W/m-k constant 202.4
Table: 3.1 Material properties
The next step is to define the atmospheric conditions. In this project
we are going to analyze our model with the Mach numbers 0.4, 0.5, 0.6. The
atmospheric values taken to analyze the model at an altitude of 30,000ft are
listed above.
The BWB surface has been defined as an aluminium material. These
values are there in the database itself. Since we are not going for any kind of
thermal calculation the thermal expansion coefficient will be taken as zero.
After defining the materials, the different conditions have to be
defined. The main condition, that to be defined is the inlet condition of the
domain, where we are going to give the different Mach numbers. The
boundary condition will be taken as no slip condition. This condition is
given because the flow is viscous. So there won‟t be any kind of slip over
the surface of the body. Then only the drag will be calculated.

50
The different conditions are listed below.
Inlet Condition for Mach 0.4,
Table: 3.2 Inlet conditions for Mach no: 0.4

51

52
After giving the condition for each Mach number the iteration is
started. The number of iteration given is 3000. If the result is converged
within this number of iteration, the result will be taken otherwise again the
iteration should be done till getting converged result.

53
CHAPTER 4
RESULTS AND DISCUSSION

54
4. RESULTS AND DISCUSSION
The solved results are obtained in the form of graphs, values and in
the form of contours. The graphs and the contours are analyzed properly.
In the software FLUENT, for 3D objects, the graphs are found by
creating a separate line, from where we obtained our values. Otherwise the
graph won‟t be that perfect. The graph must represent one axis as distance,
and the other one as any required parameter.
The contours are just like the graph which shows different area with
different colors according to the variation of amount of that particular
property that we need to exhibit. The color codes are given on the left hand
side, with respective values of that color. Since the object is in 3D, we could
rotate the object and select whatever sides we need. The major disadvantage
of this result is that we need to compare the values on comparing the scale
given on the left hand side.
The major result that we got is the drag and lift. The drag and the lift
can be obtained as values. The values are compared with that of the
conventional body. The values are obtained as the forces. Since both forces
are perpendicular to each other, it can be obtained by finding the forces
along that particular axis. According to our design, the X-axis represents the
flow direction, Z-axis represents the vertical, and Y-axis represents the
lateral axis. Hence in order to get drag we took forces in the direction of X-
axis and to get lift force, the Z direction is taken.
The obtained results are in agreement with many research results, that
is, BWB is aerodynamically efficient than conventional configuration. Here

55
we can see that, the main load is concentrated over the fuselage, so that we
get a more efficient structure. The wing loading is distributed over the entire
body. This is because the fuselage geometry is in aerodynamic shape. This
also contributes to the lift. Compared to the conventional configuration
BWB produces more lift.
4.1 Lift
As already described we took the force along the Z-direction. The lift
obtained for Mach no: 0.4 is given below.
Table: 4.1 Lift obtained for Mach no: 0.4(BWB)
The lift obtained for Mach no: 0.5
The lift obtained for Mach no: 0.6

56
The lift force obtained for the conventional bodies are given below,
Lift force for Mach no: 0.4
Table: 4.4 Lift force for Mach no: 0.4(CB)
The result obtained shows that the lift produced on the BWB is higher
than those of the conventional body. This is because of its highly integrated
structure and aerodynamic body. The lift is also produced even in the 0o
angle attack of the aircraft body. The lift increases with the increase in the
speed of the flight. As described earlier, the lift force is obtained by finding
the force along Z-axis, since it is designed like that. The lift force obtained
for both the bodies are given below,

57
Mach no:
Type
0.4 0.5 0.6
BWB 764929.52 N 1207534.2 N 1789761.8 N
CB 16270.21 N 23107.893 N 36642.67 N
Table: 4.7 Lift force
From the above table itself we can conclude that BWB produces much
more lift than compared to the conventional body. As explained earlier this
is due to the aerodynamic and integrated shape of the BWB. This proves that
BWB is more efficient than the conventional body.
4.2 Drag
The drag is obtained by taking the force along the X-axis. Drag
obtained for different Mach no‟s is given down.
Drag obtained for Mach 0.4
Table: 4.8 Drag for Mach no: 0.4(BWB)

58
The drag values obtained for the conventional body are given below
for different Mach no‟s:
Drag for Mach no: 0.4
Table: 4.11 Drag for Mach no: 0.4(CB)

59
The drag is another important part to be discussed in our project. The
drag contributes to the main reason for excessive fuel consumption. So we
are here to prove that drag can be reduced to an extent by implementing the
blended wing body design even at subsonic Mach no‟s. The main reason for
the reduced drag is the increased sweepback angle of the blended wing body
design.
The drag of the body is calculated by taking force along the X-axis,
since the longitudinal axis is along the X-axis.
Mach no:
Type
0.4 0.5 0.6
BWB 155957.21 N 242630.91 N 356583.56 N
CB 84587.431 N 121620.49 N 188990.88 N
Table: 4.14 Drag force
From the table, it is visible that the drag for the BWB is nearly twice
that of the conventional body. But on comparing the L/D ratio of both the
aircraft, that nullifies this small change. That contributes to the maximum
efficiency of the aircraft. The project shows that this is due to the increased
wetted area compared to the conventional aircraft. The most important thing
to be noted is that, with same configuration, BWB can accommodate more
no. of people compared to the conventional body. This also improves the
efficiency. Here we have taken only the total lift force. So we are not able to
exhibit what are the values of different drag forces present in this total drag
force.

60
4.3 L/D ratio
The L/D ratio is one of the main factors to be discussed. The result
shows that L/D ratio for BWB is much higher than that of the conventional
body. Nearly 24% increase is obtained for the BWB. Which shows that
BWB configuration is more efficient to implement in passenger flight. The
L/D ratio is tabulated below.
Mach no:
Type
0.4 0.5 0.6
BWB 4.90 4.97 5.01
CB 0.19 0.19 0.19
Table: 4.15 L/D ratio
4.4 Pressure
In order to analyse the pressure distribution over the model , we
created two lines just above and below of it . Hence graph is generated. It is
shown below.
Figure: 4.1 BWB with reference lines

61
Figire: 4.2 Pressure variation
Here we have created two lines just above and below the model in
order to analyze the pressure distribution. Generally lift is being generated
due to the distribution of low and high pressure. The analyzed model and the
generated graph are as shown in figure 4.1 and 4.1.
The graph 4.2 clearly shows that, the pressure on the line 29 is less
compared to that of the pressure in the line 21, which indicates that it
produces sufficient lift even in the zero angle of attack. The maximum
pressure variation is obtained near the fuselage that means the maximum lift
will be produced on the fuselage. This improves the wing loading, which in
turn improves the structural efficiency.

62
Figure: 4.3 Pressure distribution of bottom surface of BWB
Figure: 4.4 Pressure distributions over BWB
The above figure shows clear view of pressure variation over the
BWB. It shows that the pressure over the body is less compared to the
pressure beneath the body. The figure shows the maximum pressure will be

63
obtained on the nose section, which will produce more drag. But it can be
reduced by using a more efficient structural body.
4.5 Velocity
Velocity and pressure are correlated. Same as the pressure plot, here
also we have drawn line forward of the body.As a result a graph is generated
which is shown in the figure below
Figure: 4.5 Velocity variation
The velocity magnitude described by pathlines is given below and
velocity variation is represented by various colors.The intensity and the
color scale is given on the left hand side of the figure
Here also we have followed the same procedure as the pressure. We
have created line just above the body and hence a graph is being generated
which is as shown in the figure 4.5. Velocity and the pressure are mutually
dependent, according to Bernoulli‟s principle. The graph shows the same as

64
that of pressure graph, i.e. the velocity is high over the BWB compared to
the velocity at bottom of the BWB.
The figure given below shows entire velocity variation over the BWB.
It shows that over the entire body velocity is high compared to velocity at
the bottom. The velocity variation ratio is being increased with increase in
Mach no: it shows that this configuration will be more efficient in higher
Mach no:. this configuration is having one morre advantage that of
CESTOL. That is, since the engine is mounted over the body, it helps to
increase the velocity over BWB body.
Figure: 4.6 Velocity distribution of bottom surface of BWB

65
Figure: 4.7 Velocity distributions over BWB
In addition, velocity magnitude is being represented by various path
lines of vivid colors in order to understand the flow over the body. That is
shown in the figure 4.8. It is obtained that a smooth flow is occurring over
the body. The intensity and the color scale is given on the left hand side of
the figure.

66
Figure: 4.8 Path lines colored by velocity magnitude
The path lines also indicates how the flow occures over the body. In
FLUENT the path lines can be created from any lines that can drawn any
where in the figure. According to the flow direction, the flow will start from
the lines.
4.6 Conclusions
The project is summarized as follows:
Based on the same requirements, two different options- conventional
and blended wing body aircraft are provided. Utilizing some analytical
software‟s, the aerodynamic characteristics are compared on the two
configurations. The effects of geometric parameters on aerodynamic
characteristics are investigated.
The main findings through the research could be concluded as:
1. From the aerodynamic point of view, the highly integrated wing and body
configuration benefits the blended wing body less lift coefficient needed for

67
cruise as well as less drag produced. The cruise lift to drag ratio of BWB
will increase about 24% compared to the CB configuration.
2. The BWB configuration seems to be better balanced in aerodynamic and
stability. According to the present configuration and internal mass
arrangement, the aft CG of BWB is unstable. Except this particular
condition, the BWB configuration has extended static margin than the FW
configuration in other conditions.
3. According to the classical theory, the elliptic span wise lift distribution is
best for minimize the induced drag. This could be achieved by arranging the
suitable twist on several control sections. However, that twist arrangement
may lead to too much nose down pitching moment, which will cause more
difficulty for trim. Since trim is quite a big issue for tailless configuration,
therefore, it is of vital importance to find the balance point to take both the
lift distribution and pitching moment into consideration.
4. The increasing of the sweep angle will make the neutral point moves
backward. At the same time, the center of gravity will also have the same
trend. Therefore, whether the static margin could be improved depends on
which moves faster. Meanwhile, the lift curve slopes will inevitable be
decreased as the increase of sweep angle.
5. The blended wing body configuration is really very sensitive to changing
geometry parameter. Several parameters are closely linked together. One
parameter change will lead to a chain reaction. This feature makes the design
and optimization of Blended Wing Body a quite complicated work.

69
5. FUTURE WORK
5.1 Suggestions for future work
Accordingly, some suggestions for future work could be provided.
1. From the models point of view, both configuration options are not well
designed, which means the general configuration, the airfoil section, the
twist as well as other aerodynamic aspects still need in-depth design and
optimize in the future work.
2. From the aerodynamic point of view, the aerodynamic forces calculation
could be more accurate. In terms of the lift calculation, it is calculated by
FLUENT. In terms of drag prediction, the engine and nacelle drag are
neglected. Besides, the drag estimation method may not be sufficiently
enough. Although there are so many drawbacks, nevertheless, it provides a
quick and convenient method to obtain the aerodynamic data.
3. Fulfill the design of three configuration options to make a better
comparison, especially on the aerodynamic design and internal mass
distribution arrangement. That further work will bring more accurate data for
analysis and comparison on the two different configurations.
4. Only the clean configuration has been considered, for the take-off or
landing these kinds of complex configuration can be investigated in the
future work.
5. Since there are so many parameters closely linked together in blended
wing body aircraft, it is of great interest to research the optimization of those
parameters. Some optimization algorithm could be added during the iteration
process.

71
REFERENCES
1. Aaron A. Crusher “Ideal Lift Distributions and Flap Settings for
Adaptive Tailless Aircraft” A thesis submitted to the Graduate Faculty of
North Carolina State University in partial fulfillment of the requirements
for the Degree of Master of Science Rayleigh NC 2005
2. Bras M, Vale J1, Lau F and Suleman “Flight Dynamics and Control of a
Vertical Tailless Aircraft” Aeronaut Aerospace Eng 2013
3. DE Castro H V, “Flying and Handling Qualities of a Fly-by-Wire
Blended Wing Body Civil Transport Aircraft” PhD Thesis. Cranfield
University .Dec 2003
4. Dmitri Kuzmin “Introduction to Computational Fluid Dynamics”
institute of applied mathematics university of Dortmund
5. Faliang Wang “The Comparison Of Aerodynamic And Stability
Characteristics Between Conventional And Blended Wing Body
Aircraft” Cranfield University by 2012
6. Friedl .J “Aerodynamic Design of a Tailless Aero plane” by Acta
Polytechnica Vol. 41 No. 4–5/2001
7. Gary B. Cosentino, “Computational Fluid Dynamics Analysis Success
Stories of X-plane Design to Flight Test” NASA Dryden Flight Research
Center Edwards, California May 2008
8. Guiler R. W. And Huebsch W.W. “control of a swept wing tailless
aircraft through wing morphing” aurora flight sciences, Bridgeport, WV
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72
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