Showing papers on "Schlieren published in 1985"
TL;DR: In this article, an experimental investigation is described of the gasdynamic processes occurring in vented explosions in which two cubical vessels are employed, with internal sides of 18 and 38 cm, repectively.
117 citations
TL;DR: The characteristics and advantages of this unique flow visualization tool are discussed in terms of one- and two-dimensional colour-coding, qualitative and quantitative visualisations, and system sensitivity, range and resolution.
76 citations
TL;DR: In this paper, the application of the schlieren technique to water flow was investigated and it was verified that small residual temperature differences initially present in the fluid, lead to substantial temperature gradients near the surface of the models.
Abstract: Experiments on flow about simple bodies dropped in water tanks and shear layers in a water tunnel, were performed to study the application of the schlieren technique to water flow. It is verified that small residual temperature differences initially present in the fluid, lead to substantial temperature gradients near the surface of the models. The resulting gradients in index of refraction make the schlieren system a viable method of flow visualization. Finally, the experimental results are explained by estimates based on the geometrical optics of the system.
47 citations
TL;DR: In this paper, the structure of a co-flowing jet diffusion flame is visualized using an optical scheme which superimposes the luminous image of the flame on its Schlieren image.
Abstract: Experiments have been carried out in a variable pressure flow facility with the objective of studying the structure of a co‐flowing jet diffusion flame. The flow is visualized using an optical scheme which superimposes the luminous image of the flame on its Schlieren image. This gives a useful picture of the relationship between the bright, yellow‐orange, soot‐laden core flow and the edge of the surrounding hot gas envelope. A loudspeaker is used to force the central fuel jet at several frequencies. In the unforced flow and over most of the driving frequency range in the forced flow, a double structure is observed with two distinct wavelengths: a long wavelength associated with the luminous, buoyancy‐driven core flow and a short wavelength associated with the shear‐driven outer flow. Excitation at the proper frequency causes strong coupling to occur. In this case the core flow pinches off and the flame breaks up into a series of flamelets moving with a single wavelength.
47 citations
TL;DR: In this paper, a device based on the measurements of the deflection of a laser beam is applied to real-time measurements of disuniformity field in a transparent medium, which has about the same sensitivity as the Schlieren and interferometric methods but overcomes many of the experimental problems of these two techniques.
25 citations
TL;DR: The rainbow schlieren apparatus is simpler, cheaper, and more easily built to large scale than the interferometer, but the accuracies of the two instruments are similar but only if refraction is properly accounted for in interferometry.
Abstract: The rainbow schlieren apparatus is simpler, cheaper, and more easily built to large scale than the interferometer. The accuracies of the two instruments are similar but only if refraction is properly accounted for in interferometry. The measurement thresholds of both instruments are similar. The rainbow schlieren device provides more detailed information because the detection threshold of the rainbow schlieren is an order of magnitude better than that of the interferometer.
23 citations
TL;DR: In this article, the authors investigated the mixed convective flows generated by a heated horizontal cylinder rotating in air and found significant qualitative and quantitative differences in the heat transfer characteristics and flow patterns generated by the rotating cylinders.
23 citations
TL;DR: In this paper, the second in a series of five papers that describe Lockheed's work on tone excited jest, the authors presented schlieren photographs of such jets obtained by an ensemble averaging method, which consisted of phase locking the large scale turbulence structures and multiple exposure of a given photographic film, and made it possible to photographically separate out the large-scale turbulence structures from the small scale random turbulence.
22 citations
TL;DR: Computer-simulated schlieren pictures are used to interpret and quantitatively analyze schlieRen pictures taken from a fast varying plasma with axial symmetry to derive structured angular distributions of deflected rays.
Abstract: Computer-simulated schlieren pictures are used to interpret and quantitatively analyze schlieren pictures taken from a fast varying plasma with axial symmetry. Structurized angular distributions of deflected rays are obtained from a ray tracing simulation, the characteristics of which are related to density, density gradients, and dimensions of the plasma. Angular distributions are transformed into intensity distributions using the optical data of a typical schlieren system. Ranges of the plasma parameters density, density gradients, and dimensions are given. As an example the method is applied to the compression phase of a fast high voltage plasma focus.
20 citations
TL;DR: In this paper, low-density regions developed in liquefied polyethylene with a point-plane electrode configuration under high electric fields have been investigated using a Schlieren technique in the temperature range from 120 to 200°C.
Abstract: Low-density regions developed in liquefied polyethylene with a point-plane electrode configuration under high electric fields have been investigated using a Schlieren technique in the temperature range from 120 to 200°C. This region, having a refractive index or a density lower than the surrounding medium, is always formed near the point electrode, irrespective of its polarity. For polyethylene in the liuqid state this disturbance region tends to spread and gradually to disappear by moving from the point to the plane electrode at a temperature-dependent ependent velocity, while in the solid state this region does not move.
19 citations
TL;DR: In this article, an investigation into the structure of premixed Bunsen flames was performed to determine whether by using laser velocimetry an unambiguous means of measuring laminar flame speed could be devised and to provide data by which theoreticians could critically evaluate their predictions.
TL;DR: In this article, a stably density-stratified liquid is produced in a rectangular glass tank by variation of the concentration of salt in water as a function of height, and the glass tank is placed into the parallel beam of a schlieren interferometer with Wollaston prism adjusted to produce straight vertical fringes.
Abstract: A stably density-stratified liquid is produced in a rectangular glass tank by variation of the concentration of salt in water as a function of height. The glass tank is placed into the parallel beam of a schlieren interferometer with Wollaston prism adjusted to produce straight vertical fringes. A gravity wave of the cross wave type is excited and the resulting periodically deforming fringes are recorded by taking photographs. A method is developed to obtain from the fringe patterns results about propagation of the wave in space and time and about amplitude attenuation. The results are compared with the linear theory of Thomas and Stevenson (1972) and excellent agreement is found within the limits of the linear approach.
TL;DR: In this article, an Schlieren method with sub-millimeter and sub-nanosecond resolution was used to investigate profile variations of a fast collapsing focus plasma, and computer simulations allowed the authors to trace rays through the plasma and the schlieren system to the film plane where they produce intensity distributions which depend on density profiles of the plasma.
Abstract: An schlieren method with sub-millimeter and sub-nanosecond resolution was used to investigate profile variations of a fast collapsing focus plasma. Computer simulations allowed the authors to trace rays through the plasma and the schlieren system to the film plane where they produce intensity distributions which depend on density profiles of the plasma. In matching simulated intensity distributions to experimentally produced schlieren pictures, parameter ranges for density, density gradients and sheath thickness have been determined.
TL;DR: In this paper, an experimental investigation of the performance of repetitively pulsed gas-flow spark gaps is presented, using pitot and hot-wire probes, while transient arc debris behavior has been studied using schlieren optical techniques.
Abstract: Results of an experimental investigation of the performance of repetitively pulsed gas-flow spark gaps are presented. Interelectrode gas-flow velocity and turbulence levels have been documented using pitot and hot-wire probes while transient arc debris behavior has been studied using schlieren optical techniques. Typical electrical recovery curves are presented at various gas velocities. Analysis of the recovery, flow, and optical diagnostic data has led to the development of a simple model for the recovery of a spark gap with gas flow.
TL;DR: In this article, the authors describe holographic methods of plasma diagnostics and the optical methods widely used for diagnostics of the plasma, and the advantages of these methods are rich information, high sensitivity and above all the minimum effect produced by measuring instruments on plasmas under investigation.
Abstract: Publisher Summary This chapter describes holographic methods of plasma diagnostics and the optical methods widely used for diagnostics of the plasma. The advantages of these methods are rich information, high sensitivity, and above all the minimum effect produced by measuring instruments on plasmas under investigation. Among optical methods, a special place is occupied by those, which study plasma characteristics by the distortions introduced into a light wave passing through the plasma. Holography makes it possible to record a transmitted wave and then reconstruct it, together with all amplitude and phase particularities. Subsequently, this wave can be investigated by any optical method: interference, Schlieren, and shadow.
TL;DR: In this paper, simultaneous measurements of the electron density in a plasma focus by a Moire-Schlieren technique and Mach-Zehnder interferometry were carried out to investigate the unavoidable error in the inter-ferometry generated by refraction of the probe beam by the density gradient.
Abstract: Simultaneous measurements of the electron density in a plasma focus by a Moire-Schlieren technique and Mach-Zehnder interferometry were carried out to investigate the unavoidable error in the interferometry generated by refraction of the probe beam by the density gradient. The refraction angle was measured precisely by the Moire-Schlieren technique, and the spatial distribution of the electron density calculated from the refraction angle agreed well with that obtained by Mach-Zehnder interferometry. The error produced by the refraction is found to be negligible if an N2-laser is employed as the light source for the plasma focus.
Dissertation•
01 Jan 1985
TL;DR: In this paper, an underexpanded jet, issuing from a convergent slot into quiescent air, as it is deflected by a convex surface of constant radius, is placed on the mechanism of breakaway.
Abstract: This study concerns an underexpanded jet, issuing from a convergent slot into quiescent air, as it is deflected by a convex surface of constant radius. Emphasis Is placed on the mechanism of breakaway, a phenomenon whereby the jet leaves the surface tangentially. An optical system based on the standard Z-type Schlieren configuration and capable of interferometric, Schlieren and shadowgraph techniques has been designed. The techniques are interchanged simply, a laser source being employed for Interferometry and a Xenon spark source for Schlieren and shadowgraph. Vibrations limit the interferometry and improvements are discussed. Shadowgraph and both spark and continuous Schlieren techniques gave good results. Total pressure traverses and surface oil flow visualization show that the influence of secondary flows on breakaway is small. Measurements of the coefficient of discharge show an increase both as the stagnation pressure Is Increased and as the slot width is reduced. The existence of a separation bubble has been established from surface static pressure measurements and shadowgraph and Schlieren photographs. Surface oil flow visualization shows a region of reversed flow withhin the bubble. The bubble grows as the stagnation pressure Is increased and eventually causes breakaway. A potential flow calculation method using the method of characteristics has been developed. Calculation of a fully attached Jet is inaccurate because the separation bubble is ignored. A calculation using the measured surface static pressures accurately predicts the main features of the first shock cell. Reattachment occurs further downstream of the jet and its breakaway should involve a coupling of the solutions of the outer shear layer, potential core and separated boundary layer, the latter including reversed flow.
01 Jan 1985
TL;DR: In this article, a colour schlieren technique based on natural dispersion of light in a stratified medium of a grating serving as a colour-separation element is described.
Abstract: A colour schlieren technique based on natural dispersion of light in a stratified medium of a grating serving as a colour-separation element is described. To illustrate, two schlieren photographs of a turbulence mixture region are presented. One a conventional photograph obtained by using the Foucault knife, and the other in a monochrome print of the coloured image, allowing one to evaluate the spatial distribution of amplitudes of internal waves along the direction of their rays.
TL;DR: In this paper, the electron density calculations in current sheath inhomogeneities and in current heath compression by choosing the simple models of electron density are described, and the modification of schlieren method using a narrow screen with changeable width in focus is described.
Abstract: The modification of schlieren method using a narrow screen with changeable width in focus and the electron density calculations in current sheath inhomogeneities and in current sheath compression by choosing the simple models of electron density are described.
TL;DR: In this paper, Schlieren interferometry is used to study mass diffusion processes of binary gas mixtures and in particular to investigate the initial region of a two-dimensional helium jet mixing with air.
Abstract: Objective of this work was to show that schlieren interferometry is a useful quantitative technique to study mass diffusion processes of binary gas mixtures and in particular to apply it to investigate the initial region of a two-dimensional helium jet mixing with air.
Patent•
31 May 1985
TL;DR: In this paper, a beam of light falling within the range of 180 to 3,000 nanometers is transmitted through a flow cell (12) in an optical compartment of an absorbance detector (16) after warm up of the equipment while the eluant flows through the flow cell from a chromatographic column (20).
Abstract: A beam of light falling within the range of 180 to 3,000 nanometers is transmitted through a flow cell (12) in an optical compartment of an absorbance detector (16) after warm up of the equipment while the eluant flows through the flow cell (12) from a chromatographic column (20). The column extends upwardly from the absorbance detector (16) into an air chamber (60) having a volume of approximately 0.25 cubic foot formed with acrylic walls. Air flows from the absorbance detector (16) under the power of a fan at approximately 10 cubic feet per minute upwardly through an air duct having a cross section of approximately 1.5 square inches to the top where it connects with the air chamber (60), the speed of the motor being adjustable until temperature varies less than one degree Celsius between the flow cell (12) and the lower 10 centimeters of the column. Under these conditions Schlieren noise from the flow cell (12) due to flow-induced thermo-optical effects is reduced.
Book•
01 Jan 1985
TL;DR: In this paper, the authors used a laser-dual-focus velocimetry and flow visualization of 3-D flows to evaluate dynamic photoelasticity of high loading rates.
Abstract: Optical methods in fluid and solid dynamics research.- Space resolved probing of gas concentration and temperature structures.- Holographic interferometry studies of the temperature field near a condensing bubble.- Laser raman techniques for gas phase fluid dynamics and combustion research.- Applied holography for drop formation of non-newtonian fluids in centrifugal atomizers.- Holographic mode shape investigation of aircraft engine impellers.- A study of heat transfer from a horizontal vibrating cylinder by means of holographic interferometry.- Study of diffraction of shock waves, at rounded corners by means of schlieren and interferometric methods.- Study of shock wave reflection in rectangular channels by means of Cranz-Schardin system in parallel beams.- Experience with laboratory LDA by measuring flow fields in rotating turbomachinery.- Application of laser-dual-focus velocimetry in a counterflow.- Laser-doppler velocimetry and flow visualization of 3-D flows.- Laser diagnostics of molecular states in non-equilibrium gas flows.- Experimental study of a turbulent boundary layer-shock wave interaction, using a monodimensional laser velocimeter.- Solution of diffuser inlet velocity field of radial impeller centrifugal turbine pumps by means of the LDA method.- Measurement of unstationary size-distribution of submicron droplets in rarefaction-wave condensation by laser scattering.- Investigation of initial stage of cavitation by diffraction optic method.- Optic and x-ray investigation of water fracture in rarefaction wave at later stages.- Experimental studies of stress waves in elastic plates with curved boundary.- Laser-doppler velocimetry applied to the impact testing of polymers.- Speckle photography of a turbulent density field.- Experimentally and theoretically generated isochromatic fringe loops of cracks propagating at a constant velocity.- Stresses and deformation pattern investigated by the Moire optical method in gears.- Photoelasticity studies of a new method of fracture toughness evaluation of high loading rates.- A new approach to evaluation of measurement in dynamic photoelasticity.- Optimization of a stiffener to stop a propagating crack.- Holographic interferometric study on propagation and focusing of underwater shock waves by microexplosions.- Flow visualization in the wake of three-dimensional bodies undergoing self-sustained oscillations.- Flow visualization of a shock wave by simple refraction of a background grid.- Flow visualization in steel casting.- Behaviour of the vortex layer generated in the flow by an impulse change of circulation around a profile.- Flow visualization of turbulent boundary layer on flat and cylindrical heated walls.- Investigation of transient phenomena in heat transfer.- Flow visualization in a steam turbine profile cascade using a colour schlieren method.- Colour schlieren method.- Photoelastic analysis of a seismoactive crack.- Study of flow of metal and stress conditions at rolling by means of optical methods.- Using interferometric measurements in caicuiation of aerodynamic forces.- Holographic interferometer to investigate deformations of mechanical and thermal stressed motorcar-cylinders.- A new application of differential interferometry for dynamic stress analysis.- Laser beam monitoring of shock waves.- Tomography of transient events.- Application of new photo-electric method to the measurement of dynamic stress intensity factor.- Experimental study of optical features of shock-heated jets.- An investigation of impulse jet outflowing from multi-nozzle blocks by means of the schlieren installation.- Karman vortex street in the supersonic wake a rough flat plate.- Migration of droplets under reduced gravity.- The methods for diagnosing velocity and temperature in the high-temperature gas flow.
01 Jan 1985
TL;DR: In this paper, a color schlieren method based upon two-dimensional dissection has been developed for flow visualization of dry and wet air in a turbine profile cascade over a wide range of transonic velocities.
Abstract: In recent years a colour schlieren method based upon two-dimensional dissection has been developed. A modification of this technique for flow visualization of dry and wet air in a turbine profile cascade over a wide range of transonic velocities is described. Colours are used to differentiate the basic physical phenomena: shock waves, expansion zones, boundary layers, and wakes.
Patent•
14 Feb 1985
TL;DR: In this article, two series-connected schlieren apparatuses are used which have one Schlieren edge each at the focal point of the beam emerging convergently from the concave mirror.
Abstract: Device for quantitative measurement of sound pressures in gases by means of a schlieren apparatus operated using steady light, in which the optical signal, which is proportional to the acoustic signal, is coupled out and continuously reproduced and/or recorded by optoelectric sensors in the imaging plane behind the schlieren edge in the bright field. In one embodiment, two series-connected schlieren apparatuses are used which have one schlieren edge each at the focal point of the beam emerging convergently from the concave mirror. In this case, it is also possible to use two oppositely extending beams, as a result of which quasi-parallel beams are achieved in each case and the sensitivity is thereby increased. An increase in the sensitivity can also be achieved by deflecting the parallel beam via at least one plane mirror in a schlieren apparatus having a parallel beam between two concave mirrors. In all the embodiments, the gap, the schlieren edge and the mid points of the mirrors are arranged together with the optical transducer in a plane which passes through the gap and schlieren edge.
TL;DR: In this article, high speed Schlieren photographs have been taken downstream of a flat-plate flame trap when the trap successfully arrests a flame and when it fails to do so.
14 Jan 1985
01 Jan 1985
TL;DR: In this article, the effect of repulsion of adjacent jets due to interaction of vortices is discovered, and during the quasistationary stage of the flow from blocks of nozzles, the gas dynamic inversion and anomalous lateral prominences were observed.
Abstract: The studies carried out with use of schlieren-camera IAB-451 with a spark light source allowed to reveal the structure of composite pulse jets. The system of vortices, which appears at the exit of nozzles in the initial stage of the flow, essentially affects the behavior of the jet flow in the stage of formation. Propagation of primary shock-waves and of contact surfaces are compared for the cases of single and composite jets. The effect of repulsion of adjacent jets due to interaction of vortices is discovered. During the quasistationary stage of the flow from blocks of nozzles, the gas-dynamic inversion and anomalous lateral prominences were observed.
03 Sep 1985
TL;DR: In this article, a Schlieren microscope is used to measure profiles of optical quality surfaces, and the intensities in the image field are measured with a photo-diode array.
Abstract: A Schlieren microscope is described which can be used to measure profiles of optical quality surfaces. The intensities in the image field are measured with a photo-diode array. By measuring a reference sample and the object, both with and without knife it is possible to correct for different errors. Shape and roughness can be measured with accuracies of 10 nm and 1 nm respectively with a horizontal resolution of about 3μm. The system is fast and relatively insensitive to vibra-tion.
01 Feb 1985
TL;DR: In the field of high speed video, frame rates of 200 and 2000 frames per second, in full image, are obtained as discussed by the authors, in which the particle scattering properties regarding the illumination light are obtained.
Abstract: During the tests in wind tunnel, flow visualization techniques offer to the aerodynamicists general views of the whole or part of flows they are studying. Even when the image observation only provides qualitative informations, the high density of these informations leads to a synthetic interpretation of the very complex physical phenomena which take place in the course of the interaction between a flow and a solid in relative motion. The variety of these techniques arises from the problem diversity according to the fluid relative velocity and to the solid wall proximity. On the wall, informations are obtained by examination of the flows of more or less viscous, colored or not, liquid spread on the surface, or still thin tufts motion. Out of the wall, the techniques to be used are different according that the external flow velocity is more or less fast as that of the sound in this medium. In subsonic flow, the air is seeded with tracers in the shape of small solid or liquid particles. Observed individualy or in groups, the particle motion informs on this of the surrounding air. Images are obtained thanks to the particle scattering properties regarding the illumination light. Changes in the illuminating conditions (total illumination or by a light sheet) allow to show particular features such as vortices, separation and recirculating zones, ..In the supersonic domain, new physical phenomena appear, providing rough or progressive changes of the gas density (particularly, shock wave apparition). These density variations involve propagation light perturbations (phase changes in a light wave or light ray de-viations in a beam). It is the domain where techniques such as interferometry, schlieren and shadowgraphy are developed. They provide not only qualitative visualizations, but, in certain cases, such as two-dimensional or axisymetrical flows, they allow density distribution determinations. Some phenomena are very brief (detonation wave propagation) or evolve fast (turbulent structures). In order to allow a detailed analysis, it is then necessary to fix temporarily some aspects of these phenomena. Separate pictures are obtained thanks to fast shutters, pulse light illuminations (spark lamps or lasers), or image converter cameras. Sequences with high repetition rate (from 25 frames per second to beyond a million of frame per second) necessitate the use of special materials: high speed cameras (ordinary or with compensating prism), rotating drum or mirror cameras, image converters,..To all these recording means on photographic film, is now added the video, recording on magnetic band. Although it does not yet reach the same number of pixels in an image, the video presents some advantages for its easy use, fast restitution and long play recording. in the field of high speed video, frame rates of 200 and 2000 frames per second, in full image, are obtained. More, the video development now allows to take advantage of the image observation informative richness to facilitate the interpretation of large data sets acquired either by measuring means or at the computer output. The aerodynamicists are particularly interested with it for their result presentation and comparison between experiment and calculation.
01 Jan 1985
TL;DR: In this article, the Cranz-Schardin system in parallel beams was used to study the reflection of the reflected shock wave with the boundary layer behind the incident shock wave.
Abstract: Shock wave reflection in narrow channels has been studied by means of Cranz-Schardin system in parallel beams The sequence of three single schlieren pictures of the flow investigated were taken along with a streak record The interaction of the reflected shock with the boundary layer behind the incident shock wave is discussed New phenomena have been observed, including the existence of vortices near the closed end of the tube The formation of pseudo-shock waves has been observed