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Journal ArticleDOI

Visualization and analysis of muzzle flow fields using the Background-Oriented Schlieren technique

30 Mar 2020-Journal of Visualization (Springer Science and Business Media LLC)-Vol. 23, Iss: 3, pp 409-423
TL;DR: The implemented experimental high-speed BOS setup has demonstrated its ability to capture clearly the salient features of the precursor and the propellant gas flow fields and their interactions, confirming the BOS capability to visualize complex density flow fields.
Abstract: Several experimental and numerical studies on muzzle blast and flow fields have been performed. However, due to the extremely short duration and the spatiotemporal evolution of these flows, experimental quantitative techniques are limited. As a consequence, the number of validated numerical calculations is limited as well. On the other hand, despite the development of computer models that have succeeded in predicting the measured pressure and velocity, they show unrealistic temperatures and densities. Therefore, temperature and/or density measurements are required to validate these codes, thus the motivation of this research. The present paper focuses on the development of a density-sensitive and non-intrusive measurement technique and the implementation of a quantitative flow visualization method based on Background-Oriented Schlieren (BOS) combined with a high-speed camera. In BOS, the experimental setup of conventional Schlieren (mirrors, lenses, and knife-edge) is replaced by a background pattern and a single digital camera. The muzzle flow fields and the flow field around a 5.56-mm projectile in flight were successfully visualized. Indeed, the implemented experimental high-speed BOS setup has demonstrated its ability to capture clearly the salient features of the precursor and the propellant gas flow fields and their interactions. The captured structures such as vortex, barrel shock, Mach disk, and blast wave show a good agreement with that issued from a realized conventional Schlieren setup and the bibliography, confirming the BOS capability to visualize complex density flow fields.

Summary (2 min read)

1 Introduction

  • Essentially for these reasons, the numerical simulations studies took the challenge.
  • These approximations concern the propellant gas properties, the shock wave propagation model and the friction between the projectile and the barrel.
  • On the other hand, the interferometry is sensitive to the density and detects the arrival time delay.

2 Intermediate ballistics

  • The intermediate ballistics is a branch of ballistics that deals with the phenomena occurring during the transition of the projectile between the interior (in-bore combustion and acceleration of the projectile) and the exterior ballistics (flight dynamics of the projectile).
  • First, the muzzle flow field development and its interaction with the projectile influences its flight and control behavior (Jiang (2003)).
  • The expulsed air exiting from the barrel, derived by the accelerated projectile (piston effect), creates compression waves that coalesce into a normal shock wave.
  • This intercepting shock will be intercepted by a Mach disc across which demarcates the boundary between the supersonic and subsonic velocities.
  • On the other hand, when the projectile disengages from the muzzle, the combustion gas expands out into the surroundings and interacts with the precursor flow.

3 Background Oriented Schlieren Technique (BOS)

  • 1 Principles of the BOS 5 The Background Oriented Schlieren (BOS) technique originally proposed by Meier (Meier (2002)) is a quantitative measurement tool of refraction index gradients field in transparent media (mainly gas and liquid).
  • The set up of the BOS technique consists in a camera that focuses on a background (usually a random dot pattern)— hence the name background oriented— in order to record at least two images of the same background taken with (flow-on) and without (flow-off/tare) the investigated flow.
  • The resulting displacements fields are then used to reconstruct the object refraction index field.
  • The determination of the experimental set-up dimensions is essentially based on the calculation of the sensitivity and the spatial resolution in order to visualize a given flow.
  • As the technique developed, since 2000, several other types of backgrounds were proposed: the colored background (CBOS), the colored grid background and the wavelet noise (this is in addition of the natural background already used by Loose et al. (2000).

4 Results and Discussion

  • To examine the ability of the BOS technique to accurately capture the muzzle flow fields, several similar cases were chosen for a qualitative comparison.
  • In 10 MOUMEN et al Fig. 5 the BOS vertical, horizontal and the magnitude of the displacements are compared respectively with schlieren images with horizontal, vertical and circular knife edges.
  • In comparison with the main propellant flow, the precursor flow, which mainly air, has the advantage to be clearly visible through the various density sensitive visualization techniques.
  • This blast wave propagates mainly in the radial direction and partly in the rear direction where it is clearly visible.

5 Conclusion and perspectives

  • The muzzle flow field of a 5.56 mm gun was visualized based on the relatively novel technique the Background Oriented Schlieren.
  • The two distinct but interacting flow fields namely the precursor and propellant gas were successfully observed by this non-intrusive and quantitative technique.
  • The interactions between the different flows, blast waves, and the projectile were 17 discussed.
  • The results presented here confirm the ability of the cited technique to analyze the muzzle flow filed qualitatively and quantitatively.
  • Furthermore, its simplicity and unlimited field of view may make it a convenient tool for the visualization in the field of ballistic especially when large scale flows must be visualized such as large caliber muzzle flow field and projectile in flight.

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Journal of visualization manuscript No.
(will be inserted by the editor)
Visualization and analysis of muzzle flow fields using the
Background Oriented Schlieren technique
Abdelhafidh MOUMEN · Jurgen GROSSEN ·
Irene NDINDABAHIZI · Johan GALLANT
Received: date / Accepted: date
Abstract Several experimental and numerical studies on muzzle blast and flow fields have
been performed (Schmidt and Shear (1974), Schmidt and Shear (1975), Schmidt (1984),
Klingenberg and M. Heimerl (1992), Fansler (1997)). However, due to the extremely short
duration and the spatiotemporal evolution of these flows, experimental quantitative tech-
niques are limited (Klingenberg and M. Heimerl (1992)). As a consequence, the number
of validated numerical calculations is limited as well (Schmidt (1984)). On the other hand,
although the development of computer models that succeeded in predicting the pressure
and velocity measurement, they show at the same time different temperatures and densi-
ties (Celmins (1979)). Thus the motivation of this research. The present paper focuses on
the development of a density sensitive and non-intrusive measurement technique and the
implementation of a quantitative flow visualization method based on Background Oriented
Schlieren (BOS) (Meier (2002)) combined with a high-speed camera. In BOS, the exper-
imental set-up of conventional schlieren (mirrors, lenses, and knife-edge) is replaced by a
background pattern and a single digital camera (Raffel (2015)). The muzzle flow fields and
the flow field around a 5.56 mm projectile in flight were successfully visualized. Indeed, the
implemented experimental high-speed BOS set-up has demonstrated its ability to capture
clearly the salient features of the precursor and the propellant gas flow fields and their in-
teractions. The captured structures such as vortex, barrel shock, Mach disk, and blast wave
show a good agreement with that issued from a realized conventional Schlieren set-up and
the bibliography (Schmidt and Shear (1975), Klingenberg and M. Heimerl (1992)). Con-
firming the BOS capability to visualize complex density flow fields.
Keywords Intermediate ballistics · Flow visualization · Muzzle flow fields · Muzzle blast ·
Background Oriented Schlieren
Abdelhafidh MOUMEN
Department of Weapon systems and Ballistics, Royal Military Academy, avenue de la Renaissance 30, Brus-
sels, 1000, Belgium
E-mail: abdelhafidh.moumen@gmail.com

2 MOUMEN et al
1 Introduction
The determination of the muzzle flow filed properties is still a challenge owing to the com-
plexity of the phenomena and the extremely high spatiotemporal evolution. Indeed it occurs
within a sphere centered on the muzzle of a radius equal to 100 caliber during less than 10
ms. Thus, a lot of attention has been given to the investigation on intermediate ballistics.
First, it aims to understand the dynamics of blast and its interaction with the projectile since
it strongly affects its flight control and stability. Second, the deep insight into this process is
essential for the development of the muzzle devices aiming at the attenuation of unwanted
firearms effects such as the recoil and the sound. Thanks to several experimental studies
based upon flow visualization (Erdos and Del Guidice (1975), Schmidt and Shear (1975),
Merlen and Dyment (1991)), the muzzle flow field structures are relatively well known.
Nevertheless, due to the dusty propellant gas proprieties and the qualitative nature of the
aforementioned work, the near-field aerodynamics is not understood as well. Essentially for
these reasons, the numerical simulations studies took the challenge. On the other hand, due
to the complexity of the phenomena, numerical simulations have to adopt several assump-
tions. These approximations concern the propellant gas properties, the shock wave propaga-
tion model and the friction between the projectile and the barrel. Sweeping the bibliography,
we noticed several ambiguities between the most important publications in the domain. This
concerns mainly the dynamic shock wave interaction and the projectile/wave interaction.
The latter phenomenon is well known by the overtaking process. Thus these studies, aiming
at plotting the projectile aerodynamic forces and acceleration, resulted in several differences
(Jiang (2003), Watanabe et al. (1995), Rajesh et al. (2007a), Muthukumaran et al. (2012)). In
addition, in these studies, although the numerical simulation of the precursor flow matched
qualitatively those of the experimental flow visualization, the main propellant flow did not
match as well (Cler (2003)). All these cited residual ambiguities impose the need to conduct
a systematic study to get more quantitative data from the muzzle flow field.
In the present study, the objective is to visualize quantitatively the muzzle flow filed as
it expands into the surrounding atmosphere in order to get a deeper comprehension of these
phenomena. Furthermore, we will develop quantitative measurement techniques in order
to enhance the body of quantitative experimental data for the comparison with numerical
simulations that come in support of other studies dedicated to the development of muz-
zle devices and the determination of aerodynamic coefficients sets. Various non-intrusive
density-sensitive visualization techniques coupled with high-speed camera technology form
a potential diagnostic tool in this field. Indeed, the density gradient within the inspected
medium affects the light beam original path that it would have followed as for a uniform
density. This perturbation may be manifested and thus detected by several ways. The light
beam different impingement angles or places are detected by schlieren and shadowgraph
techniques which are sensitive to the first and the second derivatives of refraction index re-
spectively (Settles (2001)). On the other hand, the interferometry is sensitive to the density
and detects the arrival time delay. Due to its low-cost, simplicity, non-intrusive nature, and
unlimited field of view, allowing the visualization of large scale phenomena such as the fir-
ing of large-caliber weapons. The BOS is considered as the first potential quantitative flow
visualization to investigate the muzzle flow fields at the Accredited Ballistic Applications
Laboratory at the Royal Military Academy.

3
2 Intermediate ballistics
The intermediate ballistics is a branch of ballistics that deals with the phenomena occurring
during the transition of the projectile between the interior (in-bore combustion and acceler-
ation of the projectile) and the exterior ballistics (flight dynamics of the projectile). Despite
its limited space-time expanse it occurs in the vicinity of the muzzle during few microsec-
onds this area of research was always attractive for the ballistician. Indeed, the launch
of the projectile and the rapid discharge of a highly hot, compressed and reactive gas is of
paramount importance. First, the muzzle flow field development and its interaction with the
projectile influences its flight and control behavior (Jiang (2003)). Second, from an oper-
ational point of view, reducing the firearms signature such us flash (after-burning process)
and sound is important for the reduction of the signature of the troops in the battlefield.
Also, from a security stand, the muzzle blast effect and prediction have been extensively
studied in order to protect the crew, ammunition, and equipment (Schmidt (1984)). Almost
all interventions of the researchers in this part of the ballistics can be subdivided into two
parts (Klingenberg and M. Heimerl (1992)). A first part is rather chemical which is based
on the modification of the propellant powder via the adjunction of additives. The second is
rather mechanical which is based on the study and the development of muzzle devices. In
both cases, the successful improvement is only possible after the deep understanding of the
muzzle flow field.
In general, the muzzle flow field is characterized by two or three jet flows. Depending
upon the weapon interior ballistics and physical dimensions, before the projectile separation
from the tube, one or two precursor flow fields are formed in the vicinity of the muzzle.
Then after the projectile launch, the combustion gas discharges in the precursor flow field
and forms the main propellant flow field.
The main precursor flow features that could be seen in a firearm are depicted in the
Fig. 1 which represents the schematic of a precursor flow filed of a small caliber weapon
(M-16 rifle) taken from (Klingenberg and M. Heimerl (1992)). It is mainly formed by the air
inside the barrel ahead of the projectile and the leakage. The expulsed air exiting from the
barrel, derived by the accelerated projectile (piston effect), creates compression waves that
coalesce into a normal shock wave. The sudden discharge of this normal shock wave and
the compressed air behind it in the ambient air creates a blast wave namely the precursor
or the primary blast wave and forms a volume known as the underexpanded jet. Indeed,
at the muzzle exiting plan, the compressed air, behind the shock wave, expands forming a
Prandtl-Meyer expansion fan. Then, once arrived at the jet boundary, these expansion waves
will be reflected to form a series of compression waves that coalesce into a barrel shock.
This intercepting shock will be intercepted by a Mach disc across which demarcates the
boundary between the supersonic and subsonic velocities. Hence, these two features border
the shock-bottle. The size of this supersonic and bonded jet develops and grows with the
increase of the muzzle exit pressure ratio P
e
/P
0
(with P
e
is the exit pressure and P
0
is the
ambient pressure). Downstream of the Mach disk, the compressed air which was initially in
the barrel and the ambient air that was perturbed earlier by the blast wave form a contact
surface.
On the other hand, when the projectile disengages from the muzzle, the combustion gas
expands out into the surroundings and interacts with the precursor flow. This main propellant
flow field exhibits the same structure as the preceding, namely an underexpanded jet flow
encapsulated by a blast wave.

4 MOUMEN et al
Fig. 1: Schematic of a precursor flow filed of a small caliber weapon (M-16 rifle) (Klingen-
berg and M. Heimerl (1992))
3 Background Oriented Schlieren Technique (BOS)
3.1 Principles of the BOS
Fig. 2: Simplified optical path in the x-y-z plane in a BOS set up. The dashed line: the path
of light with the refractive field. The dotted line: the path of light without refractive index
field adapted from (Venkatakrishnan and Meier (2004)).

5
The Background Oriented Schlieren (BOS) technique originally proposed by Meier
(Meier (2002)) is a quantitative measurement tool of refraction index gradients field in
transparent media (mainly gas and liquid). The principle of the BOS technique is similar
to the conventional Schlieren technique. Indeed, it exploits the deviation of the light pass-
ing through a phase object (heterogeneous medium). The classical technique is qualitative
in nature and requires several optical equipments such as lenses, mirrors, camera and knife
edge. On the other side, BOS employs only an appropriate background and a digital still
camera. The set up of the BOS technique consists in a camera that focuses on a background
(usually a random dot pattern)— hence the name background oriented— in order to record
at least two images of the same background taken with (flow-on) and without (flow-off/tare)
the investigated flow. The introduction of the Schlieren object in between the camera and the
background produces a deflection of the light rays captured by the camera sensor. Thereby,
the resulting image from the second exposure will appear distorted. The second step con-
sists in the calculation of the deflection in the image plane, which can be done by numerical
comparison of the two exposures. This evaluation is usually performed by cross-correlation
methods obtained from particle imagery velocimetry (PIV) (Settles and Hargather (2017)).
The resulting displacements fields are then used to reconstruct the object refraction index
field. Indeed, the displacements y and x measured in the image plane contain informa-
tion about the refractive index integrated along the line of sight (Fig.2). Assuming a paraxial
recording and small deflection ε, the displacement y can be expressed as (Raffel (2015)):
y =
f
Z
B
+ Z
C
f
· Z
B
· ε
y
= M · Z
B
· ε
y
(1)
with M the magnification factor in the background plane, f the camera lens focal length, Z
B
and Z
c
are respectively the distances that separate the middle plan of the flow with width
Z
D
from the background and the camera. The integration of Eikonal equation along the
light path yields the relationship between the integrated refraction index and the ε
x
and ε
y
component of the angular ray deflection ε:
ε
y
=
1
n
0
·
Z
Z
D
n
y
dz (2)
Once the displacement fields are determined, the refraction index can be reconstructed by
solving the Poisson equation derived from Equations 1 and 2 (Beermann et al. (2017)):
2
n
2
x
+
2
n
2
y
=
2n
0
Z
D
· ( Z
D
+ 2Z
B
)
· (
y
y
+
x
x
) (3)
with n
0
the reference refractive index. Thanks to the Gladstone-Dale law, the density can be
directly retrieved:
n 1 = kρ (4)
where n denotes the refractive index, ρ stands for the density of the medium, and k denotes
the Gladstone-Dale coefficient which depends on the fluid composition and the wavelength
used.

Citations
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TL;DR: In this paper , the authors present insights into the establishment of a laboratory scale technique to generate a combined blast loading and single or multiple projectile impacts on a target, where steel ball bearings are used to simulate the projected fragments.
Abstract: This work is a part of a larger research effort to better understand the combined effect of the blast wave and fragment impacts following the detonation of a shrapnel bomb. It is known that the time interval Δt, which represents the difference in arrival time between the blast wave front and the fragment at the position of a given target object, has a significant influence on its response mode. This paper presents insights into the establishment of a laboratory scale technique to generate a combined blast loading and single or multiple projectile impacts on a target. The objective of the setup is to control the time interval Δt to a certain extent so that the different response modes of the tested structures can be investigated. In order to reduce the complexity associated with the random nature of the shrapnel, steel ball bearings are used to simulate the projected fragments. They are embedded in a solid explosive charge, which is detonated at the entrance of an explosive driven shock tube. The experimental work demonstrates that it is possible to orient the path of a single projectile inside the tube when aiming at a target positioned at its exit. The setup guarantees the generation of a well-controlled planar blast wave characterized by its peak pressure, impulse and blast wave arrival time at the exit of the tube. The influence of the mass of the charge and the diameter of the projectile on its velocity study shows that for the same charge mass, the time interval increases with increasing projectile diameter. The experiments are numerically simulated based on an Eulerian approach using the LS-DYNA finite element software. The computational model allows to reveal details about the projectile flight characteristics inside the tube. Both the experimental and numerical data show the influence of the charge and projectile parameters on the time interval.

3 citations

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TL;DR: In this paper , the applicability of the Particle Image Velocimetry (PIV) technique to provide accurate velocity measurements in the challenging environment of the propellant flow of a .300 blackout weapon was evaluated.

3 citations

Journal ArticleDOI
TL;DR: In this paper , a new method for the reconstruction of three-dimensional axisymmetric refractive index fields is presented, which takes advantage of the bi-sensitivity quality of BOS to gain more accuracy in the reconstructed fields.
Abstract: Background-oriented schlieren (BOS) is an optical visualization technique that reconstructs a whole-field flow based on its density gradient. Thanks to the cost-effectiveness of its optical setup and its unlimited field of view, BOS has become an attractive technique for laboratory and large-scale experiments. In BOS, the reconstruction of the refractive index field involves various mathematical calculations, which depend on the flow geometry. In this context, the present study presents a new method for the reconstruction of three-dimensional axisymmetric refractive index fields. The proposed method takes advantage of the bi-sensitivity quality of BOS to gain more accuracy in the reconstructed fields. We demonstrate the method’s precision and robustness against experimental noise throughout a synthetic axisymmetric refraction index field. The application of this new approach is not restricted to the BOS technique but can be extended to several other measurement techniques such as moiré deflectometry, laser speckle photography, and rainbow schlieren.

1 citations

Journal ArticleDOI
TL;DR: In this article , a new method for the reconstruction of three-dimensional axisymmetric refractive index fields is presented, which takes advantage of the bi-sensitivity quality of BOS to gain more accuracy in the reconstructed fields.
Abstract: Background-oriented schlieren (BOS) is an optical visualization technique that reconstructs a whole-field flow based on its density gradient. Thanks to the cost-effectiveness of its optical setup and its unlimited field of view, BOS has become an attractive technique for laboratory and large-scale experiments. In BOS, the reconstruction of the refractive index field involves various mathematical calculations, which depend on the flow geometry. In this context, the present study presents a new method for the reconstruction of three-dimensional axisymmetric refractive index fields. The proposed method takes advantage of the bi-sensitivity quality of BOS to gain more accuracy in the reconstructed fields. We demonstrate the method’s precision and robustness against experimental noise throughout a synthetic axisymmetric refraction index field. The application of this new approach is not restricted to the BOS technique but can be extended to several other measurement techniques such as moiré deflectometry, laser speckle photography, and rainbow schlieren.

1 citations

Journal ArticleDOI
TL;DR: In this paper , a detailed approach for an a posteriori estimation of uncertainty when using background-oriented schlieren (BOS) measurements to reconstruct the refractive index/density field is presented.
Abstract: Background-oriented schlieren (BOS) technique is a density-based optical measurement technique. BOS measurement is similar to particle image velocimetry (PIV) ones in terms of experiments design and the computation of the displacements. However, in the BOS technique, the reconstruction of the refractive index field involves further mathematical calculations, which depend on the flow geometry, such as Poisson solver, Abel inversion, algebraic reconstruction technique, and filtered back-projection. This lengthy combination of experimental measurements, cross-correlation evaluation, and mathematical computation complicates the uncertainty quantification of the reconstructed field. In this study, we present a detailed approach for an a posteriori estimation of uncertainty when using BOS measurements to reconstruct the refractive index/density field. The proposed framework is based on the Monte Carlo simulation (MCS) method and can consider all kinds of sources of error, ranging from experimental measurements to those arising from image processing. The key features of this methodology are its capacity to handle different mathematical reconstruction procedures and the ease with which it can integrate additional sources of error. We demonstrate this method first by using synthetic images and a Poisson solver with mixed boundary conditions in a 2D domain. The accuracy of the proposed approach is assessed by comparing analytical and MCS results. Then, the modular nature of the proposed framework is experimentally demonstrated using a combination of Abel inversion and inverse gradient techniques to reconstruct a 3D axisymmetric density field around a transonic projectile in free-flight. The results are compared with computational fluid dynamics (CFD) and show high levels of agreement with only limited discrepancies, which are attributed to the space-filtering effect within cross-correlation resulting from shock waves.
References
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Journal ArticleDOI
TL;DR: The accuracy of several algorithms was determined and the best performing methods were implemented in a user-friendly open-source tool for performing DPIV flow analysis in Matlab.
Abstract: Digital particle image velocimetry (DPIV) is a non-intrusive analysis technique that is very popular for mapping flows quantitatively. To get accurate results, in particular in complex flow fields, a number of challenges have to be faced and solved: The quality of the flow measurements is affected by computational details such as image pre-conditioning, sub-pixel peak estimators, data validation procedures, interpolation algorithms and smoothing methods. The accuracy of several algorithms was determined and the best performing methods were implemented in a user-friendly open-source tool for performing DPIV flow analysis in Matlab.

1,783 citations

Book
19 Oct 2012
TL;DR: In this article, the Schlieren approach is used to estimate the sensitivity and range of the Schlieser image. But, the sensitivity of the image is not a function of the light source, but of the background.
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.

935 citations

Book
01 Jan 2001
TL;DR: A review of recent developments in shadowgraph and schlieren visualization can be found in this paper, where the authors present a detailed overview of the shadowgraph technique for flow visualization.
Abstract: a review of recent developments in schlieren and schlieren visualization joseph shepherd lecture # 09: flow visualization techniques: schlieren and shadowgraph, schlieren and interferometry part 01 schlieren and shadowgraph techniques osfp schlieren and shadowgraph techniques module 5: schlieren and shadowgraph lecture 26 shadowgraph and schlieren techniques schlieren techniques for the visualization of current visualization based on refractive-index affects shadowgraph and schlieren techniques towards a schlieren camera northwestern university schlieren photography principles rit scholar works introduction to shadowgraph and schlieren imaging chapter 2 laser schlieren and shadowgraph springer background oriented schlieren applied to study shock mae 123 : mechanical engineering laboratory ii -fluids recent developments in schlieren and shadowgraphy schlieren and shadowgraph techniques: visualizing optical considerationsand limitations of the schlieren method principles and techniques of schlieren imaging systems mice a simple classroom demonstration of natural convection module 5: schlieren and shadowgraph lecture 27: schlieren retroreflective shadowgraph technique for large-scale flow optical methods for visualization of ultrasound fields schlieren & shadowgraph techniques steps forward physically-based interactive schlieren flow visualization schlieren and shadowgraph techniques pdf download shadow, schlieren and color interferometry physically-based interactive flow visualization based on schlieren & shadowgraph techniques steps forward background oriented schlieren (bos) and other flow size 50,24mb doc book schlieren and shadowgraph techniques 6 shadowgraph techniques springer pradipta kumar panigrahi krishnamurthy muralidhar schlieren and shadowgraph techniques jlip application of the shadowgraph flow visualization shadowgraph, schlieren and interferometry in a 2d a fluid motion estimator for schlieren image velocimetry schlieren and shadowgraph techniques springer shadowgraph, schlieren and interferometry in a 2d quantitative fourier analysis of schlieren masks: the schlieren, shadowgraph and direct photography fkm.utm schlieren and shadowgraph techniques for °uid physics four decades of utilizing shadowgraph techniques to study color schlieren imaging with a two-path, double knife edge schlieren and shadowgraph techniques gerrymarshall free download schlieren & shadowgraph techniques book shadow-schlieren-book-1 rit people

906 citations


"Visualization and analysis of muzzl..." refers methods in this paper

  • ...The light beam different impingement angles or places are detected by schlieren and shadowgraph techniques which are sensitive to the first and the second derivatives of refraction index respectively (Settles (2001))....

    [...]

Journal ArticleDOI
TL;DR: The improved cross-correlation algorithm has been applied to the measurement of the turbulent flow past a backward facing step (BFS) and a systematic comparison is presented with Direct Numerical Simulation data available on the subject.
Abstract: The features of an improved algorithm for the interrogation of (digital) particle image velocimetry (PIV) pictures are described. The method is based on cross-correlation. It makes use of a translation of the interrogation areas. Such a displacement is predicted and corrected by means of an iterative procedure. In addition, while iterating, the method allows a refinement of the size of the interrogation areas. The quality of the measured vectors is controlled with data validation criteria applied at each intermediate step of the iteration process. A brief section explains the expected improvements in terms of dynamic range and resolution. The accuracy is assessed analysing images with imposed displacement fields. The improved cross-correlation algorithm has been applied to the measurement of the turbulent flow past a backward facing step (BFS). A systematic comparison is presented with Direct Numerical Simulation (DNS) data available on the subject.

533 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe the implementation of a novel technique called background-oriented Schlieren that can produce quantitative visualization of density in a flow using only a digital still camera, a structured background, and inverse tomographic algorithms which can extract two-dimensional slices from a three-dimensional sional flow.
Abstract: This paper describes the implementation of a novel technique called Background Oriented Schlieren that can produce quantitative visualization of density in a flow. This technique uses only a digital still camera, a structured background, and inverse tomographic algorithms which can extract two-dimensional slices from a three-dimen- sional flow. This has been applied to obtain the density field for an axisymmetric supersonic flow over a cone- cylinder model. Comparisons with cone tables show excellent agreement. List of symbols b wave angle h viewing angle q density (kg/m 3 ) k wavelength (m) e angle of deflection D diameter of cylinder f focal length of imaging lens G(k) Gladstone-Dale number j ffiffiffiffiffiffi 1 p

290 citations

Frequently Asked Questions (1)
Q1. What are the contributions in "Visualization and analysis of muzzle flow fields using the background oriented schlieren technique" ?

Thus the motivation of this research. The muzzle flow fields and the flow field around a 5. 56 mm projectile in flight were successfully visualized.