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Статті в журналах з теми "Swirling cross flows"
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KISHI, Takeo, Hideaki SATO, Satoshi Yanagisawa, and Tadamasa Anmi. "303 Cross-Flow Microfiltration of Grinding Fluids Using Swirling Flows : Fractional Void." Proceedings of the Symposium on Environmental Engineering 2006.16 (2006): 245–47. http://dx.doi.org/10.1299/jsmeenv.2006.16.245.
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YANAGISAWA, Satoshi, Hideaki SATO, and Sadamasa AMMI. "756 Cross-Flow Microfiltration of Grinding Fluids Using Swirling Flows : Fractional Void." Proceedings of Yamanashi District Conference 2004 (2004): 225–26. http://dx.doi.org/10.1299/jsmeyamanashi.2004.225.
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Kashkousha, OA, MM Kamal, AM Abdulaziz, and MA Nosier. "Inverse diffusion and partially premixed flames with elliptical/swirling- and cross-flows." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 229, no. 1 (September 18, 2014): 44–59. http://dx.doi.org/10.1177/0957650914552155.
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Ao-kui, Xiong, and Wei Qing-ding. "The decay of swirling flows in a type of cross-section-varying pipes." Applied Mathematics and Mechanics 22, no. 8 (August 2001): 983–88. http://dx.doi.org/10.1007/bf02436398.
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Nursen, E. Cezmi, and Erkan Ayder. "Numerical Calculation of the Three-Dimensional Swirling Flow Inside the Centrifugal Pump Volutes." International Journal of Rotating Machinery 9, no. 4 (2003): 247–53. http://dx.doi.org/10.1155/s1023621x03000228.
Повний текст джерелаАнотація:
The flow inside the volute of a centrifugal pump is threedimensional and, depending upon the position of the inlet relative to the cross-section center line, a single or double swirling flow occurs. The purpose of this study was the calculation of the three-dimensional swirling flow inside the centrifugal pump volute.The developed flow solver provides detailed pressure and velocity distribution information inside the volute, and the calculated results are verified by means of the experimental results presented in the literature.Three-dimensional continuity and momentum equations are solved by means of an artificial compressibility technique. The finite volume approach is applied for space discretization, and an explicit fourth-order modified Runge-Kutta scheme is used for time discretizetion.Calculations are performed at three different mass flows, one of which corresponds to the design's point mass flow. The calculated volute flow conditions—namely, the variation in static pressure and total pressure and the through-flow and swirling component of the flow velocity over the cross-sections, which are located at various circumferential positions—are compared with the experimental data in detail, and they exhibit a good agreement with the measured flow field.
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Maldonado, Ana Luisa P., and R. Jeremy Astley. "SwirlProp: A tool for sound propagation and attenuation in swirling flows." International Journal of Aeroacoustics 20, no. 5-7 (September 2021): 588–609. http://dx.doi.org/10.1177/1475472x211052591.
Повний текст джерелаАнотація:
The current trends for next generation turbofan engines are towards shorter nacelles and increased distances between the fan and the outlet guide vanes. This leads to an overall reduction in lined surface areas as well as an increase in the relative importance of the interstage liner, which is the liner placed between the rotor blades and the stator vanes. So far most of the efforts have been on liners for intakes and bypass ducts. The interstage is different in that the liner is subject to a mean flow with a strong swirl component and shear. The SwirlProp code was developed to contribute to understanding and predicting the effect of the swirl on liner attenuation. The code is based on the linearized Euler equations together with the Ingard–Myers boundary condition. An eigenvalue problem is formulated and discretized using a finite difference method. The code is exhaustively compared against predicted values obtained by other methods for uniform, sheared and swirling mean flows and hard-walled and lined ducts. A cross-validation between SwirlProp and an in-house code from Rolls-Royce was carried out for a more realistic case. Also, details on the implementation of the boundary condition are proposed and details are presented.
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OVENDEN, N. C., and F. T. SMITH. "NONSYMMETRIC BRANCHING OF FLUID FLOWS IN 3D VESSELS." ANZIAM Journal 59, no. 4 (April 2018): 533–61. http://dx.doi.org/10.1017/s144618111800010x.
Повний текст джерелаАнотація:
Nonsymmetric branching flow through a three-dimensional (3D) vessel is considered at medium-to-high flow rates. The branching is from one mother vessel to two or more daughter vessels downstream, with laminar steady or unsteady conditions assumed. The inherent 3D nonsymmetry is due to the branching shapes themselves, or the differences in the end pressures in the daughter vessels, or the incident velocity profiles in the mother. Computations based on lattice-Boltzmann methodology are described first. A subsequent analysis focuses on small 3D disturbances and increased Reynolds numbers. This reduces the 3D problem to a two-dimensional one at the outer wall in all pressure-driven cases. As well as having broader implications for feeding into a network of vessels, the findings enable predictions of how much swirling motion in the cross-plane is generated in a daughter vessel downstream of a 3D branch junction, and the significant alterations provoked locally in the shear stresses and pressures at the walls. Nonuniform incident wall-shear and unsteady effects are examined. A universal asymptotic form is found for the flux change into each daughter vessel in a 3D branching of arbitrary cross-section with a thin divider.
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Dulin, Vladimir, Yuriy Kozorezov, Dmitriy Markovich, and Mikhail Tokarev. "Stereo Piv Diagnostics of Flow Structure in Swirling Turbulent Propane Flames." Siberian Journal of Physics 4, no. 3 (October 1, 2009): 30–42. http://dx.doi.org/10.54362/1818-7919-2009-4-3-30-42.
Повний текст джерелаАнотація:
This paper is devoted to experimental study of the instantaneous and average flow structure in the pre-mixed propaneair swirling flames using optical noncontact PIV (Particle Image Velocimetry) method in stereoscopic configuration. A visualization of the typical regimes of combustion for the swirling and non-swirling flame in a wide range of Reynolds numbers and equivalence ratios is presented. In addition, boundaries of steady combustion are defined. Measurements of instantaneous velocity fields for typical combustion regimes are performed. Instantaneous velocity fields were used to calculate the spatial distribution of the mean velocity and turbulence kinetic energy component. Interaction of the flame with a large-scale vortex structures is studied. It shows significantly different effects of burning on the turbulent structure of twisted jet. The paper describes algorithms of data processing, in particular, adaptive cross-correlation method of calculating the instantaneous velocity fields based on an analysis of the local particle image concentration. This method allows to effectively filtering out the velocity vector outliers, which appear in areas with low concentration of tracers during gas flows diagnostics, and calculate the spatial distribution of such characteristics as the intensity of turbulent pulsations.
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Najjari, Mohammad Reza, Christopher Cox, and Michael W. Plesniak. "Formation and interaction of multiple secondary flow vortical structures in a curved pipe: transient and oscillatory flows." Journal of Fluid Mechanics 876 (August 1, 2019): 481–526. http://dx.doi.org/10.1017/jfm.2019.510.
Повний текст джерелаАнотація:
Transient, steady and oscillatory flows in a $180^{\circ }$ curved pipe are investigated both numerically and experimentally to understand secondary flow vortex formation and interactions. The results of numerical simulations and particle image velocimetry experiments are highly correlated, with a low error. To enable simulations in a smaller domain with shorter inlet section, an analytical solution for the unsteady Navier–Stokes equation is obtained with non-zero initial conditions to provide physical velocity profiles for the simulations. The vorticity transport equation is studied and its terms are balanced to find the mechanism of vorticity transfer to structures in the curved pipe. Several vortices are identified via various vortex identification (ID) methods and their results are compared. Isosurfaces of the $\unicode[STIX]{x1D706}_{2}$ vortex ID are used to explain the temporal and spatial evolution of vortices in the curved pipe. Eigenvalues and eigenvectors of the velocity gradient tensor are calculated for the swirling strength vortex ID method, which also determines vortex axis orientation. The classical Lyne vortex in oscillatory flow with an inviscid core is also revisited and its results are compared with the transient and steady flows. These in-depth analyses provide a better understanding and characterization of vortical structures in the curved pipe flow. Our findings show that, although there are some visual similarities between cross-sectional views of steady/transient flows and oscillatory flows, the structure herein designated as Lyne-type vortex detected in the cross-sections (under steady, transient and pulsatile flows) is not the same as the classical Lyne vortex pair (in oscillatory flows).
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Urmancheev, S. F. "Dispersed media: scattering of sound waves, stratification in swirling flows and sedimentation processes." Multiphase Systems 17, no. 1-2 (2022): 97–112. http://dx.doi.org/10.21662/mfs2022.1.008.
Повний текст джерелаАнотація:
A brief review on three problems from the multiphase media mechanics area related to the study of the dynamic behavior of disperse systems under various conditions and methods of interaction with external fields or the environment is presented. The problems are an integral part of the scientific project “Hydrodynamic effects in multiphase and thermoviscous media under wave and thermal effects”. The review is carried out in the context of the vector of development of modern research in the relevant areas. As a part of solving the problem of acoustic wave scattering by a set of spherical bubbles or drops, taking into account their sound permeability, the fast multipole method was developed to expand the possibilities of its application in the considered cases. On the basis of addition theorems for spherical wave functions, a new formula for the total scattering cross section for a set of interacting sound-permeable spheres arbitrarily located in space is obtained. An important aspect of the research was the estimation of the region in the parameter space of the problem, in which the effects of multiple scattering are significant. The second problem is related to mathematical modeling of a swirling turbulent flow containing particles of a dispersed phase. For numerical studies of temperature stratification in a vortex tube, an algorithm and a computer code were created using an orthogonalized finite-volume mesh with separation of the near-wall layer. A number of parametric studies have been carried out, in particular, the dependence of the temperature of the outgoing air in the cold diaphragm channel depending on the diameter of the diaphragm has been considered. In order to increase the efficiency of geological exploration in solving the third problem for describing the process of magmatic ore formation, a system of equations based on the methods of mechanics of multiphase media and thermohydrodynamics is proposed. The mathematical model provides for the heat exchange of the magmatic melt flow with the surrounding host rocks, as well as the release of heavy and light fractions from basaltic magma during its cooling. The results obtained in the course of the computational experiment indicate the possibility of a periodically inhomogeneous nature of the distribution of ore-forming fractions.
Дисертації з теми "Swirling cross flows"
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Lin, Chao-An. "Three-dimensional computations of injection into swirling cross-flow using second-moment closure." Thesis, University of Manchester, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280543.
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Surya, Prakash R. "Liquid Jet in Swirling Cross Flow." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5257.
Повний текст джерелаАнотація:
Liquid jets in cross flows (JICF) have been an important part of spray research in the last few decades owing to the wide spectrum of applications ranging from agricultural sprays to aircraft gas turbine engines. However, the current study focuses on the liquid jet injected in swirling cross flows (JISCF), which is more specific to aircraft gas turbine engines. Since this configuration is relatively new in the research domain, various closely related problems are investigated for a better understanding of the spray dynamics. To begin with, the classical-JICF configuration is used to study the influence of liquid jet exit conditions on the resultant spray behaviour. The liquid jet exit velocity profiles are varied by altering the L/D ratio of the plain orifice nozzles between 10 and 100. While the smaller L/D nozzles produce laminar jets, the larger L/D nozzles allow the liquid to transition to fully turbulent conditions. Laser diagnostics are employed to measure the spray trajectory and drop sizes. It is observed that the laminar jets penetrate further into the cross flow as compared to the turbulent jet counterparts for similar flow conditions and produce larger droplets. This is attributed to the turbulent jet undergoing early breakup due to the inherent instabilities in the jet.
This learning is then carried forward to experimental studies on liquid jet in swirling cross flow (JISCF) by employing longer L/D nozzles to promote better atomization. The swirl flow is generated with the aid of 3-D contoured axial swirl vanes with 30º and 45º exit angles and compared with baseline no-swirl case. The resultant spray shows interesting and counter-intuitive behaviour under the influence of swirl flows. While the centrifugal forces are expected to carry the droplets radially outward, the aerodynamics in the annular space has the opposing effect in the
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wake regions of the jet. The drop size measurements also reveal the presence of coalescence among the droplets, which was not observed to be significant in classical JICF studies. Higher swirl numbers also caused the spray to bifurcate resulting in the larger droplets impinging on the outer wall much earlier as compared to the lower swirl conditions, whereas droplet impingement on the wall is not observed for no-swirl conditions.
The JISCF problem is also studied computationally using an open source code, Gerris. As part of a validation study, secondary breakup is first simulated at a realistic density ratio of 1000:1. The Weber numbers were varied to cover the known regimes of breakup. Bag-and-stamen breakup, multi-bag breakup and shear breakup were captured with a close match to experimental results. The JISCF simulations are then carried out using similar annular geometry as that of the experiments for a density ratio of 180:1 owing to inherent limitations existing in the multi-phase numerical methodology. The spray characteristics such as trajectory and drop size distributions are analysed. The spray trajectory is observed to move radially outwards with increasing swirl numbers. The drop size measurements again indicate coalescence as the SMDs are observed to increase along the downstream direction. The numerical model is observed to effectively predict the qualitative behaviour of the spray in swirling cross flow.
Overall, the present study helps further our understanding of the spray characteristics produced by liquid jets in swirling cross flows with combined efforts on experimental and numerical fronts.
Книги з теми "Swirling cross flows"
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B, True, Holdeman J. D, and United States. National Aeronautics and Space Administration., eds. Effects of initial conditions on a single jet in crossflow. [Washington, DC]: National Aeronautics and Space Administration, 1995.
Знайти повний текст джерелаТези доповідей конференцій з теми "Swirling cross flows"
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Lakeh, Reza Baghaei, and Majid Molki. "Heat Transfer Enhancement of Laminar Internal Flows Using Electrically-Induced Swirling Effect." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-86473.
Повний текст джерелаАнотація:
A computational and experimental approach is conducted to enhance the convective heat transfer in fully developed laminar flow in parallel-plates configuration. Laminar internal flows are associated with unchanging Nusselt number along the channel due to the fully developed condition of the boundary layer. Inducing a swirling effect along the flow can disturb the flow field and enhance the convective heat transfer from the plates to the flow. The interaction between an electrically-induced secondary flow and the pressure-driven main flow complicates the flow field and causes a swirling effect. In this study, the electric field governing equations are solved numerically using finite volume method. In order to obtain a proper boundary condition for the charge density, an experimental setup was utilized to measure the time-averaged corona current. The distribution of electric field and charge density on the cross section of the channel is obtained and adopted to find the electric body-force at each point. The flow field computations are performed with FLUENT CFD code on a three-dimensional model using second-order upwind scheme. The secondary flow field is imposed on the cross section of the channel by corona discharge. An array of emitting and receiving flat electrodes are embedded in the parallel plates to induce a corona jet on the cross section of the channel. The axial component of velocity along with an array of corona jets gives birth to a swirling flow which can significantly enhance the convection coefficient and Nusselt number in the fully developed regime. This investigation indicated that the convective heat transfer can be enhanced up to 173% with an applied potential of 24 kV.
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Jin, Tai, Gaofeng Wang, Kun Luo, and Jianren Fan. "Hybrid Eulerian-Lagrangian simulations of liquid jet atomization in swirling cross flow." In GPPS Xi'an21. GPPS, 2022. http://dx.doi.org/10.33737/gpps21-tc-250.
Повний текст джерелаАнотація:
Studies on liquid jet breakup and spray formation in swirling cross flows is of great significance to the combustors of gas turbine engines. In this study, hybrid Eulerian-Lagrangian method is utilized for the modelling of liquid jet atomization, which combines the Volume-of-Fluid (VOF) scheme to capture the gas-liquid interface, and a Lagrangian droplet tracking method to resolve the secondary breakup and the dilute spray cloud. Adaptive mesh refinement (AMR) scheme is adopted to refine mesh points around the gas-liquid interface, to save the computational cost appreciably. The liquid jet of fuel (Kerosene) is injected radially outwards into the non-swirling and swirling air crossflow from the inner tube of the annular computational domain. The transient multi-mode breakup process of the fuel jet, such as shear break up, bag formation, ligament and droplet formation, has been analyzed. The effect of swirl on the penetration of the fuel jet is compared with the empirical models. The size distribution of droplets is statistically compared under different swirling conditions.
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Bishara, Fady, Milind A. Jog, and Raj M. Manglik. "Heat Transfer and Pressure Drop of Periodically Fully Developed Swirling Laminar Flows in Twisted Tubes With Elliptical Cross Sections." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11285.
Повний текст джерелаАнотація:
Periodically fully-developed swirling laminar flows in twisted tubes with elliptical cross sections are computationally simulated. The tubes are helically twisted and their geometry is described by the 180° twist ratios y of 3.0, 4.5 and 6.0, and ellipse cross-section aspect ratio of 0.7. Constant-property flow of water (nominal Pr = 3.0) with a Reynolds number range of 10 to 1200 is considered. The analysis quantifies the improvement in the Nusselt number as well as the increase in friction factor in order to map the effective heat transfer enhancement due to the twisted-tube-geometry-induced swirl flows. To this effect, the numerical results are compared with the baseline cases having a twist ratio of y = infinity, or straight elliptical cross-section tubes for which well established correlations are available. Numerical results show that the friction factor and the Nusselt number are a strong function of the twist ratio and the Reynolds number. The increase in fRe and Nu is higher as the twist becomes tighter (lower values of y). For Reynolds numbers below about 100, the heat transfer results do not deviate significantly from the straight-tube values, but at higher values of Re, significant enhancement in heat transfer is evident for all twist ratios considered here. The friction factor and Nusselt number results provided in this paper will help practicing engineers in integrating twisted elliptical tubes in various heat transfer applications.
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Kao, Yi-Huan, Samir B. Tambe, and San-Mou Jeng. "Effect of Chamber Length With Converging Exhaust on Swirling Flow Field Characteristics of a Counter-Rotating Radial-Radial Swirler." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-95345.
Повний текст джерелаАнотація:
An experimental study has been conducted to examine the effect of chamber length on the aerodynamic characteristics of an enclosed, non-reacting, swirling, flow field. The swirling flow was generated by a counter-rotating radial-radial swirler consisting of an inner, primary swirler generating counter-clockwise rotation and an outer, secondary swirler generating clockwise rotation. The enclosures used were square cross-section chambers of differing lengths. The internal cross section of all chambers was 50.8 mm × 50.8 mm (2 inch × 2 inch). 3 different lengths of chamber used for the tests were 76.2 mm (3″), 101.6 mm (4″), and 152.4 mm (6″) respectively. A nozzle was used at the downstream end of the enclosure to ensure the absence of reverse flow back to test chamber and to simulate the area reduction in typical combustor. The nozzle reduced the cross-section area from 50.8 mm × 50.8 mm (2″ × 2″) to 22.2 mm × 22.2 mm (0.875″ × 0.875″) via 45° slope. A two-component laser doppler velocimetry (LDV) system was used to measure the velocities in the flow fields. The chamber length has been observed to have a clear influence on the mean and turbulent velocity profile near the exit of swirler. However, this effect is not as evident further downstream in the flow field. For the short chamber length, higher values of axial and tangential velocities were observed in the swirling jet due to the proximity of the downstream nozzle to the swirler. For this chamber length, higher turbulence intensities were observed in the swirling jet and inside center toroidal recirculation zone. The magnitudes of the swirling jet velocity and the turbulence intensities decreased with an increase in the chamber length. Two counter-rotating flows could merge more complete in the exit of swirler with the chamber length decreasing.
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Bockeria, Leo A., Gennady I. Kiknadze, Andrei V. Agafonov, Ivan A. Gachechiladze, and Alexander Y. Gorodkov. "Application of Tornado-Flow Fundamental Hydrodynamic Theory to the Study of Blood Flow in the Heart and Main Vessels: Design of New Implantable and Accessory Devices for Cardiovascular Surgery." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-87403.
Повний текст джерелаАнотація:
The study of the hydrodynamic structure of Tornado-like swirling viscous flows has proved that these flows possess a strictly organized laminar structure which can be exhaustively described using the exact solution of nonstationary Navier-Stocks and Continuity equations [6]. The flows of this type belong to the class of quasi-potential self-organizing swirling flows that serve the restoration of equilibrium in nature. These flows are characterized by a high efficiency of medium transportation while the energy losses are minimized. This is manifested in a significant decrease of hydrodynamic resistance and special organization of the boundary layer. Recent studies performed in Bakulev Research Center for Cardiovascular Surgery (Moscow, RF) have proved that the structure of blood flow corresponds to the class of Tornado-like swirling flows. This allows modeling the optimum geometry of the surgically reconstructed flow channel of the heart and major arteries in order to exclude excessive flow disturbances. Most currently used substituting implantable devices contacting with the blood do not take into account the peculiar hydrodynamic properties of blood flow in the heart and great vessels. This leads to the formation of undesirable disturbance of the hydrodynamic flow structure, i.e. stagnant or separation zones, which can create conditions for thrombus formation and hyperplasia. Therefore, the exact solution can serve as a basis for the design of implantable devices contacting with blood flow without significant distortion of its structure. The following devices have been proposed. - The aortic valve prosthesis, whose flowing surface has a convergent circular cross-section in the open position. Use of this prosthesis should provide significant reduction in the intensity of anticoagulant therapy after implantation. - Blood vessel prosthesis with radial elasticity and convergent shape in accordance with the replaced section of artery. - Circulatory assist device, whose working chamber contains directing profile on the inner surface corresponding to the Tornado-like flow streamlines. - Hydrodynamic bench for physical modeling of the Tornado-like flow with specified characteristics, allowing testing of implantable devices contacting with blood flow under physiological conditions. The implantable devices for cardiovascular surgery designed on the basis of exact solutions of nonstationary hydrodynamics equations for the Tornado-like swirling flows will be more effective and safe, will reduce the rehabilitation time, and improve the quality of life of patients after surgery.
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Luna, J. M., R. Romero-Mendez, A. Hernandez-Guerrero, and J. L. Luviano-Ortiz. "Analysis and Experimental Visualization of the Flow Behavior Between Parallel Separated Cross-Corrugated Plates." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11224.
Повний текст джерелаАнотація:
The experimental visualization of the flow patterns developed in a channel formed by parallel separated cross-corrugated plates is presented in this work. The flow visualization was carried out by seeding reflective micro-particles in water. The cross-corrugated plates were characterized by corrugations with sinusoidal profile, 0.083 m wavelength and 0.075 m amplitude, placed at ±45° relative to the main flow direction. While the wavelength-amplitude aspect ratio was kept fixed, both the uniform spacing between plates and Reynolds number were varied. The essential feature of the flow is the secondary swirling motion developed by the furrow flows because of the crossing among streams. Three flow regimes were found: steady, unsteady and chaotic mixing. At some critical Reynolds numbers, depending upon the separation between plates, the flow becomes unsteady and chaotic mixing appears first in the outlet of the channel. Chaotic mixing moves closer to the inlet of the channel as the Reynolds number is increased. The results show that the onset of chaotic mixing occurs at larger Reynolds numbers as the spacing is increased. The flow pattern of this channel configuration is compared to that reported for the chevron arrangement.
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Ait Mouheb, Nassim, Agnes Montillet, Camille Solliec, Jacques Comiti, Patrick Legentilhomme, and Dalimil Snita. "Characterisation of Flow and Mass Transfer in Cross Shape and T-Shape Micromixers." In ASME 2009 7th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2009. http://dx.doi.org/10.1115/icnmm2009-82069.
Повний текст джерелаАнотація:
The understanding of physical phenomena such as flow behaviour and mass transfer performance is needed in order to develop appropriate micromixers for industrial or biomedical applications. In this work, CFD is used to characterize the flow and the liquid mixing quality in a micromixer as a function of the Reynolds number. Two micromixers are studied in steady flow conditions; they are based on two geometries, respectively T-shaped (⊤) and cross-type (+). Simulations allow, in the case of ⊤ micromixers, to chart the topology of the flow and to describe the evolution of species concentration downstream the crossing. The streamlines layout and the mixing quality curves reveal three characteristic types of flow previously reported in the literature, depending on Reynolds number: stratified, vortex and engulfment flows. In the case of cross-type micromixers, the structure of the flow is strongly three-dimensional and is characterized by symmetrical vortices in both output channels. The results show that the + shaped system can improve the mixing process in comparison with the micromixers having ⊤ geometry. The second part of the study is experimental. Two cells are constructed, for both geometries (T-shaped and cross) using square channels with 400 μm hydraulic diameter. In order to use particle image velocimetry (PIV), a system has been adapted to measure velocity fields for various channel plans at different channel depths. This allows observing the evolution of the flow and the vortices development along the microchannels. A second experimental technique, the electrochemical one involving microelectrodes implemented at several positions on the channel wall located near the crossing, has been used. The electrochemical method can locally characterize the formation of swirling flows. These two complementary experimental results will be analysed and a comparison with the CFD results will be performed.
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Zimmermann, Markus, Xu Cheng, Ivan Otic, Norbert Alleborn, and Galina Sieber. "Application of a CFD-Based Forced Cross Flow Model to a Sub-Channel Analysis Tool." In 2014 22nd International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icone22-30927.
Повний текст джерелаАнотація:
A detailed CFD analysis was performed to investigate the effect of mixing vanes on single-phase flow distribution in a 5×5 rod bundle simulating PWR operating conditions. The simulation model was 1 m long and contains one split-type mixing vane grid. For the inlet, a fully developed velocity profile from a previous rod-bundle simulation was used. The simulation case was isothermal to avoid a superposition with wall boiling effects. For the simulation of turbulence effects a non-linear k-ε model was used. This model is able to reproduce the swirling flow in the wake of the grid spacer as well as secondary flow patterns that typically occur in sub-channel flows and needs less computational time compared to Reynolds Stress models. The results show that two large vortices are formed at the mixing vane tips in the center of an interior sub-channel. These vortices are co-rotating within the sub-channel and counter-rotating compared to the adjacent sub-channels. The presence of these vortices influence the radial pressure distribution and the cross-flows significantly. A new model approach was developed, which accounts for the effects of mixing vanes and the vortex structures. The new model requires additional input parameters that can be derived from the CFD results. The proposed model was implemented into the sub-channel analysis tool COBRA-FLX™. A comparison between the old and the new approaches for modeling the forced cross-flow shows a significant improvement of prediction of the mass flux distribution.
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Xie, Zhenqiang, Xuewen Cao, Fachun Liang, and Jun Zhang. "The Study of Exhausting Accumulated Liquid in Upward Inclined Pipe Using a Swirl Tool." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-4913.
Повний текст джерелаАнотація:
Abstract The problem of accumulated liquid is very common in wet gas gathering pipelines which varies with the topography, this phenomenon is much more serious especially in upward inclined pipelines. The existence of accumulated liquid at the bottom of the pipeline would decrease the area of the cross section that gas flows through. This makes the gas velocity fluctuate unpredictably and even results in shocks and blocks in pipelines which may cause danger in the safety management of oil and gas production. Swirl tool is a kind of rigid tool which can transfer different flow patterns to a flow pattern similar to annular flow and it has been successfully used to exhaust accumulated liquid in oil fields. However, the mechanism of swirling flow generation in a swirl tool is not fully understood and few researchers have explained how the annular-similar flow decays. In this paper, the formation mechanism of swirling flow in a swirl tool is analyzed using a physical method. The flow pattern transfer procedure and distribution of gas and liquid in the cross section of the pipeline in the swirl tool is simulated with FLUENT (a commercial CFD code). Following the swirling flow formation analysis, the decay of the annular-similar flow from the outlet of the swirl tool is also simulated with FLUENT (a commercial CFD code). Also, the effects of different superficial gas velocities and different liquid rates on the decay of the annular-similar flow are studied with the swirl tool fixed at the bottom of the upward inclined pipeline. The results show that the formation of swirling flow in a swirl tool is mostly affected by the geometric structure of the swirl tool. The centrifugal force is the main force which transfers different flow patterns to a flow pattern similar to annular flow. The centrifugal force that acts on liquid is larger than that of gas since the density of the liquid is much bigger than gas. The annular-similar flow starts to take shape in the swirl tool after the first thread pitch, but the annular-similar flow is nonuniform. After about three thread pitches, the annular-similar flow becomes uniform with liquid surrounding the inner wall of the pipe and gas flowing in the core region of the pipe. The distance of the annular-similar flow sustains longer when the superficial gas velocity increases which means the decay of the swirling flow is slower. Since sufficient liquid rate is critical to maintain annular-similar flow after the tool when the gas flow rate is fixed, the distance of the annular-similar flow goes longer if there is a little increase in liquid rate.
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Pfau, A., M. Treiber, M. Sell, and G. Gyarmathy. "Flow Interaction From the Exit Cavity of an Axial Turbine Blade Row Labyrinth Seal." In ASME Turbo Expo 2000: Power for Land, Sea, and Air. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/2000-gt-0481.
Повний текст джерелаАнотація:
The structure of labyrinth cavity flow has been experimentally investigated in a three fin axial turbine labyrinth seal (four cavities). The geometry corresponds to a generic steam turbine rotor shroud. The relative wall motion has not been modeled. The measurements were made with specially developed low-blockage pneumatic probes and extensive wall pressure mapping. Instead of the classical picture of a circumferentially uniform leakage sheet exiting from the last labyrinth clearance, entering the channel, and uniformly spreading over the downstream channel wall, the results reveal uneven flow and the existence of high circumferential velocity within the entire exit cavity. The circumferential momentum is brought into the cavity by swirling fluid from the main channel. This fluid penetrates the cavity and breaks up the leakage sheet into individual jets spaced according to the blade passages. This gives rise to strong local cross flows that may also considerably disturb the performance of a downstream blade row.