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1
Vargas-Dilaz, Salvador. "Numerical simulations of hydrodynamic particle interactions at low particle Reynolds number." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/11500.
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When solid particles are suspended in the fluid and are not in a jammed state, a fruitful approach to modelling the system can be to describe it as a system of particles interacting both with each other and with an external field. In the specific case when the particles are far enough apart, the dominant interactions between particles are those mediated by the surrounding fluid rather than direct particle-particle interactions, possibly only when the particles are touching. One of the most important phenomena observed in this regime is particle roping – rather than being evenly dispersed throughout the fluid, particles congregate in one or more ‘ropes’ aligned with the flow direction. This can be a serious problem in coal fired power stations, which require coal dust to be evenly distributed to operate at maximum efficiency. This thesis presents a basic numerical study of particle-fluid-particle interactions under conditions characteristic of the roping phenomenon found after bends in the pneumatic transport systems of coal fired power plants. The main objectives of this work are to: 1. Obtain a pair potential hydrodynamic force field from computational fluid dynamics (CFD) simulations of two fixed spherical particles at low particle Reynolds number; 2. Estimate the magnitude of errors introduced by the pair potential approximation by comparing the two fixed spherical particles results with CFD simulations of systems of three fixed spherical particles; and 3. Use many-particle Monte Carlo simulations to investigate the conditions under which clustering or roping occurs.
2
Stoos, James Arthur Leal L. Gary Leal L. Gary Herbolzheimer Eric. "Particle dynamics near fluid interfaces in low-Reynolds number flows /." Diss., Pasadena, Calif. : California Institute of Technology, 1988. http://resolver.caltech.edu/CaltechETD:etd-02022007-110333.
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Staben, Michelle Elizabeth. "Low-Reynolds-number particle transport in narrow channels for microfluidics and other applications." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/dissertations/fullcit/3178360.
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Hammer, Patrick Richard. "A Discrete Vortex Method Application to Low Reynolds Number Aerodynamic Flows." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1311792450.
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Hashemi, Mohammadabad Saeed. "Collision efficiency of a pollutant particle onto a long cylinder in low Reynolds number fluid flow." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=24057.
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A method for calculating the collision efficiency of a small pollutant particle onto a solid long circular cylinder in a low Reynolds number fluid flow with inertia affects is presented. The cylinder is considered at rest in a uniform undisturbed flow at infinity, in the direction perpendicular to the cylinder axis.Assuming that the Reynolds number R based on cylinder radius b is very small but not zero ($R ll 1$), and the Reynolds number Re based on cylinder length l is of order unity, the force per unit length of the cylinder, correct to the order of R, is obtained, first for a general flow direction and then for the case of flow perpendicular to the cylinder axis. This is done by using the Naiver-Stokes equations in long slender bodies theory and applying matched asymptotic expansions in terms of the ratio $ kappa$ of radius to body length. Flow field around the cylinder is calculated and the equation of particle motion is developed by applying Newton's second law of motion. The initial particle velocity far from the cylinder is calculated analytically and the particle trajectory course is solved numerically as an initial value problem by using Richardson Extrapolation and the Bulirsch-Stoer method.
The collision Efficiency E is obtained by trial and error and is plotted against the dimensionless particle parameter p for different values of R (from 10$ sp{-6}$ to 1). The numerical calculations show that the curves have a tendency to move to the right and become like a straight-line as R gets very small. The points at which E is less than 0.005 are also predicted.
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Clark, Thomas Henry. "Measurement of three-dimensional coherent fluid structure in high Reynolds number turbulent boundary layers." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/243622.
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The turbulent boundary layer is an aspect of fluid flow which dominates the performance of many engineering systems - yet the analytic solution of such flows is intractable for most applications. Our understanding of boundary layers is therefore limited by our ability to simulate and measure them. Tomographic Particle Image Velocimetry (TPIV) is a recently developed technique for direct measurement of fluid velocity within a 3D region. This allows new insight into the topological structure of turbulent boundary layers. Increasing Reynolds Number increases the range of scales at which turbulence exists; a measurement technique must have a larger 'dynamic range' to fully resolve the flow. Tomographic PIV is currently limited in spatial dynamic range (which is also linked to the spatial and temporal resolution) due to a high degree of noise. Results also contain significant bias error. This work proposes a modification of the technique to use more than two exposures in the PIV process, which (for four exposures) is shown to improve random error by a factor of 2 to 7 depending on experimental setup parameters. The dynamic range increases correspondingly and can be doubled again in highly turbulent flows. Bias error is reduced by up to 40%. An alternative reconstruction approach is also presented, based on application of a reduction strategy (elimination of coefficients based on a first guess) to the tomographic weightings matrix Wij. This facilitates a potentially significant increase in computational efficiency. Despite the achieved reduction in error, measurements contain non-zero divergence due to noise and sampling errors. The same problem affects visualisation of topology and coherent fluid structures. Using Projection Onto Convex Sets, a framework for post-processing operators is implemented which includes a divergence minimisation procedure and a scale-limited denoising strategy which is resilient to 'false' vectors contained in the data. Finally, developed techniques are showcased by visualisation of topological information in the inner region of a high Reynolds Number boundary layer (δ+ = 1890, Reθ = 3650). Comments are made on the visible flow structures and tentative conclusions are drawn.
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Ullah, Al Habib. "Advanced Measurements and Analyses of Flow Past Three-Cylinder Rotating System." Thesis, North Dakota State University, 2020. https://hdl.handle.net/10365/31833.
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Interaction of flow structures from a three-cylinder system is complex and important for fundamental and engineering applications. In this study, experiments using hotwire, 2D PIV, and Tomography are to be conducted to characterize the fluid flow at various Re number and rotation speeds. The Reynolds number considered based on the diameter of the single-cylinder ranges from 37 to 1700. The peaks in the frequency spectrum obtained from the hotwire study show a unique relation of Strouhal number as a function of static incident angle, RPM, and Reynolds number. From the 2D PIV and 3D tomography experiment, vorticity and velocity results characterize the interaction of wake flow from individual cylinders and as a function of the rotational speeds. Besides, the Standard deviation map shows the turbulence intensity variation at the various static and rotating conditions. The obtained results at static conditions are found to be consistent with the previous computational study.
8
Bloxham, Matthew Jon. "The effects of vortex generator jet frequency, duty cycle, and phase on separation bubble dynamics /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1760.pdf.
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Nessler, Chase A. "Characterization of Internal Wake Generator at Low Reynolds Number with a Linear Cascade of Low Pressure Turbine Blades." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1270749309.
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Sharma, Amit. "Effect of Vortex Shedding on Aerosolization of a Particle from a Hill using Large-Eddy Simulation." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1617105212418248.
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Apsilidis, Nikolaos. "Experimental Investigation of Turbulent Flows at Smooth and Rough Wall-Cylinder Junctions." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/71713.
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Junction flows originate from the interaction between a fluid moving over a wall with an obstacle mounted on the same surface. Understanding the physics of such flows is of great interest to engineers responsible for the design of systems consisting of wall-body junctions. From aerodynamics to turbomachinery and electronics to bridge hydraulics, a number of phenomena (drag, heat transfer, scouring) are driven by the behavior of the most prominent feature of junction flows: the horseshoe vortex system (HVS). Focusing on turbulent flows, the complex dynamics of the HVS is established through its unsteadiness and non-uniformity. The fundamentals of this dynamically-rich phenomenon have been described within the body of a rapidly-expanding literature. Nevertheless, important aspects remain inadequately understood and call for further scrutiny. This study emphasized three of them, by investigating the effects of: model scale, wall roughness, and bed geometry. High-resolution experiments were carried out using Particle Image Velocimetry (PIV). Statistical analyses, vortex identification schemes, and Proper Orthogonal decomposition were employed to extract additional information from the large PIV datasets. The time-averaged topology of junction flows developing over a smooth and impermeable wall was independent of the flow Reynolds number, Re (parameter that expresses the effects of scale). On the contrary, time-resolved analysis revealed a trend of increasing vorticity, momentum, and eruptions of near-wall fluid with Re. New insights on the modal dynamics of the HVS were also documented in a modified flow mechanism. Wall roughness (modeled with a permeable layer of crushed stones) diffused turbulence and vorticity throughout the domain. This effect manifested with high levels of intermittency and spatial irregularity for the HVS. Energetic flow structures were also identified away from the typical footprint of the HVS. Finally, a novel implementation of PIV allowed for unique velocity measurements over an erodible bed. It was demonstrated that, during the initial stages of scouring, the downflow at the face of the obstacle becomes the dominant flow characteristic in the absence of the HVS. Notwithstanding modeling limitations, the physical insight contributed here could be used to enhance the design of systems with similar flow and geometrical characteristics.Ph. D.
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Memory, Curtis Lynn. "Numerical Simulation of Vortex Generating Jets in Zero and Adverse Pressure Gradients." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2098.pdf.
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Kim, JaeMo. "Dynamic simulation of suspended particles and drops at finite Reynolds numbers by dissipative particle dynamics /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.
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Ghahremanian, Shahriar. "Near-Field Study of Multiple Interacting Jets : Confluent Jets." Doctoral thesis, Linköpings universitet, Energisystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-113259.
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This thesis deals with the near-field of confluent jets, which can be of interest in many engineering applications such as design of a ventilation supply device. The physical effect of interaction between multiple closely spaced jets is studied using experimental and numerical methods. The primary aim of this study is to explore a better understanding of flow and turbulence behavior of multiple interacting jets. The main goal is to gain an insight into the confluence of jets occurring in the near-field of multiple interacting jets. The array of multiple interacting jets is studied when they are placed on a flat and a curved surface. To obtain the boundary conditions at the nozzle exits of the confluent jets on a curved surface, the results of numerical prediction of a cylindrical air supply device using two turbulence models (realizable 𝑘 − 𝜖 and Reynolds stress model) are validated with hot-wire anemometry (HWA) near different nozzles discharge in the array. A single round jet is then studied to find the appropriate turbulence models for the prediction of the three-dimensional flow field and to gain an understanding of the effect of the boundary conditions predicted at the nozzle inlet. In comparison with HWA measurements, the turbulence models with low Reynolds correction (𝑘 − 𝜖 and shear stress transport [SST] 𝑘 − 𝜔) give reasonable flow predictions for the single round jet with the prescribed inlet boundary conditions, while the transition models (𝑘 − 𝑘l − 𝜔𝜔 and transition SST 𝑘 − 𝜔) are unable to predict the flow in the turbulent region. The results of numerical prediction (low Reynolds SST 𝑘 − 𝜔 model) using the prescribed inlet boundary conditions agree well with the HWA measurement in the nearfield of confluent jets on a curved surface, except in the merging region. Instantaneous velocity measurements are performed by laser Doppler anemometry (LDA) and particle image velocimetry (PIV) in two different configurations, a single row of parallel coplanar jets and an inline array of jets on a flat surface. The results of LDA and PIV are compared, which exhibit good agreement except near the nozzle exits. The streamwise velocity profile of the jets in the initial region shows a saddle back shape with attenuated turbulence in the core region and two off-centered narrow peaks. When confluent jets issue from an array of closely spaced nozzles, they may converge, merge, and combine after a certain distance downstream of the nozzle edge. The deflection plays a salient role for the multiple interacting jets (except in the single row configuration), where all the jets are converged towards the center of the array. The jet position, such as central, side and corner jets, significantly influences the development features of the jets, such as velocity decay and lateral displacement. The flow field of confluent jets exhibits asymmetrical distributions of Reynolds stresses around the axis of the jets and highly anisotropic turbulence. The velocity decays slower in the combined regio of confluent jets than a single jet. Using the response surface methodology, the correlations between characteristic points (merging and combined points) and the statistically significant terms of the three design factors (inlet velocity, spacing between the nozzles and diameter of the nozzles) are determined for the single row of coplanar parallel jets. The computational parametric study of the single row configuration shows that spacing has the greatest impact on the near-field characteristics.
15
Siu, Yam Wing. "Particle tracking in separated flows." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243911.
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Bregulla, Andreas Paul. "Role of thermo-osmotic flows at low Reynolds numbers for particle driving and collective motion." Doctoral thesis, Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-206615.
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The main subject of this thesis is to examine thermo-osmotic flows, which occur on interfaces of non-uniform temperature. Such thermo-osmotic flows are purely non-thermal equilibrium phenomena. Along the non-isothermal interface, specific interaction of a liquid and its solutes with a boundary vary in strength across the interface, according to the local temperature. This boundary can be a solid, a membrane or a phase boundary. The flow is thereby continuously pumping fluid across the interface in direction of the local temperature gradient, resulting in an extended flow pattern in the bulk due to mass conservation. In a system containing particles and heat sources in a liquid under spatial confinement, the thermo-osmotic flow may drive particles in a directed manner, or can lead to collective phenomena. To approach this broad topic of (self-)thermophoresis and collective motion of active particles and quantify the role of the thermo-osmotic flow upon the latter effects, different experiments have been performed:
The first experiments aim to quantify the thermo-osmotic flow at a non-isothermal liquid/solid interface for two fundamentally different substrate properties. Further, the bulk flow was investigated for two different systems. The form and spatial extension of this bulk flow pattern depends sensitively on the form of the container and the interface, as well as on the thermo-osmotic flow. The first system is a liquid film confined between two planar glass cover slips. The second case is a Janus particle immobilized on one of the glass slips. In the first case, the non-uniform temperature profile is generated by optical heating of a nanometer sized gold colloid, and in the second case, the heat source is the Janus particle. The bulk flow pattern consists, for the second case, of the flow pattern created by the glass cover slips and the one created by the Janus particle.
The following experiments are focusing on the dynamics of mobile self-thermophoretic Janus particles. In particular, their dynamics and the contributions of the thermo-osmotic flow to the interaction of multiple active particles are investigated. To investigate those particles under controlled conditions and examine their interactions at low concentrations for an effectively unlimited amount of time, a real-time feedback algorithm was co-developed to gain control of the motion of multiple active particles simultaneously, called ”photon nudging”. With the help of this method, first experiments have been performed to quantify the dynamics of a Janus particle located close to a heat source.
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Guo, Zhifeng. "Numerical methods for the motion of particles in low Reynolds number hydrodynamics." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24144.pdf.
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Ohmura, Takuya. "Near-wall Dynamics of Active and Passive Particles at Low Reynolds Number." Kyoto University, 2018. http://hdl.handle.net/2433/232226.
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Küchler, Christian [Verfasser]. "Measurements of Turbulence at High Reynolds Numbers : From Eulerian Statistics Towards Lagrangian Particle Tracking / Christian Küchler." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2021. http://d-nb.info/1230138072/34.
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Palma, Moya Sergio Andrés. "Sedimentation of polydisperse particles at low Reynolds numbers in inclined geometries. Numerical and laboratory experiments." Tesis, Universidad de Chile, 2016. http://repositorio.uchile.cl/handle/2250/141016.
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Doctor en Ciencias de la Ingeniería, Mención FluidodinámicaEl transporte hidráulico de partículas a altas concentraciones es una tecnología ampliamente utilizada en la industria para transportar diferentes tipos de materiales granulares mediante la mezcla con fluidos, agua en la mayoría de los casos. En el primer capítulo de esta tesis, vamos a discutir los aspectos más importantes de la dinámica de las suspensiones. En particular, vamos a explicar la física de las suspensiones diluidas, suspensiones semi-diluidas y suspensiones concentradas. Adicionalmente, una revisión de la sedimentación de partículas será mostrada. La sedimentación es un proceso por el cual las partículas sólidas se separan de un líquido, generalmente bajo la acción de fuerzas gravitacionales. La sedimentación es una de las técnicas más antiguas conocidas utilizadas en la industria para limpiar fluidos o, alternativamente, para recuperar partículas. En el segundo capítulo, vamos a mostrar los resultados de un trabajo numérico experimental de sedimentación de partículas ligeramente polidispersas. Una serie de simulaciones numéricas y experimentos de sedimentación se han realizado para comprender los factores que controlan el ángulo final de una capa de sedimento estática formada por partículas cuasi-monodispersas que sedimentan en un contenedor inclinado. El conjunto de experimentos incluye varias combinaciones de la viscosidad del fluido, ángulo del contenedor y concentración de sólidos. Una comparación entre los experimentos y un conjunto de simulaciones numéricas en dos dimensiones muestra que el mecanismo físico responsable de la disipación de energía en el sistema son las colisiones entre las partículas. Los resultados proporcionan nuevos conocimientos sobre el mecanismo que establece la morfología de la capa de sedimento formada por la sedimentación de las partículas en el fondo de un contenedor inclinado. El seguimiento de la interfaz entre los sólidos de la suspensión y la zona clara de fluido revela que el ángulo final adoptada por la capa de sedimento muestra fuertes dependencias de la concentración inicial de partículas y la inclinación del recipiente, pero no la viscosidad del fluido dentro de un rago de números de Reynolds de partículas pequeños. Se concluye que (1) la función de escondimiento juega un papel importante en el ángulo de la capa de sedimentos, (2) la relación entre el efecto de fricción y la pendiente puede ser explicado como una función casi lineal de la velocidad proyectada a lo largo del fondo del contenedor, y ( 3) antes de la finalización de la sedimentación hay una interacción entre partículas significativa a través del fluido que afecta a la organización de la capa final. Podemos expresar la pendiente del lecho de sedimentos como una funci|ón de dos números adimensionales, una versión del número inercial y la concentración de partículas. Los presentes experimentos confirman algunos resultados anteriores sobre el papel del fluido intersticial en los flujos a bajos número de Stokes de partículas. Por último, vamos a mostrar los resultados de un trabajo numérico. Aquí, hemos utilizado un modelo de mezcla continuo para resolver numéricamente las ecuaciones de momento y continuidad asociadas con la dinámica de sedimentación de mezclas de líquido y sólido altamente concentradas en un conducto inclinado abajos números de Reynolds. El conjunto de simulaciones numéricas incluye varias combinaciones de la viscosidad del fluido, ángulo de conducto y concentración de partículas. Esta investigación tiene como objetivo mostrar la fenomenología y dinámica asociada a la sedimentación de partículas monodispersas bajo diferentes condiciones físicas y la caracterización de la etapa final de la capa de sedimento en dos tipos de geometrías inclinadas, con y sin una sección horizontal. Usando argumentos de escala, una expresión matemática formada por tres grupos a dimensionales, incluyendo el número inercial, la concentración de partículas y la relación entre el número de sedimentación Grashof para el número de Reynolds se propone para explicar la altura de la capa de sedimento en la zona de cambio de pendiente de un conducto. Además, encontramos que la concentración inicial es una variable muy importante para saber bajo qué condición es el conducto podría obstruirse. Los principales resultados de esta tesis se presentaron como dos artículos científicos, el primero publicado en el Journal Physics of Fluids, y el segundo trabajo bajo revisión en el International Journal of Multiphase Flow.
Esta tesis ha sido parcialmente financiada por Conicyt Beca de Doctorado Nacional N° 21110766
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Hackl, Jason F. "Fixed-scale statistics and the geometry of turbulent dispersion at high reynolds number via numerical simulation." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41100.
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The relative dispersion of one fluid particle with respect to another is
fundamentally related to the transport and mixing of contaminant species in
turbulent flows. The most basic consequence of Kolmogorov's 1941 similarity
hypotheses for relative dispersion, the Richardson-Obukhov law that mean-square
pair separation distance grows with the cube of time
at intermediate times in the inertial subrange, is notoriously difficult to
observe in the environment, laboratory, and direct numerical simulations (DNS).
Inertial subrange scaling in size parameters like the mean-square pair separation requires
careful adjustment for the initial conditions of the dispersion process as well
as a very wide range of scales (high Reynolds number) in the flow being studied.
However, the statistical evolution of the shapes of clusters of more than two
particles has already exhibited statistical invariance at intermediate times in
existing DNS. This invariance is identified with inertial-subrange scaling and
is more readily observed than inertial-subrange scaling for seemingly simpler quantities such as the mean-square pair separation
Results from dispersion of clusters of four particles (called tetrads) in
large-scale DNS at grid resolutions up to 4096 points in each of three directions and Taylor-scale Reynolds
numbers from 140 to 1000 are used to explore the question of
statistical universality in measures of the size and shape of tetrahedra in
homogeneous isotropic turbulence in distinct scaling regimes at very small times
(ballistic), intermediate times (inertial) and very late times (diffusive).
Derivatives of fractional powers of the mean-square pair separation with respect to time normalized by the
characteristic time scale at the initial tetrad size constitute a powerful
technique in isolating cubic time scaling in the mean-square pair separation. This technique
is applied to the eigenvalues of a moment-of-inertia-like tensor formed from the
separation vectors between particles in the tetrad. Estimates of the
proportionality constant "g" in the Richardson-Obukhov law from DNS at a
Taylor-scale Reynolds number of 1000 converge towards the value g=0.56 reported in
previous studies. The exit time taken by a particle pair to first reach
successively larger thresholds of fixed separation distance is also briefly
discussed and found to have unexplained dependence on initial separation
distance for negative moments, but good inertial range scaling for positive
moments. The use of diffusion models of relative dispersion in the inertial
subrange to connect mean exit time to "g" is also tested and briefly discussed
in these simulations.
Mean values and probability density functions of shape
parameters including the triangle aspect ratio "w," tetrahedron
volume-to-gyration radius ratio, and normalized moment-of-inertia
eigenvalues are all found to approach invariant forms in the inertial subrange
for a wider range of initial separations than size parameters such as
mean-square gyration radius. These results constitute the
clearest evidence to date that turbulence has a
tendency to distort and elongate multiparticle configurations more severely in
the inertial subrange than it does in the diffusive regime at asymptotically
late time. Triangle statistics are found to be independent of
initial shape for all time beyond the ballistic regime.
The development and testing of different schemes for parallelizing the cubic
spline interpolation procedure for particle velocities needed to track particles in DNS is also covered. A "pipeline" method of moving batches of particles
from processor to processor is adopted due to its low memory overhead, but there are challenges in achieving good performance scaling.
22
Ascoli, Edward Paul Leal L. Gary Leal L. Gary. "The effects of a planar wall on the low Reynolds number motion of solid particles, drops and bubbles /." Diss., Pasadena, Calif. : California Institute of Technology, 1988. http://resolver.caltech.edu/CaltechETD:etd-11062007-130109.
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Rivedal, Nikolai Hydle. "Two-dimensional Simulations of Particle Deposition on a Cylinder in a Turbulent Cross Flow at Intermediate Reynolds Numbers." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13994.
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The behaviour of particles in turbulent flow, with emphasis on particle deposition on both the frontside and backside of a cylinder, was investigated by means of Direct Numerical Simulations. One-way coupling between the fluid and the particles was applied. Simulations of turbulence forced at small, intermediate and large scales were run on a three-dimensional domain. The turbulence was used as inlet on a two-dimensional flow domain, where a Lagrangian tracker was used to compute the particle motions. The Reynolds numbers used were Rec = 421 and Rec = 1685. For intermediate Stokes numbers, or particle sizes, the number of particles deposited increased when the Reynolds number was raised. The presence of turbulence lead to a further increase in the deposition for these Stokes numbers, compared to the deposition in laminar flow. The increase was at its highest for large scale forced turbulence. The increased deposition of intermediate Stokes numbers on the frontside of the cylinder in turbulent flow was found to be related to the variance of the effective Stokes number, resulting from the fluctuating nature of the turbulent velocity. The deposition of particles with small Stokes numbers was also altered by the presence of turbulence, but this could not be explained by the variance of Stokes number. The mechanism leading to deposition of these smallest particles is related to the turbulent eddies close to the boundary layer of the cylinder, and will need further study. At the backside of the cylinder, the increased deposition at raised Reynolds number and at the presence of turbulence was related to the magnitude of vorticity. Furthermore, preferential concentration of particles in turbulence was observed in the Rec = 1685 cases, demonstrating the effect of the vorticity magnitude being sustained throughout the domain.
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Souzy, Mathieu. "Mélange dans les suspensions de particules cisaillées à bas nombre de Reynolds." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4719/document.
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J'ai étudié expérimentalement, à l'échelle de la taille des particules, les mécanismes à l'origine de l'intensification des transferts ayant lieu dans les suspensions cisaillées de particules non-inertielles et non-Browniennes. Dans un premier temps, l'expérience de Taylor est revisitée en étudiant l'évolution d'une goutte de colorant soumise à un cisaillement périodique. Au-delà d'une amplitude critique de déformation, la présence des particules brise la réversibilité du système et induit une forte dispersion de la goutte de colorant. Ensuite, en m'intéressant au transfert en proche paroi, j'ai montré que la rotation des particules sur la paroi induit un transport à flux constant d'un scalaire jusque dans le bulk de la suspension, brisant la couche limite diffusive. Une solution analytique du profil de concentration dans cette zone est proposée, en bon accord avec les expériences. Finalement, des mesures PIV haute résolution du fluide interstitiel dans le bulk de la suspension ont été réalisées. A partir de ces champs de vitesses, on a reconstruit l'historique d'étirement de lignes matérielles du fluide et ainsi déterminé les lois d'étirement, information fondamentale pour la compréhension du processus de mélange. La présence des particules change les lois d'étirement qui passent de linéaires dans un fluide pur, à exponentielles en présence de particules. Un modèle d'étirements multiplicatifs est proposé, qui prédit quantitativement l'évolution de la moyenne, de la variance, et la forme log-normale des distributions d'étirements mesurées expérimentalement. L'inhomogénéité des étirements dans les suspensions cisaillées implique une large distribution du temps de mélangeMainly based on experiments, I investigated at a particle scale the mechanisms at the origin of the transfer enhancement in sheared non-Brownian and non-inertial particulate suspensions. First, I revisited Taylor's experiment, investigating the evolution of a drop of dye in a periodic shear. Beyond a critical strain amplitude, the presence of the particles breaks the reversibility of the system and the drop of dye is rapidly dispersed in the surrounding medium. Then, investigating the transfer process in the wall vicinity, I showed that in this region, the rotation of the particles convectively transport a scalar at a constant rate directly from the wall towards the bulk of the suspension, breaking the diffusive boundary layer. An analytical solution for the concentration profile in this region is proposed, in good agreement with experimental measurements. Lastly, high-resolution PIV measurements of the fluid phase were performed in the bulk of the suspension. Using these velocity fields, we reconstructed the stretching histories of fluid material lines to determine the stretching laws, crucial for the understanding of the mixing process. The presence of the particles changes the very nature of the stretching laws from linear, in a pure fluid, to exponential in the presence of particles. A multiplicative stretching model is proposed, which quantitatively predicts the experimentally measured evolution of the mean and the variance of the elongations of the fluid material lines as well as their evolution towards a log-normal distribution. The strong stretching inhomogeneity in sheared suspensions results in a broad distribution of the mixing time
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Kantharaju, Jahnavi. "Large scale structures in the near field of turbulent round jets at high Reynolds numbers." Thesis, Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAX017.
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Cette thèse contribue aux connaissances fondamentales sur les structures à grande échelle dans le champ proche des jets ronds turbulents. Tout d'abord, une interaction spécifique entre les anneaux tourbillonnaires et les tourbillons longitudinaux dans la couche de cisaillement est explorée. Le résultat de cette interaction est supposé se manifester par une organisation radiale des tourbillons longitudinaux, par opposition à leur réseau azimutal rapporté dans la littérature. Des mesures par PIV stéréoscopique à haute cadence sont effectuées dans un plan transversal, deux diamètres en aval de la sortie de la buse. L’intensité des anneaux tourbillonnaires est modifiée par une excitation axisymétrique (nombre d'onde azimutal m=0) et l'organisation résultante des tourbillons longitudinaux est caractérisée. On constate qu'à mesure que la force relative entre les anneaux et les tourbillons longitudinaux augmente, l'organisation de ces derniers se déplace progressivement vers le réseau azimutal, ce qui corrobore l'hypothèse mentionnée ci-dessus. Les résultats suggèrent l'influence des tourbillons longitudinaux sur les anneaux tourbillonnaires, plus faibles, formés dans les jets ronds à des nombres de Reynolds élevés. Un modèle simple est ensuite construit pour isoler et étudier l'interaction ci-dessus à l'aide de simulations numériques. À cet égard, l'évolution d'un anneau tourbillonnaire isolé est d'abord étudiée. Cet anneau est ensuite placé dans le cisaillement moyen d'un jet. Une comparaison entre l'évolution de l'anneau en présence et en absence de cisaillement permet de comprendre le rôle joué par le cisaillement dans la rupture de l'anneau tourbillonnaire.Dans un deuxième temps, les données de PIV stéréoscopique à haute cadence sont analysées plus en détail pour caractériser les stries dans les jets ronds turbulents. Leur coexistence avec les anneaux tourbillonnaires et les tourbillons longitudinaux est étudiée. Les résultats indiquent que les stries sont situées dans le bord extérieur de la couche de cisaillement, et y sont quasi-stationnaires, tandis que le système convectif formé par les anneaux tourbillonnaires et les tourbillons longitudinaux les alimente en éjectant du fluide vers l'extérieur du jet. Le renforcement des anneaux tourbillonnaires par forçage ne semble pas modifier de manière significative la présence des stries, ce qui suggère un quasi-découplage entre les deux.Enfin, différents modes m=0 dans le champ proche des jets ronds sont étudiés, pour mettre en évidence les différences entre ce que la littérature qualifie de "mode de jet préférentiel", et le mode le plus énergétique (correspondant à la fréquence de passage des anneaux). Les mesures d'anémométrie fil chaud à différents emplacements axiaux et les données de PIV stéréoscopique à haute cadence à deux diamètres indiquent que les deux modes ont des structures radiales différentes. On constate également que l'excitation du mode le plus énergétique du jet pourrait fournir des taux d'évasement plus élevés que le mode de jet préférentiel, pour un même niveau de forçage d'entréeThis thesis aims at gaining fundamental understanding of the large scale structures in the near field of turbulent round jets. First, a specific interaction between vortex rings and streamwise vortices within the shear layer is explored. The result of this interaction is hypothesized to manifest itself in a radial organization of streamwise vortices, as opposed to the azimuthal one reported in the literature. High-speed stereo particle image velocimetry (HS-SPIV) is performed in a cross-sectional plane, two diameters downstream of the nozzle exit. The strength of the vortex rings is varied through axisymmetric (azimuthal wavenumber m=0) excitation and the resulting organization of streamwise vortices is monitored. It is found that as the relative strength between the rings and streamwise vortices increases, the organization of the latter vortices gradually shifts towards azimuthal array, thus corroborating the above mentioned hypothesis. The results confirm the influence of streamwise vortices on the weaker vortex rings formed in round jets at high Reynolds numbers. Next, a simple model is built to isolate and study the above interaction using numerical simulations. In this regard, first the evolution of an isolated vortex ring is studied. This ring is then placed in a mean shear of a jet. A comparison between the evolution of the ring in the presence and absence of shear provides insights into the role played by shear in the vortex ring breakdown.As a second part, the HS-SPIV data is further analyzed to characterize streaks in turbulent round jets, and their co-existence with vortex rings and streamwise vortices is explored. The results indicate that streaks are found in the outer edge of the shear layer where they remain almost steady, while the convecting system of vortex rings and streamwise vortices feed them by ejecting fluid outwards from the jet core. Strengthening the vortex rings through forcing is not seen to significantly alter the presence of the streaks, suggesting an almost decoupling between the two.At last, different m=0 modes in the near field of round jets are studied, to highlight the differences between the so-called “jet preferred mode” and the most-energetic mode (corresponding to the passage frequency of rings). Hot-wire anemometry measurements at different axial locations and the HS-SPIV data at two diameters indicate that the two modes have different radial structures. It is also found that exciting the jet at its most energetic mode could provide higher spreading rates than the jet preferred mode for the same input forcing level
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Marchetti, Benjamin. "Sédimentation de particules : effets collectifs et filaments déformables." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0364/document.
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Une étude expérimentale et numérique traitant de l'influence de structures tourbillonnaires sur la sédimentation de nuage de particules sphériques sous l'effet de la gravité est présentée dans une première partie de ce manuscrit. L'écoulement est créé par électro-convection, ce qui permet de générer un réseau de vortex contrôlés en vitesse et de taille constante qui imite un écoulement tourbillonnaire. Des techniques de PIV (Particle image-velocimetry) et de suivi de particules sont utilisés pour étudier la sédimentation du nuage.Le nuage est modélisé comme un ensemble de particules ponctuelles pour lesquelles les forces d'interaction hydrodynamiques entre particules sont prépondérantes. Le comportement du nuage est comparé aux prédictions obtenues avec des modèles numériques. Dans une seconde partie est présentée une étude expérimentale et numérique concernant la sédimentation à faible nombre de Reynolds de fibres flexibles dans un fluide visqueux au repos. L'état d'équilibre atteint par la fibre flexible est étudié. Nous identifions trois régimes ayant des signatures différentes sur l'état stationnaire de la fibre flexible: un régime de faibles déformations dans lequel la force de traînée est proportionnelle à celle d'une fibre sédimentant horizontalement par rapport à la gravité; un régime de grandes déformations dans lequel la force de traînée est aussi proportionnelle à la vitesse de la fibre, mais avec un coefficient de traînée qui est celui d'une fibre chutant parallèlement à la gravité; et un régime de reconfiguration élastique où le filament se déforme avec une traînée plus faible qui n'est plus proportionnelle à sa vitesse, mais à la racine carrée de celle-ciIn the first part, a jointed experimental and numerical study examining the influence of vortical structures on the settling of a cloud of solid spherical particles under the action of gravity at low Stokes numbers is presented. We use electro-convection to generate a two-dimensional array of controlled vortices which mimics a simplified vortical flow. Particle image-velocimetry and tracking are used to examine the motion of the cloud within this vortical flow. The cloud is modeled as a set of point-particles for which the hydrodynamic interaction is preponderant. The cloud behavior (trajectory, velocity, aspect ratio, break-up time …) is compared to the predictions of a two-way-coupling numerical simulation. In the second part, a jointed experimentally and numerical study on the dynamics of slender flexible filaments settling in a viscous fluid at low Reynolds number is presented. The equilibrium state of a flexible fiber settling in a viscous fluid is examined using a combination of macroscopic experiments, numerical simulations and scaling arguments. We identify three regimes having different signatures on this equilibrium configuration of the elastic filament: a weak deformation regime wherein the drag is proportional to the fiber velocity settling perpendicular to the gravity; a large deformation regime wherein the drag is proportional to the fiber velocity settling parallel to the gravity and an intermediate elastic reconfiguration regime where the filament deforms to adopt a shape with a smaller drag which is no longer linearly proportional to the velocity but to the square root of the velocity
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Spiller, Martin Werner. "Physical and numerical experiments of flow and transport in heterogeneous fractured media : single fracture flow at high Reynolds numbers, and reactive particle transport." Phd thesis, kostenfrei, 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=975641778.
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Spiller, Martin [Verfasser]. "Physical and Numerical Experiments of Flow and Transport in Heterogeneous Fractured Media : Single Fracture Flow at High Reynolds Numbers, and Reactive Particle Transport / Martin Spiller." Aachen : Shaker, 2005. http://d-nb.info/1186587210/34.
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Spiller, Martin Werner [Verfasser]. "Physical and Numerical Experiments of Flow and Transport in Heterogeneous Fractured Media : Single Fracture Flow at High Reynolds Numbers, and Reactive Particle Transport / Martin Spiller." Aachen : Shaker, 2005. http://nbn-resolving.de/urn:nbn:de:101:1-2019051908320496307739.
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Bregulla, Andreas Paul [Verfasser], Frank [Akademischer Betreuer] Cichos, Frank [Gutachter] Cichos, and Clemens [Gutachter] Bechinger. "Role of thermo-osmotic flows at low Reynolds numbers for particle driving and collective motion / Andreas Paul Bregulla ; Gutachter: Frank Cichos, Clemens Bechinger ; Betreuer: Frank Cichos." Leipzig : Universitätsbibliothek Leipzig, 2016. http://d-nb.info/1240482930/34.
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Machicoane, Nathanaël. "Particules matérielles en écoulement turbulent. Transport, dynamique aux temps longs et transfert thermique." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2014. http://tel.archives-ouvertes.fr/tel-01070651.
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Nous nous intéressons au transport turbulent de particules de taille grande devant l'échelle de Kolmogorov. Cette situation se retrouve à la fois dans les écoulements naturels (comme le transport de sédiments) et dans les écoulements industriels (solutés solides dans un mélangeur par exemple). Pour aborder ce problème, nous étudions la dynamique de particules de taille proche de l'échelle intégrale, de densité égale ou légèrement différente de celle du fluide, dans un écoulement turbulent de von Kármán contra-rotatif, à l'aide d'un montage de suivi lagrangien rapide. L'étude de la dynamique rapide des particules montre une diminution forte des fluctuations selon la taille, mais aussi l'apparition d'un phénomène nouveau : à partir d'une certaine taille, les particules n'explorent plus l'écoulement de façon homogène. Cette exploration préférentielle est liée à la structure moyenne de l'écoulement de von Kármán, qui crée une force de piégeage. Cette force devient alors supérieure aux fluctuations des particules quand leur taille dépasse une taille critique. Une étude dans le régime laminaire, où l'écoulement moyen domine largement les fluctuations, a en effet mis en évidence un piégeage fortement accru. Les particules orbitent alors pendant des temps très longs autour des attracteurs stables des particules fluides de l'écoulement laminaire. Même en régime pleinement turbulent, le déplacement des particules entre ces zones s'effectue sur des durées longues, décorrélées des temps de la dynamique turbulente. Nous avons adapté les outils d'analyse pour caractériser cette dynamique et l'avons comparée à celle de particules isodenses dans un écoulement de von Kármán qui possède deux états asymétriques. Nous avons également élaboré un modèle qui reproduit ces caractéristiques dans les cas symétrique et asymétrique. Ces questions sont intimement liées au transfert de masse ou de chaleur entre une particule et l'écoulement. Nous avons donc aussi étudié la fusion de grosses billes de glace en turbulence développée, analysant l'influence de la taille des billes et de la vitesse de glissement sur le transfert thermique, à l'aide d'un montage d'ombroscopie afocale. Nous avons notamment montré que les grosses billes de glace fondent dans un régime ultime de convection forcée lorsqu'elles sont librement advectées par l'écoulement.
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Belkhelfa, Yazid. "Etude du comportement dynamique et du transfert de matière et de chaleur entre des particules sphériques et un écoulement laminaire ou turbulent." Phd thesis, INSA de Rouen, 2008. http://tel.archives-ouvertes.fr/tel-00560879.
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A caractérisation de l'écoulement, du transfert de chaleur et de masse lors du déplacement de gouttelettes de diamètre inferieur au millimètre dans un milieu extérieur font l'objet de notre étude. La première partie présente l'état de l'art des connaissances théoriques et expérimentales des comportements aérodynamiques ainsi que les mécanismes de transfert thermiques et massiques intervenant entre une phase dispersée et une phase continue. La deuxième partie est consacrée à l'étude du phénomène d'évaporation d'une gouttelette mono-dispersée en chute libre dans l'air. Pour cela, nous avons réalisé un dispositif expérimental. Les mesures, nous permettent de prédire l'évaporation de la gouttelette en fonction des caractéristiques physico-chimiques et de l'hygrométrie du milieu extérieur. Pour la modélisation du transfert de chaleur et de masse nous avons utilisé un modèle simple qui tient en compte du couplage entre le mouvement et les phénomènes de transferts, validé dans une précédente étude au sein du laboratoire. Un bon accord est observé. La troisième partie traite de la simulation numérique de l'interaction entre les particules sphériques dans un régime laminaire. Tout d'abord, nous avons proposé et validé un modèle simple qui ne tient pas en compte des phénomènes d'interaction. Les résultats obtenus sont en concordance avec la littérature. Par la suite, nous avons étudié l'interaction entre trois particules identiques et co-alignées. Ce modèle tient compte de la nature de la particule, du nombre du Reynolds et de la distance de séparation. Nous avons validé ce travail par une comparaison avec une étude précédente que nous avons généralisé. La dernière partie est cernée sur l'étude de la dispersion des gouttelettes dans un écoulement turbulent homogène et isotrope. Pour cela, nous avons proposé un modèle Lagrangien de suivi des trajectoires. La production de la turbulence est assurée par une condition de turbulence de grille. Nous avons considéré que les caractéristiques moyennes de l'écoulement fluide sont connues. La sélection des fluctuations de vitesse turbulente est assurée par une méthode probabiliste gaussienne que nous avons développée. La fluctuation est conservée durant un certain temps lié à turbulence, elle est renouvelée au cours du calcul. Ce renouvellement est donné par le temps caractéristique de turbulence.
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Dekou, Tiomajou Raoul Florent. "Organisation à grandes échelles de la turbulence de paroi." Thesis, Ecole centrale de Lille, 2016. http://www.theses.fr/2016ECLI0006/document.
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Ce travail porte sur l’étude des structures cohérentes dans une couche limite de plaque plane à hauts nombres de Reynolds (Reθ=9830 et Reθ=19660). L'estimation Stochastique Linéaire est utilisée pour reconstruire un champ de vitesses résolu en espace et en temps à partir des mesures aux fils chauds à 30 KHz et des mesures PIV à 4 Hz. Une base de données DNS d’un écoulement de canal turbulent a été utilisée pour valider la procédure de reconstruction. Le champ de vitesse reconstruit est comparé à un champ de référence extrait de la DNS avec la visualisation des contours du champ de vitesse, l’analyse spectrale, les corrélations, etc. Par ailleurs, une analyse statistique est réalisée sur le champ de PIV originale, les données issues des fils chauds et celles reconstruites. Les résultats obtenus sont comparés à ceux de Carlier et Stanislas (2005) qui servent de référence. Des algorithmes ont été développés pour extraire les structures cohérentes du champ reconstruit. Les régions de vitesse uniforme sont caractérisées avec leur diamètre hydraulique, leur durée de vie et leur contribution aux tenseurs de Reynolds. Pour les tourbillons, on leur associe un rayon, une circulation et une vorticité en plus de leur durée de vie et leur nombre calculé à une distance fixe de la paroi. L’organisation spatiale des structures est étudiée avec la corrélation de leurs fonctions indicatives. Le modèle simplifié à grandes échelles qui en découle est comparé à ceux qui existent dans la littératureThis study lies in the context of large scale coherent structures (uniform momentum regions and vortical motions) investigation in a near wall turbulent boundary layer at high Reynolds numbers (Reθ=9830 and Reθ=19660). With a Linear Stochastic Estimation procedure based on correlations computation, a full time-resolved 3 component field is reconstructed at high frequency from stereo-PIV at 4 Hz and hot wire data at 30 kHz . A DNS database of turbulent channel flow was used to validate the reconstruction method. To evaluate the quality of the method, reconstructed velocity fluctuations are compared to refence ones extracted directly from the DNS database. Furthermore, a statistical analysis is performed on HWA, PIV and LSE velocity fields. The results obtained are compared to those from Carlier and Stanislas (2005). Algorithms were developed to extract coherent structures from the reconstructed field. Uniform momentum regions are characterized with their mean hydraulic diameter in the YZ plane, their life time and their contribution to Reynolds stresses. The vortical motions are characterized by their position, radius, circulation and vorticity in addition to their life time and their number computed at a fixed position from the wall. The spatial organization of the structures was investigated through a correlation of their respective indicative functions in the spanwise direction . The simplified large scale model that arised is compared to the ones in the literature
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Браженко, В. М. "Очищення робочих рідин повнопотоковим гідродинамічним фільтром з обертовим перфорованим циліндром та бункером для осаду." Thesis, Сумський державний університет, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67879.
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В дисертації вирішена актуальна науково-технічна задача – підвищення ефективності очищення робочих рідин від механічних частинок повнопотоковим гідродинамічним фільтром, а саме ротаційним, в якому запропоновано використовувати у якості фільтроелемента обертовий перфорований циліндр та
бункер для осаду для збору відсепарованих частинок. На основі чисельного моделювання, яке базується на усереднених по Рейнольдсу рівняннях Нав’є-Стокса (RANS) зі застосуванням моделі турбулентності
переносу зсувних напруг (SST k-ω модель) Ментера, проведено дослідження течії несучої рідини біля обертової фільтруючої поверхні та області бункера для осаду ротаційного фільтра. Доведено нерівномірність протікання рідини у радіальному напрямку крізь перфорований циліндр. Крізь отвори розташовані біля вхідного перетину в робочу область проходить більше рідини ніж через отвори, які
максимально віддалені від даного перетину, що негативно впливає на реалізацію гідродинамічного ефекту очищення. Досліджено еволюцію течії рідини біля отворів уздовж поверхні перфорованого циліндра в залежності від зміни параметрів Reφ, Rer та показано, що зі збільшенням Reφ, що характеризує обертовий рух рідини, збільшується перекриття отворів набігаючим потоком. У тривимірній постановці досліджено траєкторії руху завислих частинок біля проникної поверхні фільтроелемента, доведено здійснення гідродинамічного ефекту очищення для перфорованого циліндра в якості фільтроелемента при різних режимах течії та відмічено наявність «буферної зони», яка виключає контакт частинок домішки з поверхнею проникного циліндра. На основі вісесиметричної постановки виявлено позитивний вплив обертання торцевої стінки фільтроелемента на гідродинаміку течії, що проявляється в
стримуванні поширення вихрових зон з області бункера в робочу область фільтра, та утримання частинок у бункері. Отримано залежності ефективності очищення фільтра від відносного діаметру і густини частинок домішки та густини рідини при заданій конструкції фільтра. Визначено найвищу ефективність утримання частинок домішки в бункері циліндричної та конічної розбіжної форми.
Проведено експериментальні дослідження, що підтвердили ефективність, яка складає 95 %, запропонованого пристрою очищення рідини АМГ-10 від частинок розміром 100…200 мкм, та адекватність отриманих теоретичних результатів реальним фізичним процесам. Розбіжність між розрахунковими й отриманими в результаті експерименту значеннями порівнюваних параметрів склала не більше 9 %.In the thesis the actual scientific and technical problem is solved – an increase in the efficiency of cleaning of working fluids from mechanical particles by a full-flow hydrodynamic filter, namely a rotational, in which it is proposed to use a rotating perforated cylinder as a filter element and a sludge hopper for collecting the separated particles. On the basis of numerical modeling based on the Navier-Stokes (RANS) averaged Reynolds equations using a shift model of the shifting stresses (SST k-ω model) of Menther, a study of the flow of a carrier fluid near the rotating filtering surface and the area of the rotor sink hopper filter. The uneven flow of a fluid in a radial direction through a perforated cylinder is proved. Through the openings located near the inlet to the working area there is more fluid than through the openings, which are as far removed from this section, which adversely affects the implementation of the hydrodynamic effect of cleaning. The evolution of the fluid flow along the holes along the surface of the perforated cylinder, depending on the change in the parameters Reφ, Rer, has been studied, and it is shown that with increasing Reφ, which characterizes the rotary motion of the liquid, the overlapping of the apertures with the incident flow increases. In the threedimensional form, the trajectories of the motion of suspended particles near the permeable surface of the filter element have been investigated, the hydrodynamic effect of purification for a perforated cylinder as a filter element has been proved under different flow regimes and the presence of a «buffer zone» is excluded, which excludes the contact of impurity particles with the penetrant cylinder surface. On the basis of an axisymmetric statement, the positive effect of the rotation of the end wall of the filter element on the hydrodynamics of the current, revealed in the containment of the diffusion of vortex zones from the bunker region to the working region of the filter, and the content of the particles in the hopper, was found. The dependence of the filter cleaning efficiency on the relative diameter and density of the particles of impurity and fluid density on the given filter design was obtained. The highest efficiency of the content of impurity particles in the bunker of the cylindrical and conical divergent configuration is determined. Experimental studies have been carried out to confirm the efficiency of 95 % of the proposed cleaning device from particles of 100…200 μm AMG-10 fluid and the adequacy of the obtained theoretical results to real physical processes. The difference between the calculated values and the resulting parameters obtained by the experiment was not more than 9 %.
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Stoos, James Arthur. "Particle Dynamics near Fluid Interfaces in Low-Reynolds Number Flows." Thesis, 1988. https://thesis.library.caltech.edu/465/3/Stoos_js_1988.pdf.
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Numerical solutions for the creeping motion of a spherical particle in a linear axisymmetric straining flow normal to a deformable interface are presented for a range of viscosity ratios, capillary numbers and Bond numbers. The parameter ranges investigated have applications in areas of flotation (small interface deformation) and material processing (large interface deformation). The accuracy of previous solutions for flotation problems, which neglect interface deformation is considered, along with the magnitude and form of interface deformation "defects" that may appear in material processing applications involving fluids containing bubbles or small particles.
Numerical solutions for the equilibrium particle-interface configuration for a neutrally buoyant spherical particle contacting a deformable fluid/gas interface in a linear axisymmetric straining flow at low Reynolds number are presented for a range of contact angles and capillary numbers. These solutions may have applications both in flotation separation processes and in contact angle and surface tension measurement. In addition, the accuracy of simply combining previous results for particle detachment due to particle buoyancy with the results for particle detachment due to viscous forces is considered. The equilibrium configuration is especially sensitive to the inclusion of a small amount of flow for small contact angles and for capillary numbers near the critical capillary number.
Trajectories of small spherical particles around a spherical drop (bubble and solid) are calculated from an approximate solution employing a matched asymptotic expansion. Viscous interaction is seen to have a large effect on the trajectory around a solid collector and a small effect on the trajectory around a bubble. Previous solutions are found to be in error in their prediction of an increase in the capture efficiency because of viscous interactions; the capture efficiency decreases significantly in this case.
Finally, the trajectories of particles around bubbles and the capture of particles by bubbles is investigated experimentally.
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Zeng, Lanying. "Interaction between a spherical particle and wall-bounded flows at finite Reynolds number /." 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3270066.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4579. Adviser: S. Balachandar. Includes bibliographical references (leaves 188-195) Available on microfilm from Pro Quest Information and Learning.
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Peng, HsiuChin, and 彭修慶. "Flow field at high incoming velocity and Reynolds number measurements using Particle Imaging Velocimetry." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/16111905132216223270.
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碩士國立臺灣大學
工程科學與海洋工程學系
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This study aims to establish a P.I.V.（Particle Image Velocimetry）system by measuring the juncture vortex come up near the intersection of a circular cylinder and a flat plate in a recurring hydraulic tank. Two identifying particle methods ,（1）Using cross-correlation principle method and（2）an artificial neural network method are used to verify the practicality of this P.I.V. system. The result shows that the P.I.V. system can get a good quantitative analysis. The result also shows that the neutral network method had a better outcome to the measurement of juncture vortices than the using cross-correlation principle methods at lower incoming velocities, but the cross-correlation principle method identifies more particles than the neutral network method at higher incoming velocity conditions.
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Ramirez, Lynnette E. S. "Dynamics Of A Spherical Particle In A Model Clinostat Or Bioreactor." Thesis, 2004. http://hdl.handle.net/10125/10492.
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Nadge, Pankaj M. "High Reynolds Number Flow Over A Backward-Facing Step." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2542.
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Flow separation and reattachment happens in many fluid mechanical situations occurring in engineering applications as well as in nature. The flow over a backward-facing step represents a geometrically simple flow situation exhibiting both flow separation and reattachment. Broadly speaking there are only two important parameters in the problem, the Reynolds number(Re) based on the step height(h),and a geometrical parameter, referred to as the Expansion ratio(ER), defined as the downstream channel height to the upstream channel height. In spite of the relative simplicity of this geometry, the flow downstream is quite complex. The main focus of the present work is to elucidate the unsteady three-dimensional coherent structures present in this flow at large Re, Re>36,000,based on the step height(h). For this, we use velocity field measurements from Particle Image Velocimetry (PIV)in conjunction with hotwire anemometry measurements.
The time-averaged structure of this flow is first studied in detail, including the effect of Reynolds number(Re) and Expansion Ratio(ER), on it. These studies show that at sufficiently large Re (Re>20,000), the reattachment length becomes independent of Re. The detailed internal structure of the separation bubble is also found to be independent of Re, but for Revalues that are relatively larger(Re>36,000). At large Re, the main effect of ER ,is found to be on the reattachment length, which increases with ER and saturates for ER values greater than about 1.8. The detailed internal structure of the separation bubble has been mapped at high Re and is found to be nearly the same for all ER, when the streamwise length is normalized by the reattachment length.
In order to elucidate the unsteady coherent vortical structures, PIV measurements are done in two orthogonal planes downstream of the backward-facing step. These measurements are done for ER= 1.50 at large Re(Re=36,000) and in a large aspect ratio facility(AR= span length/step height= 24); the latter being important to avoid any effects due to span-wise confinement. In the spanwise plane parallel to the lower wall(x-z plane),instantaneous velocity fields show counter rotating vortex pairs, which is a signature of the three-dimensional vortical structures in this plane. Using conditional averaging, this counter-rotating vortex pair signature is captured right from upstream of the step, to well after reattachment. Spatial correlations are used to get the length scale of these coherent vortical structures, which varies substantially from the attached boundary layer before separation to the region after reattachment. The variation of these structures in the cross-stream (vertical) direction at reattachment and beyond gives an idea about their three dimensional shape. The circulation of these counter-rotating pairs is measured from the conditionally aver-aged fields, and is found to increase with streamwise distance reaching normalized circulation values (Γ/Uoh) of about 0.5 around reattachment.
Velocity spectra downstream of the step show peaks corresponding to both the shear layer frequency(Stsl)and a relatively lower frequency that corresponds to large-scale shedding from the separation bubble (Stb); the latter in particular being quasi-periodic. Small amplitude sinusoidal forcing at the shedding frequency(Stb) is applied close to the step, by blowing and suction, to make the quasi-periodic shedding more regular. Measurements show that this has a very small effect on both the mean separation bubble and on the counter-rotating structures in the x-z plane. This mild forcing however enables phase locked PIV measurements to be made which shows the bubble shedding phenomenon in the cross-stream plane(side view or x-y plane).
The phase-averaged velocity fields show significant variations from phase to phase. Although there is some hint of structures being shed, from these phase-averaged fields, it is not very clear. One of the primary reasons is the fact that the flow is effectively spanwise averaged, as the three-dimensional structures are not locked in the spanwise direction. To get a three dimensional view of the sheddin gphenomenon, it is necessary to lock the spanwise location with respect to the three-dimensional vortical structures before averaging across the different phases. We use the condition, u’<- urms, to locate the central plane between the counter-rotating structures, which in effect are the “legs” of the three-dimensional structure. With this condition, we effectively get a slice of the shedding cycle cutting through the “head” of the three-dimensional structure. Apart from this cut, we also get a cut between adjacent structures from the weak sweep events, with the condition u’<- urms. Using these conditions, on the phase-locked velocity fields, we effectively lock the structures in time, as well as in the spanwise direction. With this ,a clearer picture of the shedding process emerges. The flow is highly three-dimensional near reattachment and the shedding of the separation bubble is modulated in the spanwise direction owing to the three-dimensional hairpin like vortical structures in the flow. The separation bubble is seen bulged out and lifted high at locations where the head of the hairpin vortex passes, owing to the strong ejection of fluid caused by the vortical structure. On the other hand, outside the hairpin vortices, weak sweep events push the flow towards the wall and make it shallow and less prominent, with the shedding being very weak in this plane. From these observations, a three-dimensional picture of the flow is proposed.
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Nadge, Pankaj M. "High Reynolds Number Flow Over A Backward-Facing Step." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2542.
Full textAbstract:
Flow separation and reattachment happens in many fluid mechanical situations occurring in engineering applications as well as in nature. The flow over a backward-facing step represents a geometrically simple flow situation exhibiting both flow separation and reattachment. Broadly speaking there are only two important parameters in the problem, the Reynolds number(Re) based on the step height(h),and a geometrical parameter, referred to as the Expansion ratio(ER), defined as the downstream channel height to the upstream channel height. In spite of the relative simplicity of this geometry, the flow downstream is quite complex. The main focus of the present work is to elucidate the unsteady three-dimensional coherent structures present in this flow at large Re, Re>36,000,based on the step height(h). For this, we use velocity field measurements from Particle Image Velocimetry (PIV)in conjunction with hotwire anemometry measurements.
The time-averaged structure of this flow is first studied in detail, including the effect of Reynolds number(Re) and Expansion Ratio(ER), on it. These studies show that at sufficiently large Re (Re>20,000), the reattachment length becomes independent of Re. The detailed internal structure of the separation bubble is also found to be independent of Re, but for Revalues that are relatively larger(Re>36,000). At large Re, the main effect of ER ,is found to be on the reattachment length, which increases with ER and saturates for ER values greater than about 1.8. The detailed internal structure of the separation bubble has been mapped at high Re and is found to be nearly the same for all ER, when the streamwise length is normalized by the reattachment length.
In order to elucidate the unsteady coherent vortical structures, PIV measurements are done in two orthogonal planes downstream of the backward-facing step. These measurements are done for ER= 1.50 at large Re(Re=36,000) and in a large aspect ratio facility(AR= span length/step height= 24); the latter being important to avoid any effects due to span-wise confinement. In the spanwise plane parallel to the lower wall(x-z plane),instantaneous velocity fields show counter rotating vortex pairs, which is a signature of the three-dimensional vortical structures in this plane. Using conditional averaging, this counter-rotating vortex pair signature is captured right from upstream of the step, to well after reattachment. Spatial correlations are used to get the length scale of these coherent vortical structures, which varies substantially from the attached boundary layer before separation to the region after reattachment. The variation of these structures in the cross-stream (vertical) direction at reattachment and beyond gives an idea about their three dimensional shape. The circulation of these counter-rotating pairs is measured from the conditionally aver-aged fields, and is found to increase with streamwise distance reaching normalized circulation values (Γ/Uoh) of about 0.5 around reattachment.
Velocity spectra downstream of the step show peaks corresponding to both the shear layer frequency(Stsl)and a relatively lower frequency that corresponds to large-scale shedding from the separation bubble (Stb); the latter in particular being quasi-periodic. Small amplitude sinusoidal forcing at the shedding frequency(Stb) is applied close to the step, by blowing and suction, to make the quasi-periodic shedding more regular. Measurements show that this has a very small effect on both the mean separation bubble and on the counter-rotating structures in the x-z plane. This mild forcing however enables phase locked PIV measurements to be made which shows the bubble shedding phenomenon in the cross-stream plane(side view or x-y plane).
The phase-averaged velocity fields show significant variations from phase to phase. Although there is some hint of structures being shed, from these phase-averaged fields, it is not very clear. One of the primary reasons is the fact that the flow is effectively spanwise averaged, as the three-dimensional structures are not locked in the spanwise direction. To get a three dimensional view of the sheddin gphenomenon, it is necessary to lock the spanwise location with respect to the three-dimensional vortical structures before averaging across the different phases. We use the condition, u’<- urms, to locate the central plane between the counter-rotating structures, which in effect are the “legs” of the three-dimensional structure. With this condition, we effectively get a slice of the shedding cycle cutting through the “head” of the three-dimensional structure. Apart from this cut, we also get a cut between adjacent structures from the weak sweep events, with the condition u’<- urms. Using these conditions, on the phase-locked velocity fields, we effectively lock the structures in time, as well as in the spanwise direction. With this ,a clearer picture of the shedding process emerges. The flow is highly three-dimensional near reattachment and the shedding of the separation bubble is modulated in the spanwise direction owing to the three-dimensional hairpin like vortical structures in the flow. The separation bubble is seen bulged out and lifted high at locations where the head of the hairpin vortex passes, owing to the strong ejection of fluid caused by the vortical structure. On the other hand, outside the hairpin vortices, weak sweep events push the flow towards the wall and make it shallow and less prominent, with the shedding being very weak in this plane. From these observations, a three-dimensional picture of the flow is proposed.
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Su, Yean Chen, and 蘇彥全. "Effects of particle residence time and Reynolds number on solid- liquid convection mass transfer coefficient in holding tubes." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/61552494483395228548.
Full text
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Sharma, Deepan. "Steady Sedimentation of Particles in Long Vertical Tube and Effect of End Boundary Conditions on Convective Motion." Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5637.
Full textAbstract:
Sedimentation – settling of particles in a fluid- is observed in nature like rain droplets and dust particles in the atmosphere, and in a variety of industrial processes, like to clarify liquid as well as separate particles of different size and density. The simplest system is the sedimentation of mono-disperse particles in a vast stationary fluid. The main parameters are Particle Reynolds Number (〖Re〗_p based on terminal velocity), ratio of particle density to fluid density (ρ_p/ρ_f ), particle volume fraction (φ), and container dimensions for experimental and numerical methods. Two main questions arise: what is the mean settling velocity (V_g), and nature and values of fluctuation in particle velocity (V^/), and how do they compare with the terminal velocity (V_t) of an isolated particle in an infinite fluid. At low particle Reynolds number, V_t is given by the Stokes law. Experiments have been typically performed in a tank containing the fluid with particles initially well mixed and tracking the motion of the particles or performing PIV to obtain mean settling velocity (V_g), fluctuating particle velocities (V^/) etc. The main focus of these studies has been to correlate different parameters like mean settling velocity, velocity fluctuation, correlation length with volume fraction, and dimension of the container. Though this apparently simple problem has been studied theoretically, experimentally, and numerically over many decades, there are several unanswered questions. For example, the experimental results for velocity fluctuations do not agree with the theoretical predictions. The origin of scalings for velocity fluctuations are unclear. In our study, we try to address some of these issues using a new type of experiment.
In our experiment, particles are fed at a constant rate at the top and allowed to settle in a long vertical tube containing quiescent fluid, closed at the bottom. The constant particle feed rate ensures mean steady particle settling in contrast to the standard experiments done previously where the settling process is transient. Also, the long vertical extent of the tube ensures Axial Homogeneity. We have done two types of experiments: water droplets (10 μm, 〖Re〗_p~〖10〗^(-3)) falling in the air, and spherical glass beads (110 μm, 〖Re〗_p~1 ) settling in water. The estimated volume fractions for the former is 〖10〗^(-7) and for the latter, it is〖 10〗^(-3). For the droplet-air system, the tube dimension is 5×5 〖cm〗^2 and for the particle-water system, three tube dimensions (4×4 〖cm〗^2 , 5×5 〖cm〗^2, 7×7 〖cm〗^2 ) have been used. Experiments have been done with different mass flux values. We have used high-speed imaging illuminated by a sheet of laser light to visualize the particle motion fields and Particle Image Velocimetry (PIV) to get the mean and fluctuating particle velocities and the spatial and temporal correlations. We have observed a variety of sedimentation-induced convective motions, including regions of particle patches moving upwards. The conditions at the tube end significantly alter the convective patterns and the fluctuating velocities. Convective motions, though hypothesized to exist, have not been observed in earlier experiments. We present results for the mean and fluctuating velocities and spatial and temporal correlations of the velocity fields for the range of mass fluxes and different tube dimensions. Besides the existence of convective motion, the main findings are: the mean settling velocity varies between 0.80-1.1 V_t. The fluctuating velocities are in the range 0.30-0.80 V_t and strongly depend on mass flux. Correlation lengths scale with tube width. We present these results in a non-dimensional form which suggest different scaling laws.
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Bhat, Shantanu. "Study Of Stall Flutter Of An Isolated Blade In A Low Reynolds Number Incompressible Flow." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2443.
Full textAbstract:
Highly-loaded turbomachine blades can stall under off-design conditions. In this regime, the flow can separate close to the leading edge of the blade in a periodic manner that can lead to blade vibrations, commonly referred to as stall flutter. Prior experimental studies on stall flutter have been at large Re (Re ~ 106). In the present work, motivated by applications in Unmanned Air Vehicles (UAV) and Micro Air Vehicles (MAV), we study experimentally the forces and flow fields around an oscillating blade at low Re (Re ~ 3 x 104). At these low Re, the flow even over the stationary blade can be quite different.
We experimentally study the propensity of an isolated symmetric and cambered blade (with chord c) to undergo self-excited oscillations at high angles of attack and at low Reynolds numbers (Re ~ 30, 000). We force the blade, placed at large mean angle of attack, to undergo small amplitude pitch oscillations and measure the unsteady loads on the blade. From the measured loads, the direction and magnitude of energy transfer to/from the blade is calculated. Systematic measurements have been made for varying mean blade incidence angles and for different excitation amplitudes and frequencies (f). These measurements indicate that post stall there is a possibility of excitation of the blade over a range of Strouhal Numbers (St = fc/U) with the magnitude of the exciting energy varying with amplitude, frequency and mean incidence angles. In particular, the curves for the magnitude of the exciting energy against Strouhal number (St) are found to shift to higher St values as the mean angle of attack is increased. We perform the same set of experiments on two different blade shapes, namely NACA 0012 and a compressor blade profile, SC10. Both blade profiles show qualitatively similar phenomena.
The flow around both the stationary and oscillating blades is studied through Particle Image Velocimetry (PIV). PIV measurements on the stationary blade show the gradual shift of the flow separation point towards the leading edge with increasing angle of attack, which occurs at these low Re. From PIV measurements on an oscillating blade near stall, we present the flow field around the blade at different phases of the blade oscillation. These show that the boundary layer separates from the leading edge forming a shear layer, which flaps with respect to the blade. As the Strouhal number is varied, the phase between the flapping shear layer and the blade appears to change. This is likely to be the reason for the observed change in the sign of the energy transfer between the flow and the blade that is responsible for stall flutter.
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Bhat, Shantanu. "Study Of Stall Flutter Of An Isolated Blade In A Low Reynolds Number Incompressible Flow." Thesis, 2012. http://etd.iisc.ernet.in/handle/2005/2443.
Full textAbstract:
Highly-loaded turbomachine blades can stall under off-design conditions. In this regime, the flow can separate close to the leading edge of the blade in a periodic manner that can lead to blade vibrations, commonly referred to as stall flutter. Prior experimental studies on stall flutter have been at large Re (Re ~ 106). In the present work, motivated by applications in Unmanned Air Vehicles (UAV) and Micro Air Vehicles (MAV), we study experimentally the forces and flow fields around an oscillating blade at low Re (Re ~ 3 x 104). At these low Re, the flow even over the stationary blade can be quite different.
We experimentally study the propensity of an isolated symmetric and cambered blade (with chord c) to undergo self-excited oscillations at high angles of attack and at low Reynolds numbers (Re ~ 30, 000). We force the blade, placed at large mean angle of attack, to undergo small amplitude pitch oscillations and measure the unsteady loads on the blade. From the measured loads, the direction and magnitude of energy transfer to/from the blade is calculated. Systematic measurements have been made for varying mean blade incidence angles and for different excitation amplitudes and frequencies (f). These measurements indicate that post stall there is a possibility of excitation of the blade over a range of Strouhal Numbers (St = fc/U) with the magnitude of the exciting energy varying with amplitude, frequency and mean incidence angles. In particular, the curves for the magnitude of the exciting energy against Strouhal number (St) are found to shift to higher St values as the mean angle of attack is increased. We perform the same set of experiments on two different blade shapes, namely NACA 0012 and a compressor blade profile, SC10. Both blade profiles show qualitatively similar phenomena.
The flow around both the stationary and oscillating blades is studied through Particle Image Velocimetry (PIV). PIV measurements on the stationary blade show the gradual shift of the flow separation point towards the leading edge with increasing angle of attack, which occurs at these low Re. From PIV measurements on an oscillating blade near stall, we present the flow field around the blade at different phases of the blade oscillation. These show that the boundary layer separates from the leading edge forming a shear layer, which flaps with respect to the blade. As the Strouhal number is varied, the phase between the flapping shear layer and the blade appears to change. This is likely to be the reason for the observed change in the sign of the energy transfer between the flow and the blade that is responsible for stall flutter.
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Kumar, Vijay. "Viscous Vortex Method Simulations of Stall Flutter of an Isolated Airfoil at Low Reynolds Numbers." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/2814.
Full textAbstract:
The flow field and forces on an isolated oscillating NACA 0012 airfoil in a uniform flow is studied using viscous vortex particle method. The simulations are carried out at very low chord (c) based Reynolds number (Re=1000), motivated by the current interest in development of Micro Air Vehicles (MAV). The airfoil is forced to oscillate in both heave and pitch at different normalized oscillation frequencies (f), which is represented by the non-dimensional reduced frequency fc/U).( From the unsteady loading on the airfoil, the net energy transfer to the airfoil is calculated to determine the propensity for the airfoil to undergo self-induced oscillations or flutter at these very low Reynolds numbers. The simulations are carried out using a viscous vortex particle method
that utilizes discrete vortex elements to represent the vorticity in the flow field. After validation of the code against test cases in the literature, simulations are first carried out for the stationary airfoil at different angles of attack, which shows the stall characteristics
of the airfoil at this very low Reynolds numbers.
For the airfoil oscillating in heave, the airfoil is forced to oscillate at different reduced frequencies at a large angle of attack in the stall regime. The unsteady loading on the blade is obtained at different reduced frequencies. This is used to calculate the net energy transfer to the airfoil from the flow, which is found to be negative in all cases studied. This implies that stall flutter or self-induced oscillations are not possible under the given heave conditions. The wake vorticity dynamics is presented for the different reduced frequencies, which show that the leading edge vortex dynamics is progressively
more complex as the reduced frequency is increased from small values. For the airfoil oscillating in pitch, the airfoil is forced to oscillate about a large mean angle of attack corresponding to the stall regime. The unsteady moment on the blade is obtained at different reduced frequencies, and this is used to calculate the net energy transfer to the airfoil from the flow, which is found to be positive in all cases studied. This implies that stall flutter or self-induced oscillations are possible in the pitch mode, unlike in the heave case. The wake vorticity dynamics for this case is found to be relatively simple compared to that in heave. The results of the present simulations are broadly in agreement with earlier stall flutter studies at higher Reynolds numbers that show that stall flutter does not occur in the heave mode, but can occur in the pitch mode. The main difference in the present very low Reynolds number case appears to be the broader extent of the excitation region in the pitch mode compared to large Re cases studied earlier.
region in the pitch mode compared to large Re cases studied earlier.
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Kumar, Vijay. "Viscous Vortex Method Simulations of Stall Flutter of an Isolated Airfoil at Low Reynolds Numbers." Thesis, 2013. http://etd.iisc.ernet.in/handle/2005/2814.
Full textAbstract:
The flow field and forces on an isolated oscillating NACA 0012 airfoil in a uniform flow is studied using viscous vortex particle method. The simulations are carried out at very low chord (c) based Reynolds number (Re=1000), motivated by the current interest in development of Micro Air Vehicles (MAV). The airfoil is forced to oscillate in both heave and pitch at different normalized oscillation frequencies (f), which is represented by the non-dimensional reduced frequency fc/U).( From the unsteady loading on the airfoil, the net energy transfer to the airfoil is calculated to determine the propensity for the airfoil to undergo self-induced oscillations or flutter at these very low Reynolds numbers. The simulations are carried out using a viscous vortex particle method
that utilizes discrete vortex elements to represent the vorticity in the flow field. After validation of the code against test cases in the literature, simulations are first carried out for the stationary airfoil at different angles of attack, which shows the stall characteristics
of the airfoil at this very low Reynolds numbers.
For the airfoil oscillating in heave, the airfoil is forced to oscillate at different reduced frequencies at a large angle of attack in the stall regime. The unsteady loading on the blade is obtained at different reduced frequencies. This is used to calculate the net energy transfer to the airfoil from the flow, which is found to be negative in all cases studied. This implies that stall flutter or self-induced oscillations are not possible under the given heave conditions. The wake vorticity dynamics is presented for the different reduced frequencies, which show that the leading edge vortex dynamics is progressively
more complex as the reduced frequency is increased from small values. For the airfoil oscillating in pitch, the airfoil is forced to oscillate about a large mean angle of attack corresponding to the stall regime. The unsteady moment on the blade is obtained at different reduced frequencies, and this is used to calculate the net energy transfer to the airfoil from the flow, which is found to be positive in all cases studied. This implies that stall flutter or self-induced oscillations are possible in the pitch mode, unlike in the heave case. The wake vorticity dynamics for this case is found to be relatively simple compared to that in heave. The results of the present simulations are broadly in agreement with earlier stall flutter studies at higher Reynolds numbers that show that stall flutter does not occur in the heave mode, but can occur in the pitch mode. The main difference in the present very low Reynolds number case appears to be the broader extent of the excitation region in the pitch mode compared to large Re cases studied earlier.
region in the pitch mode compared to large Re cases studied earlier.
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Forghani, Marveh. "Consolidation of large spherical particles at low Reynolds numbers." Thesis, 2015. http://hdl.handle.net/1959.13/1308128.
Full textAbstract:
Masters Research - Master of Philosophy (MPhil)This study was concerned with the validation of a new theoretical model (Galvin et al., 2015) to describe sediment consolidation, focussing on systems having negligible surface and inertial forces, and hence a minimal compressive yield stress. The study was also concerned with providing a detailed description of this model and its relationship to other work.The particles were assumed to be homogeneous, incompressible and spherical, and to settle in accordance with Stokes` law. The model assumed that the material depositing onto the bed carried three quantities, a fixed portion of solids ΔS, a fixed portion of retained water ΔR, and a variable portion of water deemed to be expressible ΔW. The sediment bed consisted of a finite number of these distinct layers, each containing fixed quantities of the solids and retained water and a variable quantity of the expressible water. The hypothesis of this research was that the reduction in the volume of expressible water declines according to a simple scaling law, ΔW ∝ t-2. The model was used to describe the entire batch settling curve, concentration profile, and velocity of the particles within the sediment bed. An experimental system was developed to validate the model. Spherical particles of Sephadex were used to form suspensions of a given volume fraction. Conventional batch settling tests were performed, and the height data versus time compared with the model predictions. Other experiments were focussed on the movement of the particles during the consolidation, using a CCD camera to record the settling. Further data on the concentration profiles at different times, for experiments conducted at different volume fractions, were produced. Again very good agreement was achieved between the theory and the experimental data.
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Wu, Chin-Liang, and 吳致良. "The Flow characteristics of an Interactive Particle at Low Reynolds Numbers." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/38737546489210645201.
Full textAbstract:
碩士國立海洋大學
機械與輪機工程學系
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The influence of surrounding particle of different sizes, located at various distance and angles with respect to the mainstream direction, on the drag and the flow characteristics of test particle has been experimentally investigated. Quantitative data and physical interpretation are provided. For drag measurements, the liquid viscosity has been increased in an effort to enlarge the magnitudes of drag to a measurable range. The drags of an interactive particle can then be exactly determined by the help of a precise electronic balance. The flow field measurements are conducted using a non-intrusive LDA system. The refractive index matching technique is also applied to overcome the optical difficulty caused by the pass of laser beam through a curve surface. Based on the relationships between the drag and the wake strength derived for a non-interactive particle, empirical correlation has been developed to calculate the drags and the wake strength of an interactive particle. The flow properties under different interactive conditions can then be closely related. Through the above approaches, this study provides not only the important quantitative data of drag and flow characteristics of an interactive particle but also the deep physical understanding of how the particles interacting with each other.
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Shekunov, Boris Yu, J. Baldyga, and Peter York. "Particle formation by mixing with supercritical antisolvent at high Reynolds numbers." 2001. http://hdl.handle.net/10454/3651.
Full textAbstract:
NoA precipitation process is considered in which completely miscible solution and supercritical antisolvent are passed through premixing and diluting zones of a turbulent flow. The influence of flow velocity on particle size and nuclei concentration is discussed in terms of mixing and precipitation time constants and their supersaturation dependencies. The proposed model allowed the major process parameters such as supersaturation profile, mixed fluid fraction and mean particle size to be calculated and compared with experimental data. For the crystallization system paracetamol/ethanol/CO2 studied, the supersaturation profile becomes established at Re104. The particle size and shape are defined, firstly, by increase of supersaturation and relative volume of mixed (on molecular scale) fluid with increase of flow velocity and, secondly, by decrease of residence time available for nucleation with increase of flow velocity. These competitive processes can result in minimum particle size at a defined flow rate.
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Wakaba, Lulama V. "On the response of a spherical particle to unsteady flows at finite Reynolds numbers /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3250340.
Full textAbstract:
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 1043. Adviser: S. Balachandar. Includes bibliographical references (leaves 170-176) Available on microfilm from Pro Quest Information and Learning.