Schlieren and Shadowgraph Techniques

Transcription

1 G. S. Settles Schlieren and Shadowgraph Techniques Visualizing Phenomena in Transparent Media With 208 Figures and 48 Color Plates Springer

2 Table of Contents List of Nomenclature, XV 1 Historical Background The 17 th Century The 18 th Century The 19 th Century The 20 th Century 15 2 Basic Concepts Light Propagation Through Inhomogeneous Media Definition of a Schliere Distinction Between Schlieren and Shadowgraph Methods Direct Shadowgraphy Simple Lens-Type Schlieren System Point Light Source Extended Light Source On the Aspect of a Schlieren Image 37 3 Toepler's Schlieren Technique Lens- and Mirror-Type Systems Lens Systems Mirror Systems Sensitivity Definition and Geometrical Theory Sensitivity Examples The Limits of Sensitivity Sensitivity Enhancement by Post-Processing Measuring Range Definition of Measuring Range Adjustment of Measuring Range Estimating the Sensitivity and Range Required Resolving Power Diffraction Effects Diffraction Halos Due to Opaque Edges in the Test Area 66

3 XII Table of Contents Diffraction at the Knife-Edge Magnification and Depth of Field Image Magnification and the Focusing Lens Depth of Field 74 4 Large-Field and Focusing Schlieren Methods Large Single- and Double-Mirror Systems Availability of Large Schlieren Mirrors Examples of Large-Mirror Systems Perm State's 1-Meter Coincident Schlieren System Traditional Schlieren Systems with Large Light Sources Lens-and-Grid Techniques Simple Background Distortion Background Grid Distortion Large Colored Grid Background The Modern Focusing/Large-Field Schlieren System Penn State's Full-Scale Schlieren System Large-Field Scanning Schlieren Systems : Scanning Schlieren Systems for Moving Objects Schlieren Systems with Scanning Light Source and Cutoff Moire-Fringe Methods Holographic and Tomographic Schlieren Specialized Schlieren Techniques Ill 5.1 Special Schlieren Cutoffs Ill Graded Filters Exponential Cutoffs and Source Filters Matched Spatial Filters at Source and Cutoff Phase Contrast Photochromic and Photorefractive Cutoffs Color Schlieren Methods Reasons for Introducing Color Conversion from Monochrome to Color Schlieren Classification of Color Schlieren Techniques Recent Developments Stereoscopic Schlieren Schlieren Interferometry The Wollaston-Prism Shearing (Differential) Interferometer Diffraction-Based Schlieren Interferometers Computer-Simulated Schlieren Various Specialized Techniques Resonant Refractivity and the Visualization of Sound Anamorphic Schlieren Systems Schlieren Observation of Tracers Two-View Schlieren 140

4 Table of Contents XHI Immersion Methods Infrared Schlieren Shadowgraph Techniques Background Historical Development The Role of Shadowgraphy Advantages and Limitations Direct Shadowgraphy Direct Shadowgraphy in Diverging Light Direct Shadowgraphy in Parallel Light "Focused" Shadowgraphy Principle of Operation History and Terminology Advantages and Limitations Magnification, Illuminance, and the Virtual Shadow Effect "Focused" Shadowgraphy in Ballistic Ranges Specialized Shadowgraph Techniques Large-Scale Shadowgraphy Microscopic, Stereoscopic, and Holographic Shadowgraphy Computed Shadowgraphy Conical Shadowgraphy Practical Issues Optical Components Light Sources Mirrors Schlieren Cutoffs and Source Filters Condensers and Source Slits L5 The Required Optical Quality Equipment Fabrication, Alignment, and Operation Schlieren System Design Using Ray Tracing Codes Fabrication of Apparatus Setup, Alignment, and Adjustment Vibration and Mechanical Stability Stray Light, Self-Luminous Events, and Secondary Images Interference from Ambient Airflows Capturing Schlieren Images and Shadowgrams Photography and Cinematography Videography High-Speed imaging Front-Lighting Commercial and Portable Schlieren Instruments Soviet Instruments Western Instruments Portable Schlieren Apparatus 198

5 XIV Table of Contents 8 Setting Up Your Own Simple Schlieren and Shadowgraph System Designing the Schlieren System Determining the Cost Choosing a Setup Location Aligning the Optics Troubleshooting Recording the Schlieren Image or Shadowgram Conclusion Applications Phenomena in Solids Glass Technology Polymer-Film Characterization Fracture Mechanics and Terminal Ballistics Specular Reflection from Surfaces Phenomena in Liquids Convective Heat and Mass Transfer Liquid Surface Waves Liquid Atomization and Sprays Ultrasonics Water Tunnel Testing and Terminal Ballistics Phenomena in Gases Agricultural Airflows Aero-Optics Architectural Acoustics Boundary Layers Convective Heat and Mass Transfer Heating, Ventilation, and Air-Conditioning Gas Leak Detection Electrical Breakdown and Discharge Explosions, Blasts, Shock Waves, and Shock Tubes Ballistics Gas Dynamics and High-Speed Wind Tunnel Testing Supersonic Jets and Jet Noise Turbomachinery and Rotorcraft Other Applications Art and music Biomedical Applications Combustion Geophysics Industrial Applications Materials Processing Microscopy Optical Processing Optical Shop Testing Outdoor Schlieren and Shadowgraphy 254

6 Table of Contents XV Plasma Dynamics Television Light Valve Projection Turbulence Quantitative Evaluation Quantitative Schlieren Evaluation by Photometry Absolute Photometric Methods Standard Photometric Methods Grid-Cutoff Methods Focal Grids Defocused Grids Defocused Filament Cutoff Quantitative Image Velocimetry Background Multiple-Exposure Eddy and Shock Velocimetry Schlieren Image Correlation Velocimetry Focusing Schlieren Deflectometry The Background-Oriented Schlieren System Quantitative Shadowgraphy Double Integration of d^dy Turbulence Research Shock-Wave Strength Quantitation Grid Shadowgraphy Methods Summary and Outlook Summary Perceptions Outside the Scientific Community Other Lessons Learned Further Comments on Historical Development Further Comments on Images and Visualization Renewed Vitality Outlook: Issues for the Future Predictions Opportunities Recommendations Closing Remarks 289 References 291 Appendix A Optical Fundamentals 333 A.I Radiometry and Photometry 333 A.2 Refraction Angle E 334 A.2.1 Small Optical Angles and Paraxial Space 334 A.2.2 Huygens' Principle and Refraction 334 A.3 Optical Components and Devices 335 A.3.1 Conjugate Optical Planes 335

7 XVI Table of Contents A.3.2 Lens f/number 335 A.3.3 The Thin-Lens Approximation 335 A.3.4 Viewing Screens and Ground Glass 336 A.3.5 Optical Density 336 A.4 Optical Aberrations 336 A.5 Light and the Human Eye 337 A.6 Geometric Theory of Light Refraction by a Schliere 338 Appendix B The Schlieren System as a Fourier Optical Processor 341 B.I The Basic Fourier Processor with no Schlieren Present 341 B.2 The Addition of a Schlieren Test Object 344 B.3 The Schlieren Cutoff. 345 B.4 Other Spatial Filters 347 B.5 Partially-Coherent and Polychromatic Illumination 350 Appendix C Parts List for a Simple Schlieren/ Shadowgraph System 353 C.I Optics 353 C.2 Illumination 354 C.3 Miscellaneous Components 354 C.4 Optical Mounts 354 Appendix D Suppliers of Schlieren Systems and Components 355 D.I Complete Schlieren Systems 355 D.2 Schlieren Field Mirrors 356 D.3 Light Sources 357 D.4 Components 358 D.5 Focusing Schlieren Lenses 359 D.6 Miscellaneous 359 Index 361 Color Plates 367