Showing papers on "Schlieren published in 1969"
TL;DR: The whole field of the application of laser technology has been exhaustively surveyed in this article, and a full bibliography is included in this article. But this article is specifically confined to combustion applications.
27 citations
TL;DR: In this article, a method is developed in which light from a laser, after being reflected, refracted, or diffracted in one selected direction by any moving solid or phase object (including particles, flames or pressure waves) is isolated by a "schlieren aperture" and then allowed to interfere with an unperturbed beam.
Abstract: A method is developed in which light from a laser, after being reflected, refracted, or diffracted in one selected direction by any moving solid or phase object (including particles, flames or pressure waves) is isolated by a 'schlieren aperture' and then allowed to interfere with an unperturbed beam. The Doppler shift in wavelength manifests itself as a beat frequency which is related theoretically to the passage of interference fringes past a small photodetector. The theoretical analysis examines various practical limitations and suggests experimental refinements. The method has been applied to moving grids, ultrasonics, flames and particles at velocities ranging from a few centimetres per second to the speed of sound.
23 citations
TL;DR: In this article, the hydrodynamic structure and ignition dynamics of a shock wave expanding into a region of detonatable gas have been studied using schlieren framing photography, and the separation of a detonation wave into a shock-deflagration complex has been observed.
18 citations
01 Jan 1969
TL;DR: The results of some experimental and analytical studies of three types of fuel injection from a wall into a supersonic air stream are presented in this paper, where the principal methods of observation are optical including interferometry, spark schlieren and high-speed motion pictures.
Abstract: The results of some experimental and analytical studies of three types of fuel injection from a wall into a supersonic air stream are presented. The specific problems considered are tangential slot injection of gases, liquid injection through a porous wall, and transverse injection of gases through isolated, normal ports. The principal methods of observation are optical including interferometry, spark schlieren and high-speed motion pictures. The special features of these flows introduced by the consideration of a supersonic air stream are discussed in detail.
12 citations
TL;DR: Holography was applied to the schlieren and phase-contrast methods and enabled the visualization of a minute phase change occurring in an object which scattered light as discussed by the authors, and the phase change due to the object is made to add to the reconstructed reference wavefront and is rendered visible by spatial filtering the point image formed by the wavefront.
Abstract: Holography was applied to the schlieren and phase-contrast methods and enabled the visualization of a minute phase change occurring in an object which scattered light. One makes a hologram first with the phase object in position and afterwards illuminates it by the object illuminating beam with the object out of the path. Then the phase change due to the object is made to add to the reconstructed reference wavefront and is rendered visible by spatial-filtering the point image formed by the wavefront. First experiment was carried out of a striation of liquid in a cell which was illuminated diffusely from behind. This principle is also applicable to the removal of aberrations of a conventional arrangement for transparent objects. The second experiment was performed of a hot soldering iron placed in a pipe of glass and a sensitivity competitive to that realized by using an aberration-free arrangement was obtained. An accuracy necessary to locate the hologram plate to its original position and the effect of the emulsion shrinkage were also discussed.
12 citations
TL;DR: In this paper, the velocity of any phenomenon which will reflect, refract or diffract a laser beam is measured, and the object of associating these principles has been to make possible the measurement of the velocity.
Abstract: THE object of associating these principles has been to make possible the measurement of the velocity of any phenomenon which will reflect, refract or diffract a laser beam. Our particular interests lie in phase objects relevant to combustion research, such as laminar and turbulent flame fronts, shock and detonation waves and other steep refractive index gradients associated with heat and mass transfer, or pressure changes, but the method is not confined to these.
10 citations
TL;DR: Construction, theory, and operation of semifocusing color schlieren systems for use in quantaitiv experimental investigations of flows are described and results showing photographs of boundary layers are included.
Abstract: Construction, theory, and operation of semifocusing color schlieren systems for use In quantaitiv experimental investigations of flows are described. Results showing photographs of boundary layers are included.
9 citations
Patent•
10 Dec 1969
TL;DR: In this paper, a beam of coherent light is expanded and reparallelized by a single lens and a parabolic mirror at 45 degrees to create fringes in the overlapping reflected images which can be visually observed or recorded directly on film.
Abstract: A beam of coherent light is expanded and reparallelized by a single lens and a parabolic mirror. The beam then passes through the test region, which may be of any convenient size and impinges on a back surface mirror at 45 degrees. About 10 percent of the light is reflected from the front surface of the glass. This is slightly offset from the image reflected from the rear surface. Any refractive index gradients perpendicular to the direction of propagation then create fringes in the overlapping reflected images which may be visually observed or recorded directly on film.
8 citations
TL;DR: A technique for producing color schlierent photographs from holograms formed in the genrualized holographic flow visualization system is presented and preliminary results of the application are shown.
Abstract: A 20-in. (51-cm) diam schlieren system was converted to a genralized holographic flow visualization system. The system has been used successfully in producing the following types of visualization from a single holographic plate: three-dimensional photography, variable focus shadowgraph, variable knife-edge position schlieren, color schlieren, and interferometry. All of these except for holographic color schlieren have previously been reported with varying degrees of success. This paper presents a technique for producing color schlieren photographs from holograms formed in the above system and shows preliminary results of the application. The method possesses a number of advantages over conventional color schlieren photography.
8 citations
TL;DR: In this paper, the influence of hydrogen concentration on the characteristics of self-sustained detonation waves propagating in H2-CO-O2 mixtures at one atmosphere initial pressure was experimentally investigated by means of Q-switched pulsed laser schlieren photography.
Abstract: The influence of hydrogen concentration on the characteristics of fully developed self-sustained detonation waves propagating in H2—CO—O2 mixtures at one atmosphere initial pressure was experimentally investigated by means of Q-switched pulsed laser schlieren photography. The main aspects of interest were the reaction zone thickness and the detailed wave front structure. The concentration of CO in the fuel ranged from zero to 97.5 % by volume; pure CO—O2 mixtures did not detonate. A rotating prism Q-switched laser was modified to achieve the synchronization purpose, thus the need for an expensive electro-optical Q-switching device was eliminated. The laser schlieren photographs indicate that the wave front becomes nonplanar and the spacing between the transverse waves becomes larger as H2 is replaced by CO in H2—O2 mixtures. It is suggested that weak shocks, produced by secondary explosions, are the propagating mechanism for the trailing portion of the transverse waves. Experimental results show ...
6 citations
TL;DR: This device has been used to find the surface pressures and flow field structure around some simple two-dimensional airfoil shapes and good agreement between the diffraction grating interferometer data and analytical data is indicated.
Abstract: A conventional schlieren system was converted into a Kraushaar interferometer by the addition of matched diffraction gratings as the beam splitting and recombination elements. Optical quality of the added features of this installation were shown to be not a limiting factor, but the optical platform must be isolated well for good results. Basic optical theory applicable to this device is summarized. Several aspects are indicated which enhance the fringe or image quality. This device has been used to find the surface pressures and flow field structure around some simple two-dimensional airfoil shapes. Comparison of these results with calculations indicates good agreement between the diffraction grating interferometer data and analytical data.
TL;DR: In this paper, the authors describe the construction details of an inexpensive yet highly sensitive schlieren system suitable for use in medical ultrasonic research, where the light path is constructed so that the beam pattern of the transducer being tested is displayed in actual size.
TL;DR: In this article, a model of astronomical seeing with particular view to solar observations is developed which assumes the atmospheric disturbances to consist of individual turbulence elements called Schlieren, which permits to explain the observational results under conditions of good seeing; furthermore, it provides a basis for the discussion of the physical phenomena in the atmosphere that cause image deterioration.
Abstract: A model of astronomical seeing with particular view to solar observations is developed which assumes the atmospheric disturbances to consist of individual turbulence elements called Schlieren. A quantitative account is given of each image motion, image blurring and scintillation as function of Schlieren properties and telescope parameters. The theory permits to explain the observational results under conditions of good seeing; furthermore, it provides a basis for the discussion of the physical phenomena in the atmosphere that cause image deterioration. As an illustration it is shown how the theory could be applied to a problem of interest to solar astronomers searching for a suitable observatory site.
TL;DR: In this article, the similarity of shock shapes (both standoff distance and shock curvature) from liquid jets and cylinders was investigated through detailed studies of the similarity between the two shapes, showing that a well-collimated liquid jet is flattened or deformed by the supersonic cross flow in a manner similar to the models proposed in Refs.
Abstract: TVm.diam, l-in.-lohg cylinder that protrudes from the model surface. A cylinder with a diameter larger than the effective orifice diameter de is required to produce a shock with a curvature similar to that for the liquid jet. Schlieren photographs of normal penetration likewise show a shock standoff distance that corresponds to a cylinder with a diameter greater than de. This observation can be explained if one assumes that the well-collimated jet is flattened or deformed by the supersonic cross flow in a manner similar to the models proposed in Refs. 5 and 6. These preliminary results suggest that the nature of jet deformation could be experimentally investigated through detailed studies of the similarity of shock shapes (both standoff distance and shock curvature) from liquid jets and cylinders.
Patent•
22 Apr 1969
TL;DR: In this paper, a Schlieren optical system comprising a medium for controlling the light of a separate light source for illuminating the image field on the control medium, and a masking system having mirrors arranged in a checkerboard pattern located in the path of the illuminating beam to divide the light into individual rays, the mirrors being so mounted as to provide a mask to prevent or allow the passage of light in an undeformed or deformed state respectively.
Abstract: This invention relates to a Schlieren optical system comprising a medium for controlling the light of a separate light source for illuminating the image field on the control medium, and a masking system having mirrors arranged in a checkerboard pattern located in the path of the illuminating beam to divide the light into individual rays, the mirrors being so mounted as to provide a masking system in the path of the image beam to prevent or allow the passage of light when the control medium is in an undeformed or deformed state respectively.
Proceedings Article•
01 Jan 1969
TL;DR: Quantitative density data from schlieren measurements by photomultiplier technique for axisymmetric flow outside diffraction bands was collected by as mentioned in this paper, where the density data was derived from Schlieren data.
Abstract: Quantitative density data from schlieren measurements by photomultiplier technique for axisymmetric flow outside diffraction bands
TL;DR: In this article, the authors investigated the characteristics of an a.c.w. arc in SF6 and developed an optical technique in which the monochromatic light from a 4 watt c.p.s. laser enables the physical dimensions of the arc and the gas flow in and around it to be photographed at up to 107 p.m.
Abstract: An investigation into characteristics of an a.c. arc in SF6 has led to the development of an optical technique in which the monochromatic light from a 4 watt c.w. laser enables the physical dimensions of the arc and the gas flow in and around it to be photographed at up to 107 p.p.s. To date, using an adapted schlieren system, results have been obtained in nitrogen at 6 & 103 p.p.s. In the immediate future the equipment will be modified to use SF6, and an Image Converter camera used to attain 107 p.p.s. Characteristics of the laser are discussed, including observations made using argon and krypton.
TL;DR: In this paper, a quantitative scanning schlieren system is described which, by the removal of one component, may be converted rapidly to a conventional qualitative system, and the accuracy of the system has been measured; the r.m.s. uncertainty in angular deflection of light in passing through the test space was 5? 10?5 rad, though this could be improved.
Abstract: A quantitative scanning schlieren system is described which, by the removal of one component, may be converted rapidly to a conventional qualitative system. The accuracy of the system has been measured; the r.m.s. uncertainty in angular deflection of light in passing through the test space was 5 ? 10?5 rad, though this could be improved. An analysis of the optics indicates the extent to which the output of the system is nonlinear.
Journal Article•
TL;DR: Holographic technique for transferring phase perturbation of subject waves onto spherical waves focusable through aperture and examinable by interferometric and schlieren methods.
Abstract: Holographic technique for transferring phase perturbation of subject waves onto spherical waves focusable through aperture and examinable by interferometric and schlieren methods
01 Jan 1969
TL;DR: Optical system for recording Schlieren images with continuous writing, ultrahigh speed framing camera as discussed by the authors was used to record images with a continuous writing and ultra-high speed camera.
Abstract: Optical system for recording Schlieren images with continuous writing, ultrahigh speed framing camera
20 Jan 1969
TL;DR: In this article, a new method of detecting boundary layer transition at supersonic speeds is described, which is based on measuring the change in the root mean square of the voltage fluctuation across surface thin film gauges operated at constant temperature.
Abstract: A new method of detecting boundary layer transition at supersonic speeds is described. rity of methods such as schlieren and those of maximum surface temperature and peak surface pitot pressure,locate positions near the end of transition, which, as will be shown in the paper, have a strong Mach number and unit Reynolds number dependence. A more complete picture of transition dependence on these parameters has been obtained by measuring the change in the root mean square of the voltage fluctuation across surface thin film gauges operated at constant temperature. effects of Mach number and unit Reynolas number on the beginning and length of transition to be established more precisely than with previously used methods. The use of thin film gauges to infer local laminar and turbulent skin friction a t supersonic speeds is also described. The majoThis technique enables the
TL;DR: The optical accessory was designed and tested for use with the Beckman models L and L2-65B preparative ultracentrifuge and has been used to determine sedimentation coefficients and molecular weight estimates.
26 Aug 1969
TL;DR: In this paper, a method for separating translational and rotational motion of turbulent structures using optical correlation of laser schlieren signals is presented. But the method is not suitable for the case of complex structures.
Abstract: Method for separating translational and rotational motion of turbulent structures using optical correlation of laser schlieren signals
15 Apr 1969
TL;DR: In this paper, the shape and location of the bow shock of a 5 deg half-angle right-circular cone at a nominal Mach number of 5.0, a nominal free-stream Reynolds number per foot of 4,800,000 and angles of attack equal to 15 and 40 deg.
Abstract: : A technique is outlined by which density gradients visible in two- dimensional schlieren photographs can be analyzed to obtain the density gradient structure (i.e., the shape and location of density gradients such as shock waves and vortices) of three-dimensional flow fields. Practical application of the technique relies on obtaining a series of schlieren photographs of the flow field from different viewing orientations. The analysis is specialized to the case of a right-circular cone at angle of attack. Results are presented which show the shape and location of the bow shock of a 5 deg half-angle right- circular cone at a nominal Mach number of 5.0, a nominal free-stream Reynolds number per foot of 4,800,000 and angles of attack equal to 15 and 40 deg.
TL;DR: In this paper, the authors investigated the use of a laser-produced plasma in Schlieren photography. But their experiments were limited to a few picoseconds and framing rates in the gigacycle range.
Abstract: The extremely short pulses of coherent radiation emitted by a mode-locked laser permit the extension of conventional Schlieren photography to events requiring exposure times of a few picoseconds and framing rates in the gigacycle range. The usefulness of this technique has been investigated by studying the initial development of a laser-produced plasma. The experimental set-up employed a Neodymium : glass laser, Q-spoiled by means of a saturable dye, emitting a 400 nsec long train of pulses having a separation of 4 nsec and a duration of approximately 5 picoseconds. By passing the laser beam through an index-matched ADP crystal it was possible to illuminate the Schlieren system with the more easily recorded second harmonic radiation. The photographs obtained, which show the growth of a plasma produced by a synchronized ruby laser, clearly demonstrate the potential of picosecond light pulses in Schlieren studies.
TL;DR: In this paper, the authors provide an overview of a light amplifier with high light output and discuss experimental results obtained with the Elmicon (ELectro-Mechanical Image CONtrol).
Abstract: Publisher Summary This chapter provides an overview of a light amplifier with high light output. Any large-scale projection of a picture signal requires the modulation of an intense light flux. Several methods involve a high-power standard light source that is modulated either by absorption as in the Sciatron or by diffraction as in the Eidophor. In case of Eidophor, modulation of the light flux is by means of Schlieren optics, this being essentially based on a diffraction effect because of distortions produced by the signal beam in a thin oil film. The principles of operation of the Eidophor are essentially the same as in the system where the oil layer is replaced by a gel. There are various methods of producing the signal-induced deformations in the gel and one example, the Elmicon (ELectro-Mechanical Image CONtrol). The gel, about 150 μm thick, is deposited on a transparent electrode and separated from the photoconductor, which is also mounted on a transparent electrode, by a space of about 20 to 50 μm. This chapter presents a detailed overview of Elmicon system and discusses experimental results obtained with Elmicon.