Structures In Mixing Layer Research Articles

Flow visualization of the large-scale structures in supersonic mixing layer with a recirculation flow region

Flow visualization of the large-scale structures in supersonic mixing layer with a recirculation flow region

Correction of Depth Bias in Upper-Ocean Temperature and Salinity Profiling Measurements from Airborne Expendable Probes

AbstractDuring the Dynamics of Madden–Julian Oscillation (DYNAMO) Experiment in 2011, airborne expendable conductivity–temperature–depth (AXCTD) probes and airborne expendable bathythermographs (AXBTs) were deployed using NOAA’s WP-3D Orion aircraft over the southern tropical Indian Ocean. From initial analysis of the AXCTD data, about 95% of profiles exhibit double mixed layer structures. The presence of a mixed layer from some of these profiles were erroneous and were introduced because of the AXCTD processing software not being able to correctly identify the starting point of the probe descent. This work reveals the impact of these errors in data processing and presents an objective method to remove such erroneous data from the profiles using spectrograms from raw audio files. Reconstructed AXCTD/AXBT profiles are compared with collocated shipborne conductivity–temperature–depth (CTD) and expendable bathythermograph (XBT) profiles and are found to be in good agreement.

Holmehus clay — A Tertiary smectitic clay of potential use for isolation of hazardous waste

The Danish Tertiary Holmehus clay belongs to the series of illite–smectite mixed-layer clays in northern Europe and has a potential to serve as an effective engineered barrier for isolating hazardous waste. Mineralogical specification was made of the components illite/smectite mixed-layer and dioctahedral vermiculite/smectite mixed-layer structures. The lower content of expandable phases than of smectite-rich clays like MX-80 gives somewhat higher hydraulic conductivity and somewhat lower swelling pressure. Both are deemed suitable for isolating canisters with high-level radioactive waste in deep repositories for densities at water saturation of at least 1900kg/m3. Holmehus clay has fulfilled the demanded parameters for swelling pressure with >0.3MPa and hydraulic conductivity with <10 E−12m s−1 under this density. The lower swelling pressure, the potential of being chemically more stable, and the high buffer capacity by providing dissolved Si makes Holmehus clay a candidate for use in both deep and near-surface repositories.

Technique for determination of the content of smectite layers in the dispersed dioctahedral K-bearing micaceous minerals

A technique was developed to determine the low contents of smectite layers in the dispersed dioctahedral K-bearing micaceous minerals of the illite-glauconite composition. To implement this technique, diffraction patterns were calculated for two-component mixed-layer mica-smectite structures, in which the content of smectite layers increased with a step of 2% from 2 to 20% at a short-range order factor R = 0 and from 2 to 14% at R = 1. On the basis of Mering’s principles (1949) and Q-rules (Moore and Reynolds, 1989), the half-width βcosθ of each basal refection and its distance Q to the nearest reflection corresponding to the periodical structure made up of 9.98 A micaceous layers were calculated for mixed-layer structures with the given content of smectite layers WSm. The Q dependence on βcosθ for the series of basal reflections observed in the calculated diffraction pattern was approximated by a straight line corresponding to the linear regression equation. Equations relating slope angles of straight line (α) and concentrations of smectite layers (WSm) were deduced for the analyzed mixed-layer structures with the short-range order factors R = 0 and R = 1, respectively. To determine the contents of smectite layers in natural micaceous varieties, the basal reflections observed in experimental patterns from the oriented ethylene glycol-saturated samples were subjected to the following procedures: (1) determination of the half-width (βcosθ)e of each 00l reflection of the analyzed sample and plotting Q dependence on (βcosθ)e for the observed series of basal reflections, with its further approximation by the linear regression equation and the corresponding straight line; (2) calculation of the slope angle of this straight line α and determination of the content of smectite layers in the sample structure using the equation relating α and WSm. Application of the described procedure showed that the content of smectite layers in the studied samples varied from 5.2 to 12.6%. The content of smectite layers was determined accurate to a few tenths of a percent. Since the half-width of reflection 003 does not depend on the content of smectite layers, its value was used to determine the thickness and number of layers in the averaged CSD of the studied sample. XRD patterns calculated for mixed-layer structures with experimentally determined WSm, WMc, R, T, and N parameters are in a good agreement with experimental patterns of the studied samples.

Experimental Investigation on the Plasma Torch Used for Scramjet Ignition Enhancement

A high frequency arc discharge plasma torch was specially designed for ignition enhancement in scramjet combustor. At first, the process of plasma injection into quiescent air was investigated experimentally through CCD camera and schlieren technology. Then, the energy property characterization of active particle distribution was measured by emission spectrometry. Several kinds of working gas under different injection pressures were compared. Finally, the typical supersonic flow-field structure with plasma cross-injection was obtained. The results show that plasma jet energy is concentrated near the jet axis, which has the maximum attenuation in the downstream as far as 2 cm from the outlet. The working gas and injection pressure have great effect on emission spectrometry and the process of jet expansion. The case with N2 under higher injection pressure shows better performance of energy exchanging process when comparing with air and argon. From the emission spectroscopy, we can see that plasma from nitrogen consists of nitrogen and oxygen atom mainly, whose intensity decreases with increasing distance from the nozzle, while it increases with the increase of pressure. When plasma was vertically injected into supersonic flow-field, bow shock wave and mixing layer structure were formed with thicken mixing layer, which helps enhance the mixing process between active particle and incoming air.

Gasdynamic structure of an axisymmetric supersonic underexpanded jet

The steady-state structure of supersonic underexpanded jet flow at Ma = 1 is experimentally investigated. The measured total pressure distributions are presented in different cross sections and along the jet axis. Certain distinctive features of the supersonic jet flow are revealed. Among these are considerable fluctuations of the density distribution in the mixing layer formed behind the triple point on the normal shock in the jet. They are due to the presence of vortex structures in the internal mixing layer. The data obtained are used in testing the results of numerical calculations.

0806 高マッハ数域での乱流混合層における音源のマッハ数及び密度比依存性

The convective Mach number and density ratio dependences of sound sources and flow structures in a compressible mixing layer are investigated by direct numerical simulations. Characteristics of sound sources are analyzed using the source terms of Lighthill equation. As the Mach number increases sound source strength decreases, because vortex motion is weakened by compressibility. For density ratio dependence, the emission angle of Mach waves becomes shallower and vortices show sparse structures as density ratio increases. In addition, larger vortex structures appear at lower density side for higher density case.

An Experimental Investigation of the Supersonic Planar Mixing Layer with Finite Thickness

Nanoparticle-based Planar Laser Scattering (NPLS) experiments were launched to get the fine structure of the supersonic planar mixing layer with finite thickness in the present study. Different from the turbulent development of supersonic planar mixing layer with thin thickness, the development of supersonic planar mixing layer with finite thickness is rapidly. The large-scale structures of mixing layer that possess the characters of quick movement and slow changes transmit to downriver at invariable speed. The transverse results show that the mixing layer is strip of right and dim and possess 3D characteristics. Results indicate that the higher the pressure of the high speed side, the thicker the mixing layer is. The development of mixing layer is restrained when the pressure of lower speed side is higher. The present study can make a contribution to the mixing enhancement.

Detached eddy simulation of shallow mixing layer development between parallel streams

Results of a high resolution Detached Eddy Simulation (DES) are used to characterize the evolution of a shallow mixing layer developing between two parallel streams in a long open channel with a smooth flat bed and medium size dunes. The study discusses the vertical non-uniformity in the mixing layer structure and provides a quantitative characterization of the growth of the large-scale quasi two-dimensional (2D) coherent structures with the distance from the splitter plate. Results show that in streamwise sections situated between 75D (D is the channel depth) and 150D from the splitter plate, the width of the mixing layer close to the free surface is 20–30% more than the width in the near-bed region. This is mostly because of the tilting of the mixing layer interface on the low-speed side toward the low speed stream as the free surface is approached. Power spectra of the horizontal velocity components near the free surface show the presence of a −3 subrange, corresponding to inverse energy cascade in two-dimensional turbulence, at streamwise locations situated more than 10D from the splitter plate, consistent with the presence of large-scale quasi 2D horizontal eddies and the transfer of energy (inverse energy cascade) from the smaller scales toward these eddies. Consistent with visualizations of the mass transport of a passive scalar within the mixing layer, close to the free surface, the estimated streamwise length of the quasi 2D mixing layer eddies is about 2.5–3.0 times larger than the local width of the mixing layer. The presence of large-scale roughness elements in the form of an array of two-dimensional dunes with a maximum height of 0.25D (D is the channel depth) induces a much more rapid and larger shift of the centerline of the mixing layer due to the increased influence of the bottom roughness.

Fourier analysis of the roll-up and merging of coherent structures in shallow mixing layers

The current study investigates the role of nonlinearity in the development of two-dimensional coherent structures (2DCS) in shallow mixing layers. A nonlinear numerical model based on the depth-averaged shallow water equations is used to investigate temporal shallow mixing layers, where the mapping from temporal to spatial results is made using the velocity at the center of the mixing layer. The flow is periodic in the stream-wise direction and the transmissive boundary conditions are used in the cross-stream boundaries to prevent reflections. The numerical results are examined with the aid of Fourier decomposition. Results show that the previous success in applying local linear theory to shallow mixing layers does not imply that the flow is truly linear. Linear stability theory is confirmed to be only valid within a short distance from the inflow boundary. Downstream of this linear region, nonlinearity becomes important for the roll-up and merging of 2DCS. While the energy required for the merging of 2DCS is still largely provided by the velocity shear, the merging mechanism is one where nonlinear mode interaction changes the velocity field of the subharmonic mode and the gradient of the along-stream velocity profile which, in turn, changes the magnitude of the energy production of the subharmonic mode by the velocity shear implicitly. The nonlinear mode interaction is associated with energy up-scaling and is consistent with the inverse energy cascade which is expected to occur in shallow shear flows. Current results also show that such implicit nonlinear interaction is sensitive to the phase angle difference between the most unstable mode and its subharmonic. The bed friction effect on the 2DCS is relatively small initially and grows in tandem with the size of the 2DCS. The bed friction also causes a decrease in the velocity gradient as the flow develops downstream. The transition from unstable to stable flow occurs when the bed friction balances the energy production. Beyond this point, the bed friction is more dominant and the 2DCS are progressively damped and eventually get annihilated. The energy production by the velocity shear plays an important role from the upstream end all the way to the point of transition to stable flow. The fact that linear stability theory is valid only for a short distance from the inflow boundary suggests that some elements of nonlinearity is incorporated in the mean velocity profile in experiments by the averaging process. The implicit nature of nonlinear interaction in shallow mixing layers and the sensitivity of the nonlinear interaction to phase angle difference between the most unstable mode and its subharmonic allows local linear theory to be successful in reproducing features of the instability such as the dominant mode of the 2DCS and its amplitude.

Palaeo-earthquake events during the late Early Palaeozoic in the central Tarim Basin (NW China): evidence from deep drilling cores

Abstract Various millimetre-, centimetre- and metre-scale soft-sediment deformation structures (SSDS) have been identified in the Upper Ordovician and Lower-Middle Silurian from deep drilling cores in the Tarim Basin (NW China). These structures include liquefied-sand veins, liquefaction-induced breccias, boudinage-like structures, load and diapir- or flame-like structures, dish and mixed-layer structures, hydroplastic convolutions and seismic unconformities. The deformed layers are intercalated by undeformed layers of varying thicknesses that are petrologically and sedimentologically similar to the deformed layers. The SSDS developed in a shelf environment during the early Late Ordovician and formed initially under shear tensile stress conditions, as indicated by boudinage-like structures; during the latest Ordovician, SSDS formed under a com-pressional regime. The SSDS in the Lower-Middle Silurian consist mainly of mixed layers and sand veins; they formed in shoreline and tidal-flat settings with liquefaction features indicating an origin under a compressional stress regime. By Silurian times, the centre of tectonic activity had shifted to the south-eastern part of the basin. The SSDS occur at different depths in wells that are close to the syn-sedimentary Tazhong 1 Fault (TZ1F) and associated reversed-thrust secondary faults. Based on their characteristics, the inferred formation mechanism and the spatial association with faults, the SSDS are interpreted as seismites. The Tazhong 1 fault was a seismogenic fault during the later Ordovician, whereas the reversed-direction secondary faults became active in the Early-Middle Silurian. Multiple palaeo-earthquake records reflect pulses and cyclicity, which supports secondary tectonic activity within the main tectonic movement. The range of SSDS structures reflects different developments of tectonic activity with time for the various tectonic units of the centralbasin. The effects of the strong palaeo-earthquake activity coincide with uplift, fault activity and syn-tectonic sedimentation in the study area during the Late Ordovician to Middle Silurian.

Effect of the hydration sequence orientation on the structural properties of Hg exchanged montmorillonite: Quantitative XRD analysis

The use of montmorillonite for removing mercury is an effective technology for the treatment of industrial wastewaters and can become an effective tool for the remediation of ecosystems polluted with this metal. In order to assess the influence of hydration/dehydration orientation on the structural properties of the Hg exchanged montmorillonite a quantitative XRD analysis at room and under controlled atmosphere (variable RH rates) is conducted. This study is based on the modeling approach which consists in the comparison of experimental 00l reflections with the calculated ones deduced from structural models. This approach allows us to determine the amount of the interlayer water molecules, structural changes along the c* axis and reaches the relative layer types contributions. The obtained main results show that all experimental profiles are simulated using a mixed layer structure with various proportions of bihydrated (0W), mono-hydrated (1W), dehydrated (2W) and three-hydrated (3W) layer types, which demonstrate the heterogeneous hydration character over all RH rates. The hydrous perturbation is accompanied by an irreversible gradual growth of the interlayer water molecules content.

Comparison of organic light emitting diodes with different mixed layer structures

A mixed-source thermal evaporation method was used to fabricate organic light emitting diodes (OLEDs) with uniformly mixed (UM), continuously graded mixed (CGM) and step-wise graded, mixed (SGM) light-emitting layers. N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine and Tris-(8-hydroxyquinoline)aluminum were used, respectively, as the hole- and electron-transport materials. As compared to the conventional, heterojunction OLED, the maximum brightness of UM-, CGM- and SGM-OLEDs without charge injection layers were improved by 2.2, 3.8 and 2.1 times, respectively, while the maximum power efficiencies improved by 1.5, 3.2 and 1.9 times. These improvements were discussed in terms of more distributed recombination zone and removal of interfacial barrier.

2D-DNS and 2D-RANS Simulations of Supersonic QUASI-2D Turbulent Reacting Shear Flow

&lt;p&gt;Numerical studies of quasi-2D supersonic turbulent hydrogen-air mixing and combustion in free shear layer configuration are performed using 2D-DNS [1] and RANS equations. In order to produce the roll-up and pairing of vortex rings, an unsteady boundary condition is applied at the inlet plane. Frequencies of&lt;br /&gt; initial velocity perturbations have been taken in accordance with linear stability theory. The influences of different inflow perturbations on mixing layer structure are presented. At the outflow, the non-reflecting boundary condition is adopted. In the case of RANS simulation two-parameter k-e turbulence model is used. Thermal conduction is described by Fourier’s law, while diffusion of species by Fick’s law. Equation of state for thermally perfect multispecies gas is used. Thermodynamic parameters, such as specific heat, enthalpy, entropy and internal energy are determined by fourth order degree polynomial formula, which has dependence on temperature. Temperature is determined using Newton-Raphson iteration procedure. The Wilke’s formula is used to determine the mixture viscosity coefficient. Approximation of convection terms are performed by the ENO-scheme of third-order accuracy and approximation of diffusion terms – by second-order central-difference operators. For the description of reaction pathways of hydrogen, a seven species chemical reaction model by Jachimowski is adopted. Chemical reaction source term implicitly includes in mass fraction transport equations, where linearization is applied using Taylor decomposition. The hydrogen flow parameters are M&lt;sub&gt;0&lt;/sub&gt; = 2.0, T&lt;sub&gt;0&lt;/sub&gt; = 2000 K, P&lt;sub&gt;0&lt;/sub&gt; = 101325 Pa, and air flow parameters are M&lt;sub&gt;¥&lt;/sub&gt; = 2.1, T&lt;sub&gt;¥&lt;/sub&gt; = 2000 K, p&lt;sub&gt;¥&lt;/sub&gt; = 101325 Pa. Convective Mach number is M&lt;sub&gt;c&lt;/sub&gt; = 0.38, where effect of compressibility is significant.&lt;/p&gt;

Correlation of band gap position with composition in high-k films

Two series of ultrathin high-k samples (mixed layers HfxAlyOz and bilayers HfO2 on Al2O3) prepared by atomic layer deposition were investigated using spectroscopic ellipsometry in the energy range of 0.7–10.0 eV. The (effective) optical gap of both mixed layer and bilayer structures can be tuned by the film composition. The optical gap of mixed layers is linearly dependent on the Hf fraction from 5.77 (±0.02) eV for pure HfO2 to 6.71 (±0.02) eV for pure Al2O3. The effective absorption gap of bilayers measured in reflection geometry is lower than that of mixed layers with a comparable Hf fraction due to the dominant effect of the top layer. An increase in film thickness as well as a decrease in refractive index and gap energy was observed after sample storage for two months in atmosphere. The aging effect is likely due to further oxidation of the oxygen deficient high-k films caused by the oxygen diffusion from air into the films.

Interlamellar Space Configuration under Variable Environmental Conditions in the Case of Ni‐Exchanged Montmorillonite: Quantitative XRD Analysis

Interlamellar space organization of low‐charge montmorillonite was studied by modeling of X‐ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Ni saturated specimens. The quantitative XRD investigation, based on an indirect method consisting of the comparison of experimental reflections with the other calculated from structural models, is used to characterize eventual nanostructural changes along c* axis of Ni‐exchanged montmorillonite. This method allowed us to determine, respectively, the relative layer types contribution, the layer thickness, nanoconfiguration of the interlamellar space, and position, amount, and organization of water molecules and exchangeable cations. Obtained theoretical models exhibit heterogeneous hydration state which is the dominating character detected all over studied cycles. Along RH cycle a modification in the main structure of the host materials is performed and the presence of a mixed layer structure (MLS) is noted. The hydration hysteresis at the low and the high RH range can be explained by fluctuations in the water retention mechanism and hydration heterogeneities created within the smectite crystallite.

粘土鉱物の鉱物学的特性と探査指標としての応用

Clay minerals widely occur as a product of the water-rock interaction in hydrothermal, diagenetic and weathering systems at the surficial part of the earth. They show highly diverse and systematic variations in mineralogical properties related to their localities and occurrences. The mineralogical properties of the clay minerals such as mineral chemistry, mixed-layer structure, polytype, particle size, etc., have been investigated to understand the environmental conditions of mineral formation. Recent studies on the chemical compositions and the particle size of clay minerals show that they can be linked to the physicochemical conditions and/or hydrogeological conditions of water-rock interactions performed in the surficial geologic systems. The chlorite geothermometer which links the chlorite compositions to temperature conditions of formation, is highly applicable as a physicochemical index of the water-rock interaction at hydrothermal systems. The particle size properties of clay minerals can be related to their crystal-growth mechanisms and to the hydrogeological conditions of mineral formations, in the water-rock interaction including kinetic reaction. These suggest that the chemical composition and the particle size property of clay minerals are usable as a mineralogical indicator also in exploration of natural resources hosted in the surficial parts of the earth.

Characteristics of Large-Scale Structures in Supersonic Planar Mixing Layer with Finite Thickness

Nanoparticle-based planar laser scattering (NPLS) experiments and large eddy simulation (LES) were launched to get the fine structure of the supersonic planar mixing layer with finite thickness in the present study. Different from the turbulent development of supersonic planar mixing layer with thin thickness, the development of supersonic planar mixing layer with finite thickness is rapidly. The large-scale structures of mixing layer that possess the characters of quick movement and slow changes transmit to downriver at invariable speed. The transverse results show that the mixing layer is strip of right and dim and possess 3D characteristics. Meanwhile the vortices roll up from two sides to the center. Results indicate that the higher the pressure of the high speed side is, the thicker the mixing layer is. The development of mixing layer is restrained when the pressure of lower speed side is higher. The momentum thickness goes higher with the increase of the clapboard thickness. Through increasing the temperature to change the compression can affect the development of the vortices. The present study can make a contribution to the mixing enhancement and provide initial data for the later investigations.

Ship-in-bottle synthesis of the mixed-layered compounds of clay silicate/zirconium phosphate.

An attempt was made to synthesize artificial mixed-layered compounds between montmorillonite silicate and α-zirconium phosphate using a ship-in-bottle approach. The interlayer cations of montmorillonite were first exchanged with hydroxy-zirconium oligomeric cations, which were then subjected to a reaction with phosphoric acid or phenylphosphoric acid to develop α-zirconium phosphate layers (Zr(R-OPO3)2; R = H, C6H5) between the clay silicate layers. The attempt of the reaction with phosphoric acid failed; hydroxy-zirconium cations were removed out of the interlayer space, forming α-zirconium phosphate outside of montmorillonite. The phenylphosphate derivative, montmorillonite/Zr(C6H5OPO3)2, with a regular mixed-layered structure has been successfully obtained, showing a basal spacing corresponding to the sum of the thicknesses of the individual layers. When a polyvinyl alcohol (PVA) aqueous solution was used in the preparation of the hydroxy-zirconium exchanged montmorillonite, PVA was incorporated with hydroxy-zirconium complex cations between the silicate layers. The resulting compound can adsorb phosphate ions. Although this is not a mixed-layered compound in the context of this study, the selective and reversible phosphate ion exchange properties are worth noting for future study.

Viscous Kelvin–Helmholtz instabilities in highly ionized plasmas

Transport coefficients in highly ionized plasmas like the intracluster medium (ICM) are still ill-constrained. They influence various processes, among them the mixing at shear flow interfaces due to the Kelvin–Helmholtz instability (KHI). The observed structure of potential mixing layers can be used to infer the transport coefficients, but the data interpretation requires a detailed knowledge of the long-term evolution of the KHI under different conditions. Here we present the first systematic numerical study of the effect of constant and temperature-dependent isotropic viscosity over the full range of possible values. We show that moderate viscosities slow down the growth of the KHI and reduce the height of the KHI rolls and their rolling-up. Viscosities above a critical value suppress the KHI. The effect can be quantified in terms of the Reynolds number Re=Uλν, where U is the shear velocity, λ the perturbation length and ν the kinematic viscosity. We derive the critical Re for constant and temperature-dependent Spitzer-like viscosities, an empirical relation for the viscous KHI growth time as a function of Re and density contrast, and describe special behaviours for Spitzer-like viscosities and high density contrasts. Finally, we briefly discuss several astrophysical situations where the viscous KHI could play a role, i.e. sloshing cold fronts, gas stripping from galaxies, buoyant cavities, ICM turbulence and high-velocity clouds.