A Novel Optimised Design Using Slots for Flow Control and High- Lift Performance of UCAVs Usman Ali Aeronautical Engineering School of Computing Science and Engineering University of Salford, Salford, UK Submitted in Partial Fulfilment of the Requirements of the Degree of Doctor of Philosophy, April 2017 ii Tables of Contents TABLES OF CONTENTS ............................................................................................................ II LIST OF FIGURES .................................................................................................................... VI LIST OF TABLES .................................................................................................................... XIV ACKNOWLEDGEMENTS ........................................................................................................ XVI ABSTRACT ........................................................................................................................... XVII CHAPTER 1. INTRODUCTION .............................................................................................. 1 CHAPTER 2. LITERATURE REVIEW ....................................................................................... 9 2.1. A Brief Review of Flying Wings ...................................................................................................... 9 2.2. Aerodynamics of Flying Wing ...................................................................................................... 12 2.2.1 Vortex Lift ..................................................................................................................................... 16 2.2.2 Vortex Breakdown ........................................................................................................................ 20 2.2.3 Swept wings.................................................................................................................................. 22 2.2.4 Flying Wings at Low Speed ........................................................................................................... 26 2.3. Introduction to Flow Control ....................................................................................................... 27 iii 2.3.1 Radar Cross Section ...................................................................................................................... 30 2.3.2 High Lift Devices ........................................................................................................................... 32 2.4. Role of UAVs ............................................................................................................................... 33 2.5. Computational Aerodynamics ..................................................................................................... 36 2.6. Computational Fluid Dynamics .................................................................................................... 39 2.6.1 Reynolds Averaged Navier Stokes Equations ............................................................................... 48 2.6.2 Turbulence Modelling .................................................................................................................. 52 2.6.3 Near-Wall Turbulence .................................................................................................................. 57 2.7. Vortex Lattice Method ................................................................................................................ 61 2.8. Introduction to Optimisation ...................................................................................................... 67 2.8.1 Optimisation Algorithms .............................................................................................................. 68 2.8.2 Direct Search Methods ................................................................................................................. 70 2.9. Previous Studies .......................................................................................................................... 72 2.9.1 Experimental Findings .................................................................................................................. 73 2.9.2 Computational Findings ............................................................................................................... 78 CHAPTER 3. RESEARCH METHODOLOGY .......................................................................... 83 3.1. Experiment Methodology ........................................................................................................... 84 3.1.1 Experiment Parameters ................................................................................................................ 84 3.1.2 Wind Tunnel Calibration ............................................................................................................... 86 3.1.3 Experiment Procedure.................................................................................................................. 90 3.2. Computational Methodology ...................................................................................................... 91 3.2.1 Geometry and Grid Details ........................................................................................................... 93 3.2.2 Boundary Conditions .................................................................................................................... 99 3.2.3 Solver Settings ............................................................................................................................ 103 iv 3.3. Vortex Lattice Method Approach .............................................................................................. 107 CHAPTER 4. FLOW VISUALISATION OF CLEAN WINGS .................................................... 111 4.1. Problem Description ................................................................................................................. 111 4.2. Results and Discussion .............................................................................................................. 114 CHAPTER 5. PREDICTIONS OF STABILITY AND CONTROL ................................................ 128 5.1. Problem Description ................................................................................................................. 128 5.2. Computational Details .............................................................................................................. 129 5.2.1 Geometry and Grid ..................................................................................................................... 129 5.2.2 Solver Settings ............................................................................................................................ 132 5.3. Stability and Control Results ..................................................................................................... 133 CHAPTER 6. FLOW CONTROL ......................................................................................... 140 6.1. Flow Control Description ........................................................................................................... 140 6.2. Flow Control Results ................................................................................................................. 146 CHAPTER 7. NUMERICAL OPTIMISATION ....................................................................... 157 7.1. CFD Approach to Optimisation .................................................................................................. 157 7.2. Computational Details of Optimised Wings ............................................................................... 167 7.2.1 Geometry and Mesh Details ....................................................................................................... 168 7.2.2 Solver Settings ............................................................................................................................ 172 7.3. Optimisation Results and Discussion ......................................................................................... 173 v CHAPTER 8. CONCLUSION .............................................................................................. 184 REFERENCES ....................................................................................................................... 188 APPENDIX ........................................................................................................................... 198 vi List of Figures Figure 1.1: Highly swept flying wing UCAV configurations (Google, 2014) .......................... 3 Figure 2.1: First turbojet-powered flying wing aircraft (Okonkwo & Smith, 2016) ............ 11 Figure 2.2: B2-Spirit Stealth Bomber (Okonkwo & Smith, 2016) ........................................ 11 Figure 2.3: Four variants of delta wing planform (J.D. Anderson, 2010) ............................ 13 Figure 2.4: Schematic of formation of leading edge vortices over the top of a delta wing at an angle of attack (Houghton & Carpenter, 2003) .............................................................. 14 Figure 2.5: Three regions within leading edge vortex (Earnshaw, 1961) ............................ 14 Figure 2.6: Schematic of the spanwise pressure coefficient distribution across a delta wing (J.D. Anderson, 2010) .......................................................................................................... 17 Figure 2.7: Lift coefficient