Schlieren Patterns Research Articles

Application of computational algorithms with higher order of accuracy to the modeling of two-dimensional problems on development of hydrodynamic instability

This article examines application of computational algorithms with an increased order of accuracy for modeling two-dimensional problems of development of hydrodynamic instabilities. The efficiency of using algorithms to improve the accuracy and reliability of modeling in this area is considered. More specifically, the paper describes a numerical algorithm for solving the problem of development of Richtmayer-Meshkov instability. To construct the algorithm, the authors use the WENO scheme of the fifth order of accuracy Several problems are solved numerically using the developed method. The article models such processes as flows at a time of 4 046 microseconds, a change in the width of the region filled with sulfur hexafluoride, numerical schlieren patterns at a time of 877 microseconds, a change in the width of the region filled with heavy gas. The results are obtained by various methods on grids of different dimensions and compared with experimental data. It is shown that schemes with WENO reconstruction of the 5th order of accuracy demonstrate results closer to full-scale experiments.

A newly fascinating approach to construct pillar[5]arene functionalized ester derivatives for nematic liquid crystalline behavior

A Pillar[5]arene linked 4-n-alkoxy benzoic acid based multifunctional supramolecular systems ((PB1-PB4) with variable alkyl chains were synthesized and well characterized. The microscopic and thermal behaviors of the compounds were investigated by using POM, DSC, and TGA analysis. All four pillar[5]arene-ester based macrocyclic compounds display nematic type mesomorphic properties, with a well-known schlieren and droplets type texture pattern observed in all four ten-side substituted pillarene derivatives. All four materials exhibit enantiotropic mesogenic behavior with a wide temperature range and thermal stability. The material with higher alkyl chain exhibit nematic phase at lower temperatures compared to materials with lower alkyl chain substitutions. Furthermore, we have investigated the structure property relationship to understand the influence of substitution on the rigid core of pillar[5]arene and its ability to induce different types of liquid crystalline behaviors.

Acoustic resonances in a pressurized discharge volume with xenon and instabilities of periodic-pulse optical discharges

One of the factors inducing instability from pulse to pulse of periodic-pulse optical discharge (POD) or continuous optical discharge with deep periodic-pulse pumping modulation, or combined POD (CPOD), is the excitation of resonant acoustic oscillations in a pressurized discharge volume. In this work authors studied the violation types of the regular pulsations of CPOD thermogravitational convection plume in a closed discharge volume with xenon at a pressure of 15-45 bar, arising at certain periodic-pulse modulation repetition rates in the range 1-50 kHz. It was found that simultaneously with the appearance of failures in the behaviour of the convective plume and plasma stability, which in some cases led to the extinction of the discharge, resonant acoustic oscillations were excited in the discharge volume. Schlieren patterns of the gas around the discharge and the frequency spectra of the excited acoustic vibrations were recorded. Several types of instabilities were found that correspond to different modes of resonant vibrations. It was also found that at certain acoustic oscillation frequencies the convection process was stabilized with the suppression of regular pulsations.

Analysis of shock metamorphic processes in the Zagami meteorite

The study of shock-metamorphic features of the Zagami meteorite revealed pseudotachylite-like melt veins with inhomogeneous chemistry and schlieren structure of silica-glass and alkali feldspar melt glass. The feldspar occurs as diaplectic glass in the interstitial area indicating short-time (few seconds) quenching of shock pressure during the impact event, with post-shock annealing. At several locations, apatite needles were identified, which are formed by fluids (cold water with dissolved ions) after the crystallization of cumulate magmatic minerals. Phosphates also could form in impact melts due to circulation of fluids after the impact event. The other signature for the high shock temperature is the presence of Ca–Ti-rich pyroxenes and titanomagnetite, which indicate temperature above 1,200 °C. The formation of silica-rich melt in interstitial area has two scenarios: (a) fractional melting of the Martian crust or (b) formation by pseudotachylite-like impact melting. According to textural observations (schlieren pattern), we propose an impact origin of the large amount of silica-rich melt in this meteorite. Pseudotachylite-like textures were mentioned earlier in terrestrial impact craters; however, we first propose them to form in a Martian meteorite based on their similarity of texture with terrestrial pseudotachylites.

Visualization and investigation of natural convection flow of CO2 in aqueous and oleic systems

Optimal storage of carbon dioxide (CO2) in aquifers requires dissolution in the aqueous phase. Nevertheless, transfer of CO2 from the gas phase to the aqueous phase would be slow if it were only driven by diffusion. Dissolution of CO2 in water forms a mixture that is denser than the original water or brine. This causes a local density increase, which induces natural convection currents accelerating the rate of CO2 dissolution. The same mechanism also applies to carbon dioxide enhanced oil recovery. This study investigates a set of high pressure visual experiments, based on the Schlieren technique, in which we observe the effect of gravity-induced fingers when sub- and super-critical CO2 at in situ pressures and temperatures is brought above the liquid, i.e., water, brine or oil. A short but comprehensive description of the Schlieren set-up and the transparent pressure cell is presented. The Schlieren set-up is capable of visualizing instabilities in natural convection flows; a drawback is that it can only be practically applied in bulk flow, i.e., in the absence of a porous medium. All the same many features that occur in a porous medium also occur in bulk, e.g., unstable gravity fingering. The experiments show that natural convection currents are weakest in highly concentrated brine (25 w/w% NaCl solution) and strongest in oil, due to the higher and lower density contrasts respectively. Therefore, the set-up can screen aqueous salt solutions or oil for the relative importance of natural convection flows. The Schlieren pattern consists of a dark region near the equator and a lighter region below it. The dark region indicates a region where the refractive index increases downward, either due to the presence of a gas liquid interface, or due to the thin diffusion layer. The experiments demonstrate the initiation and development of the gravity induced fingers.

Multistage magma emplacement and progressive strain accumulation in the shallow‐level Krkonoše‐Jizera plutonic complex, Bohemian Massif

AbstractField relationships combined with new U‐Pb zircon geochronology suggest that the shallow‐level Krkonoše‐Jizera plutonic complex, northern Bohemian Massif, was assembled successively from bottom to top, starting with emplacement of the separately evolved S‐type Tanvald granite (317.3 ± 2.1 Ma), followed by at least two voluminous batches of the I‐type porphyritic Liberec (319.5 ± 2.3 Ma) and Jizera (320.1 ± 3.0 Ma and 319.3 ± 3.7 Ma) granites. The intrusive sequence was completed by uppermost, minor intrusions of the equigranular Harrachov (315.0 ± 2.7 Ma) and Krkonoše granites. The I‐type granites exhibit an unusually complex pattern of superposed feldspar phenocryst and magnetic fabrics as revealed from the anisotropy of magnetic susceptibility (AMS). The outer Liberec granite preserves margin‐parallel foliations and lineations, interpreted to record emplacement‐related strain captured by cooling from the pluton floor and walls. In contrast, the inner Jizera, Harrachov, and Krkonoše granites were overprinted by synmagmatic strain resulting from dextral movements along regional strike‐slip faults cutting the opposite ends of the plutonic complex. Late‐stage felsic dikes in the Liberec and Jizera granites reorient from horizontal to vertical (lineation‐perpendicular) attitude in response to changing the least principal stress direction, whereas mafic schlieren do not do so, representing only randomly oriented small‐scale thermal‐mechanical instabilities in the phenocryst framework. In general, this case example challenges the common approach of inferring pluton‐wide magma flow from interpolated foliation, lineation, and schlieren patterns. More likely, magmatic fabrics in large plutons record complex temporal succession of superposed strains resulting from diverse processes at multiple scales.

Hilbert diagnostics of Rayleigh-Benard convection in fluids

An combined optical and thermal imaging experimental system was designed to investigate Rayleigh-Benard convection of a fluid in a layer with two rigid isothermal boundaries and a free upper boundary under steady and unsteady thermal boundary conditions. The fluid surface structure was visualized using methods of reflected-light Hilbert optics. Noncontact control of the fluid layer thickness was performed using a specially designed remote meter based on an MBR-1 microscope with a smooth focusing unit based on the Meyer mechanism. The evolution of the dynamic structure of the surface and temperature field of the fluid being analyzed were studied experimentally, and the existence of flows in the form of two-dimensional rolls with axes of rotation parallel to the lateral boundaries (the walls of the cavity) was confirmed. It is shown that the highly viscous fluid flow has a thermal gravitational nature. Correspondence is found between the evolution of the thermograms and Hilbert schlieren patterns of surface structures in different modes of Rayleigh-Benard convection.

Experimental investigation of magnetohydrodynamic action on a heat flux toward the surface of a model

Experimental data for magnetohydrodynamic (MHD) action on a supersonic nitrogen flow about an axisymmetric model are presented. The experiments were carried out in the Big Shock Tube (Ioffe Physical-Technical Institute), at the end of which a test section equipped with a supersonic nozzle was mounted. A test conic model coupled with a cylinder is attached to the output cross section of the nozzle. A magnetic field is produced by a solenoid placed on the cylindrical part of the model through which a pulsed current due to an external voltage source discharging passes. Electrodes on the conic part of the model initiate a gas discharge, which rotates about the axis of the model in the solenoidal magnetic field. The influence of the magnetic field on the gasdynamic pattern of the flow near the model and on the heat flux toward its surface is investigated. Schlieren patterns of the flow about the model, photographic scans of the discharge glow, and heat flux measurements are taken. It is found that the magnetic field has an effect on the gasdynamic pattern of the flow near the model and on the heat flux toward its surface. The dependence of MHD effects on the external voltage polarity is also revealed.

High transmittance of a twisted-vertical aligned liquid crystal display

A high transmittance continuum domain twisted-vertical alignment (CDTVA) liquid crystal display (LCD) without domain walls defect and complex fabrication process has been developed. The CDTVA mode has no optical schlieren pattern occurring in the TVA cell. The optimum conditions for liquid crystal phase retardation (Γ) and cell gap-to-helical pitch ratio (d/p) were studied using three-dimensional finite element simulation, which showed good agreement with the experimental results. The results indicate that the maximum transmittance of the proposed CDTVA cell is similar to that of the twisted nematic mode thin-film-transistor LCD. Thus, CDTVA cell has potential applications for wide-viewing angle LCDs.

Effect of Airy disk on schlieren diffraction interferometer

Schlieren is among the oldest and widely used optical techniques for detection of change in refractive index in transparent media. Present work demonstrates the effect of the position of schlieren element in the Airy pattern on the schlieren interferogram. It has been shown that the amplitude of the diffracted wave, starting from schlieren element and serving as an inbuilt reference beam for the schlieren diffraction interferometer, becomes maximum when schlieren element diffracts light from the Airy disk. Effect of F-number of the optical system on schlieren pattern is also demonstrated via observations on the amplitude of diffracted light.

Nematic textures in colloidal dispersions of Na-fluorohectorite synthetic clay

We have studied stable strata of gravity-induced phase separation in suspensions of synthetic Na-fluorohectorite clay in saline solutions. We have observed how the strata depend on clay concentration as well as on salt content. The mass distribution and density variation at the isotropic-nematic interface indicate that existing models and assumptions in existing simulations are able to relatively well account for the observed behavior. We suggest that discrepancies could be due to the high polydispersity and the irregular shape of our Na-fluorohectorite particles, as well as diffusive double-layer effects, which could result in a competition between nematic ordering and gelation. The dependence on ionic strength displays three main regimes irrespective of clay concentration. At low ionic strength (approximately 0.1-5 mM NaCl), the Debye screening length is longer than the van der Waals force range. In this regime, the particles repel each other electrostatically and entropy-driven Onsager-type nematic ordering may occur, although gelation effects could also play a role. For ionic strengths above about 5 mM, we believe that the van der Waals force comes into play and that particles attract each other locally according to the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) model of colloid interactions, resulting in a small-domain regime of attractive nematiclike ordering. In the third regime, for ionic strengths above approximately 10 mM, the clay particles aggregate into larger assemblies, due to the dominant van der Waals force, and the observed birefringency is reduced. We have studied the nematic phase in detail between crossed polarizers and have found textures showing nematic Schlieren patterns. By rotating the polarizers as well as the samples, we have observed examples of disclinations of strengths -1, -1/2, and +1.

Folding mirror schlieren diffraction interferometer

We demonstrate the use of a mirror as a viewing diaphragm to generate a built-in diffracted reference beam in schlieren diffraction interferometry (SDI). The use of a mirror edge as a diffracting element instead of a conventional knife edge considerably enhances the contrast of the schlieren pattern, and it is shown to be equal to that of a phase knife edge. This increase in contrast is due to the fact that the otherwise unutilized diffracted beam in SDI is recombined in the described folding mirror geometry.

Characteristics of a magnetogasdynamic diffuser under different modes of electric current switching

This paper elaborates upon a previous investigation into the influence of external electric and magnetic fields on a flow through a supersonic diffuser. The aim of the present study is to correlate a change in the configuration of a shock wave emerging near the diffuser inlet at magnetohydrodynamic interaction with the amount of force and energy actions and with total pressure losses. For this purpose, the main parameters of the shock wave structure and the total pressure are measured at the diffuser outlet when the flow is subjected to magnetic and electric fields of various strengths at different routes of current passage. In the experiments, a shock tube with a supersonic nozzle is employed. The shock tube forms a flow behind the shock wave reflecting from the end of the tube, which terminates in the nozzle. The diffuser is located directly downstream of the nozzle. The investigation is carried out in xenon. The flow is subjected to external fields at the inlet of the diffuser. The shock wave structure is visualized by frame sweeping of Schlieren patterns of the flow. The total pressure is measured with a piezoelectric transducer located at the end of the channel. The results obtained make it possible to optimize the action on the flow in terms of power consumption and total pressure losses for a given design of the diffuser.

Experimental Study of the Scattering of Ultrasound from Wake Flows in a Linearly Stratified Fluid

An experimental study of the vertical acoustic sounding of stratified flows is carried out. The flows include two-dimensional wakes behind cylinders and three-dimensional wakes behind single ring vortices. A simultaneous optical visualization of the sound-scattering zones is performed. By the spectral processing of the schlieren patterns (in the wave number domain) and echo signal arrays (in the frequency domain), the most probable structure-forming elements of the scattering region are determined. These elements are internal boundary layers whose vertical size (thickness) is determined by the local frequency of internal waves and the kinematic viscosity.

A color schlieren method

This paper discusses questions of the use of a color schlieren method for quantitative measurements of two-dimensional vectors of the deflection of light rays by optical inhomogeneities when gas and liquid fluxes are studied. A comparative analysis of bright- and dark-field versions with square and circular shapes of the radiation source and of the Foucault knife is presented. An illustration of a two-coordinate color schlieren pattern obtained on an IAB-451 schlieren device is given. © 2004 Optical Society of America

Method of shaping the front profile of metallic mirrors with a given relief of its back surface

This paper analyzes the properties of "magic" mirrors fabricated by contemporary masters using the technology of ancient China. Interferograms and schlieren patterns obtained from one of the samples confirm that there is a connection between the relief on its back side and the shape of the front reflective surface. © 2004 Optical Society of America

Analysis of the effect of regular and stochastic phase structures on the optical quality of the active medium flow in gas-dynamic lasers

The detailed structure of the active medium in a gas-dynamic laser is analysed. The parameters of regular and stochastic phase field components are reconstructed from the results of processing the schlieren patterns of the flow field simulated by cold air. The second-order characteristics are obtained in the form of the spectral density of power and correlation distribution function of stochastic inhomogeneities; the integral scale of the phase perturbation is also determined. The standard deviations in perturbations of the regular and stochastic components are compared and a correct prediction of laser radiation parameters is made for several cases of the laser beam propagation through the phase-perturbing active medium.

Investigation of the variability of the structure of a stratified wake behind a horizontal cylinder using optical and acoustic methods

The shadow flow pattern behind a horizontal cylinder uniformly towed in a stratified fluid with constant buoyancy frequency (in the imbedded vortex and turbulent wake regime) is recorded synchronously with acoustic echo sounding (basic frequency equal to 1 MHz) in a laboratory tank. Using computer processing, the illumination profiles in the schlieren pattern are constructed on scales comparable with the sounding acoustic ray width. Although the optical and acoustic profiles are not similar, nevertheless they enable the basic structural elements of the wake, including its high-gradient core to be identified, and their time variability traced. The features of the integral acoustic scattering characteristic, in particular, the volume scattering strength, allow this characteristic to be used, together with optical images of the flow pattern, to distinguish the flow regime identification criteria.

Surface-tension-gradient-induced flow in freely suspended liquid crystalline films.

Flow was created in freely suspended liquid crystal films (FSLCFs) in the smectic-C phase using gradients in the surface tension to drive the motion. The director field was distorted into a pattern of vortices which wind upon themselves while a temperature gradient was applied. A dependence of the pattern in the director field on the topological defects of index s=+1,0, or -1 that are isolated in the vortex of the flow was observed. The flow pattern for the s=-1 defect has not been observed in FSLCFs with other flow fields. The diffusion constant for the c\ensuremath{\rightarrow}^-director orientation is extracted from the orientation field patterns under flow and is com- pared to other independent measurements. The Schlieren pattern of the c\ensuremath{\rightarrow}^-director field will be shown to arise from the coupling between the fluid velocity and director orientation and will also be shown to be mediated by the topological index of the defect through the use of a model of the dynamical equations of a two-dimensional nematic. \textcopyright{} 1996 The American Physical Society.

Synthesis of Novel Coordination Polyurethanes

New coordination polyurethanes based on novel diols bis[N-[[2-hydroxyphenyl]methylene]hydroxyl-ethyleneamino]-copper (II), cobalt (II), and nickel (II) were synthesized successfully. The products are elastomeric materials or powders. Similar to other polyurethane elastomers, the block copolymers synthesized in this paper exhibit two-phase microstructure and thermoplastic properties. Some samples show a Schlieren pattern under the polarizing optical microscope. The geometric structure of the ionic domains, which plays an important role in the properties of these materials, was determined by the nature of the metal ions.