Chapter 1: Introduction to Automobile Aerodynamics...1

Preface...xv Acknowledgments...xix Chapter 1: Introduction to Automobile Aerodynamics...1 1.1 Scope... 1 1.1.1 The Role of Aerodynamics in Vehicle Design... 1 1.1.2 The Character of Vehicle Aerodynamics... 2 1.1.3 Related Fields... 5 1.2 Historical Development of Vehicle Aerodynamics... 7 1.2.1 Literature... 7 1.2.2 Ahead of Its Time... 9 1.2.3 Dominant Reference Number c D... 10 1.2.4 Creating Shapes for Cars...11 1.2.5 Borrowed Shapes... 12 1.2.6 The Streamline Era... 14 1.2.7 Early Investigations with Parameters... 25 1.3 From Horseless Carriage to Automobile... 26 1.3.1 Stamping... 26 1.3.2 Bathtub Body... 27 1.3.3 One-Volume Bodies..................................... 30 1.4 Rear-End Shapes... 34 1.4.1 Kamm-Back... 34 1.4.2 Fastback... 37 1.4.3 Notchback... 38 1.4.4 Hatchback... 39 1.5 Directional Stability... 39 1.6 Commercial Vehicles... 42 1.7 Motorcycles and Helmets... 46 1.8 Internal Flows... 47 1.8.1 Engine Compartment... 47 1.8.2 Passenger Compartment... 48 1.9 Development Strategies... 49 1.9.1 Detail Optimization... 49 1.9.2 Shape Optimization... 53 1.9.3 Limit Strategy... 57 1.10 Design and Aerodynamics... 60 1.11 Development Tools... 63 1.11.1 Wind Tunnels... 63 1.11.2 Rating... 65 v 6584_Book.indb 5

1.11.3 Classical Approach... 68 1.11.4 CFD Integrated Methods... 70 Chapter 2: The Physical Principles of Aerodynamics...75 2.1 Basic Equations in Fluid Dynamics... 75 2.1.1 Conservation Laws... 75 2.1.2 Kinematics and Dynamics of Flow Fields... 76 2.1.3 The Continuity Equation... 81 2.1.4 The Euler Equation... 82 2.1.5 The Bernoulli Equation... 83 2.1.6 Potential Theory... 84 2.1.7 The Navier- Stokes Equation... 85 2.1.8 Integral Forms of the Conservation Laws... 88 2.2 Dynamics of Inviscid Flow... 93 2.2.1 Interpreting Streamline Patterns... 93 2.2.2 Planar Model Flows... 95 2.2.3 Vortex Flows... 105 2.3 The Dynamics of the Frictional Flow...111 2.3.1 The Reynolds Number...111 2.3.2 The Prandtl Boundary Layer Concept...112 2.3.3 Boundary Layer Separation...115 2.3.4 Boundary Layer Turbulence...118 2.3.5 Drag of Simple Bodies... 123 2.3.6 Multi-Body Systems... 131 2.3.7 Pipe Systems with Internal Flow... 134 2.4 Appendix... 146 2.4.1 Density and Viscosity of Air... 146 2.4.2 Compressibility Effects... 148 Chapter 3: Consumption and Performance... 151 3.1 The Significance of Aerodynamic Drag... 151 3.2 Theory of Driving Resistance... 154 3.2.1 Rolling Resistance... 154 3.2.2 Aerodynamic Drag... 156 3.2.3 Grade Resistance... 158 3.2.4 Acceleration... 158 3.2.5 Overall Driving Resistance... 159 3.2.6 Example... 159 3.3 Performance... 160 3.3.1 Acceleration and Elasticity.............................. 160 3.3.2 Ascending Ability... 162 3.3.3 Top Speed... 163 3.4 Consumption... 165 3.4.1 Calculating Fuel Consumption... 166 vi 6584_Book.indb 6

3.4.2 Consumption Measurement and CO 2 and Energy Equivalents.. 168 3.5 Driving Cycles... 170 3.5.1 History... 171 3.5.2 New European Driving Cycle (NEDC)... 171 3.5.3 NEDC Cycle for Hybrid Drives... 173 3.5.4 United States Cycles... 173 3.5.5 Asian Cycles... 175 3.5.6 WLTP Worldwide Harmonized Light Vehicles Test Procedure... 176 3.5.7 Realistic Driving Cycles... 177 3.6 Possibilities for Reducing Fuel Consumption... 177 3.6.1 Energy Flow Diagram... 177 3.6.2 Engine Efficiency and Engine Maps... 179 3.6.3 Ancillary Components... 181 3.6.4 Transmission... 183 3.6.5 Vehicle Mass... 185 3.6.6 Rolling Resistance... 186 3.6.7 Aerodynamic Drag... 186 3.7 Reducing Aerodynamic Drag... 187 3.7.1 Possibilities for Reducing Resistance... 188 3.7.2 Weight Equivalency... 189 3.7.3 Amortization Analysis... 189 3.8 CO 2 Legislation and Labels... 191 3.8.1 EU Legislation... 191 3.8.2 CO 2 Labels in the EU... 192 3.8.3 Legislation in the United States.......................... 193 3.8.4 CO 2 Labels in the United States... 194 3.8.5 Legislation in Asia... 196 Chapter 4: Aerodynamic Forces and Their Influence on Passenger Vehicles...197 4.1 Aerodynamic Forces and Force Coefficients... 201 4.1.1 Buckingham Π Theorem... 205 4.2 Flow Field Around Cars... 206 4.2.1 Dead Wake... 208 4.2.2 Longitudinal Vortices... 215 4.2.3 Internal Flow... 216 4.2.4 Environmental Influences... 217 4.2.5 Influence of the Reynolds Number... 219 4.3 Analysis of Aerodynamic Drag Components... 220 4.3.1 Pressure and Friction Drag... 220 4.3.2 Microdrag... 223 4.3.3 Analysis by Individual Components... 226 vii 6584_Book.indb 7

4.4 Other Components of Aerodynamic Force and Aerodynamic Moment... 246 4.4.1 Lift and Pitching Moment... 246 4.4.2 Side Force and Yaw Moment... 248 4.4.3 Roll Moment.......................................... 250 4.5 Influence on Aerodynamic Forces... 250 4.5.1 The Influence of Basic Shape... 252 4.5.2 Cooling Air Effect... 320 4.5.3 Add-On Parts... 334 4.5.4 Interference... 367 4.6 The Aerodynamic Development Process... 380 4.6.1 Goal Definition... 382 4.6.2 Project Milestones and Tools... 383 4.6.3 Examples............................................. 388 4.7 Drag and Lift of Passenger Cars in Production... 390 4.7.1 Overview of Competitors by Vehicle Class... 390 4.7.2 Drag Surface Area c D A x... 392 4.7.3 Intercomparison in Accordance with EADE... 394 4.7.4 Influence of Vehicle Concepts... 396 4.7.5 Influence of Equipment and Engine... 400 4.7.6 Driving on the Ceiling?... 402 4.8 Future Development... 403 4.9 Reference Bodies... 406 4.9.1 SAE Reference Body... 406 4.9.2 Ahmed Body... 409 4.9.3 DrivAer Body... 410 Chapter 5: Aerodynamics and Driving Stability...413 5.1 Unsteady Aerodynamic Forces and Moments... 414 5.1.1 Overtaking Maneuvers... 414 5.1.2 Side Wind... 416 5.2 Dynamic Driving Effects... 445 5.2.1 Single-Track Model... 445 5.2.2 Reaction to Lift Forces... 449 5.2.3 Aerodynamic Axle Load Relief Settings... 459 5.2.4 Reaction to Crosswinds... 461 Chapter 6: Functionality, Safety, and Comfort... 473 6.1 Component Loads... 474 6.1.1 Component Loads and Pinpointing Them... 474 6.1.2 Doors, Flaps, and Outside Mirrors... 476 6.1.3 Windshield Wipers... 480 6.2 Comfort When Driving with the Top Down... 487 6.2.1 Objective... 487 viii 6584_Book.indb 8

6.2.2 Airflow with Convertible Top Open... 488 6.2.3 Wind Noise... 489 6.2.4 Thermal Comfort... 489 6.2.5 Design Solutions for Convertibles... 496 6.2.6 Design Solutions for Sunroofs... 501 6.3 Prevention of Vehicle Soiling... 503 6.3.1 Basics of Vehicle Soiling... 503 6.3.2 External Contamination... 508 6.3.3 Vehicle-Induced Contamination... 523 Chapter 7: Cooling and Internal Flow...527 7.1 Cooling Requirements... 527 7.1.1 Representative Operating Conditions... 528 7.1.2 Components and Systems... 529 7.1.3 Other Requirements... 531 7.2 Cooling System... 532 7.2.1 Engine Cooling System Circuit... 532 7.2.2 Fundamentals of Heat Transfer... 533 7.2.3 Design of Heat Exchanger... 535 7.2.4 Heat Exchangers in the Vehicle... 537 7.3 Internal Flow... 541 7.3.1 Operating Conditions... 541 7.3.2 Cooling Module... 544 7.3.3 Fan... 545 7.4 Optimizing the Overall System... 547 7.4.1 Calculation of the Cooling Air Mass Flow... 548 7.4.2 Influence Parameters of the Internal Flow... 551 7.4.3 Air Intakes and Cooling Air Ducts... 553 7.4.4 Cooling Matrix... 554 7.4.5 Fan... 559 7.4.6 Engine Compartment... 561 7.4.7 Cooling Air Outlets... 562 7.5 Measurement Technology for Cooling Airflow... 563 7.5.1 Vane Anemometers... 564 7.5.2 Pressure Measurements... 564 7.5.3 Optical Measuring Methods... 565 7.5.4 Hot-Wire Anemometry... 566 Chapter 8: Aeroacoustics... 569 8.1 The Influence of Airflow on the Interior and Exterior Noise of Motor Vehicles... 569 8.2 Aerodynamic Noise Generation... 573 8.3 Aeroacoustic Measuring Systems... 574 8.3.1 Aeroacoustic Wind Tunnels... 574 ix 6584_Book.indb 9

8.3.2 Measuring Interior Noise... 576 8.3.3 Measuring Exterior Noise... 576 8.3.4 Measuring Structure- Borne Sound... 581 8.3.5 Sound Source Location with Special Instruments... 582 8.4 Main Noise Sources and Options for Their Reduction... 583 8.4.1 Leaks... 583 8.4.2 Rear View Mirrors... 584 8.4.3 Windshield Wipers... 586 8.4.4 Antennas... 586 8.4.5 A-Pillar... 587 8.4.6 Cavity Resonances... 589 8.4.7 Sun Roof Opening Noise... 591 8.4.8 Wheel Housings... 591 8.4.9 Underbody... 592 8.4.10 Reduction of Interior Noise by Using Special Acoustic Glass Windows... 593 8.4.11 Convertibles... 593 8.5 Psycho-Acoustic Aspects... 594 8.5.1 Assessing Different Behavior Under Yaw Conditions... 596 8.5.2 Simulation with Static Vortex Generators... 597 8.5.3 Simulation with Dynamic Vortex Generators... 597 8.5.4 Noise Synthesis... 597 Chapter 9: High-Performance Vehicles...601 9.1 Introduction... 601 9.1.1 Definition... 601 9.1.2 Preview... 602 9.2 Outline of the History... 602 9.2.1 Racing Cars... 602 9.2.2 Record-Breaking Vehicles... 609 9.2.3 Sports Cars... 618 9.3 Vehicle Classes... 623 9.4 Race Tracks... 629 9.5 Regulations... 631 9.6 Aerodynamics, Performance, and Handling Characteristics... 635 9.6.1 Drag... 635 9.6.2 Downforce... 639 9.6.3 Balance... 643 9.6.4 Road Performance... 649 9.6.5 Efficiency... 651 9.6.6 Cooling and Ventilation... 654 9.6.7 Oblique Incident Flow... 656 9.6.8 Slipstream... 659 x 6584_Book.indb 10

9.7 Aerodynamics of Components... 661 9.7.1 Basic Body... 662 9.7.2 Wings... 666 9.7.3 Spoiler and Gurneys... 677 9.7.4 Ground Effect... 682 9.7.5 Diffusers... 686 9.7.6 Inlets and Outlets... 696 9.7.7 Air Guiding Elements (Vanes)... 703 9.7.8 Wheels... 707 Chapter 10: Commercial Vehicles... 711 10.1 Target Group...711 10.2 Driving Resistances and Fuel Consumption....................... 713 10.3 History of Commercial Vehicle Aerodynamics... 718 10.4 Principles of Commercial Vehicle Aerodynamics... 721 10.4.1 Straight/Oblique Flow... 723 10.4.2 Legislative Framework... 727 10.5 Tools for Optimizing Commercial Vehicle Aerodynamics...728 10.5.1 Challenges Posed by Commercial Vehicles... 728 10.5.2 Model- Scale Wind Tunnel... 728 10.5.3 Full- Scale Wind Tunnel................................. 732 10.5.4 CFD Simulation... 735 10.5.5 Test Drives with Wheel Hub Measurement Device... 736 10.6 Optimizing Aerodynamic Drag on Trucks... 739 10.6.1 Characteristic Airflow and Pressure Conditions... 739 10.6.2 Cab... 741 10.6.3 Mirrors and Attachments on the Cab... 748 10.6.4 Airflow Through the Engine Compartment... 751 10.6.5 Chassis... 754 10.6.6 Semitrailers and Bodies... 758 10.6.7 Concept Vehicles... 769 10.7 Optimizing Aerodynamic Drag on Buses and Coaches... 772 10.7.1 Characteristic Airflow and Pressure Conditions... 772 10.7.2 Front... 773 10.7.3 Rear View Mirrors... 775 10.7.4 Windscreen Wipers... 777 10.7.5 Underbody... 778 10.7.6 Wheels and Wheel Covers... 778 10.7.7 Airflow Through the Engine Compartment... 780 10.7.8 Rear... 781 10.8 Aerodynamic Interaction... 782 10.8.1 Nose-to-Tail Driving... 782 10.8.2 Tipping and Susceptibility to Side Winds... 784 10.8.3 Aerodynamic Loads on Components... 786 xi 6584_Book.indb 11

10.8.4 Dust Turbulence... 786 10.8.5 Intake of Warm Air... 787 10.8.6 Management of Exhaust Gas... 788 10.9 Vehicle Soiling... 789 10.9.1 Task Description and Testing Methods... 789 10.9.2 Foreign Soiling... 791 10.9.3 Self-Soiling... 792 Chapter 11: Motorcycle Aerodynamics... 795 11.1 Introduction... 795 11.2 Historical Review and Current Types... 796 11.2.1 History of Motorcycle Aerodynamics... 796 11.2.2 Current Motorcycle Categories... 801 11.2.3 Special Bikes... 807 11.3 Aerodynamic Tasks...811 11.3.1 Aerodynamic Forces and Moments...811 11.3.2 Aerodynamics and Longitudinal Dynamics... 813 11.3.3 Aerodynamics and Lateral Dynamics... 821 11.3.4 Cooling and Internal Flow... 831 11.3.5 Wind and Weather Protection... 835 11.3.6 Aeroacoustics... 837 11.4 Development Methods... 838 11.4.1 Development Process... 838 11.4.2 Simulation (CFD)... 839 11.4.3 Wind Tunnel... 853 11.4.4 Road Test... 864 11.4.5 Outlook The Future of Development Methods... 868 11.5 Aerodynamic Design Practical Examples... 869 11.5.1 Measures to Optimize Drag and Lift... 869 11.5.2 Design of Internal Flows, Cooling, and Heat Protection... 872 11.5.3 Measures for Wind and Weather Protection... 875 11.6 Outlook... 876 Chapter 12: Helmets...877 12.1 Head Protection Technology... 877 12.2 Motorcycle Helmets... 879 12.2.1 Aerodynamics... 879 12.2.2 Aeroacoustics... 887 12.2.3 Ventilation and Rain Tests... 896 12.3 Helmets for Open Race Cars... 901 12.3.1 History... 901 12.3.2 Aerodynamics and Ventilation... 901 12.3.3 Acoustics... 903 xii 6584_Book.indb 12

12.4 Measurement and Simulation Technology... 906 12.4.1 Introduction... 906 12.4.2 Wind Tunnel... 906 12.4.3 Aerodynamic Forces... 907 12.4.4 Aeroacoustic and Artificial-Head-Measurement Technology... 909 12.4.5 Computational Fluid Dynamics (CFD)... 909 Chapter 13: Wind Tunnels and Measurement Technique...913 13.1 Scope of Wind Tunnels... 913 13.2 Wind Tunnel Physics... 916 13.2.1 Design and Function of Wind Tunnels... 916 13.2.2 Wind Tunnel Nozzle... 920 13.2.3 The Test Section... 926 13.2.4 The Collector... 934 13.2.5 Plenum... 937 13.2.6 Diffusers... 940 13.2.7 Turning Vanes... 941 13.2.8 Flow Conditioning Screens... 941 13.2.9 Honeycombs... 942 13.2.10 Acoustic and Anti- Buffeting Measures... 942 13.2.11 Ground Simulation... 955 13.2.12 Unsteady Flow and Gust Simulation... 963 13.2.13 Wind Tunnel Correction Methods... 967 13.3 Wind Tunnel Measurements... 981 13.3.1 Test Sequence... 981 13.3.2 Measurement of Flow Velocity... 984 13.3.3 Pressure Measurements... 990 13.3.4 Measurements of Aerodynamic Loads... 997 13.3.5 Flow Visualization... 1006 13.3.6 Investigation of Vehicle Soiling...1011 13.3.7 Engine Cooling Tests... 1014 13.3.8 Heating and Climatization Tests... 1017 13.3.9 On-Road Measurements... 1021 13.3.10 Additional Equipment in Climatic and Thermal Wind Tunnels... 1032 13.4 Model Testing Dimensionless Numbers... 1034 13.5 Existing Wind Tunnels for Motor Vehicles... 1039 13.5.1 Full- Scale Wind Tunnels... 1041 13.5.2 Model- Scale Wind Tunnels... 1048 13.5.3 Climatic and Thermal Wind Tunnels... 1050 13.5.4 Overview and Correlation Measurements... 1054 13.6 Outlook... 1062 xiii 6584_Book.indb 13

Chapter 14: Numerical Methods...1065 14.1 Simulation of Three- Dimensional Viscous Flows... 1066 14.1.1 Requirements and Properties of CFD Methods... 1068 14.1.2 Basics of Kinetic Theory... 1070 14.1.3 Lattice Methods... 1072 14.1.4 Navier-Stokes Methods... 1084 14.1.5 Potential Flow Methods (BEM)...1103 14.1.6 One- Dimensional Methods for Cooling Module Design...1113 14.1.7 Rotating Geometries (Wheels, Fans)...1119 14.1.8 Porous Media (Heat Exchanger)...1121 14.1.9 The Solution Process...1123 14.1.10 Hardware and Benchmarking...1138 14.1.11 Integration of CFD in the Development Process...1144 14.1.12 Outlook...1146 14.2 Computational Aeroacoustics for Motor Vehicles...1148 14.2.1 Introduction...1148 14.2.2 Calculation of Aerodynamic and Aeroacoustic Sources...1151 14.2.3 Sources and Exterior Sound Field...1153 14.2.4 Transfer into the Vehicle Cabin...1157 14.2.5 Examples of Applications...1161 14.2.6 Conclusion and Outlook...1172 Abbreviations...1175 Symbols...........................................................1179 Literature...1193 The Authors...1245 Index...1253 xiv 6584_Book.indb 14