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Schlieren, Shadowgraph and Direct Photography
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Dr. Mazlan Abdul WahidFaculty of Mechanical EngineeringUniversiti Teknologi Malaysia
www.fkm.utm.my/~mazlan
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Deflection of Light Rays
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
• Looking through a fluid
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
• Shadowgraph - measure • Schlieren - measure• Mach-Zendner Interferometer - measure phase-shift
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Schlieren vs. Shadowgraph
• Displays a mere shadow • Displays a focused image
Shadowgraph Schlieren
xn
∂∂2n∂
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
• Displays a mere shadow
• Shows light ray displacement
• Illuminance level responds to
• No knife edge used
• Displays a focused image
• Shows ray refraction angle, ε• Illuminance level responds to
• Knife edge used for cutoff
x∂2
2
xn
∂∂
Schlieren Technique
• From German word “schlire” denotes optical inhomogeneitiesglass, which causes an irregular light deflection (Merzkirch, 1987).
• Robert Hooke (1635-1703) observed atmospheric refraction (Rienitz, 1997)
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
(Rienitz, 1997) • Attributed to Focault (1859) and Toepler (1864)• Focault developed the knife-edge test for telescope mirrors • Elaborated by Toepler, now often referred to as the “Toepler
method”• Ph.D. thesis by Schardin (1933), “The Toepler Schlieren
Technique – Principles for its Application and Quantitative Evaluation”
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Schlieren Technique
• Idea: Introduce knife edge at focal point– light bent down is removed darker-spots
– light bent up is kept brighter-spots
• Direction of density gradient known
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
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Publication related to schlieren application in thermofluid are
• Experiments in Fluids
• Shock Wave
• Fluid Dynamics
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
• Fluid Dynamics
• Journal of Engineering Physics and Thermophysicsand
• Combustion, Explosion, and Shock Waves.
Models of Light
8o 3x10cV ≈= m/s
Physical (wave) modelWave Peaks
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Geometric model
Light Rays
Light From a Point Source
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Speed of Light in a Medium
Index of Refraction:
c
cn o= c = speed of light in the medium
Typical values:
Medium n = c /cFor gases:
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Medium n = co/c
Air 1.0003
Water 1.33
Crown glass 1.52
Plexiglas 1.51
Diamond 2.42
kρ1n +=
= gas densityρ
k = 0.23 cm3/g for air
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Light Refraction
Medium 1
1θ
21 nn <
Snell’s Law:
2211 θsin nθsin n =
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Medium 2
2θ
Example, Refraction in Water
Water Surface
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Pole
Lenses
Focus
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The Basic Schlieren System
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Point Source
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The Real Schlieren System
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Extended Source
Schlieren Image
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Schlieren Image
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Mirrors
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Z-type Schlieren System
Light Source
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1st Field Mirror 2nd Field Mirror
Screen/Instrument PanelTest SectionKnife Edge
Light Source
LampCondenser Lens
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Section A-A
A-A
Setting Up The Schlieren System
Step 1: Find the focal length of the field mirrors
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Focal Length
Setting Up The Schlieren System
Step 2: Set up the first field mirrorLight Source
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1st Field Mirror
Test Section
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Setting Up The Schlieren System
Step 3: Set up the second field mirrorLight Source
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1st Field Mirror
Test Section
2nd Field Mirror
Screen/Instrument Panel
Setting Up The Schlieren System
Step 4: Set up the knife edge
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Focus the source image on the knife
Adjust the cutoff Obtain a uniform darkening of the image
Uniform Darkening
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Knife edge too close to second field mirror
Knife edge too far from second field mirror
Uniform darkening
Schlieren in Combustion• Durox and Ducruix (1999) performed an experiment to study the schlieren
limit in premixed flames of CH4 and air.
• Study on the position of a schlieren image of an axisymmetric premixed flame, in three cases: a flat flame, a flame concave towards the fresh gases and, on the contrary, towards the burnt gases
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Experimental set-up on location of the Schliren limit in premixed flames
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• Takizawa et al (2005) has measured burning velocity of four hydrofluorocarbons (HFCs), i.e., difluoromethane (HFC-32), 1,1,2-trifluoroethane (HFC-143), 1,1,1-trifluoroethane (HFC-143a), and 1,1-difluoroethane (HFC-152a) using the spherical-vessel (SV) method
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Experimental and optical set-up
• Ilbas et al. (2006) has measured laminar flame velocities of hydrogen–air and different composition of hydrogen–methane–air mixtures (from 100% hydrogen to 100% methane) at ambient temperatures for variable equivalence ratios (ER = 0.8-3.2)
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006Experimental and optical set-up on
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Ilbas et al. (2006) schlieren photographs for different fuel compositions, ∅∅∅∅= 1.0. (a) 100% CH4; (b) 30% H2 + 70% CH4; (c) 70% H2 + 30% CH4; (d) 100% H2.
Application of Rainbow Schlieren Deflectometry (RSD) in Combustion
• Greenberg et al. (1995) developed quantitative Rainbow Schlieren Deflectometry (RSD) technique utilizing computer-
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Schlieren Deflectometry (RSD) technique utilizing computer-based imaging approach
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• Al-Ammar et al. (1998) used rainbow schlieren deflectometry technique to measure oxygen concentrations in a laminar, isothermal helium jet discharged vertically into ambient air.
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
rainbow schlieren image of the helium jet Experimental and optical set-up on
• Flow structure of a flickering gas-jet diffusion flame was investigated by Albers and Agrawal (1999) using quantitative rainbow schlieren deflectometry (RSD).
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Experimental and optical set-up on
• Ibaretta et al. (2005) determined the premixed sooting flame speed of an ethylene/air mixture using two quasi-onedimensional flame configurations: a counterflow configuration in normal gravity and a spherical flame in microgravity
• A compact rainbow Schlieren deflectometry (RSD) system was developed and utilized to characterize the flame radius and temperature field
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
• In 2006, Ibaretta et al. conducted an experiment to characterize premixed spherical ethylene/air flames under sooting condition
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
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Ibaretta et al. (2006) sample time sequence of a microgravity drop (Φ = 3.5 and
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Ibaretta et al. (2006) sample time sequence of a microgravity drop (Φ = 3.5 and =0.046 g/s). Top panels: direct imaging; bottom panels: RSD imaging. Time t = 0 corresponds to the release of the drop package. Ignition occurred at –0.5 s before the drop. The retractable igniter is seen in the first frame of the RSD image. The minor asymmetry on the left side of the RSD image is caused by the intrusion of
the thermocouple.Experimental and optical set-up on
Advantages
• Simple and able to provide quantitative information under sooting conditions.
• Can be used to obtain the entire temperature field of a symmetric flow field from a single image.
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
symmetric flow field from a single image.
Schlieren in Shock Wave Phenomena
• Ernst Mach was the person who observed and took the first photograph of shock waves (Weistein and Settles, 2003)
• In 1996, Weinstein patented system of schlieren system for moving objects. The basic components of the system comprises:
• 1) A vertical line light source
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
• 1) A vertical line light source• 2) An imaging lens• 3) A vertical cut-off knife edge and • 4) A moving film strip or other detector matching the motion of the
image of the test subject. The imaging lens, detector format, and subject distance determines the field of view
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Diagram of the large-field scanning schlieren system
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Weistein and Settles (2003) of scanning-camera schlieren for aircraft in flight is shown
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Weistein and Settles (2003) schlieren for Aircraft-in-flight image of T-38 aircraft at
Mach 1.1 and 9.6 km slant range
Schlieren in Fluids Flow Phenomena
• Tanda and Devia (1998) applied the quantitative schlierentechnique to the study of two-dimensional free convection heat transfer.
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Experimental and optical set-up on
Tanda and Devia (1998) curves of equal light displacement D for natural convection on a single heated vertical plate (Tw-T∞=20.9 K, Ra=5x105)
• Garg and Settles (1998) described novel, non-intrusive, high-frequency, localized optical measurements of turbulence incompressible flows. The technique is based upon focusingschlieren optics coupled with high-speed quantitativemeasurement of light intensity fluctuations in the schlieren image.
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Venkatakrishnan and Meier (2004) the background dot pattern a) without the flow and b) with the flow
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Venkatakrishnan and Meier (2004) a) experimental geometry of a cone-cylinder in the 0.3 m tunnel. b)
Schematic of experimental set-upVenkatakrishnan and Meier (2004) computed Schlieren (horizontal
knife-edge)
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FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Meier (2002) supersonic jet from a rectangular nozzle (experiment by M. Rein, DLR). The top image is a real schlieren picture (taken with a horizontal
knife) of the supersonic jet. The middle frame shows in comparison the density gradient field of the same jet.
Elsinga et al. (2004) color schlieren image of the Mach 2 supersonic flow
around the 2D wedge-plate model
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Elsinga et al. (2004) The Prandtl-Meyer expansion.
• The schlieren technique has proven to be particularly well suited in fluids and combustion and has been widely implemented.
• Newer variations of this technique have extended it to wide range of applications, from examining the free convection of air to visualizing the shock waves about aircraft in flight.
• Many recent developments have expanded the optical techniques. The development of digital cameras and
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
techniques. The development of digital cameras and computers give a new tool to take and enhance schlieren images, so that improved image quality and sensitivity are obtained.
• The combination of old and new schlieren techniques, and the wide range of problems could be used to study, should result in expanded use of schlieren as diagnostic tool in the near future.
SHADOWGRAPH
• Optical method which that reveals non-uniformities in transparent media like glass, water and air.
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
• Example� the plume of hot air rising from a fire can be seen by way of its shadow cast upon a nearby surface by the uniform sunlight.
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• The result or image captured by the shadowgraph technique is known as a shadowgram
• In the shadowgram, the differences in light intensity are proportional to the second spatial derivative (Laplacian) of the refractive index
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
derivative (Laplacian) of the refractive indexfield in the transparent medium under study
HISTORY
• Johann Wiesel (the first optician in Germany to make microscopes as well as telescopes) was the first person that using the shadowgraph technique. Johann was found to
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
shadowgraph technique. Johann was found to use the technique to see the state of cataracts, a clouding of the lens of the eye, so that the user can see when an operation is required.
• The sunlight shadowgraphy was first scientifically demonstrated by Robert Hooke
• �Discovered this effect while observing the shadow of a burning candle cast by sunlight. He saw a plume of hot air above the flame that cast a shadow because the heat changes the density of the air, which refracts light rays.
• The infamous Jean Paul Marat who first used it
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
• The infamous Jean Paul Marat who first used it to study fire.
• Then Settles was the person who given a modern account in the shadowgraphytechnique.
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
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PRINCIPLE
• The parallel light or a parallel beam of light is passed through the flow in a test section and projected on the screen or a photographic film.
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
photographic film.
• The irradiance depends on the second derivative of the refractive index or density of the flow fluid.
• Refractive disturbanceof lateral size d occurs at distance g from a screen upon which the shadowgramis cast
SUNLIGHT SHADOWGRAPH
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
shadowgramis cast • Irrespective of standoff
distance g, ray deflections by the refractive disturbance must compete with a substantial blur angle in order to be visible
APPLICATION
• Combustion measurement, shadowgraph usually used to monitor or visualized the flame characteristics which is hardly defined by other method.
• Flow visualization; to get the physical picture of complicated phenomenon which is usually a
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
complicated phenomenon which is usually a transparent image.
• Without a conceptual image, working with fluid and gases is like working with solid objects in darker
Lenses
Shadowgraph
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Point Source
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Direct Shadowgraphy
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Point Source
Bubble of high density gas
Direct Shadowgraphy
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Shadowgraph Image
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Shadowgraph Technique
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Some Notes
• The angle between the illuminator axis and the collimated beam should be kept to a minimum– Coma: Smearing of the mirror focus into a comet shape (cancelled out by
tilting the mirrors in opposite directions, i.e. z-type system)
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
– Astigmatism: Changes the focus into two short lines perpendicular to each other (limited by orienting the knife edge the same as the light source)
• A sheet of white paper is a good alignment tool
• A threaded bolt works well as a focusing tool
• The schlieren technique is well suited in fluids andcombustion and has been widely implemented.
• Newer variations of this technique have extended it towide range of applications, from examining the freeconvection of air to visualizing the shock waves aboutaircraft in flight.
• Many recent developments have expanded the opticaltechniques. The development of digital cameras andcomputersgive a new tool to takeandenhanceschlierenimages,sothatimprovedimagequality andsensitivityare
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
computersgive a new tool to takeandenhanceschlierenimages,sothatimprovedimagequality andsensitivityareobtained.
• The combination of old and new schlieren techniques,and the wide range of problems could be used to study,should result in expanded use of schlieren as diagnostictool in the near future.
Direct Photography
FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
Direct Photography
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Direct Photography
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An experimental setup of fan stirred bomb facility at Leeds University tostudy the premixed turbulent flame of various mixtures
Soot photographsSoot photographs
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Wild forest firesWild forest fires
Alaska forest fires Canada forest fires
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Alaska forest fires Canada forest fires
US wild forest fireFKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006
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References
• G.S. Settles, Schlieren & Shadowgraph Techniques, Springer-Verlag, 2001.
• D.C. Giancoli, Physics for Scientists & Engineers, Prentice Hall, 1988.
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Hall, 1988.