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

3.3 Inlet conditions for Mach no: 0.5 38

3.4 Inlet conditions for Mach no: 0.6 39

4.1 Lift obtained for Mach 0.4(BWB) 42

4.2 Lift obtained for Mach 0.5(BWB) 42

4.3 Lift obtained for Mach 0.6(BWB) 42

4.4 Lift obtained for Mach 0.4(CB) 43

4.5 Lift obtained for Mach 0.5(CB) 43

4.6 Lift obtained for Mach 0.6(CB) 43

4.7 Lift force 44

4.8 Drag obtained for Mach 0.4(BWB) 44

4.9 Drag obtained for Mach 0.5(BWB) 44

4.10 Drag obtained for Mach 0.6(BWB) 45

4.11 Drag obtained for Mach 0.4(CB) 45

4.12 Drag obtained for Mach 0.5(CB) 45

4.13 Drag obtained for Mach 0.6(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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CHAPTER 1

INTRODUCTION

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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

32

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.

42

CHAPTER 3

METHODOLOGY

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

Inlet Condition for Mach 0.5,

Table: 3.3 Inlet conditions for Mach no: 0.5

52

Inlet Condition for Mach 0.6,

Table: 3.4 Inlet conditions for Mach no: 0.6

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

Table: 4.2 Lift obtained for Mach no: 0.5(BWB)

The lift obtained for Mach no: 0.6

Table: 4.3 Lift obtained for Mach no: 0.6(BWB)

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)

Lift force for Mach no: 0.5

Table: 4.5 Lift force for Mach no: 0.5(CB)

Lift force for Mach no: 0.6

Table: 4.6 Lift force for Mach no: 0.6(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)

Drag obtained for Mach 0.5

Table: 4.9 Drag for Mach no: 0.5(BWB)

58

Drag obtained for Mach 0.6

Table: 4.10 Drag for Mach no: 0.6(BWB)

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)

Drag for Mach no: 0.5

Table: 4.12 Drag for Mach no: 0.5(CB)

Drag for Mach no: 0.6

Table: 4.13 Drag for Mach no: 0.6(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.

68

CHAPTER 5

FUTURE 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.

70

REFERENCES

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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

west Virginia university, Morgantown, WV

72

9. Howard Smith, DES 1100/1: “Advanced Blended Wing Body High

Capacity Airliner BW-11 Project Specification”. Cranfield University.

2011

10. Lecomte. P and Fage. E “'Flight Handling Quality Problems Posed By

Swept-Wing Transport Planes Without Tail Units” NASA 1966

11. LI Wen-qiang MA Jian-jun ZHENG Zhi-qiang PENG “Robust

Controller Design to Uncertain Nonlinear Tailless Aircraft” College of

Mechatronics and Automation, National University of Defense

Technology, Changsha, Hunan, P.R, China, Proceedings of the 17th

World Congress The International Federation of Automatic Control

Seoul, Korea, July 6-11, 2008

12. Paulus. D, Salmon. T, Mohr. B, Rössler. C, Petersson. O, Stroscher. F,

Baier. H, and Hornung. M, “Configuration Selection for a 450 Passenger

Ultra-Efficient 2020 Aircraft”, 4th European Conference For Aerospace

Sciences (Eucass) 2007-13

13. Sachs G, “Tail effects on yaw stability in birds”, J Theor Biol 249:464-

472 (2007)

14. Thorpe A.W, M.F Curtis “Lateral stability of tailless aircraft”, London :

his majesties stationary office 1948

15. Timothy Shaw Peterson, “Handling Qualities of a Blended Wing Body

Aircraft”, Master of Applied Science Institute for Aerospace Studies

University of Toronto 2011

16. Tjoekjoek Eko Pambagjo, “Aerodynamic Design of a Medium size

blended wing body airplane”, AIAA-2001-0129

17. www.encyclopedia.com

18. www.engineeringessay.com