Schlieren and Shadowgraph Techniques

Schlieren and shadowgraph techniques are basic and valuable tools in various scientific and engineering disciplines. They allow us to see the invisible: the optical inhomogeneities in transparent media like air, water, and glass that otherwise cause only ghostly distortions of our normal vision.
These techniques are discussed briefly in many books and papers, but there is no up-to-date complete treatment of the subject before now. The book is intended as a practical guide for those who want to use these methods, as well as a resource for a broad range of disciplines where scientific visualization is important. The colorful 400-year history of these methods is covered in an extensive introductory chapter accessible to all readers.

Contenu

1 Historical Background.- 1.1 The 17th Century.- 1.2 The 18th Century.- 1.3 The 19th Century.- 1.4 The 20th Century.- 2 Basic Concepts.- 2.1 Light Propagation Through Inhomogeneous Media.- 2.2 Definition of a Schliere.- 2.3 Distinction Between Schlieren and Shadowgraph Methods.- 2.4 Direct Shadowgraphy.- 2.5 Simple Lens-Type Schlieren System.- 2.5.1 Point Light Source.- 2.5.2 Extended Light Source.- 2.6 On the Aspect of a Schlieren Image.- 3 Toepler's Schlieren Technique.- 3.1 Lens- and Mirror-Type Systems.- 3.1.1 Lens Systems.- 3.1.2 Mirror Systems.- 3.2 Sensitivity.- 3.2.1 Definition and Geometrical Theory.- 3.2.2 Sensitivity Examples.- 3.2.3 The Limits of Sensitivity.- 3.2.4 Sensitivity Enhancement by Post-Processing.- 3.3 Measuring Range.- 3.3.1 Definition of Measuring Range.- 3.3.2 Adjustment of Measuring Range.- 3.4 Estimating the Sensitivity and Range Required.- 3.5 Resolving Power.- 3.6 Diffraction Effects.- 3.6.1 Diffraction Halos Due to Opaque Edges in the Test Area.- 3.6.2 Diffraction at the Knife-Edge.- 3.7 Magnification and Depth of Field.- 3.7.1 Image Magnification and the Focusing Lens.- 3.7.2 Depth of Field.- 4 Large-Field and Focusing Schlieren Methods.- 4.1 Large Single- and Double-Mirror Systems.- 4.1.1 Availability of Large Schlieren Mirrors.- 4.1.2 Examples of Large-Mirror Systems.- 4.1.3 Perm State's 1-Meter Coincident Schlieren System.- 4.2 Traditional Schlieren Systems with Large Light Sources.- 4.3 Lens-and-Grid Techniques.- 4.3.1 Simple Background Distortion.- 4.3.2 Background Grid Distortion.- 4.3.3 Large Colored Grid Background.- 4.3.4 The Modern Focusing/Large-Field Schlieren System.- 4.3.5 Penn State's Full-Scale Schlieren System.- 4.4 Large-Field Scanning Schlieren Systems.- 4.4.1 Scanning Schlieren Systems for Moving Objects.- 4.4.2 Schlieren Systems with Scanning Light Source and Cutoff.- 4.5 Moiré-Fringe Methods.- 4.6 Holographic and Tomographic Schlieren.- 5 Specialized Schlieren Techniques.- 5.1 Special Schlieren CutoffsIll.- 5.1.1 Graded Filters.- 5.1.2 Exponential Cutoffs and Source Filters.- 5.1.3 Matched Spatial Filters at Source and Cutoff.- 5.1.4 Phase Contrast.- 5.1.5 Photochromic and Photorefractive Cutoffs.- 5.2 Color Schlieren Methods.- 5.2.1 Reasons for Introducing Color.- 5.2.2 Conversion from Monochrome to Color Schlieren.- 5.2.3 Classification of Color Schlieren Techniques.- 5.2.4 Recent Developments.- 5.3 Stereoscopic Schlieren.- 5.4 Schlieren Interferometry.- 5.4.1 The Wollaston-Prism Shearing (Differential) Interferometer.- 5.4.2 Diffraction-Based Schlieren Interferometers.- 5.5 Computer-Simulated Schlieren.- 5.6 Various Specialized Techniques.- 5.6.1 Resonant Refractivity and the Visualization of Sound.- 5.6.2 Anamorphic Schlieren Systems.- 5.6.3 Schlieren Observation of Tracers.- 5.6.4 Two-View Schlieren.- 5.6.5 Immersion Methods.- 5.6.6 Infrared Schlieren.- 6 Shadowgraph Techniques.- 6.1 Background.- 6.1.1 Historical Development.- 6.1.2 The Role of Shadowgraphy.- 6.1.3 Advantages and Limitations.- 6.2 Direct Shadowgraphy.- 6.2.1 Direct Shadowgraphy in Diverging Light.- 6.2.2 Direct Shadowgraphy in Parallel Light.- 6.3 "Focused" Shadowgraphy.- 6.3.1 Principle of Operation.- 6.3.2 History and Terminology.- 6.3.3 Advantages and Limitations.- 6.3.4 Magnification, Illuminance, and the Virtual Shadow Effect.- 6.3.5 "Focused" Shadowgraphy in Ballistic Ranges.- 6.4 Specialized Shadowgraph Techniques.- 6.4.1 Large-Scale Shadowgraphy.- 6.4.2 Microscopic, Stereoscopic, and Holographic Shadowgraphy.- 6.4.3 Computed Shadowgraphy.- 6.4.4 Conical Shadowgraphy.- 7 Practical Issues.- 7.1 Optical Components.- 7.1.1 Light Sources.- 7.1.2 Mirrors.- 7.1.3 Schlieren Cutoffs and Source Filters.- 7.1.4 Condensers and Source Slits.- 7.1.5 The Required Optical Quality.- 7.2 Equipment Fabrication, Alignment, and Operation.- 7.2.1 Schlieren System Design Using Ray Tracing Codes.- 7.2.2 Fabrication of Apparatus.- 7.2.3 Setup, Alignment, and Adjustment.- 7.2.4 Vibration and Mechanical Stability.- 7.2.5 Stray Light, Self-Luminous Events, and Secondary Images.- 7.2.6 Interference from Ambient Airflows.- 7.3 Capturing Schlieren Images and Shadowgrams.- 7.3.1 Photography and Cinematography.- 7.3.2 Videography.- 7.3.3 High-Speed imaging.- 7.3.4 Front-Lighting.- 7.4 Commercial and Portable Schlieren Instruments.- 7.4.1 Soviet Instruments.- 7.4.2 Western Instruments.- 7.4.3 Portable Schlieren Apparatus.- 8 Setting Up Your Own Simple Schlieren and Shadowgraph System.- 8.1 Designing the Schlieren System.- 8.2 Determining the Cost.- 8.3 Choosing a Setup Location.- 8.4 Aligning the Optics.- 8.5 Troubleshooting.- 8.6 Recording the Schlieren Image or Shadowgram.- 8.7 Conclusion.- 9 Applications.- 9.1 Phenomena in Solids.- 9.1.1 Glass Technology.- 9.1.2 Polymer-Film Characterization.- 9.1.3 Fracture Mechanics and Terminal Ballistics.- 9.1.4 Specular Reflection from Surfaces.- 9.2 Phenomena in Liquids.- 9.2.1 Convective Heat and Mass Transfer.- 9.2.2 Liquid Surface Waves.- 9.2.3 Liquid Atomization and Sprays.- 9.2.4 Ultrasonics.- 9.2.5 Water Tunnel Testing and Terminal Ballistics.- 9.3 Phenomena in Gases.- 9.3.1 Agricultural Airflows.- 9.3.2 Aero-Optics.- 9.3.3 Architectural Acoustics.- 9.3.4 Boundary Layers.- 9.3.5 Convective Heat and Mass Transfer.- 9.3.6 Heating, Ventilation, and Air-Conditioning.- 9.3.7 Gas Leak Detection.- 9.3.8 Electrical Breakdown and Discharge.- 9.3.9 Explosions, Blasts, Shock Waves, and Shock Tubes.- 9.3.10 Ballistics.- 9.3.11 Gas Dynamics and High-Speed Wind Tunnel Testing.- 9.3.12 Supersonic Jets and Jet Noise.- 9.3.13 Turbomachinery and Rotorcraft.- 9.4 Other Applications.- 9.4.1 Art and music.- 9.4.2 Biomedical Applications.- 9.4.3 Combustion.- 9.4.4 Geophysics.- 9.4.5 Industrial Applications.- 9.4.6 Materials Processing.- 9.4.7 Microscopy.- 9.4.8 Optical Processing.- 9.4.9 Optical Shop Testing.- 9.4.10 Outdoor Schlieren and Shadowgraphy.- 9.4.11 Plasma Dynamics.- 9.4.12 Television Light Valve Projection.- 9.4.13 Turbulence.- 10 Quantitative Evaluation.- 10.1 Quantitative Schlieren Evaluation by Photometry.- 10.1.1 Absolute Photometric Methods.- 10.1.2 Standard Photometric Methods.- 10.2 Grid-Cutoff Methods.- 10.2.1 Focal Grids.- 10.2.2 Defocused Grids.- 10.2.3 Defocused Filament Cutoff.- 10.3 Quantitative Image Velocimetry.- 10.3.1 Background.- 10.3.2 Multiple-Exposure Eddy and Shock Velocimetry.- 10.3.3 Schlieren Image Correlation Velocimetry.- 10.3.4 Focusing Schlieren Deflectometry.- 10.3.5 The Background-Oriented Schlieren System.- 10.4 Quantitative Shadowgraphy.- 10.4.1 Double Integration of ð2n/ ðy2.- 10.4.2 Turbulence Research.- 10.4.3 Shock-Wave Strength Quantitation.- 10.4.4 Grid Shadowgraphy Methods.- 11 Summary and Outlook.- 11.1 Summary.- 11.1.1 Perceptions Outside the Scientific Community.- 11.1.2 Other Lessons Learned.- 11.1.3 Further Comments on Historical Development.- 11.1.4 Further Comments on Images and Visualization.- 11.1.5 Renewed Vitality.- 11.2 Outlook: Issues for the Future.- 11.2.1 Predictions.- 11.2.2 Opportunities.- 11.2.3 Recommendations.- 11.3 Closing Remarks.- References.- Appendix A Optical Fundamentals.- A. 1 Radiometry and Photometry.- A.2 Refraction Angle 8.- A.2.1 Small Optical Angles and Paraxial Space.- A.2.2 Huygens' P…