Contents 1 Introduction to Automobile Aerodynamics 1 Wolf-Heinrich Hucho 1.1 Scope 1 1.1.1 Basic Principles 1 1.1.2 Peculiarities of Vehicle Aerodynamics 7 1.1.3 Related Fields 11 1.2 History of Vehicle Aerodynamics 13 1.2.1 Survey 13 1.2.2 "Borrowed" Shapes 14 1.2.3 The Eraof the Streamline 16 1.2.4 Parameter Studies 27 1.2.5 One-Volume Bodies 32 1.2.6 The "Bathtub" Body 37 1.2.7 Commercial Vehicles 39 1.2.8 Motorcycles 43 1.3 Present and Future Trends 43 1.3.1 State of the Art 43 1.3.2 Detail Optimization 48 1.3.3 Shape Optimization 49 1.3.4 Development Expenditure 51 1.4 Aerodynamics and Design 52 1.5 Notation 57 2 Some Fundamentals of Fluid Mechanics 59 Dietrich Hummel 2.1 Properties of Incompressible Fluids 59 2.1.1 Density 59 2.1.2 Viscosity 59 2.1.3 Thermal Conductivity 60 2.2 Flow Phenomena Related to Vehicles 61 2.2.1 ExternalFlow 61 2.2.2 Internal Flow 62
viii Aerodynamics ofroad Vehicles 2.3 Externa! Flow Problems 63 2.3.1 Basic Equations for Inviscid Incompressible Flow 63 2.3.2 Applications 63 2.3.3 Effects ofviscosity 66 2.3.3.1 Laminar and Turbulent Boundary Layer Development 66 2.3.3.2 Separation 68 2.3.3.3 Friction Drag 68 2.3.3.4 Pressure Drag 70 2.3.3.5 Overall Forces and Moments 74 2.3.3.6 Thermal Boundary Layers 76 2.3.4 Special Problems 80 2.3.4.1 Aerodynamic Noise 80 2.3.4.2 Body to Body Interference 81 2.3.4.3 Transport ofsolids 84 2.4 Internal Flow Problems 86 2.4.1 Basic Equations for Incompressible Flow 86 2.4.2 Applications 88 2.4.2.1 Laminar and Turbulent Pipe Flow 88 2.4.2.2 Curved Pipes 90 2.4.2.3 Inlets 91 2.4.2.4 Local Contractions 92 2.4.2.5 Cross-Section Enlargement 92 2.5 Relations Between External and Internal Flow 94 2.6 Notation 95 3 Performance of Cars and Light Trucks 99 Hans-Joachim Emmelmann and Wolf-Heinrich Hucho 3.1 Objectives 99 3.2 Resistances to Vehiclc Motion 101 3.2.1 Equation of Motion 101 3.2.2 Analysis of Resistances to Motion 102 3.2.2.1 Aerodynamic Drag 102 3.2.2.2 Tire Rolling Resistance 103 3.2.2.3 Ratio of Aerodynamic Drag to Tire Rolling Resistance 104 3.2.2.4 Climbing Resistance 104 3.2.2.5 Vehiclc Mass 104 3.3 Performance 105 3.3.1 Traction Diagram 105 3.3.2 Maximum Speed 107 3.3.3 Acceleration Time and Elasticity 108 3.4 Fuel Consumption, Fuel Economy 109 3.4.1 Dcfinitions 109 3.4.2 Analysis of Fuel Consumption 110 3.4.3 Gear-Ratio Matching 113 3.4.4 Driving Schedules 115 3.4.4.1 EPA Urban and Highway Cycle 115 3.4.4.2 Present European Driving Cycle 116
Table of Contents ix 3.4.4.3 New European Driving Cycle, and Others 122 3.5 Strategy for Lowest Fuel Consumption 125 3.6 Fuel Consumption of Light Tracks 126 3.7 Outlook 127 3.8 Notation 129 4 Aerodynamic Drag of Passenger Cars 131 Wolf-Heinrich Hucho 4.1 The Passenger Car as a Bluff Body 131 4.2 Flow Field Around a Car 133 4.3 Analysis of Drag 142 4.3.1 Possible Approaches 142 4.3.2 Physical Mechanisms 143 4.3.3 Local Origins 145 4.3.4 Effect on the Environment 147 4.3.5 Drag and Lift 148 4.4 Drag Fractions and Their Local Origins 151 4.4.1 Methodof Observation 151 4.4.2 Front End 152 4.4.3 Windshield and A-Pillar 159 4.4.4 Roof 163 4.4.5 RearEnd 164 4.4.5.1 Geometry and Flow Separation 164 4.4.5.2 Boat-Tailing 164 4.4.5.3 Fastback 167 4.4.5.4 Notchback 174 4.4.6 Plan View and Side Panels 177 4.4.7 Underbody 180 4.4.8 Wheels and Wheel Housings 180 4.4.9 Front Spoiler 185 4.4.10 Rear Spoiler 191 4.4.11 Attachments 196 4.4.12 Drag from Flow Through a Car 197 4.4.13 Car with Trailer 201 4.4.14 Convoy Driving 207 4.5 Strategies for Body Shape Development 209 4.5.1 Objectives 209 4.5.2 Detail Optimization 210 4.5.3 Shape Optimization 212 4.5.4 Facelift 214 4.5.5 Adaptation of Attachments 214 4.5.6 Forecasting Systems and Expert Systems 215 4.6 Drag of Passenger Cars in Production 217 4.6.1 Evaluation of Test Results 217 4.6.2 Vehicle Features 218 4.6.3 Vehicle Position, Side Wind 219 4.6.4 Drag Coefficients of Production Cars 222 4.7 Research 224
x Aerodynamics ofroad Vehicles 4.7.1 Objectives 224 4.7.2 Basic Bodies 224 4.7.3 UnconventionalMeasures 227 4.7.4 Concept Vehicles 229 4.7.5 Record Vehicles 232 4.8 Notation 235 5 Directional Stability 239 Alfons Gilhaus and Ralf Hoffmann 5.1 Introduction 239 5.2 History of Directional Stability 240 5.3 Aerodynamic Forces and Moments 244 5.3.1 Development 244 5.3.2 Aerodynamic Stability 247 5.3.3 Non-Stationary Forces and Moments 249 5.4 Aerodynamics and Driving Behavior 250 5.4.1 Lift Force in Straight-Ahead Driving 250 5.4.2 Cornering 253 5.4.3 Power On/Off Reaction 257 5.4.4 Influence of the Aerodynamic Forces on Braking Performance 258 5.4.5 Driving Behavior in Crosswinds 262 5.4.5.1 Natural Wind and Crosswind 262 5.4.5.2 Side Wind Reactions 266 5.4.6 Pass-By Maneuvers 275 5.4.7 Driving with Trailer 278 5.5 Influence of Vehicle Shape on Aerodynamic Forces and Moments 280 5.5.1 Aerodynamic Properties of the Basic Shapes 281 5.5.1.1 Lift and Pitching Moment 281 5.5.1.2 Side Force and Yawing Moment 282 5.5.1.3 Rolling Moment 288 5.5.1.4 Comparison ofthe Key Basic Shapes 289 5.5.2 Aerodynamic Effects ofthe Features of Actual Vehicles 292 5.5.2.1 Cooling Airflow 292 5.5.2.2 Gaps and Openings 294 5.5.2.3 Exterior Rearview Mirrors 294 5.5.2.4 Wheels, Tires, and Underbody 294 5.5.3 RoofLoads 298 5.6 Test and Evaluation Methods 300 5.6.1 Wind Tunnel Tests 300 5.6.2 Road Tests 301 5.6.3 Computation of Vehicle Dynamics 305 5.6.4 Driving Simulator 306 5.7 Notation 309
Table of Contents xi 6 Function, Safety and Comfort 311 Raimund Piatek and Johannes Schmitt 6.1 Differentiated View 311 6.2 The Flow Field Around a Vehicle 311 6.3 Inlets and Outlets 316 6.3.1 CoolingDucts 316 6.3.2 Air Inlets and Outlets to the Cabin 316 6.4 Forces on Bodywork Components 321 6.4.1 Components with Attached Flow 321 6.4.2 Components with Separated Flow 323 6.4.3 Components with Periodic Flow 324 6.5 Function of Individual Components 324 6.5.1 External Mirrors 324 6.5.2 Windshield Wipers 326 6.5.3 Sunroofs 327 6.5.4 Convertibles 327 6.6 Waterand Dirt Accumulation on Vehicles 330 6.6.1 Safety and Aesthetics 330 6.6.2 Water Flow 331 6.6.3 Dirt Deposits 334 6.7 Reducing Splash and Spray 337 6.7.1 Obstruction to Visibility 337 6.7.2 Measuring Impaired Visibility 338 6.7.3 Measures to Rcduce Spray Formation 339 6.8 Notation 341 7 Wind Noise 343 John R. Callister and Albert R. George 7.1 Introduction 343 7.2 Mechanisms of Noise Generation and Transmission 344 7.2.1 Source-Path-Receiver 344 7.2.2 Idealized Models of Acoustic Sources 344 7.2.3 Physical Wind Noise Source Types 345 7.2.3.1 Leak Noise 345 7.2.3.2 Cavity Noise 346 7.2.3.3 Wind Rush Noise 347 7.2.4 Airflow Velocity Effect on Wind Noise Levels 348 7.3 Design Features 349 7.3.1 A-Pillar 349 7.3.2 Outside Rearview Mirrors 350 7.3.3 Windshield Wipers 350 7.3.4 Radio Antenna 351 7.3.5 RoofRacks 352 7.3.6 Doors 352
xii Aerodynamics ofroad Vehicles 13.1 Side Window Systems 353 7.3.8 Fixed Windows 354 7.3.9 HatchRoofs 354 7.4 Wind Noise Measurement and Testing Techniques 354 7.4.1 Wind Tunnel versus On-Road Measurements 354 7.4.2 Wind Tunnel Considerations 355 7.4.2.1 Wind Tunnel Background Noise 355 7.4.2.2 Simulation of Crosswinds and Gusts in the Wind Tunnel 355 7.4.3 On-Road Measurement Procedures 356 7.4.4 Importance of Narrow Band Spectra for Wind Noise Measurements 356 7.4.5 Overviewof Measurement of Interior Wind Noise 358 7.4.5.1 Use of Artificial Head Device for Subjective Evaluation 358 7.4.5.2 Source Identification and Localization 358 7.4.6 Overview of Exterior Wind Noise Measurements 358 7.4.6.1 Microphone Nose Cones 359 7.4.6.2 Sound Intensity and Microphone Array Methods 359 7.5 Buffeting of Open Windows, Open Sunroofs, and Convertibles 360 7.5.1 Side Windows 360 7.5.2 Sunroofs 360 7.5.3 Convertibles 360 7.6 Manufacturing Concerns 362 7.6.1 Process 362 7.6.2 Inspection 362 7.6.2.1 Leak Detection Using a Smoke Generator 363 7.6.2.2 Ultrasonic Leak Detector 363 7.6.2.3 Simple, Quick Inspection Techniques 363 7.6.3 Feedback to the Design Organization 364 7.7 Notation 364 8 High-Performance Vehicles 365 Helmut Flegl and Norbert Singer 8.1 Defmitions 365 8.2 Some Historical Milestones 368 8.3 The Meaning of Aerodynamics for High-Performance Cars 379 8.3.1 Drag and Lift 379 8.3.2 Handling 379 8.3.2.1 Driving Tests 380 8.3.2.2 Angle of Attack and Yawed Airflow 381 8.3.2.3 Slipstreaming 385 8.3.2.4 Theoretical Investigations 386 8.3.3 Cooling and Ventilation 387 8.4 Design Alternatives 388 8.4.1 Drag and Lift 388 8.4.1.1 Influence of the Basic Vehicle Configuration 391 8.4.1.2 Wings 391 8.4.1.3 Ground Effect 392 8.4.1.4 Special Body Configurations, Monoposti 397
Table of Contents xiii 8.4.2 Handling HQQ 8.4.3 Cooling and Ventilation 4Q? Special Problems 404 8.5.1 Lap Time and Fuel Economy 404 8.5.2 Near-Sonic Speeds 407 8.5.3 Uncovered Wheels 40g 8.5.4 Rotating versus Stationary Wheels of Monoposti 409 8.5.4.1 Road Version 409 8.5.4.2 High-Speed Version 410 8.5.5 Effect of Boundary Layer Variation on Wind Tunnel Results 411 8.5.6 Development Methods and Simulation Techniques 411 Trends in Future High-Performance Vehicle Development 413 Notation,,. Commercial Vehicles Hans Götz and Günter Mavr 41^ Target Group 4, <- Tractive Resistance and Fuel Consumption 4lg Drag Reduction and Fuel Consumption 41g Aerodynamic Drag Coefficients of Various Commercial Vehicles 420 9.4.1 Operation in Still Air 40] 9.4.2 Drag as a Function of Yawing Angle 42? 9.4.3 Wind Influence Definition of Yawing Angle 423 9.4.4 Characterization of Air Resistance in Actual Operating Conditions 424 Reducing Aerodynamic Drag A~>^ 9.5.1 Scope for Aerodynamic Changes on Commercial Vehicles 425 9.5.2 Optimization in the Wind Tunnel Problems with Reduced-Scale Models 425 9.5.3 Drag Minimization on Trucks 497 9.5.3.1 Characteristic Flow and Pressure Conditions 427 9.5.3.2 Partial Resistance Interference Problem 429 9.5.3.3 Cab Shape 43] 9.5.3.4 Drag-Reducing Add-On Devices for Trucks 433 9.5.3.5 Füll Trailer 430 9.5.3.6 Future Trends in Tractor-Trailer Design 440 9.5.3.7 Reduction of Aerodynamic Drag on "Truckaway" Units 443 9.5.4 Minimizing Drag of Buses and Delivery Vans 445 9.5.4.1 Boundary Conditions 445 9.5.4.2 Characteristic Flow Conditions on Simple Geometrie Bodies 445 9.5.4.3 Optimization of the Front End 449 9.5.4.4 Optimization ofthe RearEnd 453 9.5.4.5 Add-On Devices on the Rear End 456 9.5.4.6 Future Bus Design Trends 459 Taking Advantage of Aerodynamic Interference Effects 460 9.6.1 Driving in Convoy 46Q 9.6.2 Driving Through Tunnels 46i Vehicle Soiling 4fi7
xiv Aerodynamics ofroad Vehicles 9.7.1 Foreign Soiling 467 9.7.2 Self-Soiling 468 9.7.2.1 Reductionof Soiling of Bus Sides 469 9.7.2.2 Reduction of Bus Rear-End Soiling 473 9.7.3 Reduction of Truck Soiling 474 9.7.4 Impingement of Spray on Following Vehicles 475 9.7.4.1 New Approach to Solution of Spray Mist Reduction 479 9.7.4.2 The Measuring System 485 9.8 Notation 487 10 Motorcycles 489 Bernward E. Bayer 10.1 One Year Before the Automobile 489 10.2 Summary of the Development of Motorcycle Aerodynamics 490 10.2.1 History 490 10.2.2 Today's State-of-the-Art Technology 494 10.3 Riding Dynamics and its Relationship with Aerodynamics 502 10.3.1 Performance Specifications 502 10.3.2 Directional Stability 504 10.3.3 C rosswind Behavior 505 10.3.4 Pitch Effects 507 10.3.5 Cornering 509 10.4 Methods of Measurement in Road Tests 511 10.5 Wind Tunnel Results 514 10.5.1 Measurements on Solo Motorcycles 514 10.5.2 Rider Influences 520 10.5.2.1 Rider and Pillion Passenger 520 10.5.2.2 Clothing and Heimets 523 10.5.3 Sidecars 526 10.6 Outlook 528 10.7 Notation 531 11 Engine Cooling 533 WulfSebheße, Peter Steinberg, Norbert Deußen, and Dieter Schlenz 11.1 Task of a Cooling System 533 11.1.1 Functional Requirements 533 11.1.2 Requirements to be Satisfied by Passive Characteristics 533 11.1.3 Development Potential of Cooling System 534 11.2 Cooling Systems 534 11.2.1 Water Cooling 534 11.2.2 Air Cooling 535 11.2.3 Cooling with Component-Temperature Control 537 11.2.4 Dual-Circuit Cooling System and Warm-Up Concept 537 11.2.5 High-Temperature Cooling 539
Table of Contents xv 11.2.6 OilCooling 540 11.2.7 Phase-Change Cooling 540 11.3 Methods of Computation 543 11.3.1 Principles of Hcat Exchange 543 11.3.1.1 Heat Transfer and Radiation 544 11.3.1.1.1 Hcat Transfer from Combustion Gas to Components Adjacent to Combustion Chamber 544 11.3.1.1.2 Heat Transfer from Cylinderto Coolant 545 11.3.1.1.3 Heat Transfer at the Engine-Block Wall 547 11.3.1.2 Heat Conduction in Components 547 11.3.1.3 Computing Model and Results of Simulation 548 11.3.2 Modular Mcthods for Cooling-System Dimensioning 549 11.3.2.1 Procedural Concept 549 11.3.2.2 Coolant Circuit 550 11.3.2.3 Fan and Fan Clutch 551 11.3.2.4 Cooling Air System 552 11.3.2.5 Heat Balance at Engine and Surface of Engine 552 11.3.2.6 Heat Balance at Radiator 553 11.3.2.7 Heat Flux Measurement on an Engine 553 11.4 Flow Within the Engine Compartment 556 11.4.1 Cooling-Air System 556 11.4.1.1 Effect of Internal Airflow on Vehicle Aerodynamics 557 11.4.1.2 Aerodynamics of Internal Flow 557 11.4.1.3 Air Velocity Distribution in the Radiator Plane 559 11.4.2 Radiator 562 11.4.3 Radiator Fan 566 11.4.3.1 Tasksofthe Radiator Fan 566 11.4.3.2 Fan and Drive 566 11.4.3.3 Design Criteria and Characteristics 567 11.4.3.3.1 Volumetrie Flow 567 11.4.3.3.2 Power Requirement and Efficiency 569 11.4.3.3.3 Noise Generation 571 11.4.3.3.4 Mass and Space Requirement 573 11.5 Notation 574 12 Heating, Ventilating, and Air Conditioning of Passenger Cars 577 Holger Großmann 12.1 Definition of Objectives: Comfort and Safety 577 12.2 Climate Physiology 577 12.2.1 Parameters Affecting the Occupants 577 12.2.2 Interior Temperaturc 578 12.2.3 Temperature Stratification 579 12.2.4 Air Speed 579 12.2.5 Inhomogeneous Airflow 580 12.2.6 Humidity 581 12.2.7 Solar Radiation 581 12.2.8 Comfort Model Devised by P.O. Fanger 582
xvi Aerodynamics ofroad Vehicles 12.2.9 Climate Measuring Dummies 583 12.2.10 Heart Rates 583 12.3 Parameters Affecting the Climate Inside a Car 585 12.4 Airflow Through the Passenger Compartment 586 12.4.1 Intake and Outlet Vents 586 12.4.2 Airflow Definition 587 12.4.3 Airflow Measuring Methods 587 12.4.4 Characteristic Curves 588 12.4.4.1 Fan Characteristics 589 12.4.4.2 Leakage Characteristics L w 590 12.4.4.3 Outlet Characteristics A w 591 12.4.4.4 Ventilation Characteristics B w 592 12.4.4.5 Ventilation Airflow 592 12.4.4.6 Ventilation Airflow with Slide-Tilt Sunroof Open 593 12.4.5 Incoming Leakage Airflow 594 12.4.5.1 Significance of Incoming Leakage Airflow 594 12.4.5.2 Determination of Incoming Leakage Airflow 594 12.4.5.3 Examples 596 12.5 Heat Flow Through the Passenger Compartment 597 12.5.1 Heat Transfer Through the Body 597 12.5.2 Interface Heater Core/Passenger Compartment 599 12.5.2.1 Characteristics of the Heater Core 600 12.5.2.2 Steady Interior Temperature in Fresh-Air Mode 600 12.5.2.3 Unsteady Interior Temperature in Fresh-Air Mode 603 12.5.2.4 Mean Interior Temperature in Recirculating Mode 603 12.5.2.5 Engine with Low Fuel Consumption 604 12.5.3 Interface Evaporator/Passenger Compartment 606 12.5.3.1 Characteristics of Evaporator 606 12.5.3.2 Mean Interior Temperature in Fresh-Air Mode 608 12.5.3.3 Mean Interior Temperature in Recirculating Mode 610 12.5.3.4 Interface Evaporator/Refrigeration Cycle 610 12.5.3.5 Unsteady Cooling in Recirculating Mode 612 12.5.4 Solar Radiation 613 12.5.4.1 Solar Radiation Through the Windows 613 12.5.4.2 Heating Up a Parked Car 615 12.5.4.3 Solar-Cell Operated Independent Ventilation 615 12.5.4.4 Heating Up While Vehicle in Motion 616 12.6 Flow of Water Vapor and Dust 617 12.6.1 Water Vapor 617 12.6.2 Gas Concentration in the Passenger Compartment 618 12.6.3 Defrosting and Defogging of Windows 618 12.6.4 Filtering 620 12.7 Control Systems 620 12.7.1 Temperature Control of a Heating System 620 12.7.2 Automatic Control of Evaporators 621 12.7.3 Automatic Control of Air Distribution and Temperature 621 12.8 Heater and A/C Units in Production 622 12.8.1 Air-Side Controlled Heater 622
Table of Contents xvii 12.8.2 Water-Side Controlled Heater 622 12.8.3 Integrated AC Systems 623 12.9 Notation 624 13 Wind Tunnels 627 Wolf Heinrich Hucho 13.1 Scope 627 13.1.1 Requirements fora Vehicle Wind Tunnel 627 13.1.2 Simulation of the Various Aspects of On-Road Driving 629 13.2 Some Fundamentals of Wind Tunnel Technique 632 13.2.1 Selection of References 632 13.2.2 Configuration Considerations 633 13.2.3 Properties of the Essential Components 634 13.2.3.1 Planning a Test 634 13.2.3.2 Test Section 635 13.2.3.3 Nozzle 643 13.2.3.4 Determination of Wind Speed 647 13.2.3.5 Plenum 651 13.2.3.6 Heat Exchanger and Sun Load 652 13.2.4 Equipment 653 13.3 Limitations of Simulation 653 13.3.1 Systematic Errors 653 13.3.2 Representation of the Road 654 13.3.3 Wind Tunnel Corrections 672 13.3.3.1 Objectives 672 13.3.3.2 ClosedTest Section 674 13.3.3.3 Open Test Section 678 13.3.3.4 Boundary Layer Effects 680 13.3.3.5 Yawed Model 680 13.3.3.6 Thermal Tests 680 13.4 Tests with Reduced-Scale Models 680 13.4.1 Advantages and Disadvantages 680 13.4.2 Details of Model Construction and Test Technique 682 13.4.3 Reynolds Number Effects 686 13.5 Existing Automobile Wind Tunnels 694 13.5.1 Classification of Test Facilities 694 13.5.2 Full-Scale Wind Tunnels 697 13.5.3 Wind Tunnels for Reduced-Scale Models 705 13.5.4 Climatic Tunnels 706 13.5.5 Dynamometers with Fan 707 13.6 Comparative Measurements 710 13.7 Final Comments and Future Prospects 713 13.8 Notation 714
xviii Aerodynamics ofroad Vehicles 14 Measurement and Test Techniques 717 Görgün A. Necati and Wigberl R. Kohl 14.1 Scope 717 14.2 Measuring Equipment and Transducers 717 14.2.1 Measurement of Aerodynamic Forces and Moments 717 14.2.1.1 Wind Tunnel Balances 717 14.2.1.2 Resolution of Aerodynamic Forces and Moments into Their Components 718 14.2.1.3 Measurement of the Projected Frontal Area 721 14.2.2 Pressure Measurements 722 14.2.2.1 Pressure Probes 722 14.2.2.2 Pressure Transducers 725 14.2.3 Measurement of the Airflow Velocity 726 14.2.3.1 Determination of the Airflow Velocity Outside and Inside a Vehicle 727 14.2.3.2 Determination of the Test Speed in a Wind Tunnel 735 14.2.3.3 Measurement of Flow Direction 736 14.2.4 Temperature Measurement 737 14.2.4.1 Temperature Sensors 738 14.2.4.2 Typical Temperature Measurement Errors 740 14.2.5 Test Data Collection and Data Management 742 14.3 Wind Tunnel Testing Methods 743 14.3.1 Measurement of the Aerodynamic Coefficients 743 14.3.2 Airflow Management Tests 744 14.3.3 Measurement of the Airflow Rate Through the Passenger Compartment 744 14.3.3.1 Airflow Rate Measurement by Means of Extraction Curves 745 14.3.3.2 Alternative Methods of Measuring Airflow Rate Through the Passenger Compartment 747 14.3.4 Passenger-Compartment Heating and Air Conditioning Tests 747 14.3.5 Defrosting and Demisting Tests 749 14.3.6 Engine Cooling Tests in a Wind Tunnel 750 14.3.7 Flow Visualization Techniques 752 14.3.8 Wind-Noise Measurement in a Wind Tunnel 754 14.3.9 Water Basin versus Wind Tunnel 754 14.4 Road Testing Methods 756 14.4.1 Measurement of the Aerodynamic Drag Force in a Coast-Down Test 756 14.4.2 Crosswind Tests 758 14.4.3 Engine Cooling Road Tests 761 14.4.4 Soil Deposits on Glass Surfaces and Vehicle Body Areas 761 14.4.5 Wind Noise Measurement on the Road 762 14.5 Notation 763 15 Computational Fluid Dynamics 765 Syed R. Ahmed 15.1 Introduction 765 15.2 Some Salient Features of Road Vehicle Flow 767
Table of Contents xix 15.3 Demands on a CFD Simulation 768 15.4 CFD Methods for Vehicle Aerodynamics 768 15.4.1 General Remarks 768 15.4.2 Approximations of the Navier-Stokes Equations 769 15.4.3 Basic Stepsofa CFD Computation 771 15.4.4 Three-Dimensional Grid Generation 771 15.5 Linear CFD Methods 776 15.5.1 The Panel Method 776 15.5.2 Some Applications of the Panel Method 776 15.6 Nonlinear CFD Methods 782 15.6.1 Solution Schemes for Nonlinear Methods 782 15.6.2 Euler Methods 785 15.6.3 Methods Based on Time-Averaged NS Equations 786 15.6.3.1 Turbulence Modeling 787 15.6.3.1.1 Eddy Viscosity Concept Turbulence Models 788 15.6.3.1.1.1 Algebraic Models 788 15.6.3.1.1.2 Transport Equation Models 790 15.6.3.1.2 Non-Eddy Viscosity Concept Turbulence Models 793 15.6.3.2 Some Applications ofrans Methods 794 15.6.4 Methods Based on Unsteady NS Equations 809 15.6.4.1 Large Eddy Simulation (LES) 809 15.6.4.2 Direct Numerical Simulation (DNS) 810 15.6.4.3 Some Applications of DNS Methods 811 15.7 Zonal Methods 824 15.8 Future Computer Requirements and Trends of Supercomputer Development 830 15.9 Evaluation and Perspective of CFD Methods 834 15.10 Notation 835 References 837 Author Index 875 Subject Index 883 Abbreviations 913 About the Authors 915