AERODYNAMICS OF PERMEABLE WINGS BY MOHAMMED …

AERODYNAMICS OF PERMEABLE WINGS

BY

MOHAMMED ABDULAMLEK ALDHEEB

A thesis submitted in fulfilment of the requirement for the

degree of Doctor of Philosophy (Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

JULY 2018

http://www.google.com.my/url?url=http://www.iium.edu.my/educ&rct=j&frm=1&q=&esrc=s&sa=U&ei=KHqFVJaTIZKyuATNwoGoBw&ved=0CBMQFjAA&usg=AFQjCNH8CPBB4-yr6XSF1EeEZS5f3iT02w

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ABSTRACT

This research investigates the effect of permeability on the aerodynamics of airfoils and wings.

The aerodynamic performance of these airfoils and wings were studied experimentally in the

IIUM-low speed wind tunnel. From the literature, it appears that a comprehensive experimental

study on permeable wings and airfoils is needed. The research comprises two main objectives;

the first of which is to investigate the aerodynamic performance of permeable wings and airfoils

using experimental and simulation methods (CFD). The second objective is to investigate

experimentally the effect of permeable wingtips on the flow field over the wingtip and its effect

on the wake vortex flow downstream using particle image velocimetry (PIV). A permeable thin

flat plate, representing a thin symmetric airfoil, as well as a finite wing of the same cross section

is used. Permeability is introduced by using a honeycomb structure. The experiment was

performed for a range of different porosity values. The results are presented in terms of lift slope

versus permeability. The lift slope reduces as the permeability increases for both wings and

airfoils. The behaviour/trend of the lift slope is similar to the analytical results available in the

literature. The effect of permeability on the aerodynamic center is plotted as well. As the

permeability increases the aerodynamic center moves towards the impermeable region. The

investigation on the applicability of the standard equation for calculating the lift slope of a wing

from an airfoil is applied to permeable wings and airfoils. The result shows that this equation is

applicable to both conventional impermeable as well as permeable wings and airfoils. The CFD

work is carried out on a thin symmetric airfoil using NACA008 as its cross section. The results

of the variation of the lift slope with permeability show a similar behavior as in the experimental

study. The results of permeability from CFD shows that a low value of permeability reduces the

drag coefficients and thus increases the lift to drag ratio by a large amount. The effect of

directional porosity of wing tips on the flow field on the wing surface and in the nearfield of the

wing is investigated through PIV. The PIV experiment was performed on seven models of

wingtips including the base model. An impermeable wing with a NACA 653218 section was

used in this study. Directional porosity is used in five wing tip configurations and one wing tip

was made of a honeycomb structure. Configurations 4 – 7 have the highest porosity and the

porosity direction in configurations 4 and 5 is 90º, and configurations 6 and 7 have a directional

porosity of 95º and 100º, respectively, the directional porosity angle is measured from the chord

line., have the highest effect on flow vortex downstream and the reduction in vorticity can reach

up to 90% and reduction in tangential velocity can reach up to 74%. These directional porosity

wing tips have a great impact on the flow field over the wingtip surface as shown by studying

the flow field over the upper surface of wingtips using PIV measurements. These configurations

have a porosity perpendicular to the chord line. Configuration 5 has the highest impact as it has

the highest porosity value. Configurations 2 and 3 result in a lesser effect on vorticity and

tangential velocity as they have porosity inclinations of 30º and 45º respectively. The PIV

results over the upper surface of the wingtip show a high disturbance of the flow on the upper

surface which results in a reduction in wake vortex downstream. The aerodynamic

performances of permeable wingtips were obtained as well and they show a negligible reduction

in lift but increase in drag coefficients in some configurations can reach up to 18% at angles of

attack [10º - 15º]. These permeable wing tip configurations can be used to alleviate the wake

vortex as they are not add-on devices and they are easy to deploy. Thus, this research

investigated the behavior of permeable airfoils and wings and compared their behavior with

analytical results. It also verified the applicability of the standard equation of calculating lift

slope of wing from airfoil lift slope for permeable wings and airfoils. The research also

introduced new directionally permeable wingtips which have high impact on vorticity reduction

downstream in the near wake field. Last, it investigated the flow behavior over the porous

wingtip surface to investigate its role in wake vortex strength reduction downstream.

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خلاصة البحثABSTRACT IN ARABIC

يدرس هذا البحث التأثير الديناميكي الهوائي للأجنحة ذات المسامات تجريبيا بإستخدام نفق الرياح منخفضة السرعة ي بالجامعة الإسلامية العالمية بماليزيا. ويتألف البحث من هدفين رئيسيين؛ أولهما هو دراسة الأداء الديناميكي الهوائ

.(CFD) ثنائية الأبعاد تجريبياً و أيضاً بإستخدام المحاكاة الحسابية الديناميكية للموائع للأجنحة ذات المسامات ثلاثية ووالهدف الثاني هو دراسة تأثير أطراف الأجنحة المسامية على مجال تدفق الهواء فوق طرف الجناح وعلى دوامة الهواء خلف

.(PIV) الجناح باستخدام مقياس السرعة بواسطة تصوير الجزيئاتو يستخدم جناح رفيع ذو مسامات بهيكل سداسي كخلية النحل. أجريت التجربة على عدة مجسمات بكثافة متفاوتة للمسامات. يتم عرض البيانات في رسم معامل الرفع مقابل النفاذية وتظهر انخفاضا في منحدر الرفع مع زيادة نفاذية في

ائج شبيهة بما ورد في الدراسات السابقة. يتم رسم تأثير مدى النفاذية على كلتا الحالتين: ثلاثية و ثنائية الأبعاد. تأتي النتيتم التحقق من انطباق المعادلة القياسية لحساب المنحدر الرفع من الجناح من جنيح الهواء على و .أيضامركز الثقل الهوائي

ليدية كما تنطبق كذلك على الأجنحة ذات النماذج المستخدمة. وتبين النتيجة أن هذه المعادلة تنطبق على الأجنحة التقو تظهر نتائج معامل الرفع سلوكا مماثلا NACA0008 للجناح ذي المقطع العرضي (CFD) المسامات. يتم عمل

أسهل بالمقارنة مع التجارب العملية، مما يمكّن من تطبيق (CFD) للدراسة التجريبية. كما أن السيطرة على النفاذية في، وبالتالي يزيد من نسبة فعالية العكسيةالنفاذية على الأجنحة مما يتسبب في تقليل معاملات القوة قيمة منخفضة منوبالقرب يتم التحقق من تأثير المسامية الاتجاهية لطرف الجناح على مجال تدفق الهواء فوق طرف الجناح .الجناح بصورة كبيرة

بما في ذلك النموذج الأجنحةلى سبعة نماذج من أطراف ع (PIV) وقد أجريت تجربة .(PIV) الجناح من خلال منيتم إستخدام المسامية NACA653218 .المقطعأستخدم الجناح ذات وقد الأساسي )النموذج غير المسامي(.

يكون لها 7 - 4نماذج و نموذج مكون من المسامية ذات الهيكل السداسي كخلية النحل. النماذج من خمسةفي الاتجاهيةة ي، وانخفاض في السرعة التماس%90كن أن تصل إنخفاض الدوامة إلى تأثير على دوامة الهواء خلف الجناح ويمأعلى

٪. هذه النماذج لها تأثير كبير على مجال تدفق الهواء فوق طرف الجناح كما هو مبين من 74للدوامة يمكن أن تصل إلى هذه النماذج حيث ان (PIV) الجناح بإستخدام قياسات خلال دراسة مجال تدفق الهواء على السطح العلوي من طرف

له أعلى تأثير لأنه يحتوي على أعلى نسبة المسامية. النماذج 5لها مسامية عمودي على خط وتر الجناح. النموذج رقم على 45درجة و 30للدوامة كما أن لديهم المسامية تميل ب التماسيهتأثيرها أقل على دوامة الهواء والسرعة 3و 2رقم

.التوالي مقاسة من خط وتر الجناحعلى السطح العلوي من طرف الجناح تظهر اضطرابات عالية للهواء المتدفق على السطح العلوي مما يؤدي (PIV) نتائج

الأجنحة ناميكية الهوائية من أطراف إلى إنخفاض في دوامة الهواء خلف الجناح. وقد تم كذلك الحصول على الأداء الديفي بعض النماذج يمكن العكسيةإنخفاضاً طفيفاً في معامل قوة الرفع ولكن زيادة في معاملات القوة وتظهر النفاذية، ذات

أطراف الأجنحة ذات المسامية لتخفيف النماذج منويمكن استخدام هذه .عند بعض زوايا الهجوم 18%أن تصل إلى .افة على الأجهزة وأنها سهلة الإستخدامدوامة الهواء خلف الأجنحة لأنها ليست إض

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APPROVAL PAGE

The thesis of Mohammed Abdulmalek Aldheeb has been approved by the following:

_____________________________

Waqar Asrar

Supervisor

_____________________________

Erwin Sulaeman

Co-Supervisor

_____________________________

Ashraf Ali Omar

Co-Supervisor

_____________________________

Sher Afghan Khan

Internal Examiner

_____________________________

Mohd Zulkifly Abdullah

External Examiner

_____________________________

Andrew Ragai Anak Henry Rigit

External Examiner

_____________________________

Md Yousuf Ali

Chairman

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DECLARATION

I hereby declare that this thesis is the result of my own investigations, except

where otherwise stated. I also declare that it has not been previously or concurrently

submitted as a whole for any other degrees at IIUM or other institutions.

Mohammed Abdulmalek Aldheeb

Signature ........................................................... Date .........................................

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COPYRIGHT PAGE

DECLARATION OF COPYRIGHT AND AFFIRMATION OF

FAIR USE OF UNPUBLISHED RESEARCH

AERODYNAMIC OF PERMEABLWINGS

I declare that the copyright holders of this thesis are jointly owned by the student

and IIUM.

Copyright © 2018 Mohammed Abdulamek Aldheeb and International Islamic University Malaysia.

All rights reserved.

No part of this unpublished research may be reproduced, stored in a retrieval system,

or transmitted, in any form or by any means, electronic, mechanical, photocopying,

recording or otherwise without prior written permission of the copyright holder

except as provided below

1. Any material contained in or derived from this unpublished research

may be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies (print

or electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieved system

and supply copies of this unpublished research if requested by other

universities and research libraries.

By signing this form, I acknowledged that I have read and understand the IIUM

Intellectual Property Right and Commercialization policy.

Affirmed by Mohammed Abdulmalek Aldheeb

………………….. ………………………..

Signature Date

vii

DEDICATION

This thesis is dedicated to my father

Abdulamlek Mohammed Aldheeb

My brother

Naif Abdulmalek Aldheeb

and

My wife

Ola Ali

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ACKNOWLEDGEMENTS

Firstly, it is my utmost pleasure to dedicate this work to my dear parents and my family,

who granted me the gift of their unwavering belief in my ability to accomplish this goal:

thank you for your support and patience.

It is my pleasure to express my gratitude and thanks to Professor Waqar Asrar

for his continuous support, encouragement, and leadership, and for that, I will be forever

grateful. Special appreciation to Prof. Ashraf for his encouragement and support

throughout my study. My thanks also to Dr. Erwin Sulaeman.

I wish to express my appreciation and thanks to those who provided their time,

effort and support for this project. To the members of my thesis committee, thank you

for sticking with me. Special thanks for the lab engineers and technicians for their help

in both mechanical and manufacturing departments.

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TABLE OF CONTENTS

Abstract .................................................................................................................... ii Abstract in Arabic .................................................................................................... iii

Approval Page .......................................................................................................... iv Declaration ............................................................................................................... v Copyright Page ......................................................................................................... vi Dedication ................................................................................................................ vii Acknowledgements .................................................................................................. viii

Table of Contents ..................................................................................................... ix

List of Tables ........................................................................................................... xii List of Figures .......................................................................................................... xiii

List of Symbols ........................................................................................................ xx

CHAPTER ONE: INTRODUCTION .................................................................. 1 1.1. Background of The Study ...................................................................... 1

1.2. Problem Statement and Significance ..................................................... 3 1.3. Hypothesis/Philosophy .......................................................................... 4

1.4. Objectives: ............................................................................................. 5 1.5. Research Scope ...................................................................................... 5

1.6. Research Methodology .......................................................................... 6 1.7. Limitations of The Study ....................................................................... 7

1.8. Research Contribution and Outcome ..................................................... 7 1.9. Thesis structure ...................................................................................... 7

CHAPTER: TWO LITERATURE REVIEW ..................................................... 9 2.1. Introduction............................................................................................ 9

2.2. Mechanism /Morphology ...................................................................... 9 2.3. A Review of Non-Flapping Bird Wing Aerodynamics ......................... 11

2.3.1. Aerodynamics of Bio Wings/Airfoils .......................................... 11 2.3.2. Porous Wings ............................................................................... 13 2.3.3. Fluid-Structure Interaction ........................................................... 16 2.3.4. Passive Control of Flow ............................................................... 16

2.3.5. Birds Wing Tip/Winglet............................................................... 19

2.3.6. Active Control .............................................................................. 22

2.3.7. Aerodynamics of Gliding Flight .................................................. 23 2.4. Structure ................................................................................................. 24 2.5. Experiments / Simulation Methods ....................................................... 25 2.1. Summary ................................................................................................ 30

CHAPTER THREE: EXPERIMENTAL APPARATUS AND

METHODOLOGY ................................................................................................ 32 3.1. Introduction............................................................................................ 32 3.2. Wind Tunnel .......................................................................................... 32

3.2.1. Force Balance in IIUM Wind Tunnel .......................................... 33

3.3. Permeable Wing and Airfoil Models ..................................................... 33

3.3.1. Airfoil Model Preparation ............................................................ 35

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3.3.2. Porosity in the Model ................................................................... 35 3.3.3. Difference Between Experimental and Analytical Model. .......... 37

3.4. Wing Model Preparation ....................................................................... 37 3.5. Permeability Calculations ...................................................................... 38 3.6. CFD Models .......................................................................................... 39

3.6.1. Airfoil Model ............................................................................... 39 3.6.2. CFD Wing Model......................................................................... 40

3.7. PIV Experiment ..................................................................................... 41 3.7.1. Measurement Process. .................................................................. 42

3.8. PIV Measurement Planes (Locations) ................................................... 43 3.8.1. Wing Geometry ............................................................................ 45

3.9. Wing Tip ................................................................................................ 48

3.9.1. Configuration 1 (Base Wing Tip) ................................................ 49 3.9.2. Configuration 2 (C2) .................................................................... 50

3.9.3. Configuration 3 (C3) .................................................................... 51 3.9.4. Configuration 4 (C4) .................................................................... 52 3.9.5. Configuration 5 (C5) .................................................................... 52 3.9.6. Configuration 6 (C6) .................................................................... 53

3.9.7. Configuration 7 (C7) .................................................................... 53 3.10. Summary .............................................................................................. 54

CHAPTER FOUR: PERMEABLE WING AND AIRFOIL

AERODYNAMICS ................................................................................................ 55

4.1. Introduction............................................................................................ 55

4.2. Symmetric Thin Airfoil ......................................................................... 57 4.2.1. Effect of Porosity on Aerodynamic Performance. ....................... 57 4.2.2. Effect of Permeability on Lift Coefficient Slope. ........................ 58

4.3. Wing ...................................................................................................... 60 4.3.1. Regional Porosity ......................................................................... 60

4.3.2. Distributed Porosity ..................................................................... 63 4.3.3. Comparison of Experimental Data with Analytical Results ........ 67

4.4. Lift Coefficient of Wing Calculated from Airfoil Data ......................... 68

4.4.1. Comparing Lift Slope of Permeable Wings and Airfoils ............. 70 4.5. Effect of Permeability on Aerodynamic Center .................................... 71 4.6. Drag ....................................................................................................... 72

4.7. Summary ................................................................................................ 76

CHAPTER FIVE: COMPUTATIONAL FLUID DYNAMICS

SIMULATION OF PERMEABLE WINGS AND AIRFOILS .......................... 77

5.1. Introduction............................................................................................ 77 5.2. Geometry in CFD .................................................................................. 77 5.3. Meshing ................................................................................................. 78

5.3.1. Mesh Sensitivity Analysis ............................................................ 80 5.3.2. Convergence................................................................................. 81

5.4. Physical Model and Boundary Conditions. ........................................... 82 5.4.1. Permeability Calculations ............................................................ 83

5.5. Permeable Wing..................................................................................... 84 5.5.1. Aerodynamic Performance of Permeable Wing .......................... 87

5.6. Permeable Airfoil................................................................................... 95

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5.7. Lift Coefficient of Permeable Wing Calculated From Lift

Coeeficient of Permeable Airfoil ............................................................ 96

5.7.1. Aerodynamic Performance of Permeable Thin Symmetric

Airfoils .......................................................................................... 98 5.8. Comparison of Experimental and CFD Results .................................... 105 5.9. Summary ................................................................................................ 107

CHAPTER SIX: EFFECT OF DIRECTIONALLY PERMEABLE TIP ON

WING TIP VORTEX ............................................................................................ 109 6.1. Introduction............................................................................................ 109 6.2. PIV Experiment ..................................................................................... 109

6.2.1. Configurations .............................................................................. 110

6.3. Results of PIV Vortex ............................................................................ 111 6.3.1. Vortex at α = 5 degrees ................................................................ 112

6.3.2. Vortex at α = 10 degrees .............................................................. 122 6.3.3. Vortex at α = 15 degrees .............................................................. 132 6.3.4. Vortex at α = 20 degrees .............................................................. 141

6.4. Tangential Velocity and Circulation ...................................................... 153

6.5. Flow Field Over Wingtip Surface.......................................................... 160 6.5.1. Flow Over Wingtip Surface at α = 0º ........................................... 163

6.5.2. Flow Over Wingtip Surface at α = 5º ........................................... 165 6.5.3. Flow Over Wingtip Surface at α = 10º ......................................... 167 6.5.4. Flow Over Wingtip Surface at α = 15º ......................................... 169

6.6. Aerodynamic Performance .................................................................... 171

6.7. Summary ................................................................................................ 173

CHAPTER SEVEN: CONCLUSION AND RECOMMENDATIONS ............. 175

7.1. Experimental Study on Permeable Wings and Airfoils ......................... 175 7.2. CFD Simulation on Permeable Wings and Airfoils. ............................. 176

7.3. Effect of Directionally Permeable Wingtip on Vortex Flow ................. 177 7.4. Recommendations for Further Studies .................................................. 177

REFERENCES ....................................................................................................... 179

PUBLICATIONS ................................................................................................... 185

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LIST OF TABLES

Table 3.1: Airfoil Properties 35

Table 5.1 Aerodynamic coefficients at different number of Mesh cells 80

Table 6.1 Comparison of Vorticity, tangential velocity, and vortex

radius to the base config (C1) 142

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LIST OF FIGURES

Figure 1.1: Topography of a pigeon wing - A dorsal view on a separated pigeon wing

(Bachmann, 2010)

2

Figure 1.2: Diagrammatic section through a bird’s wing at the level of the lower arm.

The shaded area indicates the impervious parts of the extremity, (Muller

& Patone, 1998).

3

Figure 2.1: Inner and outer vane of a feather. 10

Figure 2.2 Characteristic of a bird feather. (H. Chen, 2013) 10

Figure 2.3: Tip of Harris’ hawk in flight (Tucker, 1995) 19

Figure 2.4: “the wrist angle e between the frontal edge of the cascade and the

propatagium sinew” (Eder et al., 2015) 28

Figure 3.1: IIUM LSWT schematic view 33

Figure 3.2 Airfoil surface (Iosilevskii, 2011). 34

Figure 3.3 Honeycomb plate used in the airfoil (5mm cell). 35

Figure 3.4 Airfoil models with different regional porosities. (a)Opening = 0%c,

(b)Opening = 5%c, (c) Opening = 10%c ,

and (d)Opening = 25%c 36

Figure 3.5 Regional (a) and distributed (b-d) porosity of half span wing. 38

Figure 3.6 Representation of Honeycomb openings in CFD model airfoil. 40

Figure 3.7 Schematic of PIV setup in the wind tunnel (vortex capture) 44

Figure 3.8 PIV CCD-CAM and Half Wing Model inside IIUM wind tunnel 44

Figure 3.9 Setup sketch for PIV experiment of flow field over porous tip 45

Figure 3.10 Measuring plane over porous tip 45

Figure 3.11 Non-assembled sections of the wing (NACA 653218) 47

Figure 3.12 Section part of NACA653218 wing 47

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Figure 3.13 Assembled wing of NACA 653218 48

Figure 3.14 (a) Sketch of directional porosity, and (b) and isotropic porosity. 49

Figure 3.15 Reference wing tip geometry (C1) 49

Figure 3.16 Reference tip of NACA 653218 (dimensions are in mm) 50

Figure 3.17 Cross section of wing tip (C2) with porosity inclination = 30º (α = 15º)

50

Figure 3.18 C2 Wing tip with a directional porosity of 30º 51

Figure 3.19 Cross section of wing tip C3 (porosity inclination is 45º) 51

Figure 3.20 Cross section of C4 with porosity inclination of 90º (α = 15º) 52

Figure 3.21 Top and sectional view of honeycomb tip (C5) 52

Figure 3.22 C6 with porosity inclination of 95º 53

Figure 3.23 C7 with porosity inclination of 100º 54

Figure 4.1 Airfoil surface (Iosilevskii, 2011). 56

Figure 4.2 Regional (a) and distributed (b-d) porosity of a half span wing. 56

Figure 4.3 Cl vs α at different airfoil porosities P (Experiment). Rec = 3.45 × 105 57

Figure 4.4 Cd vs α at different airfoil porosities P. Rec = 3.45 × 105 58

Figure 4.5 Cm vs α at different airfoil porosities p. Rec = 3.45 x 105 58

Figure 4.6 Lift slope of airfoil vs. permeability (Experiment) Rec = 3.45 × 105 59

Figure 4.7 CL vs α of wing at different regional porosities P (Experiment)

Rec = 3.45 × 105 61

Figure 4.8 CD vs α of wing at different regional porosities P (Experiment).

Rec = 3.45 × 105 61

Figure 4.9 CM vs α of wing at different regional porosities P (Experiment).

Rec = 3.45 × 105 62

Figure 4.10 CL vs CD of wing at different regional porosities P (Experiment)

Rec = 3.45 × 105 62

Figure 4.11 CLα vs. permeability of wing (regional porosity) (Experiment).

Rec = 3.45 × 105 63

Figure 4.12 Different distributed porosities of a wing. 63

xv

Figure 4.13 CL vs α of the wing at different distributed porosities (Experiment).

Rec = 3.45 × 105 64

Figure 4.14 CD vs α of the wing at different distributed porosity (Experiment). Rec =

3.45 × 105 65

Figure 4.15 CM vs α of the wing at different distributed porosities P (Experiment).

Rec = 3.45 ×105 65

Figure 4.16 CL vs CD of the wing at different distributed porosities P (Experiment).

Rec = 3.45 × 105 (Experiment) 66

Figure 4.17 CLα vs. permeability of wing (distributed porosity) (Experiment).

Rec = 3.45 × 105 66

Figure 4.18 CLα vs. permeability of wing (Exp.) and analytical solution (Iosilevskii,

2011) 68

Figure 4.19 CLα vs porosity of wing (calculated and actual) and Clα of the airfoil. 69

Figure 4.20 CLα vs. permeability of wing (exp. and calculated). Rec = 3.45 × 105 69

Figure 4.21 Lift slope vs. permeability of both wing and airfoil with the same type of

permeability. Rec = 3.45 × 105 70

Figure 4.22 xac vs. permeability of airfoil (experimental results) Rec = 3.45 × 105 72

Figure 4.23 Analytical Solution of Aerodynamic center variation with permeability

(Iosilevskii, 2011). Right hand side indicates the ‘a’ value. 72

Figure 4.24 Cd vs permeability at α = 20 for different values of ‘a’ Rec = 3.45 × 105

74

Figure 4.25 Cd vs permeability at α = 80 for different vales of ‘a’ Rec = 3.45 × 105

74

Figure 4.26 Cd vs permeability at ‘a’= -1 for different vales α (Experiment) Rec =

3.45 × 105 75

Figure 4.27 Cd vs permeability at ‘a’= 0.5 for different vales α (Experiment) Rec =

3.45 × 105 75

Figure 5.1 airfoil sketches permeable front part and impermeable aft part 78

Figure 5.2 Trimmed mesh section of NACA0008 79

Figure 5.3 3D mesh of NACA0008 wing 80

Figure 5.4 Number of cells vs CL 81

Figure 5.5 Residuals of CFD simulation (convergence) 82

xvi

Figure 5.6 Boundary conditions of NACA 0008 83

Figure 5.7: Streamlines and velocity through the permeable wing, 86

Figure 5.8 CLα vs permeability for NACA0008 wing (CFD) 86

Figure 5.9 Aerodynamic Center Xac vs permeability of NACA0008 wing (CFD) 87

Figure 5.10 Aerodynamic performance of permeable wing at ‘a’ = -0.8 89

Figure 5.11 Aerodynamic performance of permeable wing at ‘a’ = -0.4 90

Figure 5.12 Aerodynamic performance of permeable wing at ‘a’ = 0 91

Figure 5.13 Aerodynamic performance of permeable wing at ‘a’ = 0.6 92

Figure 5.14 Flow behavior over wing section with different permeabilities at

‘a’ = -0.8, α = 8º 93

Figure 5.15 Flow behavior over wing section with different permeabilities

at ‘a’ = -0.8, α = 8º 94

Figure 5.16 Clα vs permeability for NACA0008 airfoil (CFD) 95

Figure 5.17 Clα vs permeability for thin airfoil ((Iosilevskii, 2011)) 95

Figure 5.18 Aerodynamic center of permeable airfoil vs permeability 96

Figure 5.19 CLα of wing calculated from airfoil CFD data 97

Figure 5.20 CLα calculated and obtained from CFD 97

Figure 5.21 Aerodynamic performance of permeable airfoil at ‘a’ = -0.8 100

Figure 5.22 Aerodynamic performance of permeable airfoil at ‘a’ = -0.4 101

Figure 5.23 Aerodynamic performance of permeable airfoil at ‘a’ = 0 102

Figure 5.24 Aerodynamic performance of permeable airfoil at ‘a’ = 0.6 103

Figure 5.25 Flow velocity over the permeable airfoil at porosity P= 0.2 (ε= 0.093)

104

Figure 5.26 Flow velocity over the permeable airfoil at porosity P= 0.2 (ε= 0.093)

105

Figure 5.27 Representation of Honeycomb openings in CFD model airfoil. 106

Figure 5.28 Clα vs Permeability of CFD and Experimental results. 107

Figure 6.1 Schematic of PIV setup in the wind tunnel. 110

xvii

Figure 6.2: Wingtip configurations, Base tip, slotted/porous and honeycomb

structure. 111

Figure 6.3 Tip porosity inclination: (a) C 2, (b) C3, (c) C4, (d) C6, and C7 111

Figure 6.4: PIV measuring locations for wingtip wake vortex 112

Figure 6.5 Tangential velocity and velocity contours at α = 5º 113

Figure 6.6 Tangential velocity and velocity contours at all measuring planes for all

configurations at α = 5º 114

Figure 6.7 Tangential Velocity, vector map and vorticity contours for C1 at α = 5º

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Figure 6.41 Tangential velocity distribution for all configurations at α = 5º 155




Figure 6.45 Circulation for all configurations at α = 5º 157




Figure 6.49 Setup sketch for PIV experiment of flow field over the porous tip and

measuring plane. 160

Figure 6.50 Streamlines, velocity vectors and velocity contours of flow over wingtip

surface at α = 0º for all configurations 163













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Figure 6.58: Aerodynamic performance for all configurations (C1-C7) (a), (b), (c),

and (d), are the lift, drag and moment coefficients, respectively, and (e) is

the drag polar. 172

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LIST OF SYMBOLS

a Porosity segment location [-1, 1]

a Wing lift slope

a0 Airfoil lift slope

AR Wing aspect ratio

α Angle of attack

c Chord

Cl Airfoil lift coefficient

CL Wing lift coefficient

Cd Airfoil drag coefficient

CD Wing drag coefficient

Cm Airfoil moment coefficient

CM Wing moment coefficient

C1, C2, … Configuration 1, 2, …

P Porosity

PIV Particle Image Velocimetry

Re Reynolds number based on chord length

t Thickness

xac Aerodynamic center

μ Viscosity (Pa.s)

ν Velocity (m/s)

x/c Measuring location

1

CHAPTER One

INTRODUCTION

1.1. BACKGROUND OF THE STUDY

Recently, the need for micro air vehicles (MAVs) has resulted in an increase in attention

to bird flight, and study their performance as they fly at low Reynolds numbers,

(Carruthers, Walker, Thomas, & Taylor, 2010). It is very important to seek the viable

aspects in studying natural flyers that can be implemented in practical applications such

as wing aerodynamics, structure, and control as noted by (Jacob, 1998).

Aerodynamics of bird airfoils and wings is classified into three categories. First,

is the analysis of airfoils /wings of birds as a fixed rigid body; second, bird

airfoils/wings in flapping phase and third, considering flexible airfoil/wings in non-

flapping flight. Bird’s wing structure is another focus in some studies where the feathers

bend and twist under aerodynamic forces. Therefore, establishing their mechanical

properties leads to an understanding of their influence on aerodynamic performance as

studied by (Bachmann, 2010; Bonser & Purslow, 1995; Jacob, 1998; Macleod, 1980;

Purslow & Vincent, 1978). Also, movement and vibration of feathers play a role in

flight control as mentioned by (Brown & Fedde, 1993; Jacob, 1998) that influence

aerodynamic performance. Adaptive wings benefit in improvement of efficiency,

manoeuvrability, control, weight, and cost, (Jacob, 1998).

Natural flyers are difficult to study experimentally due to the complexity in their

structural surface, control, and agility in manoeuvring (Shyy et al., 2008). The wing

structure, surface flexibility, flexibility of feathers, vane and surface hair are one huge

challenge to mimic. Another challenge is that the fluid motion is unsteady and has many

2

different phases as the birds’ flap bend and wings move based on the flight conditions.

“A challenge is that the scaling of both fluid dynamics and structural dynamics between

smaller natural flyer and practical flying hardware/lab experiment (larger dimension) is

fundamentally difficult” (Shyy et al., 2008). An experimental study of the

aerodynamics of wings with porous surfaces has not yet been performed. Figure 1.1

shows a dorsal view of a bird wing planform with its nomenclature that highlights the

complex geometry of the multi-layer planforms with different functionality for each

layer and its sub-layer components. Figure 1.2 describes the sub layer component

structure that exposes the nature of the non-prismatic, flexible slender beam structure

with flexible connections.

Figure 1.1: Topography of a pigeon wing - A dorsal view on a separated pigeon wing

(Bachmann, 2010)

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Figure 1.2: Diagrammatic section through a bird’s wing at the level of the lower arm.

The shaded area indicates the impervious parts of the extremity, (Muller & Patone,

1998).

The wings of natural flyers specifically birds have porous wings. The porosity

/permeability differs from one wing to another and with flying conditions. Birds have

the ability to increase or decrease the flow permeability throughout the wing by

extending or retracting the primary feathers. It is the intention of this thesis to study the

effect of permeability on rigid airfoils and wings in an effort to understand the wings of

natural flyers.

Porosity and permeability can be considered the same in general, however,

permeability is a function of porosity. The term ‘Porosity’ reflects the ratio of void

volume to the total volume or the void area to the total area. While the term

‘permeability’ is the ability of the flow to penetrate through the porous region, thus, it

depends on the Reynolds number and type of porosity. In this thesis, both terms will be

used, where porosity represents the physical geometry (open area to total area ratio of

airfoil/wing) and permeability, which represents porosity as a function of flow

properties.

1.2. PROBLEM STATEMENT AND SIGNIFICANCE

Considering the bird’s wing in cruise non-flapping flight, the surface of the wing is

directionally partially porous through surface and feathers. Bird’s wing surface is

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AERODYNAMICS OF PERMEABLE WINGS BY MOHAMMED …