Schlieren, Shadowgraph and Direct Photographymazlan/?download=TFMD+Schlieren... · schlieren images, so that improved image quality and sensitivity are obtained. • The combination

1

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


Deflection of Light Rays


• Looking through a fluid


• Shadowgraph - measure • Schlieren - measure• Mach-Zendner Interferometer - measure phase-shift

2

Schlieren vs. Shadowgraph

• Displays a mere shadow • Displays a focused image

Shadowgraph Schlieren

xn

∂∂2n∂


• 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)


(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”


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


3

Publication related to schlieren application in thermofluid are

• Experiments in Fluids

• Shock Wave

• Fluid Dynamics


• Fluid Dynamics

• Journal of Engineering Physics and Thermophysicsand

• Combustion, Explosion, and Shock Waves.

Models of Light

8o 3x10cV ≈= m/s

Physical (wave) modelWave Peaks


Geometric model

Light Rays

Light From a Point Source


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:


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

4

Light Refraction

Medium 1

1θ

21 nn <

Snell’s Law:

2211 θsin nθsin n =


Medium 2

2θ

Example, Refraction in Water

Water Surface


Pole

Lenses

Focus


The Basic Schlieren System


Point Source

5

The Real Schlieren System


Extended Source

Schlieren Image


Schlieren Image


Mirrors


6

Z-type Schlieren System

Light Source


1st Field Mirror 2nd Field Mirror

Screen/Instrument PanelTest SectionKnife Edge

Light Source

LampCondenser Lens


Section A-A

A-A

Setting Up The Schlieren System

Step 1: Find the focal length of the field mirrors


Focal Length


Step 2: Set up the first field mirrorLight Source


1st Field Mirror

Test Section

7


Step 3: Set up the second field mirrorLight Source


1st Field Mirror

Test Section

2nd Field Mirror

Screen/Instrument Panel


Step 4: Set up the knife edge


Focus the source image on the knife

Adjust the cutoff Obtain a uniform darkening of the image

Uniform Darkening


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


Experimental set-up on location of the Schliren limit in premixed flames

8

• 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


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


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-


Schlieren Deflectometry (RSD) technique utilizing computer-based imaging approach

9

• 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.


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).


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


• In 2006, Ibaretta et al. conducted an experiment to characterize premixed spherical ethylene/air flames under sooting condition


10

Ibaretta et al. (2006) sample time sequence of a microgravity drop (Φ = 3.5 and


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.


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


• 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


Diagram of the large-field scanning schlieren system

11

Weistein and Settles (2003) of scanning-camera schlieren for aircraft in flight is shown


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.


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.


Venkatakrishnan and Meier (2004) the background dot pattern a) without the flow and b) with the flow


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)

12


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


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


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.


• 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.

13

• 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


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


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


• 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.


14

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.


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


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


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


Point Source

15

Direct Shadowgraphy


Point Source

Bubble of high density gas

Direct Shadowgraphy


Shadowgraph Image

FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006 FKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006

Shadowgraph Technique

16



17

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)


– 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


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


Direct Photography


18

Direct Photography


An experimental setup of fan stirred bomb facility at Leeds University tostudy the premixed turbulent flame of various mixtures

Soot photographsSoot photographs



19


Wild forest firesWild forest fires

Alaska forest fires Canada forest fires


Alaska forest fires Canada forest fires

US wild forest fireFKM UTM FKM UTM Thermal Fluid Measurement and Diagnostic MMJ 2413 DR MAZLAN 2006

20


References

• G.S. Settles, Schlieren & Shadowgraph Techniques, Springer-Verlag, 2001.

• D.C. Giancoli, Physics for Scientists & Engineers, Prentice Hall, 1988.


Hall, 1988.

Documents

Schlieren, Shadowgraph and Direct Photographymazlan/?download=TFMD+Schlieren... · schlieren images, so that improved image quality and sensitivity are obtained. • The combination