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Gary S. Settles - One of the best experts on this subject based on the ideXlab platform.

  • Schlieren imaging: a powerful tool for atmospheric plasma diagnostic
    EPJ Techniques and Instrumentation, 2018
    Co-Authors: Enrico Traldi, Marco Boselli, Emanuele Simoncelli, Augusto Stancampiano, Matteo Gherardi, Vittorio Colombo, Gary S. Settles
    Abstract:

    Schlieren imaging has been widely used in science and technology to investigate phenomena occurring in transparent media. In particular, it has proven to be a powerful tool in fundamental studies and process optimization for atmospheric pressure plasma diagnostics, providing qualitative and (in some cases) also quantitative information on the fluid-dynamic characteristics of plasmas generated by many different types of sources. However, obtaining significant and reliable results by Schlieren imaging can be challenging, especially when considering the variety of geometries and applications of atmospheric pressure plasma sources. Therefore, it is necessary to adopt solutions that can address the specific issues of different plasma-assisted processes. In this paper, an overview on the use of the Schlieren imaging technique for atmospheric pressure plasma characterization is presented. In the first part, the physical principles behind this technique and the different setups that can be adopted to perform it are presented. In the second part, examples of Schlieren imaging applied to different kinds of atmospheric pressure plasmas (non-equilibrium plasma jets, plasma actuators for flow control and thermal plasma sources) are presented, showing how it was used to characterize the fluid-dynamic behavior of plasma-assisted processes and reporting best practices in performing this diagnostic technique.

  • Schlieren and shadowgraph techniques visualizing phenomena in transparent media
    2012
    Co-Authors: Gary S. Settles, E E Covert
    Abstract:

    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 Moire-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 d2n/ dy2.- 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' Principle and Refraction.- A.3 Optical Components and Devices.- A.3.1 Conjugate Optical Planes.- A.3.2 Lensf/number.- A.3.3 The Thin-Lens Approximation.- A.3.4 Viewing Screens and Ground Glass.- A.3.5 Optical Density.- A.4 Optical Aberrations.- A.5 Light and the Human Eye.- A.6 Geometric Theory of Light Refraction by a Schliere.- Appendix B The Schlieren System as a Fourier Optical Processor.- B. 1 The Basic Fourier Processor with no Schlieren Present.- B.2 The Addition of a Schlieren Test Object.- B.3 The Schlieren Cutoff.- B.4 Other Spatial Filters.- B.5 Partially-Coherent and Polychromatic Illumination.- Appendix C Parts List for a Simple Schlieren/ Shadowgraph System.- C.l Optics.- C.2 Illumination.- C.3 Miscellaneous Components.- C.4 Optical Mounts.- Appendix D Suppliers of Schlieren Systems and Components.- D.l Complete Schlieren Systems.- D.2 Schlieren Field Mirrors.- D.3 Light Sources.- D.4 Components.- D.5 Focusing Schlieren Lenses.- D.6 Miscellaneous.- Color Plates.

  • a comparison of three quantitative Schlieren techniques
    Optics and Lasers in Engineering, 2012
    Co-Authors: Michael Hargather, Gary S. Settles
    Abstract:

    Abstract We compare the results of three quantitative Schlieren techniques applied to the measurement and visualization of a two-dimensional laminar free-convection boundary layer. The techniques applied are Schardin's “calibrated” Schlieren technique, in which a weak lens in the field-of-view provides a calibration of light deflection angle to facilitate quantitative measurements, “rainbow Schlieren”, in which the magnitude of Schlieren deflection is coded by hue in the image, and “background-oriented Schlieren” (BOS), in which quantitative Schlieren-like results are had from measuring the distortion of a background pattern using digital-image-correlation software. In each case computers and software are applied to process the data, thus streamlining and modernizing the quantitative application of Schlieren optics. (BOS, in particular, is only possible with digital-image-correlation software.) Very good results are had with the lens-calibrated standard Schlieren method in the flow tested here. BOS likewise produces good results and requires less expensive apparatus than the other methods, but lacks the simplification of parallel light that they feature. Rainbow Schlieren suffers some unique drawbacks, including the production of the required rainbow cutoff filter, and provides little significant benefit over the calibrated Schlieren technique.

  • Seedless Velocimetry Measurements by Schlieren Image Velocimetry
    AIAA Journal, 2011
    Co-Authors: Michael Hargather, Gary S. Settles, Michael J. Lawson, Leonard M. Weinstein
    Abstract:

    Schlieren optical systems have been used to perform velocity measurements in refractive turbulent flows using particle image velocimetry algorithms. This Schlieren image velocimetry (Schlieren "particle image velocimetry") technique makes use of naturally occurring refractive turbulent eddies in a flow as virtual "seed particles" upon which velocimetry is performed. Current experiments are performed in a supersonic wind tunnel to measure the Mach 3 turbulent boundary-layer mean velocity profile. Results from Schlieren, shadowgraph, and focusing Schlieren image velocimetry are compared with the boundary-layer velocity profile derived from a pitot-pressure survey. Focusing Schlieren optics allow the visualization of refractive disturbances within a limited depth of focus, resulting in seedless velocimetry within a narrower depth of field. The natural intermittency of the turbulent boundary layer complicates Schlieren image velocimetry, but useful measurements are still possible. The velocity profile in a subsonic turbulent boundary layer is also measured using this technique through thermal seeding of the boundary layer to provide refractive turbulent structures for velocimetry. An important improvement in Schlieren image velocimetry, the use of a pulsed light-emitting-diode light source in place of the twin pulsed lasers required for traditional particle image velocimetry measurements, is introduced. This comparatively inexpensive white-light source eliminates traditional problems of coherent laser illumination in Schlieren imaging and improves the overall results.

  • recent developments in Schlieren and shadowgraphy
    27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, 2010
    Co-Authors: Michael Hargather, Gary S. Settles
    Abstract:

    Schlieren and shadowgraph techniques are hundreds of years old, yet several important developments have occurred in the last decade, as summarized in this paper. Progress has been made in using the turbulent eddies of a refractive flow as “particle” tracers for seedless velocimetry. This approach will never supplant standard PIV, but “Schlieren PIV” can be useful, for example, in cases where particles cannot be seeded in a turbulent flow under study. Background-oriented Schlieren (BOS) has become very popular in just a few years. Given modern image-processing software for PIV or digital image correlation, a digital camera and a proper background, Schlieren-like images of all sorts are easy to make without parabolic mirrors or even a knife-edge. “Rainbow Schlieren” is the name for a quantitative Schlieren instrument that uses color to make density, temperature, or species measurements in steady and unsteady planar or axisymmetric flows. Data acquisition and reduction are highly automated and the range of applications is very broad. Finally, shadowgraphy has not been forgotten: it is the simplest of all the optical flow visualization methods, but is often the best choice for imaging shock waves and turbulence. The addition of a retroreflective screen and a high-speed camera makes direct shadowgraphy a robust tool for the study of large-scale events in harsh environments.

Kazuo Maeno - One of the best experts on this subject based on the ideXlab platform.

  • Improvement in spatial resolution of background-oriented Schlieren technique by introducing a telecentric optical system and its application to supersonic flow
    Experiments in Fluids, 2015
    Co-Authors: Masanori Ota, Friedrich Leopold, Ryusuke Noda, Kazuo Maeno
    Abstract:

    A telecentric optical system is applied to the background-oriented Schlieren (BOS) technique to improve accuracy, overcoming the drawbacks of conventional diverging light observation. This paper describes the optical arrangement and formula for telecentric BOS measurement and presents measurement results obtained by the colored-grid background-oriented Schlieren technique to confirm the theoretical prediction. The application of the new approach for a large-scale supersonic wind tunnel test is reported.

  • quantitative measurement and reconstruction of 3d density field by cgbos colored grid background oriented Schlieren technique
    2012
    Co-Authors: Masanori Ota, Hiroko Kato, Ryuki Sakamoto, Kazuo Maeno
    Abstract:

    The Background Oriented Schlieren (BOS) technique was proposed by Meier [1], and it enables us to have the quantitative density measurement with computer-aided image analysis. In the past several years, BOS technique had applied to various experiments [2],[3]. The principle of BOS is similar to conventional Schlieren technique, it exploit the bending of light caused by refractive index change corresponding to density change in the medium and both techniques are sensitive to density gradient. Conventional Schlieren technique employs many optical elements - pinhole, concave mirror, knife edge or color filter, camera...etc, however it is difficult to realize quantitative measurement and this technique is commonly used for qualitative measurement like flow visualization. On the other hand BOS requires only a background and a digital still camera and it can realize the quantitative measurement of density.

  • comparison between cbos colored background oriented Schlieren and cgbos colored grid background oriented Schlieren for supersonic flow
    2012
    Co-Authors: Masanori Ota, Friedrich Leopold, F Jagusinski, Kazuo Maeno
    Abstract:

    The Background Oriented Schlieren (BOS) technique is one of the novel visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup (1). The principle of BOS is similar to conventional Schlieren technique and both techniques are sensible to density gradient. In recent years, CBOS (Colored Background Oriented Schlieren) technique using colored random dot pattern for background is developed to improve the performance of conventional BOS technique using monochromatic random dot pattern, and it is applied to various measurements of flow (2). On the other hand, Colored- Grid Background Oriented Schlieren (CGBOS) technique using colored-grid pattern for background is developed and applied to measurement of supersonic flow field and reconstruction of 3D density field (3). CGBOS is based on the image processing technique developed for the analysis of finite-fringe interferogram and using color information is based on the ideas of CBOS technique. In this report comparison of the measurement result between CBOS and CGBOS will be reported. Measurements of Mach 3.0 flow around a blunt body with a spike were performed for both CBOS and CGBOS at supersonic wind tunnel at ISL with same optical arrangements. The difference is only background and image processing procedure. Figure 1 shows pseudo-color images of vertical displacement obtained from CBOS (left) and CGBOS (center), and plots of calculated displacement on x-axis (y = 2100 pixel) in pseudo-color image. Resultant displacement from both techniques agrees very well. Detailed analysis between two techniques will be very important for the future development of BOS technique.

  • computed tomographic density measurement of supersonic flow field by colored grid background oriented Schlieren cgbos technique
    Measurement Science and Technology, 2011
    Co-Authors: Masanori Ota, Kenta Hamada, Hiroko Kato, Kazuo Maeno
    Abstract:

    The background oriented Schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. The principle of BOS is similar to the conventional Schlieren technique, which exploits the bending of light caused by refractive index change corresponding to density change in the medium and both techniques are sensible to density gradient. In this report we propose colored-grid background oriented Schlieren (CGBOS) technique. The experiments were carried out in a supersonic wind tunnel of test section size 0.6 × 0.6 m2 at JAXA-ISAS. A colored-grid pattern was used as background image and density gradient in vertical and horizontal direction was obtained. Computed tomographic reconstructions of 3D density information of the supersonic flow field around an asymmetric body from multi-directional CGBOS images were examined.

  • three dimensional density measurement and reconstruction of asymmetric flow field by colored grid background oriented Schlieren cgbos technique
    29th AIAA Applied Aerodynamics Conference, 2011
    Co-Authors: Masanori Ota, Kenta Hamada, Hiroko Kato, Ryuki Sakamoto, Kazuo Maeno
    Abstract:

    The background oriented Schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. The principle of BOS is similar to conventional Schlieren technique, it exploit the bending of light caused by refractive index change corresponding to density change in the medium and both techniques are sensible to density gradient. In this report we propose the Colored Grid Background Oriented Schlieren (CGBOS) technique. The experiments were carried out in the 0.6 m × 0.6 m test section of supersonic wind tunnel at JAXA-ISAS. A colored grid pattern was used as background image and density gradient in vertical and horizontal direction was obtained. Computed tomographic reconstruction of 3D density information of supersonic flow field around asymmetric body from multidirectional CGBOS images is examined.

Markus Raffel - One of the best experts on this subject based on the ideXlab platform.

  • Background-oriented Schlieren (BOS) techniques
    Experiments in Fluids, 2015
    Co-Authors: Markus Raffel
    Abstract:

    This article gives an overview of the background-oriented Schlieren (BOS) technique, typical applications and literature in the field. BOS is an optical density visualization technique, belonging to the same family as Schlieren photography, shadowgraphy or interferometry. In contrast to these older techniques, BOS uses correlation techniques on a background dot pattern to quantitatively characterize compressible and thermal flows with good spatial and temporal resolution. The main advantages of this technique, the experimental simplicity and the robustness of correlation-based digital analysis, mean that it is widely used, and variant versions are reviewed in the article. The advantages of each variant are reviewed, and further literature is provided for the reader.

  • blade tip vortex detection in maneuvering flight using the background oriented Schlieren technique
    Journal of Aircraft, 2014
    Co-Authors: Andre Bauknecht, Christoph B Merz, Markus Raffel, Andrin Landolt, Alexander H Meier
    Abstract:

    The background-oriented Schlieren technique was used to visualize the blade-tip vortices of a Eurocopter AS532UL Cougar helicopter in maneuvering flight. The test program covered a large part of the flight envelope, including maneuvers such as hover flight, fast forward flight, flare maneuvers, and high-speed turns. For selected flight conditions, the aerodynamic results are presented here. It is shown that, with the reference-free background-oriented Schlieren method, the detection of vortex filaments up to vortex ages of ψv=540  deg is possible. The visualization of the vortex system is used to detect aerodynamic phenomena such as blade–vortex interactions, vortex–airframe interactions, and the occurrence of smooth sinuous disturbances. A detailed description of the applied reference-free background-oriented Schlieren setup is given, and the suitability of different natural backgrounds for the background-oriented Schlieren method is analyzed.

  • principle and applications of the background oriented Schlieren bos method
    Measurement Science and Technology, 2001
    Co-Authors: Hugues Richard, Markus Raffel
    Abstract:

    The practical aspects of an advanced Schlieren technique, which has been presented by Meier (1999) and Richard et al (2000) and in a similar form by Dalziel et al (2000), are described in this paper. The application of the technique is demonstrated by three experimental investigations on compressible vortices. These vortices play a major role in the blade vortex interaction (BVI) phenomenon, which is responsible for the typical impulsive noise of helicopters. Two experiments were performed in order to investigate the details of the vortex formation from the blade tips of two different helicopters in flight: a Eurocopter BK117 and a large US utility helicopter. In addition to this, simultaneous measurements of velocity and density fields were conducted in a transonic wind tunnel in order to characterize the structure of compressible vortices. The background oriented Schlieren technique has the potential of complementing other optical techniques such as shadowgraphy or focusing Schlieren methods and yields additional quantitative information. Furthermore, in the case of helicopter aerodynamics, this technique allows the effect of Reynolds number on vortex development from blade tips to be studied in full-scale flight tests more easily than through the use of laser-based techniques.

D. Klatt - One of the best experts on this subject based on the ideXlab platform.

  • Reconstruction of the density field using the Colored Background Oriented Schlieren Technique (CBOS)
    Optics and Lasers in Engineering, 2012
    Co-Authors: F. Sourgen, F. Leopold, D. Klatt
    Abstract:

    Abstract In this paper the improved Background Oriented Schlieren technique called CBOS (Colored Background Oriented Schlieren) is described and used to reconstruct density fields of three-dimensional flows. The Background Oriented Schlieren technique (BOS) allows to measure the light deflection caused by density gradients in a compressible flow. For this purpose the local image displacements of the image of a background pattern observed through the flow is used. In order to increase the performance of the conventional Background Oriented Schlieren technique, the monochromatic background is replaced by a colored dot pattern. The different colors are treated separately using suitable correlation algorithms. Therefore, the accuracy and the spatial resolution can be increased. A tomographic reconstruction method is then used to reconstruct the density field in three-dimensional flows from CBOS measurements.

Masanori Ota - One of the best experts on this subject based on the ideXlab platform.

  • Improvement in spatial resolution of background-oriented Schlieren technique by introducing a telecentric optical system and its application to supersonic flow
    Experiments in Fluids, 2015
    Co-Authors: Masanori Ota, Friedrich Leopold, Ryusuke Noda, Kazuo Maeno
    Abstract:

    A telecentric optical system is applied to the background-oriented Schlieren (BOS) technique to improve accuracy, overcoming the drawbacks of conventional diverging light observation. This paper describes the optical arrangement and formula for telecentric BOS measurement and presents measurement results obtained by the colored-grid background-oriented Schlieren technique to confirm the theoretical prediction. The application of the new approach for a large-scale supersonic wind tunnel test is reported.

  • quantitative measurement and reconstruction of 3d density field by cgbos colored grid background oriented Schlieren technique
    2012
    Co-Authors: Masanori Ota, Hiroko Kato, Ryuki Sakamoto, Kazuo Maeno
    Abstract:

    The Background Oriented Schlieren (BOS) technique was proposed by Meier [1], and it enables us to have the quantitative density measurement with computer-aided image analysis. In the past several years, BOS technique had applied to various experiments [2],[3]. The principle of BOS is similar to conventional Schlieren technique, it exploit the bending of light caused by refractive index change corresponding to density change in the medium and both techniques are sensitive to density gradient. Conventional Schlieren technique employs many optical elements - pinhole, concave mirror, knife edge or color filter, camera...etc, however it is difficult to realize quantitative measurement and this technique is commonly used for qualitative measurement like flow visualization. On the other hand BOS requires only a background and a digital still camera and it can realize the quantitative measurement of density.

  • comparison between cbos colored background oriented Schlieren and cgbos colored grid background oriented Schlieren for supersonic flow
    2012
    Co-Authors: Masanori Ota, Friedrich Leopold, F Jagusinski, Kazuo Maeno
    Abstract:

    The Background Oriented Schlieren (BOS) technique is one of the novel visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup (1). The principle of BOS is similar to conventional Schlieren technique and both techniques are sensible to density gradient. In recent years, CBOS (Colored Background Oriented Schlieren) technique using colored random dot pattern for background is developed to improve the performance of conventional BOS technique using monochromatic random dot pattern, and it is applied to various measurements of flow (2). On the other hand, Colored- Grid Background Oriented Schlieren (CGBOS) technique using colored-grid pattern for background is developed and applied to measurement of supersonic flow field and reconstruction of 3D density field (3). CGBOS is based on the image processing technique developed for the analysis of finite-fringe interferogram and using color information is based on the ideas of CBOS technique. In this report comparison of the measurement result between CBOS and CGBOS will be reported. Measurements of Mach 3.0 flow around a blunt body with a spike were performed for both CBOS and CGBOS at supersonic wind tunnel at ISL with same optical arrangements. The difference is only background and image processing procedure. Figure 1 shows pseudo-color images of vertical displacement obtained from CBOS (left) and CGBOS (center), and plots of calculated displacement on x-axis (y = 2100 pixel) in pseudo-color image. Resultant displacement from both techniques agrees very well. Detailed analysis between two techniques will be very important for the future development of BOS technique.

  • computed tomographic density measurement of supersonic flow field by colored grid background oriented Schlieren cgbos technique
    Measurement Science and Technology, 2011
    Co-Authors: Masanori Ota, Kenta Hamada, Hiroko Kato, Kazuo Maeno
    Abstract:

    The background oriented Schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. The principle of BOS is similar to the conventional Schlieren technique, which exploits the bending of light caused by refractive index change corresponding to density change in the medium and both techniques are sensible to density gradient. In this report we propose colored-grid background oriented Schlieren (CGBOS) technique. The experiments were carried out in a supersonic wind tunnel of test section size 0.6 × 0.6 m2 at JAXA-ISAS. A colored-grid pattern was used as background image and density gradient in vertical and horizontal direction was obtained. Computed tomographic reconstructions of 3D density information of the supersonic flow field around an asymmetric body from multi-directional CGBOS images were examined.

  • three dimensional density measurement and reconstruction of asymmetric flow field by colored grid background oriented Schlieren cgbos technique
    29th AIAA Applied Aerodynamics Conference, 2011
    Co-Authors: Masanori Ota, Kenta Hamada, Hiroko Kato, Ryuki Sakamoto, Kazuo Maeno
    Abstract:

    The background oriented Schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. The principle of BOS is similar to conventional Schlieren technique, it exploit the bending of light caused by refractive index change corresponding to density change in the medium and both techniques are sensible to density gradient. In this report we propose the Colored Grid Background Oriented Schlieren (CGBOS) technique. The experiments were carried out in the 0.6 m × 0.6 m test section of supersonic wind tunnel at JAXA-ISAS. A colored grid pattern was used as background image and density gradient in vertical and horizontal direction was obtained. Computed tomographic reconstruction of 3D density information of supersonic flow field around asymmetric body from multidirectional CGBOS images is examined.

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