The Vortex and The Jet : A Journey Into the Beauty and Mystery of Flight

"This open access book is an introduction for the lay reader to understand the basics of flight. The exposure is to the mysteries of lift generation by wings and the basic function of the jet propulsion engine. The text relies on simple descriptions of the physics of air flow without unduly involving mathematics. The text is richly illustrated with sketches and photographs to enrich verbal descriptions. The book takes the viewpoint that a reader does not have a background in the engineering of airplane components but is interested in the subject. The description is in terms of easy-to-understand terminology, occasional use of humor, references to everyday experiences, and occasionally to an algebraic relationship when that is unavoidable. This book would serve a student aspiring to be an engineer to begin grappling with the phenomena involved and the techniques used to analyze these phenomena. The practitioner, as well as the beginner, in the art of flying an airplane is well served with the knowledge exposed here. The text makes no apology for technical complexity. Its introduction is rigorous and provides a sound footing for further study."-- Back cover Acknowledgements 6 A Note on Images 7 Contents 8 Abbreviations 11 1 The Vortex—A Journey into Beauty and Mystery 12 2 The Vortex and Wing Lift 16 2.1 The Bound Vortex 20 2.2 Circulation 21 2.3 Friction to the Rescue 21 3 Frictionless Air Cannot Provide Lift: A Paradox 27 3.1 The Trailing Edge 28 3.2 The Leading Edge 30 3.3 A Better Model 31 4 Drag, a Nightmare and a Challenge 33 4.1 The Air Near a Surface 33 4.1.1 The Boundary Layer Comes in Various Thicknesses 34 4.2 How Important is Fluid Friction? 37 4.3 Mr. Reynolds and His Number 37 4.4 Scale Model Testing 38 4.5 Turbulent Flow 39 4.6 Vortex Generators 43 5 Pressure: The Bernoulli Principle and Flow Energy Conservation 47 5.1 Air is Compressible (Sometimes) 48 5.1.1 An Aside: How Good is Air? 48 5.2 Entropy (Arrrgh!@*#*!) 49 5.3 Energy Conservation on a Streamline 51 5.4 Enthalpy is a Property. Really? Really! 52 5.4.1 A Few Details About Specific Heats 54 5.5 Total Temperature 54 5.6 Bernoulli at Last 56 5.7 Total Pressure 57 6 Pressure, Pressure, It’s All About Pressure! 59 6.1 Forces and Moments 59 6.2 Data for a Simple Airfoil 61 6.3 Calculation Iterations Toward Realism 64 6.4 Vorticity Provides More Than Lift, It Adds to Drag! 65 6.5 Flight in Ground Effect 69 6.6 Dynamic Pressure and Those Convenient and Pesky Coefficients 69 6.7 The Pitot Probe and Dynamic Pressure 70 7 Putting It All Together 75 7.1 Wing Lift Performance with Viscous Air 76 7.2 Stall 78 7.3 Why Does a Wing Stall? 78 7.4 Adverse Pressure 79 7.5 Transonic Flight 80 7.6 Shock Waves 83 7.7 Condensation at High Speed 85 7.8 Supersonic Wings 86 7.9 All the Airplane Aerodynamics in One Place 88 7.10 The Computer to the Rescue 89 7.11 Aerodynamic Heating is Not Due to Friction 91 8 The Jet: Fluid in Motion and More Vorticity 95 8.1 Prop Tip Vortices 96 8.2 Jet Boundaries Are Cylindrical Sheets of Vorticity 98 8.3 An Aircraft Can Never Have 100% Propulsive Efficiency 99 8.3.1 A Quantitative Aside 99 8.4 Counter-Rotating Props 100 9 Propulsion for Flight: Power or Thrust? 104 9.1 The Engines: Stark Differences 105 9.2 Limits of the Old 106 9.2.1 The First Jet? 109 9.3 The Gas Turbine or ‘Jet’ Engine 109 9.4 Is the Gas Turbine Engine Like Another Familiar Engine? 110 9.4.1 Yes, the Steam Engine! 111 9.5 Energy Conservation Again, for Steady Flow Through Engines 113 9.5.1 A Little Mathematics, Briefly 113 9.5.2 What Happens in a Real Jet Engine? 114 9.6 Design Issues 115 10 The Compressor: Gas Turbine Engine Keystone 117 10.1 Axial Flow Compressor: The Bedrock of Modern Engines 119 10.2 Compressor Pressure Ratio 121 10.3 Compressor Aerodynamics 122 10.4 How Well?—Efficiency 125 10.5 The Control Problem 126 11 Bypass and Other Engines 128 11.1 The Fan on a Turbofan Engine Has No IGV 128 11.2 Bypass Ratio 130 11.3 Turboprops and Turboshaft Engines 130 12 Other Components of the Jet Engine 132 12.1 The Turbine 132 12.2 The Combustor 133 12.3 Putting It Together into an Engine 138 12.4 How Do You Start This Thing? 140 12.5 Bleed Valves and Variable Stator Geometry 140 13 More Components: Inlets, Mixers, and Nozzles 143 13.1 Inlets 143 13.1.1 An Old Wives’ Tale About Inlets 143 13.2 Inlet Geometry and Diverters 146 13.3 Mixing 149 13.4 The Nozzle 149 13.5 Choking 153 13.6 More Extreme Nozzles: The Rocket Engine 154 13.6.1 Overexpansion 155 13.6.2 Under-Expansion 155 13.6.3 Staging 158 13.6.4 Specific Impulse and a Little Chemistry 158 13.7 Airplane Range 159 Epilogue 161 Appendix A Equations for Quantitative Descriptions 162 A.1 Motion with Circular Streamlines 162 A.2 Air as a Medium 162 A.3 The Descriptive Constants 163 A.4 The Gas Properties 163 A.5 The Flight Equations 163 A.6 The Equations of Aerothermodynamics 164 A.6.1 The Energy Equation Along a (Steady) Streamline 164 A.6.2 Compressibility 165 A.6.3 Isentropic Relation Between Two States 1 and 2 165 A.6.4 Heating Total Pressure Loss 165 Appendix B Some Quantitative Aspects of Aerodynamics and Thermodynamics 166 B.1 Entropy is a Fact 166 B.2 Compressibility 168 B.3 Boundary Layers 169 Appendix C Induced Drag 170 Appendix D Aerodynamic Performance Summary 171 -4pt- Glossary of Technical Terms 173 References 175 Index 176