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1
Juraeva, Makhsuda, et Dong Jin Kang. « Mixing Performance of a Cross-Channel Split-and-Recombine Micro-Mixer Combined with Mixing Cell ». Micromachines 11, no 7 (15 juillet 2020) : 685. http://dx.doi.org/10.3390/mi11070685.
Texte intégralRésumé :
A new cross-channel split-and-recombine (CC-SAR) micro-mixer was proposed, and its performance was demonstrated numerically. A numerical study was carried out over a wide range of volume flow rates from 3.1 μL/min to 826.8 μL/min. The corresponding Reynolds number ranges from 0.3 to 80. The present micro-mixer consists of four mixing units. Each mixing unit is constructed by combining one split-and-recombine (SAR) unit with a mixing cell. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the present micro-mixer performs better than other micro-mixers based on SARs over a wide range of volume flow rate. The mixing enhancement is realized by a particular motion of vortex flow: the Dean vortex in the circular sub-channel and another vortex inside the mixing cell. The two vortex flows are generated on the different planes perpendicular to each other. They cause the two fluids to change their relative position as the fluids flow into the circular sub-channel of the SAR, eventually promoting violent mixing. High vorticity in the mixing cell elongates the flow interface between two fluids, and promotes mixing in the flow regime of molecular diffusion dominance.
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Zazymko, V. O., M. F. Kalinina, V. Y. Shibetsky et O. M. Nedbailo. « Hydrodynamics of a reactor with updated structure of frame mixing device ». Кераміка : наука і життя, no 3(52) (30 septembre 2021) : 7–14. http://dx.doi.org/10.26909/csl.3.2021.1.
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This article is devoted to computer simulation of the hydrodynamic situation in a reactor with a standard design and an upgraded design of a frame stirrer. A comparative analysis of the hydrodynamics of fluid flows occurring in the volume due to the use of classical and modernized design was performed. An upgraded design of a frame stirrer for homogenizing the medium in a reactor has been proposed.
The aim of this work was to study the influence of the geometry of the stirrer blades and their location in space on the speed and direction of flows in the reactor.
The basis for the new design of the mixing device was the standard design of the frame mixer with two horizontal jumpers. Installation of additional blades and their placement at a certain angle to the vertical and horizontal planes and relative to each other was considered as one of the methods of improving the design.
For this work, the study was conducted in the universal software system of finite element analysis ANSYS. Computer simulation is used to analyze complex systems and processes based on a computer model.
The simulation was performed to analyze the influence of the geometry of the mixing device on the speed and direction of fluid flow in the apparatus. To conduct the study, 3D-models of two different types of geometry of the mixing device were built, physicomechanical parameters of the environment in the reactor were set and on the basis of these data the mixing process in the apparatus was modeled. In this work, the influence of plate geometry and their location in space on hydrodynamics is investigated. The basis of the proposed design of the mixing device is the task of intensifying the mixing process by increasing the mixing efficiency along the height of the apparatus.
A comparative analysis of the direction of fluid flow, its velocity and temperature change using a standard and upgraded design of the mixing device was performed.
It was found that when installing additional plates that are located at an angle to the horizontal and vertical planes in the reactor there are additional axial and radial fluid flows, which improves homogeneity and increases the intensity of mixing.
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Robens, Tania. « Two-Real-Singlet-Model Benchmark Planes ». Symmetry 15, no 1 (22 décembre 2022) : 27. http://dx.doi.org/10.3390/sym15010027.
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In this manuscript, I briefly review the Benchmark Planes in the Two-Real-Singlet Model (TRSM), a model that enhances the Standard Model (SM) scalar sector by two real singlets that obey a Z2⊗Z2′ symmetry. In this model, all fields acquire a vacuum expectation value, such that the model contains in total three CP-even neutral scalars that can interact with each other. All interactions with SM-like particles are inherited from the SM-like doublet via mixing. I remind the readers of the previously proposed benchmark planes and briefly discuss possible production at future Higgs factories, as well as regions in a more generic scan of the model. For these, I also discuss the use of the W-boson mass as a precision observable to determine allowed/excluded regions in the models’ parameter space. This work is an extension of a white paper submitted to the Snowmass process.
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Andrievschi, Serghei, Valeriu Lungu, Ala Carcea et Alexandru Lozan. « The Quality of Mixing in Mixers with Bars and Radial and Longitudinal Scrapers ». Romanian Journal of Transport Infrastructure 2, no 1 (1 juillet 2013) : 10–20. http://dx.doi.org/10.1515/rjti-2015-0008.
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Abstract The process of division - combining of streams in mixers with bars and radial and longitudinal scrapers was studied. The number of unique streams that are formed after passing each row of longitudinal bars and the total amount of them were determined. This is demonstrated by migration of the particles along the mixer from left to right and vice versa, from the center of the drum towards the periphery and vice versa. In the process of mixing the particles in the center gain normal distribution and the ones on the side - sectioned normal distribution. The sum of normal distribution with the sectioned normal distribution leads to an equable distribution along the drum and transverse planes and to a homogeneous mixing of the components. The quality of mixing had been investigated and an optimal mixing regime for the mixer with radial and longitudinal bars and scrapers was proposed.
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Dawes, W. N. « Toward Improved Throughflow Capability : The Use of Three-Dimensional Viscous Flow Solvers in a Multistage Environment ». Journal of Turbomachinery 114, no 1 (1 janvier 1992) : 8–17. http://dx.doi.org/10.1115/1.2928002.
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A methodology is presented for simulating turbomachinery blade rows in a multistage environment by deploying a standard three-dimensional Navier–Stokes solver simultaneously on a number of blade rows. The principal assumptions are that the flow is steady relative to each blade row individually and that the rows can communicate via inter-row mixing planes. These mixing planes introduce circumferential averaging of flow properties but preserve quite general radial variations. Additionally, each blade can be simulated in three-dimensional or axisymmetrically (in the spirit of throughflow analysis) and a series of axisymmetric rows can be considered together with one three-dimensional row to provide, cheaply, a machine environment for that row. Two applications are presented: a transonic compressor rotor and a steam turbine nozzle guide vane simulated both isolated and as part of a stage. In both cases the behavior of the blade considered in isolation was different to when considered as part of a stage and in both cases was in much closer agreement with the experimental evidence.
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Stelmach, Jacek, Czesław Kuncewicz, Łukasz Adrian, Tomaš Jirout et Frantisek Rieger. « Change in Mixing Power of a Two-PBT Impeller When Emptying a Tank ». Processes 9, no 2 (13 février 2021) : 341. http://dx.doi.org/10.3390/pr9020341.
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The paper presents research on the phenomenon of an increase in mixing power during the emptying of a tank with two 6-PBT45° axial impellers in operation, located on a common shaft, pumping the liquid to the bottom of the mixing tank. A large increase in mixing power took place when the free surface of the liquid was just above the upper edge of one of the impellers (hp/D < 0.1). This increase was even more than 50% compared to the design power for a fully filled mixing vessel. Admittedly, high motor overload, while not very long, may damage it. The study investigated the instantaneous torques acting on the impeller shaft during the emptying of the tank and the velocity distributions in planes r-z. On their basis, the mechanism of the phenomenon observed was determined and correlation relationships were given that permitted the calculation of the numerical values of the power increase factors.
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Gevorkyan, L., T. Shoji, D. R. Getsinger, O. I. Smith et A. R. Karagozian. « Transverse jet mixing characteristics ». Journal of Fluid Mechanics 790 (2 février 2016) : 237–74. http://dx.doi.org/10.1017/jfm.2016.5.
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This experimental study explores and quantifies mixing characteristics associated with a gaseous round jet injected perpendicularly into cross-flow for a range of flow and injection conditions. The study utilizes acetone planar laser-induced fluorescence imaging to determine mixing metrics in both centreplane and cross-sectional planes of the jet, for a range of jet-to-cross-flow momentum flux ratios ($2\leqslant J\leqslant 41$), density ratios ($0.35\leqslant S\leqslant 1.0$) and injector configurations (flush nozzle, flush pipe and elevated nozzle), all at a fixed jet Reynolds number of 1900. For the majority of conditions explored, there is a direct correspondence between the nature of the jet’s upstream shear layer instabilities and structure, as documented in detail in Getsingeret al.(J. Fluid Mech., vol. 760, 2014, pp. 342–367), and the jet’s mixing characteristics, consistent with diffusion-dominated processes, but with a few notable exceptions. When quantified as a function of distance along the jet trajectory, mixing metrics for jets in cross-flow with an absolutely unstable upstream shear layer and relatively symmetric counter-rotating vortex pair cross-sectional structure tend to show better local molecular mixing than for jets with convectively unstable upstream shear layers and generally asymmetric cross-sectional structures. Yet the spatial evolution of mixing with downstream distance can be greater for a few specific convectively unstable conditions, apparently associated with the initiation and nature of shear layer rollup as a trigger for improved mixing. A notable exception to these trends concerns conditions where the equidensity jet in cross-flow has an upstream shear layer that is already absolutely unstable, and the jet density is then reduced in comparison with that of the cross-flow. Here, density ratios below unity tend to mix less well than for equidensity conditions, demonstrated to result from differences in the nature of higher-density cross-flow entrainment into lower-density shear layer vortices.
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Hart, M., T. Koga et Y. Takano. « Mixing Symmetric and Oblique Bragg Reflections in Rigid Channel-Cut Crystals ». Journal of Applied Crystallography 28, no 5 (1 octobre 1995) : 568–70. http://dx.doi.org/10.1107/s0021889895003992.
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Because the Bragg angle and Darwin range of total reflection in symmetric and oblique Bragg reflections vary with the angle between the Bragg planes and the crystal surface, it is generally believed that the resulting mismatch causes a loss of intensity in monolithic channel-cut crystals that is unacceptable in practice. It has been discovered that in the unique case of the 220 Bragg reflection from germanium no mismatch occurs, so that oblique and symmetric reflections can be mixed in one rigid channel-cut crystal. The results are valid for both X-ray and neutron channel-cut monochromators.
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Kapulla, R., U. Doll, E. Kirkby, S. Paranjape et D. Paladino. « Growth laws and self-similarity in the confined mixing zone of unstratified and strongly stably stratified isokinetic mixing-layers past a splitter plate ». Physics of Fluids 34, no 3 (mars 2022) : 035129. http://dx.doi.org/10.1063/5.0082950.
Texte intégralRésumé :
The velocity U and the mixing scalar field Θ of turbulent wake flows developing downstream of a slender splitter plate were studied experimentally for unstratified and strongly stably stratified conditions in a square channel with water as fluid. The experimental program comprises five different Reynolds numbers spanning [Formula: see text]–60 000 for [Formula: see text] (isokinetic conditions) between the two planar, initially separated streams and five relative density stratifications from [Formula: see text] to 10%, since mixing studies for these stratification strengths are rather limited. This full-channel Reynolds number uses the hydraulic diameter [Formula: see text] of the mixing section as the characteristic length scale. These experiments challenge the corresponding numerical calculations based on Reynolds-averaged Navier–Stokes approaches relying on the Boussinesq approximations of the first and second kind. The development of the mixing scalar field Θ was measured by two fundamentally different approaches: laser induced fluorescence (LIF) in the downstream x– y mid-plane and wire-mesh sensors (WMSs) in discrete lateral y– z planes. This allows for a direct comparison of both sensing techniques at locations where both planes intersect. For the unstratified conditions, it is shown that the downstream developing wake velocity deficit decay agrees well with the theoretical approach. The concentration fields based on LIF and WMS profiles of the mean and fluctuating (root mean square, RMS) data confirm self-similarity by introducing a mixing scalar Θ for both techniques. In the approximate limit, it is shown that the mean concentration field can be well described by an error function and the corresponding RMS data by a Gaussian profile in self-similar coordinates. By using the momentum thickness θm at the splitter plate as the normalization parameter, the downstream developing width of the mixing zone [Formula: see text] becomes independent for [Formula: see text]. The mean and the RMS values of the concentration field Θ for the stably stratified experiments show self-similarity in the core of the concentration field but also a departure from the error function and Gaussian profile in the outer parts. Introducing a local gradient Richardson number Rig, it is shown that both the growth and growth-suppression of the mixing zone are well described by the Miles–Howard criterion for all the stratified experiments considered, even though this criterion was originally developed for shear layers.
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Lu, Tao, Xing Guo Zhu, Ping Wang et Wei Yyu Zhu. « Numerical Simulation of Flow and Heat Transfer with Large-Eddy Simulation in a Mixing T-Junction ». Applied Mechanics and Materials 152-154 (janvier 2012) : 1319–24. http://dx.doi.org/10.4028/www.scientific.net/amm.152-154.1319.
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In the present paper, large-eddy simulation (LES) based on commercial computational fluid dynamics (CFD) software FLUENT for prediction of flow and heat transfer in a mixing T-junction was completed. Mean and root mean square (RMS) temperature and velocity were defined to describe the distributions and fluctuations of temperature and velocity. Numerical results indicate that profiles between symmetrical planes are almost same and the root mean square temperature and velocity close to the center of the main duct in the downstream are larger than those near the main duct wall. The prediction of the fluctuations of temperature and velocity is significant to understand the knowledge of the cause of thermal fatigue in a mixing T-junction.
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B S, Lokesh, et Dr Manjunatha M B. « A Novel Partial Thermal Image Encryption Scheme Based on Multiple Chaotic Systems ». International Journal of Engineering & ; Technology 7, no 3 (24 août 2018) : 1948. http://dx.doi.org/10.14419/ijet.v7i3.15880.
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In this paper, proposed an novel partial encryption scheme for protecting thermal images during transmission. The adopted technique having pixel level and bit level permutation process. To reduce time and computational complexity, an partial encryption technique is adopted. Arnold cat map technique involved in the pixel level permutation process to decrease correlation of original image. The proposed scheme selects only higher four binary planes for the bit level shuffling process. Where this process consists of row and column wise circular shift operation with the help of pseudo random numbers generated from chaotic map system. Mixing of binary planes of the thermal image will leads to prevent the differential attacks. Experimental results shows that proposed scheme exhibits good performance in terms entropy, NPCR and the speed of system.
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Moore, J., et R. Y. Adhye. « Secondary Flows and Losses Downstream of a Turbine Cascade ». Journal of Engineering for Gas Turbines and Power 107, no 4 (1 octobre 1985) : 961–68. http://dx.doi.org/10.1115/1.3239842.
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The loss mechanisms and the behavior of secondary flows downstream of a large scale, linear turbine cascade have been investigated experimentally. A five-blade replica of the cascade used by Langston et al. at United Technologies Research Center was used for the present tests. Detailed flow measurements, using five-hole and three-hole probes, were made at four different planes, one just upstream of the trailing edge and the rest downstream. The secondary flow field at each measurement plane was found to be dominated by a single large passage vortex, which decayed in strength because of the mixing occurring in the flow. More than one-third of the losses were found to occur downstream of the trailing edge. This rise in total pressure loss in the present tests was almost entirely explained by a corresponding dissipation of the secondary kinetic energy of the flow. A mixing analysis of the flow was done to predict the additional losses due to “mixing” until the flow became completely uniform.
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Shah, Imran, Emad Uddin, Aamir Mubashar, Muhammad Yamin Younis, Hudair Samad et Kyung Hyun choi. « Numerical Investigation of Surface Acoustic Wave (SAW) Interacting with a Droplet for Point-of-Care Devices ». International Journal of Acoustics and Vibration 24, no 4 (31 décembre 2019) : 632–37. http://dx.doi.org/10.20855/ijav.2019.24.41312.
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A three-dimensional numerical simulation of the interaction of a surface acoustic wave (SAW) with a droplet of water is carried out. The mixing produced inside the droplet due to the incident with the SAW and the droplet is investigated by undertaking a parametric study, with parameters such as frequency, drop size, and the lateral position of the droplet on the surface of the substrate. The linear relationship between the input voltage and the mixing velocity inside the droplet is obtained with variation of the input voltage of the inter-digital transducer (IDT) of the SAW device within a 10--40 V range. With the variation in frequency, the maximum mixing velocity is observed at 20 MHz and it appears to be independent of the size of the droplet. Varying the substrate material with lead zirconate titanate and lithium niobate produces better mixing. Lithium niobate is preferred due to its availability and cost-effectiveness. A drop of 600 um diameter produces better mixing. The different velocities inside the drop and the SAW device are obtained by changing the droplet position in the lateral direction (asymmetrical position) from the centre of the substrate. Cut planes parallel and perpendicular to the SAW at the core of a half-spherical droplet are observed to visualise the mixing effects inside the droplet during the interaction. To achieve the best mixing criteria, the droplet is moved in a lateral direction. An efficient parametric design for the mixing phenomena in micro-fluidic devices is presented for point-of-care devices.
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Xue, Wanyun, Wenxin Huai, Zhongdong Qian, Zhonghua Yang et Yuhong Zeng. « Numerical simulation of initial mixing of marine wastewater discharge from multiport diffusers ». Engineering Computations 31, no 7 (30 septembre 2014) : 1379–400. http://dx.doi.org/10.1108/ec-06-2013-0148.
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Purpose – The purpose of this paper is to examine the initial mixing of wastewater discharged from submerged outfall diffusers and the influence of port configurations on wastewater distribution based on computational results. Design/methodology/approach – Marine wastewater discharges from multiport diffusers are investigated by numerically solving three-dimensional and uncompressible two-phase flow fields. A mixture model simulates this flow and the standard k-e model to resolve flow turbulence; inter-phase interactions were described in terms of relative slip velocity between phases. Computations were performed for two values of the port spacings s/H with different current Froude numbers F. Findings – Computational results compared well with previous laboratory measurements. Numerical results reveal that for both the closely spaced (s/H=0.21) and widely spaced (s/H=3.0) ports, the normalized dilution Sn becomes independent of F; further, the length of the near field xn and the spreading layer thickness hn are functions of F. For the closely spaced ports, the wastewater discharge behaves like a line plume, the Coanda effect is obvious, quasi-bifurcation is present, horseshoe structures of the jets in the planes are rapidly produced and then squashed and elongated, and the jet trajectories based on maximum velocity precede those based on maximum concentration. For the widely spaced ports, the wastewater discharge behaves like a point plume, the Coanda effect is not obvious, bifurcation is present, horseshoe structures of the jets in the planes are gradually produced and become ellipses, and the jet trajectories based on maximum velocity are similar to those based on maximum concentration. Originality/value – Semi-empirical equations are presented to predict major near field characteristics. These provide guidance for designing multiport diffusers and assessing environmental impact.
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Xie, Sheng-Wu, et Xue-Lin Yang. « Phase matching conditions for four-wave mixing in the principal planes of biaxial crystals ». Optics Communications 135, no 4-6 (février 1997) : 321–26. http://dx.doi.org/10.1016/s0030-4018(96)00663-3.
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Cwudziński, A. « Chemical Homogenization Of Liquid Steel Flowed Through Continuous Casting Slab Tundish During Alloying Process ». Archives of Metallurgy and Materials 60, no 2 (1 juin 2015) : 561–65. http://dx.doi.org/10.1515/amm-2015-0174.
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AbstractThis paper presents the results of research on the behaviour of an alloy addition in steel flowing through the tundish used for casting slabs. The device under examination is a wedge-shaped single-nozzle tundish of a capacity of 30 Mg. Due to the complexity of alloy addition dissolution and dispersion in metallurgical processes, a decision was made to use the Species Model available within the Ansys-Fluent®program. For describing the turbulence, the Realizable k-ɛmodel was chosen. By defining the heat losses on respective planes making up the virtual model, the non-isothermal conditions existing during the flow of liquid steel through the tundish were considered. From the performed numerical simulations, the fields of steel flow and steel temperature and alloy addition concentration in the tundish working space were obtained. In order to accurately illustrate the process of chemical homogenization in the tundish working space, mixing curves were recorded. Based on the obtained results (mixing curves), the mixing time needed for achieving the 95% level of chemical homogenization was calculated.
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Chen, L. D., et S. L. Dixon. « Growth of Secondary Flow Losses Downstream of a Turbine Blade Cascade ». Journal of Engineering for Gas Turbines and Power 108, no 2 (1 avril 1986) : 270–76. http://dx.doi.org/10.1115/1.3239899.
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Endwall total pressure losses downstream of a low-speed turbine cascade have been measured at several planes in order to determine the changes in secondary flow loss coefficients and the growth of the mixing loss with distance downstream. The results obtained are compared with various published secondary flow loss correlations in an attempt to explain some of the anomalies which presently exist. The paper includes some new correlations including one for the important gross secondary loss coefficient YSG with loading and aspect ratio parameters as well as the upstream boundary layer parameters.
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Kouadri, A., Y. Lasbet et M. Makhlouf. « High mixing performances of shear-thinning fluids in two-layer crossing channels micromixer at very low Reynolds numbers ». Journal of Mechanical Engineering and Sciences 13, no 4 (30 décembre 2019) : 5938–60. http://dx.doi.org/10.15282/jmes.13.4.2019.15.0471.
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In a recent study, the Two-Layer Crossing Channels Micromixer (TLCCM) exhibited good mixing capacities in the case of the Newtonian fluids (close to 100%) for all considered Reynolds number values. However, since the majority of the used fluids in the industrial sectors are non-Newtonians, this work details the mixing evolution of power-law fluids in the considered geometry. In this paper, the power-law index ranges from 0.73 to 1 and the generalized Reynolds number is bounded between 0.1 and 50. The conservation equations of momentum, mass and species transport are numerically solved using a CFD code, considering the species transport model. The flow structure at the cross-sectional planes of our micromixer was studied using the dynamic systems theory. The evolutions of the intensity, also the axial, radial and tangential velocity profiles were examined for different values of the Reynolds number and the power-law index. Besides, the pressure drop of the power-law fluids under different Reynolds number was calculated and represented. Furthermore, the mixing efficiency is evaluated by the computation of the mixing index (MI), based on the standard deviation of the mass fraction in different cross-sections. In such geometry, a perfect mixing is achieved with MI closed to 99.47 %, at very small Reynolds number (from the value 0.1) whatever the power-law index and generalized Reynolds numbers taken in this investigation. Consequently, the targeted channel presents a useful tool for pertinent mass transfer improvements, it is highly recommended to include it in various microfluidic systems.
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DRAZEN, DAVID A., et W. KENDALL MELVILLE. « Turbulence and mixing in unsteady breaking surface waves ». Journal of Fluid Mechanics 628 (1 juin 2009) : 85–119. http://dx.doi.org/10.1017/s0022112009006120.
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Laboratory measurements of the post-breaking velocity field due to unsteady deep-water breaking are presented. Digital particle image velocimetry (DPIV) is used to measure the entire post-breaking turbulent cloud with high-resolution imagery permitting the measurement of scales fromO(1m) down toO(1mm). Ensemble-averaged quantities including mean velocity, turbulent kinetic energy (TKE) density and Reynolds stress are presented and compare favourably with the results of Melville, Veron & White (J. Fluid Mech., vol. 454, 2002, pp. 203–233; MVW). However, due to limited resolution, MVW's measurements were not spatially coherent across the turbulent cloud, and this restricted their ability to compute turbulent wavenumber spectra. Statistical spatial quantities including the integral length scaleL11, Taylor microscale λfand the Taylor microscale Reynolds numberReλare presented. Estimation of an eddy viscosity for the breaking event is also given based on analysis of the image data. Turbulent wavenumber spectra are computed and within 12 wave periods after breaking exhibit what have been termed ‘spectral bumps’ in the turbulence literature. These local maxima in the spectra are thought to be caused by an imbalance between the transport of energy from large scales and the dissipation at small scales. Estimates of the dissipation rate per unit mass are computed using both direct and indirect methods. Horizontally averaged terms in the TKE budget are also presented up to 27 wave periods after breaking and are discussed with regard to the dynamics of the post-breaking flow. Comparisons of the TKE density in the streamwise and cross-stream planes with the three-dimensional full TKE density are given in an appendix.
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Zhang, J. P., D. J. Li, C. Boldt, R. Plass, V. Dravid, L. D. Marks, C. H. Lin et al. « Microstructure and properties of Cu-rich 123 : Part II. Homogeneous copper and high magnetic Jc ». Journal of Materials Research 8, no 6 (juin 1993) : 1232–39. http://dx.doi.org/10.1557/jmr.1993.1232.
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Copper- and yttrium-rich YBa2Cu3O7 bulk superconductors have been prepared by mixing copper oxide or yttrium oxide in nitric acid and adding the solution to premade stoichiometric YBa2Cu3O7 followed by annealing. In contrast to materials made by mixing oxide powders, both samples contain copper-rich defects spread homogeneously throughout the grains, either small platelet copper oxide precipitates or bundles of planar defects (Cu–O double planes). These materials also show large magnetic hysteresis at 77 K, comparable to the results obtained from decomposed YBa2Cu4O8. This implies that small copper oxide precipitates and bundles of planar defects are strong flux pinners, and indicates a processing route to producing large amounts of strongly intragranular pinned superconductors. However, the materials also show clean grain boundaries, so an equally valid interpretation is that there is a substantial component of intergranular superconductivity in field, enhancing the effective circuit size to a value far larger than the grain size.
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Johnson, David A. « Analysis of the Immediate Boundary Conditions of an Axial Flow Impeller ». Journal of Fluids Engineering 123, no 4 (8 août 2001) : 771–79. http://dx.doi.org/10.1115/1.1412846.
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The design and analysis of impellers for mixing applications such as stirred tank reactors (STR) have significant application in many engineering processes. In particular, the evaluation of the turbulent flow boundary conditions immediately around a model impeller has been examined using flow visualization, laser Doppler anemometry (LDA) and particle image velocimetry (PIV). Mean and fluctuating velocities are presented for all three velocity components. Good agreement between LDA and PIV measurements was obtained once an optimized PIV arrangement was defined. Turbulence parameters such as kinetic energy, dissipation, and length scales are estimated from the measurements. Several approaches to evaluating dissipation were used. Triggered PIV measurements were used to evaluate the variation in radial and tangential velocities in the entire planes above and below the impeller at constant axial distances. The size and orientation of the vortices shed from the impeller blade tips and the corresponding regions of high kinetic energy and dissipation indicate the importance of these structures in mixing.
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Mobarak, A., M. G. Khalafallah, A. M. Osman et H. A. Heikal. « Experimental Investigation of Secondary Flow and Mixing Downstream of Straight Turbine Cascades ». Journal of Turbomachinery 110, no 4 (1 octobre 1988) : 497–503. http://dx.doi.org/10.1115/1.3262223.
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The purpose of this paper is to investigate the flow field downstream of turbine cascades of low aspect ratio, often used in vehicles and small turbomachines. Experimental investigation was carried out to study the flow downstream of three sets of turbine cascades having the same blade turning angle of about 83 deg but different profiles. The total energy losses were measured at several planes downstream of the cascade of blades in order to determine the changes in gross secondary flow loss coefficient and the growth of the mixing loss with distance downstream. Influence of inlet boundary layer thickness, aspect ratio, and exit Mach number on the nature of the flow at the exit plane of the cascade and total energy loss were studied. The tests were performed with four values of aspect ratio: 1.16, 0.8, 0.5, and 0.25. Some new correlations were deduced that predict energy loss coefficients as a function of distance downstream, aspect ratio, and exit Mach number as well as the upstream boundary layer thickness. The test results compare well with other published correlations.
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Lockwood, C., P. C. Ivey et R. G. Wells. « Experimental audit of the mixing-plane approach to turbomachinery analysis and a review of alternative multi-row techniques ». Aeronautical Journal 104, no 1033 (mars 2000) : 117–24. http://dx.doi.org/10.1017/s0001924000025306.
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Abstract Detailed numerical comparisons of pressure and flow angle measurements made in stage three of a four-stage, large scale, low speed, axial compressor are presented. The measurements are in both the rotating and stationary frame and were obtained as part of a BRITE/EURAM collaborative study of cantilevered and shrouded-stator compressor configurations. The numerical analysis is 3D, considers three blade rows simultaneously and incorporates multiple row effects by use of a conservative mixing-plane model allowing circumferential variation at the mixing plane. The paper discusses the early results of a study sponsored by Alstom Gas Turbines to examine steady-state, multiple blade-row modelling techniques. Growth in the endwall flow region due to multi-row effects is revealed from both the numerical and experimental results. The numerical simulation is conducted without altering blade gap spacings to assist numerical stability; the axial gap is increasingly being seen as a critical performance parameter for multiple row analysis. The limitations inherent in an approach using mixing-planes are presented and a review of alternative, more rigourous, treatments of these effects is then discussed. These treatments attempt to retain the unsteady flow structure in a steady-state model by the derivation of so-called deterministic stresses.
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Hasan, Nahida B., et Mohammed Jasim Mohammed. « Structural and Morphological Studies of (NiO)1-x(CuO)x Thin Films Prepared by Chemical Spray Paralysis Technique ». International Letters of Chemistry, Physics and Astronomy 58 (septembre 2015) : 102–12. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.58.102.
Texte intégralRésumé :
(NiO)1-x(CuO)x Thin Films have been deposited on glass substrates by chemical spray paralysis technique for with different ratios at temperature (375±10) °C with spray rate 4s./1min. The structural properties of thin films have been investigated by the study of X-Ray diffraction analysis and morphological by study atomic forces microscope (AFM) . From the XRD result showed all simples are polycrystalline and various structural parameters were calculated. all the films show most preferred orientation along (111), (200) and (220) planes. The (AFM) results shows that the roughness decreases with mixing ratios.
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Hasan, Nahida B., et Mohammed Jasim Mohammed. « Structural and Morphological Studies of (NiO)<sub>1-x</sub>(CuO)<sub>x </sub> ; Thin Films Prepared by Chemical Spray Paralysis Technique ». International Letters of Chemistry, Physics and Astronomy 58 (2 septembre 2015) : 102–12. http://dx.doi.org/10.56431/p-7ul205.
Texte intégralRésumé :
(NiO)1-x(CuO)x Thin Films have been deposited on glass substrates by chemical spray paralysis technique for with different ratios at temperature (375±10) °C with spray rate 4s./1min. The structural properties of thin films have been investigated by the study of X-Ray diffraction analysis and morphological by study atomic forces microscope (AFM) . From the XRD result showed all simples are polycrystalline and various structural parameters were calculated. all the films show most preferred orientation along (111), (200) and (220) planes. The (AFM) results shows that the roughness decreases with mixing ratios.
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Mahdi, Tawfiq S., et Firas J. Kadhim. « Effect depositions parameters on the characteristics of Ni0.5Co0.5Fe2O4 nanocomposite films prepared by DC reactive magnetron Co-Sputtering technique ». Iraqi Journal of Physics (IJP) 18, no 45 (30 mai 2020) : 76–88. http://dx.doi.org/10.30723/ijp.v18i45.546.
Texte intégralRésumé :
In this work, spinel ferrites (NiCoFe2O4) were prepared as thin films by dc reactive dual-magnetron co-sputtering technique. Effects of some operation parameters, such as inter-electrode distance, and preparation conditions such as mixing ratio of argon and oxygen in the gas mixture, on the structural and spectroscopic characteristics of the prepared samples were studied. For samples prepared at inter-electrode distance of 5 cm, only one functional group of OH- was observed in the FTIR spectra as all bands belonging to the metal-oxygen vibration were observed. Similarly, the XRD results showed that decreasing the pressure of oxygen in the gas mixture lead to grow more crystal planes in the samples prepared at inter-electrode distance of 5 cm. The energy band gap was determined for the sample prepared with mixing ratio of 65:35 and found to be 2.7, 2 and 3.35 eV for direct allowed, direct forbidden and indirect allowed transitions, respectively. The high structural purity was confirmed as no traces for any elements other than Co, Ni, Fe and O were found in the final samples.
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Pinarbasi, A., et M. W. Johnson. « Three-Dimensional Flow Measurements in Conical and Straight Wall Centrifugal Compressor Vaneless Diffusers ». Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science 210, no 1 (janvier 1996) : 51–61. http://dx.doi.org/10.1243/pime_proc_1996_210_169_02.
Texte intégralRésumé :
In the current work three-dimensional flow measurements in two types of centrifugal compressor vaneless diffuser were obtained using hot wire anemometry. The first diffuser was conical, designed to give a constant flow area, while the second straight wall diffuser had a constant axial width. Measurements of mean velocity, flow angle and velocity fluctuation level were obtained on eight cross-sectional planes in each diffuser. The jet-wake flow pattern and the impeller blade wakes are clearly visible at the inlet of both diffusers. Mixing out of the blade wake proceeds more rapidly in the straight diffuser. The hub boundary layer also develops more rapidly in this diffuser because of the adverse pressure gradient. Velocity fluctuation level measurements highlight the mixing regions within the diffusers. Recommendations are also made for the design of vaned diffusers. A larger vaneless space would be required with a straight wall diffuser and significant twisting of the vane would be required for both diffuser geometries if significant incidence losses are to be avoided.
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Zhao, Fengnian, Mengqi Liu, Penghui Ge, David L. S. Hung, Xuesong Li, Min Xu, Xiaofeng Yang et Cherian Idicheria. « Multi-plane time-resolved Particle Image Velocimetry (PIV) flow field measurements in an optical Spark-Ignition Direct-Injection (SIDI) engine for Large-Eddy Simulation (LES) model validations ». Oil & ; Gas Science and Technology – Revue d’IFP Energies nouvelles 74 (2019) : 52. http://dx.doi.org/10.2516/ogst/2019022.
Texte intégralRésumé :
In-cylinder flow characteristics play a significant role in the fuel–air mixing process of Spark-Ignition Direct-Injection (SIDI) engines. Typically, planar Particle Image Velocimetry (PIV) is used to measure a representative velocity field sectioning through the center plane of the engine cylinder. However, a single flow field offers very limited perspective regarding the Three-Dimensional nature of the flow fields. Since the in-cylinder flow is stochastically complex, large datasets of flow field measurements along multiple planes are needed to provide a complete panoramic understanding of the flow dynamics. In this study, a high-speed PIV is applied to measure the crank-angle resolved flow fields inside a single-cylinder four-valve optical SIDI engine. Five flow fields along different tumble planes are captured. These five planes include two orthogonal planes cutting through the spark plug tip, two parallel planes sectioning through middle point of the intake and exhaust valves, and one plane through the centers of two intake valves. In addition, numerical computations are carried out with Large-Eddy Simulation (LES) model in CONVERGE. With the guidance from multi-plane PIV measurements, a novel validation approach is proposed in this study. The quantitative analysis and comparison between LES simulations and PIV experiments are divided in terms of global and local comparison indices. The global comparison indices provide a quantitative single value to quickly check the overall similarity of velocity directions and magnitudes between PIV and LES results of a specific individual plane. The local comparison indices further evaluate the similarity between the flow fields of LES and PIV point by point to identify any dissimilar regions and vortex features, which are likely to indicate the complex flow structures at low-speed regions. In summary, not only can the combined data analysis approach provide a reliable way for LES model validations, it can also reveal the physical quantifications of the complex in-cylinder flow characteristics.
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Callies, J., et J. Marotzke. « A simple and self-consistent geostrophic-force-balance model of the thermohaline circulation with boundary mixing ». Ocean Science 8, no 1 (27 janvier 2012) : 49–63. http://dx.doi.org/10.5194/os-8-49-2012.
Texte intégralRésumé :
Abstract. A simple model of the thermohaline circulation (THC) is formulated, with the objective to represent explicitly the geostrophic force balance of the basinwide THC. The model comprises advective-diffusive density balances in two meridional-vertical planes located at the eastern and the western walls of a hemispheric sector basin. Boundary mixing constrains vertical motion to lateral boundary layers along these walls. Interior, along-boundary, and zonally integrated meridional flows are in thermal-wind balance. Rossby waves and the absence of interior mixing render isopycnals zonally flat except near the western boundary, constraining meridional flow to the western boundary layer. The model is forced by a prescribed meridional surface density profile. This two-plane model reproduces both steady-state density and steady-state THC structures of a primitive-equation model. The solution shows narrow deep sinking at the eastern high latitudes, distributed upwelling at both boundaries, and a western boundary current with poleward surface and equatorward deep flow. The overturning strength has a 2/3-power-law dependence on vertical diffusivity and a 1/3-power-law dependence on the imposed meridional surface density difference. Convective mixing plays an essential role in the two-plane model, ensuring that deep sinking is located at high latitudes. This role of convective mixing is consistent with that in three-dimensional models and marks a sharp contrast with previous two-dimensional models. Overall, the two-plane model reproduces crucial features of the THC as simulated in simple-geometry three-dimensional models. At the same time, the model self-consistently makes quantitative a conceptual picture of the three-dimensional THC that hitherto has been expressed either purely qualitatively or not self-consistently.
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Callies, J., et J. Marotzke. « A simple and self-consistent geostrophic-force-balance model of the thermohaline circulation with boundary mixing ». Ocean Science Discussions 8, no 4 (24 août 2011) : 1819–63. http://dx.doi.org/10.5194/osd-8-1819-2011.
Texte intégralRésumé :
Abstract. A simple model of the thermohaline circulation (THC) is formulated, with the objective to represent explicitly the geostrophic force balance of the basinwide THC. The model comprises advective-diffusive density balances in two meridional-vertical planes located at the eastern and the western walls of a hemispheric sector basin. Boundary mixing constrains vertical motion to lateral boundary layers along these walls. Interior, along-boundary, and zonally integrated meridional flows are in thermal-wind balance. Rossby waves and the absence of interior mixing render isopycnals zonally flat except near the western boundary, constraining meridional flow to the western boundary layer. The model is forced by a prescribed meridional surface density profile. This two-plane model reproduces both steady-state density and steady-state THC structures of a primitive-equation model. The solution shows narrow deep sinking at the eastern high latitudes, distributed upwelling at both boundaries, and a western boundary current with poleward surface and equatorward deep flow. The overturning strength has a 2/3-power-law dependence on vertical diffusivity and a 1/3-power-law dependence on the imposed meridional surface density difference. Convective mixing plays an essential role in the two-plane model, ensuring that deep sinking is located at high latitudes. This role of convective mixing is consistent with that in three-dimensional models and marks a~sharp contrast with previous two-dimensional models. Overall, the two-plane model reproduces crucial features of the THC as simulated in simple-geometry three-dimensional models. At the same time, the model self-consistently makes quantitative a conceptual picture of the three-dimensional THC that hitherto has been expressed either purely qualitatively or not self-consistently.
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Janzen, N., M. Kononenko, S. Ren et A. Lupascu. « Aluminum air bridges for superconducting quantum devices realized using a single-step electron-beam lithography process ». Applied Physics Letters 121, no 9 (29 août 2022) : 094001. http://dx.doi.org/10.1063/5.0103165.
Texte intégralRésumé :
In superconducting quantum devices, air bridges enable increased circuit complexity and density, and mitigate the risk of microwave loss arising from mode mixing. We implement aluminum air bridges using a simple process based on single-step electron-beam gradient exposure. The resulting bridges have sizes ranging from 20 µm to 100 µm, with a yield exceeding 99% for lengths up to 36 µm. When used to connect ground planes in coplanar waveguide resonators, the induced loss contributed to the system is negligible, corresponding to a loss per bridge less than [Formula: see text]. The bridge process is compatible with Josephson junctions and allows for the simultaneous creation of low loss bandages between superconducting layers.
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Lignarolo, L. E. M., D. Ragni, F. Scarano, C. J. Simão Ferreira et G. J. W. van Bussel. « Tip-vortex instability and turbulent mixing in wind-turbine wakes ». Journal of Fluid Mechanics 781 (23 septembre 2015) : 467–93. http://dx.doi.org/10.1017/jfm.2015.470.
Texte intégralRésumé :
Kinetic-energy transport and turbulence production within the shear layer of a horizontal-axis wind-turbine wake are investigated with respect to their influence on the tip-vortex pairwise instability, the so-called leapfrogging instability. The study quantifies the effect of near-wake instability and tip-vortex breakdown on the process of mean-flow kinetic-energy transport within the far wake of the wind turbine, in turn affecting the wake re-energising process. Experiments are conducted in an open-jet wind tunnel with a wind-turbine model of 60 cm diameter at a diameter-based Reynolds number range $\mathit{Re}_{D}=150\,000{-}230\,000$. The velocity fields in meridian planes encompassing a large portion of the wake past the rotor are measured both in the unconditioned and the phase-locked mode by means of stereoscopic particle image velocimetry. The detailed topology and development of the tip-vortex interactions are discussed prior to a statistical analysis based on the triple decomposition of the turbulent flow fields. The study emphasises the role of the pairing instability as a precursor to the onset of three-dimensional vortex distortion and breakdown, leading to increased turbulent mixing and kinetic-energy transport across the shear layer. Quadrant analysis further elucidates the role of sweep and ejection events within the two identified mixing regimes. Prior to the onset of the instability, vortices shed from the blade appear to inhibit turbulent mixing of the expanding wake. The second region is dominated by the leapfrogging instability, with a sudden increase of the net entrainment of kinetic energy. Downstream of the latter, random turbulent motion characterises the flow, with a significant increase of turbulent kinetic-energy production. In this scenario, the leapfrogging mechanism is recognised as the triggering event that accelerates the onset of efficient turbulent mixing followed by the beginning of the wake re-energising process.
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Arobone, Eric, et Sutanu Sarkar. « Evolution of a stratified rotating shear layer with horizontal shear. Part 2. Nonlinear evolution ». Journal of Fluid Mechanics 732 (6 septembre 2013) : 373–400. http://dx.doi.org/10.1017/jfm.2013.383.
Texte intégralRésumé :
AbstractDirect numerical simulation is used to investigate the nonlinear evolution of a horizontally oriented mixing layer with uniform stable stratification and coordinate system rotation about the vertical axis. The important dimensional parameters governing inviscid dynamics are maximum shear $S(t)$, buoyancy frequency $N$, angular velocity of rotation $\Omega $ and characteristic shear thickness $L(t)$. The effect of rotation rate, $\Omega $, on the development of fluctuations in the shear layer is systematically studied in a regime of strong stratification. An instability mechanism, qualitatively distinct from the inertial instability, is found to deform columnar vortex cores in vertical planes for a strongly stratified rotating mixing layer. This mechanism emerges when centreline absolute vertical vorticity, $\langle {\omega }_{3} \rangle (t)+ 2\Omega $, is nearly zero as predicted by the linear stability analysis in Part 1 (J. Fluid. Mech., vol. 703, 2012, pp. 29–48). When the initial rotation rate is moderately anticyclonic, strong destabilization and a cascade to small scales is observed, consistent with prior studies involving horizontally sheared flow in the presence of rotation. Examination of enstrophy budgets in cases which are initially inertially unstable reveal the importance of baroclinic torque in maintaining lateral enstrophy fluctuations substantially beyond the time when the flow becomes inertially stable. The cyclonic stratified cases show weak nonlinearity in vortex dynamics. At high Reynolds number, despite the strong stratification, the flow exhibits three-dimensional, nonlinear dynamics and significant vertical mixing except for cases where the rotation is stabilizing.
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Kaviani, Ramin, et Mansour Nikkhah-Bahrami. « Improved Navier–Stokes Boundary Conditions Based on Generalized Characteristics ». Journal of Computational Acoustics 23, no 02 (7 mai 2015) : 1550006. http://dx.doi.org/10.1142/s0218396x1550006x.
Texte intégralRésumé :
In this paper, the three-dimensional Navier–Stokes characteristic boundary conditions for large-eddy and aeroacoustic simulations are extended to curvilinear coordinates formulations. A robust way of treating the transverse and gradient terms on boundary planes is presented which is different from previous generalized characteristic boundary conditions. The performance of the new formulation is examined via four test problems: an inviscid convective vortex, a two-dimensional mixing layer, a Mach 0.75 round jet, and a Mach 0.51 nozzle/jet. For each test problem, the numerical schemes used to implement the boundary conditions, the numerical parameters employed, and the predicted three-dimensional flow fields are presented. Based on the numerical experiments conducted, the new boundary conditions show promise for high-fidelity simulations of compressible viscous flows.
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Pinarbasi, A., et M. W. Johnson. « Detailed Stress Tensor Measurements in a Centrifugal Compressor Vaneless Diffuser ». Journal of Turbomachinery 118, no 2 (1 avril 1996) : 394–99. http://dx.doi.org/10.1115/1.2836654.
Texte intégralRésumé :
Detailed flow measurements have been made in the vaneless diffuser of a large low-speed centrifugal compressor using hot-wire anemometry. The three time mean velocity components and full stress tensor distributions have been determined on eight measurement planes within the diffuser. High levels of Reynolds stress result in the rapid mixing out of the blade wake. Although high levels of turbulent kinetic energy are found in the passage wake, they are not associated with strong Reynolds stresses and hence the passage wake mixes out only slowly. Low-frequency meandering of the wake position is therefore likely to be responsible for the high kinetic energy levels. The anisotropic nature of the turbulence suggests that Reynolds stress turbulence models are required for CFD modeling of diffuser flows.
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Harrison, S. « Secondary Loss Generation in a Linear Cascade of High-Turning Turbine Blades ». Journal of Turbomachinery 112, no 4 (1 octobre 1990) : 618–24. http://dx.doi.org/10.1115/1.2927702.
Texte intégralRésumé :
Flow through a linear cascade of high-turning, low aspect ratio turbine blades has been measured in great detail at five planes within the cascade and two downstream in order to trace the generation of stagnation pressure loss in the passage. Five-hole probes were used in the main flow, but as it is important to resolve the boundary layers accurately, three-hole and single flattened probes were used near the endwall and blade surfaces, respectively. Endwall shear stresses have been measured using a hot-film probe and an oil-drop viscosity balance technique. Numerical predictions and simple aerodynamic models are used in conjunction with the experimental data to estimate the relative importance of different loss mechanisms, including boundary layer shear stresses and mixing processes.
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Pinarbasi, A., et M. W. Johnson. « Detailed Flow Measurements in a Centrifugal Compressor Vaneless Diffuser ». Journal of Turbomachinery 116, no 3 (1 juillet 1994) : 453–60. http://dx.doi.org/10.1115/1.2929432.
Texte intégralRésumé :
Hot-wire anemometer measurements have been made in the vaneless diffuser of a 1-m-dia low-speed backswept centrifugal compressor using a phase lock loop technique. Radial, tangential, and axial velocity measurements have been made on eight measurement planes through the diffuser. The flow field at the diffuser entry clearly shows the impeller jet-wake flow pattern and the blade wakes. The passage wake is located on the shroud side of the diffuser and mixes out slowly as the flow moves through the diffuser. The blade wakes, on the other hand, distort and mix out rapidly in the diffuser. Contours of turbulent kinetic energy are also presented on each of the measurement stations, from which the regions of turbulent mixing can be deduced.
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Huang, Jianyu, Yuntian T. Zhu et Hirotaro Mori. « Structure and phase characteristics of amorphous boron–carbon–nitrogen under high pressure and high temperature ». Journal of Materials Research 16, no 4 (avril 2001) : 1178–84. http://dx.doi.org/10.1557/jmr.2001.0162.
Texte intégralRésumé :
An amorphous boron–carbon–nitrogen (a-BCN) phase was synthesized by ball milling of a mixture of hexagonal BN (h-BN) and graphite with a nominal composition of (BN)0.5C0.5 in atomic ratio. Electron energy-loss spectroscopy studies indicated that the bonding of the a-BCN is in an sp2 configuration and the mixing between the BN and the C species was achieved at a nanometer scale, but the a-BCN phase was more likely a mechanical mixture rather than a chemical mixture. High-pressure and high-temperature (HPHT) treatment at 7.7 GPa and 2300 °C of the a-BCN phase resulted in complete segregation of the carbon and BN species, forming a nanocrystalline composite material comprising cubic BN (c-BN), amorphous carbon, and turbostratic graphite. The grain size of the c-BN phase was about 70 nm. No mutual solubilities between c-BN and carbon were found, and the two different species (C and BN) were well separated. An epitaxial relationship, i.e., the (0002) planes of graphite being parallel to the (111) planes of c-BN, was also found. The formation of ternary BCN phases was never found in the present experiment. Our experimental results also suggest the possibility of synthesizing c-BN grains encapsulated with graphite under controlled HPHT conditions.
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Beard, P. F., A. D. Smith et T. Povey. « Experimental and computational fluid dynamics investigation of the efficiency of an unshrouded transonic high pressure turbine ». Proceedings of the Institution of Mechanical Engineers, Part A : Journal of Power and Energy 225, no 8 (13 août 2011) : 1166–79. http://dx.doi.org/10.1177/0957650911407979.
Texte intégralRésumé :
This article presents an experimental and computational study of the efficiency of an unshrouded transonic turbine. This research formed part of the EU Turbine Aero-Thermal External Flows II programme. The experiments were performed in the Oxford Turbine Research Facility (previously the Turbine Test Facility at QinetiQ, Farnborough). This facility is an engine scale, short duration, rotating transonic facility, in which M, Re, [Formula: see text], and [Formula: see text] are matched to engine conditions. For these experiments, the MT1 turbine stage was installed. Historically, turbine efficiency measurements are conducted in steady state adiabatic facilities. However, short-duration facilities allow simultaneous aerodynamic and heat transfer measurements with a significant reduction in cost. An efficiency measurement system was developed for this investigation, and this is briefly described. The system allows efficiency to be evaluated to bias and precision errors of approximately ±1.45 per cent and ±0.16 per cent, respectively, to 95 per cent confidence. The results of accurate area surveys of the turbine inlet and exit flows are presented and discussed. At the turbine exit, data were taken at two traverse planes, approximately 0.5 and 4.5 rotor axial chords downstream of the rotor. The turbine efficiency was experimentally evaluated based on the data at both planes, using a number of mixing models, which are discussed and compared. The experimental result of turbine efficiency is also compared to that estimated from a mean-line prediction. Full-stage steady and unsteady computational fluid dynamics of the experiment using the Rolls-Royce HYDRA code was conducted and is also presented. The predicted and measured rotor exit flow-fields are compared at both downstream traverse planes.
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Sataev, A. A., V. V. Andreev, A. M. Samoilov et A. A. Blokhin. « Development of test facilities and procedure for system-based assessment of spatial orientation changes upon thermohydraulic processes ». Transactions of the Krylov State Research Centre S-I, no 2 (21 décembre 2021) : 70–75. http://dx.doi.org/10.24937/2542-2324-2021-2-s-i-70-75.
Texte intégralRésumé :
This paper discusses thermohydraulic processes in marine nuclear reactor in order to develop test models and testing methods for assessment of unsteady thermohydraulic processes in the hydraulic circuit of nuclear reactor taking into account external dynamic factors typical for marine environments, like motions and heel. This work was an experimental study on non-isothermal mixing in one and two motion planes, and mostly followed experimental methods (thermal probing), as well as the methods of visualization and system analysis. Non-isothermal mixing of flows in the channel of marine nuclear power plant was investigated for both static conditions and dynamic environment (uni- and bi-planar motions), which yielded a generalized model of motion effects upon thermohydraulic processes. Visualization methods served to identify hot/cold areas. The study also highlighted how spatial orientation of the reactor’s flow channel changes thermal parameters exactly at the boundary of thermal front. It is shown that flow channel of marine nuclear power plant is a complex unsteady system. Motion tests are practicable to perform varying not only the amplitude (angle) of motions, but also their period, as well as to discriminate between high- and low-frequency motions and investigate joint effect of different motion types that have to be simulated and analysed in its own way.
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Holdeman, J. D., D. S. Liscinsky et D. B. Bain. « Mixing of Multiple Jets With a Confined Subsonic Crossflow : Part II—Opposed Rows of Orifices in Rectangular Ducts ». Journal of Engineering for Gas Turbines and Power 121, no 3 (1 juillet 1999) : 551–62. http://dx.doi.org/10.1115/1.2818508.
Texte intégralRésumé :
This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the orifices investigated were often very large (jet-to-mainstream mass-flow ratio > 1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5, respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.
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Li, G. L., G. H. Wang et J. M. Hong. « Synthesis and characterization of rutile TiO2 nanowhiskers ». Journal of Materials Research 14, no 8 (août 1999) : 3346–54. http://dx.doi.org/10.1557/jmr.1999.0453.
Texte intégralRésumé :
Rutile TiO2 nanowhiskers have been synthesized by annealing a precursor powder in which NaCl and Ti(OH)4 particles were homogeneously mixed. The precursor powder was prepared by mixing three kinds of inverse microemulsions (μE) containing TiCl4 aqueous solution, ammonia, and NaCl aqueous solution, respectively, followed by washing with acetone. Annealing temperature and packing density of Ti(OH)4 in the precursor powder influenced the formation of rutile nanowhiskers. The optimum temperature was 750 °C. TiO2 nanowhiskers obtained by annealing a precursor powder in which the molar ratio of sodium to titanium was 400 at 750 °C for 2 h had diameters of 10–50 nm and lengths of several micrometers. They were straight rods with square cross sections, and the side surfaces were composed of four equivalent {110} planes.
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MILLER, RICHARD S., KENNETH G. HARSTAD et JOSETTE BELLAN. « Direct numerical simulations of supercritical fluid mixing layers applied to heptane–nitrogen ». Journal of Fluid Mechanics 436 (10 juin 2001) : 1–39. http://dx.doi.org/10.1017/s0022112001003895.
Texte intégralRésumé :
Direct numerical simulations (DNS) are conducted of a model hydrocarbon–nitrogen mixing layer under supercritical conditions. The temporally developing mixing layer configuration is studied using heptane and nitrogen supercritical fluid streams at a pressure of 60 atm as a model system related to practical hydrocarbon-fuel/air systems. An entirely self-consistent cubic Peng–Robinson equation of state is used to describe all thermodynamic mixture variables, including the pressure, internal energy, enthalpy, heat capacity, and speed of sound along with additional terms associated with the generalized heat and mass transport vectors. The Peng–Robinson formulation is based on pure-species reference states accurate to better than 1% relative error through comparisons with highly accurate state equations over the range of variables used in this study (600 [les ] T [les ] 1100 K, 40 [les ] p [les ] 80 atm) and is augmented by an accurate curve fit to the internal energy so as not to require iterative solutions. The DNS results of two-dimensional and three-dimensional layers elucidate the unique thermodynamic and mixing features associated with supercritical conditions. Departures from the perfect gas and ideal mixture conditions are quantified by the compression factor and by the mass diffusion factor, both of which show reductions from the unity value. It is found that the qualitative aspects of the mixing layer may be different according to the specification of the thermal diffusion factors whose value is generally unknown, and the reason for this difference is identified by examining the second-order statistics: the constant Bearman–Kirkwood (BK) thermal diffusion factor excites fluctuations that the constant Irwing–Kirkwood (IK) one does not, and thus enhances overall mixing. Combined with the effect of the mass diffusion factor, constant positive large BK thermal diffusion factors retard diffusional mixing, whereas constant moderate IK factors tend to promote diffusional mixing. Constant positive BK thermal diffusion factors also tend to maintain density gradients, with resulting greater shear and vorticity. These conclusions about IK and BK thermal diffusion factors are species-pair dependent, and therefore are not necessarily universal. Increasing the temperature of the lower stream to approach that of the higher stream results in increased layer growth as measured by the momentum thickness. The three-dimensional mixing layer exhibits slow formation of turbulent small scales, and transition to turbulence does not occur even for a relatively long non-dimensional time when compared to a previous, atmospheric conditions study. The primary reason for this delay is the initial density stratification of the flow, while the formation of strong density gradient regions both in the braid and between-the-braid planes may constitute a secondary reason for the hindering of transition through damping of emerging turbulent eddies.
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Klocker, Andreas, et Trevor J. McDougall. « Quantifying the Consequences of the Ill-Defined Nature of Neutral Surfaces ». Journal of Physical Oceanography 40, no 8 (1 août 2010) : 1866–80. http://dx.doi.org/10.1175/2009jpo4212.1.
Texte intégralRésumé :
Abstract In the absence of diapycnal mixing processes, fluid parcels move in directions along which they do not encounter buoyant forces. These directions define the local neutral tangent plane. Because of the nonlinear nature of the equation of state of seawater, these neutral tangent planes cannot be connected globally to form a well-defined surface in three-dimensional space; that is, continuous “neutral surfaces” do not exist. This inability to form well-defined neutral surfaces implies that neutral trajectories are helical. Consequently, even in the absence of diapycnal mixing processes, fluid trajectories penetrate through any “density” surface. This process amounts to an extra mechanism that achieves mean vertical advection through any continuous surface such as surfaces of constant potential density or neutral density. That is, the helical nature of neutral trajectories causes this additional diasurface velocity. A water-mass analysis performed with respect to continuous density surfaces will have part of its diapycnal advection due to this diasurface advection process. Hence, this additional diasurface advection should be accounted for when attributing observed water-mass changes to mixing processes. Here, the authors quantify this component of the total diasurface velocity and show that locally it can be the same order of magnitude as diasurface velocities produced by other mixing processes, particularly in the Southern Ocean. The magnitude of this diasurface advection is proportional to the ocean’s neutral helicity, which is observed to be quite small in today’s ocean. The authors also use a perturbation experiment to show that the ocean rapidly readjusts to its present state of small neutral helicity, even if perturbed significantly. Additionally, the authors show how seasonal (rather than spatial) changes in the ocean’s hydrography can generate a similar vertical advection process. This process is described here for the first time; although the vertical advection due to this process is small, it helps to understand water-mass transformation on density surfaces.
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Holdeman, J. D., D. S. Liscinsky, V. L. Oechsle, G. S. Samuelsen et C. E. Smith. « Mixing of Multiple Jets With a Confined Subsonic Crossflow : Part I—Cylindrical Duct ». Journal of Engineering for Gas Turbines and Power 119, no 4 (1 octobre 1997) : 852–62. http://dx.doi.org/10.1115/1.2817065.
Texte intégralRésumé :
This paper summarizes NASA-supported experimental and computational results on the mixing of a row of jets with a confined subsonic crossflow in a cylindrical duct. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observations were that the momentum-flux ratio and the number of orifices were significant variables. Jet penetration was critical, and jet penetration decreased as either the number of orifices increased or the momentum-flux ratio decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the number of orifices was proportional to the square root of the momentum-flux ratio. In the cylindrical geometry, planar variances are very sensitive to events in the near-wall region, so planar averages must be considered in context with the distributions. The mass-flow ratios and orifices investigated were often very large (mass-flow ratio >1 and ratio of orifice area-to-mainstream cross-sectional area up to 0.5), and the axial planes of interest were sometimes near the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations. The results shown also seem to indicate that nonreacting dimensionless scalar profiles can emulate the reacting flow equivalence ratio distribution reasonably well. The results cited suggest that further study may not necessarily lead to a universal “rule of thumb” for mixer design for lowest emissions, because optimization will likely require an assessment for a specific application.
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POULSEN, H. F., N. H. ANDERSEN, J. V. ANDERSEN, H. BOHR et O. G. MOURITSEN. « LATTICE GAS SIMULATION OF OXYGEN ORDERING IN YBa2Cu3O6+x SHOWING DYNAMICAL SCALING ». Modern Physics Letters B 05, no 12 (20 mai 1991) : 827–32. http://dx.doi.org/10.1142/s0217984991001015.
Texte intégralRésumé :
A 2-dimensional anisotropic lattice model for the oxygen ordering in the high Tc superconductor of the YBa 2 Cu 3 O 7+x type is shown to exhibit an ordering dynamics that obey algebraic growth laws which depend on whether it is an Ortho-I or Ortho-II phase. It is possible to relate this dynamical scaling behavior to a similar scaling in the experimentally observed temporal variation of the superconductivity transition temperature and hence suggesting a specific coupling between the coherence of oxygen order in the basal Cu-O planes and the superconducting state. Furthermore it is possible to explain the variation in the transition temperature with the oxygen density x by a phase mixing model of Ortho-II/Ortho-I domains and an assumption about the charge transfer between the basal and superconducting plane.
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Sakthi Sri V., Swathi Pon, A. Vijayakumar et Mary George. « Synthesis, Optical, Morphological and Magnetic Properties of Hematite Nanorods in Deep Eutectic Solvent with its Antibacterial and Photocatalytic Applications ». Asian Journal of Chemistry 31, no 4 (27 février 2019) : 879–85. http://dx.doi.org/10.14233/ajchem.2019.21817.
Texte intégralRésumé :
Deep eutectic solvent comprising of choline chloride and D(+)-glucose was synthesized by mixing in the molar ratio 2:1. Iron oxide nanoparticles were successfully synthesized by co-precipitation method. Deep eutectic solvent consisting of D(+)-glucose acts as a promising reducing agent for the synthesis of iron oxide nanoparticles. Direct optical band gap of iron oxide nanoparticles was found to be 2.262 eV. Powder X-ray diffraction technique was used to identify the crystalline phases. Surface morphology analysis by Field emission scanning electron microscopy and high resolution transmission electron microscopy confirmed the rod shape structure of the iron oxide nanoparticles. Selected area electron diffraction pattern revealed the identity of lattice planes with the XRD data. The antibacterial and photocatalytic activities of the iron oxide nanoparticles were also studied. The synthesized iron oxide nanoparticles showed appreciable antibacterial and photocatalytic activities
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Dale, L., et J. M. Slack. « Fate map for the 32-cell stage of Xenopus laevis ». Development 99, no 4 (1 avril 1987) : 527–51. http://dx.doi.org/10.1242/dev.99.4.527.
Texte intégralRésumé :
A complete fate map has been produced for the 32-cell stage of Xenopus laevis. Embryos with a regular cleavage pattern were selected and individual blastomeres were injected with the lineage label fluorescein-dextran-amine (FDA). The spatial location of the clones was deduced from three-dimensional (3D) reconstructions of later stages and the volume of each tissue colonized by labelled cells in each tissue was measured. The results from 107 cases were pooled to give a fate map which shows the fate of each blastomere in terms of tissue types, the composition of each tissue by blastomere, the location of each prospective region on the embryo and the fate of each blastomere in terms of spatial localization. Morphogenetic movements up to stage 10 (early gastrula) were assessed by carrying out a number of orthotopic grafts at blastula and gastrula stages using donor embryos uniformly labelled with FDA. Although there is a regular topographic projection from the 32-cell stage this varies a little between individuals because of variability of positions of cleavage planes and because of short-range cell mixing during gastrulation. The cell mixing means that the topographic projection fails for anteroposterior segments of the dorsal axial structures and it is not possible to include short segments of notochord or neural tube or individual somites on the pregastrulation fate map.
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Rodehorst, U., M. A. Carpenter, S. Marion et C. M. B. Henderson. « Structural phase transitions and mixing behaviour of the Ba-aluminate (BaAl2O4)– Sr-aluminate (SrAl2O4) solid solution ». Mineralogical Magazine 67, no 5 (octobre 2003) : 989–1013. http://dx.doi.org/10.1180/0026461036750139.
Texte intégralRésumé :
AbstractPhase transitions in the BaAl2O4–SrAl2O4 solid solution have been analysed as a function of temperature and composition using infrared (IR) powder absorption spectroscopy. The improper ferroelectric phase transition P6322 → P63 (2A superstructure) in the BaAl2O4 end-member can be detected through a change in slope of the wavenumbers of hard modes at ∽450 K. A change in line widths at ∽520 K appears to correlate with the development of diffuse intensity in a*-b* planes of electron diffraction patterns reported elsewhere in the literature. The same shift in wavenumber of hard modes is not observed in spectra from samples with compositions corresponding to 60, 80 and 90% of BaAl2O4 component, but a change in line widths at ∽500 K has been tentatively explained in terms of a different phase transition, from a P6322 parent structure to a P63 (√3A superstructure) product. Strain analysis of published high-temperature lattice parameter data suggests that the hexagonal → monoclinic transition in Sr-rich members of the solid solution may consist of two discrete transitions, and a sequence P6322 → C2 → P21 is suggested. The second transition could be related to instabilities in the hexagonal solid solution. Autocorrelation analysis of the IR spectra reveals a large positive deviation from linear behaviour across the solid solution, which is interpreted in terms of microscopic strain effects. These microscopic strains are probably responsible for the different transformation behaviour shown by samples with different compositions across the solid solution.
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Rabitti, Anna, et Leo R. M. Maas. « Meridional trapping and zonal propagation of inertial waves in a rotating fluid shell ». Journal of Fluid Mechanics 729 (24 juillet 2013) : 445–70. http://dx.doi.org/10.1017/jfm.2013.310.
Texte intégralRésumé :
AbstractInertial waves propagate in homogeneous rotating fluids, and constitute a challenging and simplified case study for the broader class of inertio-gravity waves, present in all geophysical and astrophysical media, and responsible for energetically costly processes such as diapycnal and angular momentum mixing. However, a complete analytical description and understanding of internal waves in arbitrarily shaped enclosed domains, such as the ocean or a planet liquid core, is still missing. In this work, the inviscid, linear inertial wave field is investigated by means of three-dimensional ray tracing in spherical shell domains, having in mind possible oceanographic applications. Rays are here classically interpreted as representative of energy paths, but in contrast to previous studies, they are now launched with a non-zero initial zonal component allowing for a more realistic, localized forcing and the development of azimuthal inhomogeneities. We find that meridional planes generally act in the shell geometry as attractors for ray trajectories. In addition, the existence of trajectories that are not subject to meridional trapping is here observed for the first time. Their dynamics was not captured by the previous purely meridional studies and unveils a new class of possible solutions for inertial motion in the spherical shell. Both observed behaviours shed some new light on possible mechanisms of energy localization, a key process that still deserves further investigation in our ocean, as well as in other stratified, rotating media.