Computational study of flow over elliptic airfoils for rotor/wing

119 Pages·2017·3 MB·English

by  Timothy William Assel

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Masters Theses Student Theses and Dissertations
Fall 2007
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Timothy William Assel
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Assel, Timothy William, "Computational study of flow over elliptic airfoils for rotor/wing unmanned aerial
vehicle applications" (2007). Masters Theses. 4598.
https://scholarsmine.mst.edu/masters_theses/4598
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COMPUTATIONAL STUDY OF FLOW OVER ELLIPTIC AIRFOILS

FOR ROTOR/WING UNMANNED AERIAL VEHICLE APPLICATIONS

BY

TIMOTHY WILLIAM ASSEL

A THESIS

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE

UNIVERSITY OF MISSOURI-ROLLA

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE

MASTER OF SCIENCE IN AEROSPACE ENGINEERING

2007

APPROVED BY

_______________________________ _______________________________
DR. FATHI FINAISH, ADVISOR DR. D.W. RIGGINS

_______________________________
DR. K.M. ISAAC
(cid:211) 2007
Timothy William Assel
All Rights Reserved
iii
ABSTRACT
Elliptic airfoil geometries have been used extensively in the development of
Rotor/Wing aircraft. Most recently elliptic airfoils have been employed in the
development of Rotor/Wing Unmanned Aerial Vehicles (UAVs). UAVs play an
expanding role in military and civil applications. Much research has been conducted
recently in the area of Vertical Take-off and Landing (VTOL) UAVs, and a significant
amount of research has gone into the development of a Rotor/Wing UAV for VTOL
applications. However, a lack of research has been published regarding the aerodynamic
performance and flow characteristics of elliptic airfoils in parameter ranges which would
be applicable in the design and development of Rotor/Wing UAVs. This data is of
significant importance to Rotor/Wing UAV design and development due to the
complexity of flow developments about elliptic airfoils including: flow separation over
the leading edge, flow reattachment over suction surface of the airfoil, and vortex
shedding downstream of the airfoil. The purpose of this study will be to conduct a
parametric investigation on the performance of elliptic airfoils for Rotor/Wing Unmanned
Aerial Vehicles. The objective of this study is to conduct a two-dimensional,
aerodynamic analysis on a various elliptic airfoil parameters, compare the results of the
analysis with theoretical predictions and experimental results, and evaluate handling and
performance characteristics of Rotor/Wing UAVs during hover, transition, and forward
flight. It is hoped that the results of this study would provide a better understanding of the
aerodynamic performance and flow characteristics of elliptic airfoils, and that the results
of this study would be employed in the research and development of future Rotor/Wing
technology and VTOL UAV designs.
iv
ACKNOWLEDGMENTS
I would first like to thank my advisor, Dr. Fathi Finaish, who has devoted time
and patience to guide me throughout my research, has spent years working with me to
develop a basis of knowledge and skills for investigation into ideas and presentation of
results, and has provided the wisdom, the insight and the opportunity for intellectual
independence and creativity which has made this thesis a possibility.
I am also very grateful to the members of my committee: Dr. Issac and Dr.
Riggins, who have been mentors during my college career and have provided the
encouragement and inspiration that has brought me through the completion of this study.
I would also like to thank the Department of Mechanical and Aerospace
Engineering at the University of Missouri-Rolla for providing the education, facilities and
funding necessary for me to complete my academic studies.
I would like to express a deep appreciation for my fellow researchers and friends
in the UMR Flight Simulation Laboratory who assisted and educated me in the most
random, diverse, and unexpected ways; including: Keith Norton, Peter Cross, Josiah
Elliot, Tyler Winter and Ben Bettis.
Lastly, I would like to express my greatest thankfulness for my family, who have
always been there for me with support, encouragement and wisdom; especially my
Father, who from my very beginning has taught me the value of hard work and
determination, the importance of learning and common sense and, most importantly, to
have faith in God and to trust always in His wisdom and grace.
v
TABLE OF CONTENTS
Page
ABSTRACT.......................................................................................................................iii
ACKNOWLEDGMENTS.................................................................................................iv
LIST OF ILLUSTRATIONS............................................................................................vii
LIST OF TABLES.............................................................................................................xi
NOMENCLATURE.........................................................................................................xii
1. INTRODUCTION......................................................................................................1
1.1. RECENT ADVANCEMENTS IN UAV TECHNOLOGY................................1
1.1.1. Expanding Interest in UAVs....................................................................1
1.1.2. Brief Survey of VTOL UAVs Currently in Development.......................1
1.2. LITERATURE SURVEY...................................................................................6
1.2.1. Brief History of Rotor/Wing Research.....................................................7
1.2.2. Recent Developments in Canard Rotor/Wing Technology......................8
1.2.3. Studies in Flow over Elliptic Airfoils and Cylinders.............................10
1.3. SCOPE OF THIS STUDY................................................................................13
1.3.1. The Flow Problem and Selected Parameter Range................................14
1.3.2. Validation of Methodology..................................................................155
2. COMPUTATIONAL APPROACH.........................................................................17
2.1. FLOWFIELD SIMULATION ABOUT AN AIRFOIL....................................17
2.1.1. Flowfield Grid Generation Technique....Error! Bookmark not defined.
2.1.1.1 Surface Geometry Definition Technique....................................17
2.1.1.2 Surface Grid Generation Technique...........................................18
2.1.1.3 Volume Grid Generation Technique...........................................21
2.1.2. Flowfield Solution Methodology............Error! Bookmark not defined.
2.1.2.1 Description of Flow Solver.........................................................26
2.1.2.2 Flow Input Parameters................................................................26
2.1.2.3 Boundary Conditions..................................................................26
2.1.2.4 Turbulence Models.....................................................................27
2.1.2.5 Post-Processing...........................................................................27
vi
2.1.2.5.1 Numerical Analysis.....................................................27
2.1.2.5.2 Visual Analysis...........................................................28
3. VALIDATION OF METHODOLOGY...................................................................29
3.1. VALIDATION TEST CASE PROCEDURES.................................................29
3.1.1. Validation Test Case Grid Generation...................................................29
3.1.2. Flow Solver Input Parameters................................................................30
3.2. RESULTS OF CFD ANALYSIS FOR A 16% ELLIPTIC AIRFOIL.............31
3.2.1. Note on Laminar Separation Bubble......................................................43
3.3. EXPERIMENTAL DATA FOR A 16% THICK ELLIPTIC AIRFOIL..........43
3.4. COMPARISON OF CFD RESULTS WITH EXPERIMENTAL DATA........47
3.4.1. Note on Pitching Moment Coefficient...................................................53
3.5. CONCLUDING REMARKS............................................................................54
4. RESULTS AND DISCUSSION..............................................................................55
4.1. PARAMETRIC STUDY OF ELLIPTIC AIRFOIL PERFORMANCE...........55
4.1.1. Influence Reynolds Number on Airfoil Lift Characteristics..................55
4.1.2. Influence of Reynolds Number on Airfoil Drag Characteristics............61
4.1.3. Influence of Reynolds Number on Lift to Drag Performance................63
4.1.4. Influence of Reynolds Number on Pitching Moment............................64
4.1.5. Influence of Reynolds Number on Flow Developments........................65
4.1.6. Influence of Thickness Ratio on Airfoil Lift Characteristics.................73
4.1.7. Influence of Thickness Ratio on Airfoil Drag Characteristics...............77
4.1.8. Influence of Thickness Ratio on Lift to Drag Performance...................79
4.1.9. Influence of Thickness Ratio on Pitching Moment................................81
4.1.10. Influence of Thickness Ratio on Flow Developments.........................82
4.2. CONCLUSIONS...............................................................................................93
5. CONCLUSIONS AND OUTLOOK........................................................................98
5.1. CONCLUSIONS...............................................................................................98
5.2. FUTURE WORK..............................................................................................99
BIBLIOGRAPHY...........................................................................................................102
VITA……………………………………………………………………………………105
vii
LIST OF ILLUSTRATIONS
Figure Page
1.1 Photo of the A160 Hummingbird on an airport taxiway near Victorville, CA...........2
1.2 Photo of MQ-8B Fire Scout in Hover........................................................................3
1.3 Goldeneye in Transition from Hover to Forward Flight.............................................4
1.4 Depiction of iSTAR UAV showing transition from hover to forward flight.............4
1.5 Photo of Bell Eagle Eye in Hover...............................................................................5
1.6 Boeing X-50A in hover mode.....................................................................................6
1.7 Photo of Sikorsky S-72 modified as X-Wing testbed.................................................7
1.8 Top, front and side view schematic of Boeing X-50A Dragonfly..............................8
1.9 Schematic of CRW conversion process from hover to fixed-wing flight.................10
1.10 Plot of wake vortex structures taken from Reference 21..........................................12
1.11 Schematic of flow configuration (not to scale).........................................................14
2.1 Surface Geometry of Elliptical Airfoil created in AGPS..........................................18
2.2 Extract-Grid Point Distribution Methods available in AGPS...................................19
2.4 Surface Grid generated in AGPS using Linear Point Distrubution..........................20
2.5 Surface Grid generated in AGPS using Cosine Point Distribution...........................21
2.6 Comparison of an Unstructured Grid (a) and a Structured Grid (b).........................21
2.7 Tecplot rendering of a non-orthoganal, structured, volume grid showing the
viscous region (top left), focus region (top right) and outer region (bottom)...........24
2.8 Computer Screenshots of a C-grid volume grid generated about a NACA 0009
surface grid using Hypgen showing far field, close-up, and boundary layer
views........................................................................................................................25
3.1 Surface grid generated in AGPS with 250 points in curvature point distribution....30
3.2 Plot of flow development over an elliptic airfoil showing pressure distribution
and streamlines.........................................................................................................31
3.3 Plot of flow development over an elliptic airfoil showing pressure distribution
and streamlines.........................................................................................................32
3.4 Plot of flow development over an elliptic airfoil showing pressure distribution
and streamlines...........................................................................................................32
3.5 Plot of flow development over an elliptic airfoil showing pressure distribution
and streamlines.........................................................................................................33
viii
3.6 Plot of flow development over an elliptic airfoil showing pressure distribution
and streamlines.........................................................................................................33
3.7 Plot of vortex development downstream of an elliptic airfoil showing pressure
distribution and streamlines......................................................................................34
3.8 Plot of vortex development downstream of an elliptic airfoil showing pressure
distribution and streamlines......................................................................................35
3.9 Plot of vortex development downstream of an elliptic airfoil showing pressure
distribution and streamlines......................................................................................35
3.10 Plot of vortex development downstream of an elliptic airfoil showing pressure
distribution and streamlines......................................................................................36
3.11 Plot of vortex development downstream of an elliptic airfoil showing pressure
distribution and streamlines......................................................................................36
3.12 Plot of normalized velocity vectors in the separated flow region of an
elliptic airfoil............................................................................................................37
3.13 Plot of normalized velocity vectors in the separated flow region of an
elliptic airfoil............................................................................................................37
3.14 Plot of normalized velocity vectors in the separated flow region of an
elliptic airfoil............................................................................................................38
3.15 Plot of normalized velocity vectors in the separated flow region of an
elliptic airfoil.............................................................................................................38
3.16 Plot of normalized velocity vectors in the separated flow region of an
elliptic airfoil............................................................................................................39
3.17 Plot of surface pressure distribution around an elliptic airfoil..................................40
3.18 Plot of surface pressure distribution around an elliptic airfoil..................................40
3.19 Plot of surface pressure distribution around an elliptic airfoil..................................41
3.20 Plot of surface pressure distribution around an elliptic airfoil..................................41
3.21 Plot of surface pressure distribution around an elliptic airfoil..................................42
3.22 Close-up of boundary layer velocity profiles within a laminar separation
bubble developed near the airfoil trailing edge........................................................43
3.23 Wake vortex structure with streamlines [Obtained from Reference 21]..................44
3.24 Wake vortex structure with streamlines [Obtained from Reference 21]..................44
3.25 Wake vortex structure with streamlines [Obtained from Reference 21]..................44
3.26 Wake vortex structure with streamlines [Obtained from Reference 21]..................45
3.27 Wake vortex structure with streamlines [Obtained from Reference 21]..................45
3.28 Surface pressure distributions at various angles of attack [Obtained from