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- Carapau, F., Sequeira, A., "Swirling motion of a second-order viscous fluid in a straight tube", Proceedings of the International Conference on Topical Problems of Fluid Mechanics, Institute of Thermomechanics AS CR, Prague, Czech Republic, February 28 – March 2, 2007, pp. 21-24.
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## ‣ Swirling motion of a second-order viscous fluid in a straight tube

Fonte: Carapau, F., Sequeira, A., "Swirling motion of a second-order viscous fluid in a straight tube", Proceedings of the International Conference on Topical Problems of Fluid Mechanics, Institute of Thermomechanics AS CR, Prague, Czech Republic, February 28 – March 2, 2007, pp. 21-24.
Publicador: Carapau, F., Sequeira, A., "Swirling motion of a second-order viscous fluid in a straight tube", Proceedings of the International Conference on Topical Problems of Fluid Mechanics, Institute of Thermomechanics AS CR, Prague, Czech Republic, February 28 – March 2, 2007, pp. 21-24.

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
47.37799%

#Cosserat theory,#nine-directors,.#unsteady flow,#axisymmetric motion,#volume flow rate,#second-order fluid#mean pressure gradient,

We consider a second-order viscous fluid with swirling motion flowing in a circular
straight tube with constant radius. Integrating the equation of conservation of linear
momentum over the tube cross section with the velocity field approximated by the
Cosserat theory, we obtain a one-dimensional system depending only on time and on
a single spatial variable. From this 1D model, we derive the relationship between
mean pressure gradient and volume flow rate over a finite section of the tube as well
the wall shear stress.

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## ‣ Theory and validation of magnetic resonance fluid motion estimation using intensity flow data

Fonte: Public Library of Science
Publicador: Public Library of Science

Tipo: Artigo de Revista Científica

Publicado em //2009
Português

Relevância na Pesquisa
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#Image Interpretation, Computer-Assisted#Magnetic Resonance Imaging#Magnetic Resonance Spectroscopy#Computer Simulation#Models, Theoretical#Algorithms

Background Motion tracking based on spatial-temporal radio-frequency signals from the pixel representation of magnetic resonance (MR) imaging of a non-stationary fluid is able to provide two dimensional vector field maps. This supports the underlying fundamentals of magnetic resonance fluid motion estimation and generates a new methodology for flow measurement that is based on registration of nuclear signals from moving hydrogen nuclei in fluid. However, there is a need to validate the computational aspect of the approach by using velocity flow field data that we will assume as the true reference information or ground truth. Methodology/Principal Findings In this study, we create flow vectors based on an ideal analytical vortex, and generate artificial signal-motion image data to verify our computational approach. The analytical and computed flow fields are compared to provide an error estimate of our methodology. The comparison shows that the fluid motion estimation approach using simulated MR data is accurate and robust enough for flow field mapping. To verify our methodology, we have tested the computational configuration on magnetic resonance images of cardiac blood and proved that the theory of magnetic resonance fluid motion estimation can be applicable practically. Conclusions/Significance The results of this work will allow us to progress further in the investigation of fluid motion prediction based on imaging modalities that do not require velocity encoding. This article describes a novel theory of motion estimation based on magnetic resonating blood...

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## ‣ Flow imaging and validation of MR fluid motion tracking

Fonte: Springer; Germany
Publicador: Springer; Germany

Tipo: Conference paper

Publicado em //2009
Português

Relevância na Pesquisa
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This paper presents flow results of a magnetic resonance imaging velocimetry system which relies on fluid motion estimation, and uses vorticity map differencing for calibrating its reliability. To validate this new concept, phase contrast magnetic resonance imaging on the right atrium of a healthy subject has been suggested. The study has demonstrated the state of change in blood flow patterns within a cardiac chamber using our implemented system and a well established flow imaging modality. Based on the gold standard imaging technique, flow fields can be used to establish a set of reference data to compare against magnetic resonance fluid motion tracking results. We conclude that our validated technique can be reliable enough for establishing a cardiac based velocimetry system.; K.K.L. Wong, R.M. Kelso, S.G. Worthley, P. Sanders, J. Mazumdar and D. Abbott

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## ‣ Bayesian Estimation of Turbulent Motion

Fonte: IEEE Computer Society
Publicador: IEEE Computer Society

Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion
Formato: application/pdf

Português

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#OPTIC FLOW#BAYESIAN STATISTICS#MOTION ESTIMATION#Ciencias de la Computación#Ciencias de la Computación e Información#CIENCIAS NATURALES Y EXACTAS

Based on physical laws describing the multiscale structure of turbulent flows, this paper proposes a regularizer for fluid motion estimation from an image sequence. Regularization is achieved by imposing some scale invariance property between histograms of motion increments computed at different scales. By reformulating this problem from a Bayesian perspective, an algorithm is proposed to jointly estimate motion, regularization hyperparameters, and to select the most likely physical prior among a set of models. Hyperparameter and model inference are conducted by posterior maximization, obtained by marginalizing out non-Gaussian motion variables. The Bayesian estimator is assessed on several image sequences depicting synthetic and real turbulent fluid flows. Results obtained with the proposed approach exceed the state-of-the-art results in fluid flow estimation.; Fil: Héas, Patrick. Rennes Bretagne Atlantique. Institut National de Recherche en Informatique et en Automatique; Francia;; Fil: Herzet, Cédric. Rennes Bretagne Atlantique. Institut National de Recherche en Informatique et en Automatique; Francia;; Fil: Mémin, Etienne. Rennes Bretagne Atlantique. Institut National de Recherche en Informatique et en Automatique; Francia;; Fil: Heitz...

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## ‣ Computation of Fluid Flows in Non-inertial Contracting, Expanding, and Rotating Reference Frames

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
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We present the method for computation of fluid flows that are characterized
by the large degree of expansion/contraction and in which the fluid velocity is
dominated by the bulk component associated with the expansion/contraction
and/or rotation of the flow. We consider the formulation of Euler equations of
fluid dynamics in a homologously expanding/contracting and/or rotating
reference frame. The frame motion is adjusted to minimize local fluid
velocities. Such approach allows to accommodate very efficiently large degrees
of change in the flow extent. Moreover, by excluding the contribution of the
bulk flow to the total energy the method eliminates the high Mach number
problem in the flows of interest. An important practical advantage of the
method is that it can be easily implemented with virtually any implicit or
explicit Eulerian hydrodynamic scheme and adaptive mesh refinement (AMR)
strategy.
We also consider in detail equation invariance and existence of conservative
formulation of equations for special classes of expanding/contracting reference
frames. Special emphasis is placed on extensive numerical testing of the method
for a variety of reference frame motions, which are representative of the
realistic applications of the method. We study accuracy...

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## ‣ Generalized squirming motion of a sphere

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 05/02/2014
Português

Relevância na Pesquisa
47.15669%

A number of swimming microorganisms such as ciliates ($\textit{Opalina}$) and
multicellular colonies of flagellates ($\textit{Volvox}$) are approximately
spherical in shape and swim using beating arrays of cilia or short flagella
covering their surfaces. Their physical actuation on the fluid may be
mathematically modeled as the generation of surface velocities on a continuous
spherical surface -- a model known in the literature as squirming, which has
been used to address various aspects of the biological physics of locomotion.
Previous analyses of squirming assumed axisymmetric fluid motion and hence
restricted all swimming kinematics to take place along a line. In this paper we
generalize squirming to three spatial dimensions. We derive analytically the
flow field surrounding a spherical squirmer with arbitrary surface motion, and
use it to derive its three-dimensional translational and rotational swimming
kinematics. We then use our results to physically interpret the flow field
induced by the swimmer in terms of fundamental flow singularities up to terms
decaying spatially as $\sim 1/r^3$. Our results will enable to develop new
models in biological physics, in particular in the area of hydrodynamic
interactions and collective locomotion.

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## ‣ Fluid fragmentation from hospital toilets

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 21/10/2013
Português

Relevância na Pesquisa
47.251104%

Hospital-acquired infections represent significant health and financial
burdens to society. Clostridium difficile (C. difficile) is a particularly
challenging bacteria with the potential to cause severe diarrhea and death. One
mode of transmission for C. difficile, as well as other pathogens, which has
received little attention is the potential air contamination by
pathogen-bearing droplets emanating from toilets. In the fluid dynamics video
submitted to the APS DFD Gallery of Fluid Motion 2013, we present flow
visualizations via high-speed recordings showing the capture of the product of
the fluid fragmentation generated by hospital toilet high-pressure flushes.
Important quantities of both large and small droplets are observed. We
illustrate how high-pressure flushes and cleaning products currently used in
hospital toilets result in aggravating, rather than alleviating, the suspension
and recirculation of tenacious airborne pathogen-bearing droplets.; Comment: The full results on the fluid dynamics of hospital flush ejecta will
be published elsewhere. The Gallery of Fluid Motion is showcase of fluid
dynamics videos

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## ‣ A New Continuum Formulation for Materials--Part I. The Equations of Motion for a Single-Component Fluid

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 16/09/2013
Português

Relevância na Pesquisa
47.15717%

The continuum equations of fluid mechanics are rederived with the intention
of keeping certain mechanical and thermodynamic concepts separate. A new
"mechanical" mass density is created to be used in computing inertial
quantities, whereas the actual mass density is treated as a thermodynamic
variable. A new set of balance laws is proposed, including a mass balance
equation with a non-convective flux. The basic principles of irreversible
thermodynamics are used to obtain linear constitutive equations that are
expansions of--not only the usual affinities involving gradients of temperature
and velocity--but also the gradient of the chemical potential. Transport
coefficients are then chosen based on an elementary diffusion model, which
yields simple constitutive laws featuring just one diffusion transport
parameter. The resulting formulation differs from the Navier-Stokes-Fourier
equations of fluid motion. In order to highlight key similarities and
differences between the two formulations, several fluid mechanics problems are
examined, including sound propagation, light scattering, steady-state shock
waves, and thermophoresis.; Comment: 63 pages, 7 figures

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## ‣ Intrinsic Geometric Structure of Turbulent Flow for Newton Fluid

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 03/01/2006
Português

Relevância na Pesquisa
47.418%

Many researches show that the complicated motion of fluid, such as
turbulence, cannot be well solved by the Navier-Stokes equation. Chen Zida has
founded that the definition of vortex, based on the Stokes decomposition,
cannot well describe the local rotation when the velocity gradient is highly
asymmetric. Chen reformulates the Stokes S+R decomposition into a general S+R
decomposition. By further extending Chen results, this research studies the
motion equation of fluid for the case where highly asymmetric velocity gradient
is exhibited. The result shows that the classical NS equation does not meet the
requirement of angular momentum conservation, which is apparently ignored for
infinitesimal velocity gradient of fluid. This paper reformulates the intrinsic
geometric description of fluid motion and two additional equations are
introduced. Combining with the classical NS equation, the reformulated motion
equations are in closed-form. The research shows that the NS equation is good
approximation for average flow, so it can not solve the turbulent problem in
essential sense. However, this conclusion does not deny that with suitable
additional condition for special engineering problem it is still a would-be
acceptable approximation.; Comment: 16 pages...

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## ‣ On the limit of large surface tension for a fluid motion with free boundary

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
57.01999%

#Mathematics - Analysis of PDEs#Mathematical Physics#Mathematics - Differential Geometry#Physics - Fluid Dynamics

We study the free boundary Euler equations in two spatial dimensions. We
prove that if the boundary is sufficiently regular, then solutions of the free
boundary fluid motion converge to solutions of the Euler equations in a fixed
domain when the coefficient of surface tension tends to infinity.

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## ‣ Sedimentation of a dilute suspension of rigid spheres at intermediate Galileo numbers: the effect of clustering upon the particle motion

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/06/2014
Português

Relevância na Pesquisa
47.418%

Direct numerical simulation of the gravity-induced settling of finite-size
particles in triply-periodic domains has been performed under dilute
conditions. For a single solid-to-fluid density ratio of 1.5 we have considered
two values of the Galileo number corresponding to steady vertical motion
(Ga=121) and to steady oblique motion (Ga=178) in the case of one isolated
sphere. For the multi-particle system we observe strong particle clustering
only in the latter case. The geometry and time scales related to clustering are
determined from Voronoi tesselation and particle-conditioned averaging. As a
consequence of clustering, the average particle settling velocity is increased
by 12% as compared to the value of an isolated sphere; such a collective effect
is not observed in the non-clustering case. By defining a local (instantaneous)
fluid velocity average in the vicinity of the finite-size particles it is shown
that the observed enhancement of the settling velocity is due to the fact that
the downward fluid motion (with respect to the global average) which is induced
in the cluster regions is preferentially sampled by the particles. It is
further observed that the variance of the particle velocity is strongly
enhanced in the clustering case. With the aid of a decomposition of the
particle velocity it is shown that this increase is due to enhanced fluid
velocity fluctuations (due to clustering) in the vicinity of the particles.
Finally...

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## ‣ Droplets bouncing over a vibrating fluid layer

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 12/10/2012
Português

Relevância na Pesquisa
47.37799%

This is an entry for the Gallery of Fluid Motion of the 65st Annual Meeting
of the APS-DFD (fluid dynamics video). This video shows the motion of levitated
liquid droplets. The levitation is produced by the vertical vibration of a
liquid container. We made visualizations of the motion of many droplets to
study the formation of clusters and their stability.; Comment: This entry contains videos for the Gallery of Fluid Motion of the
65st Annual Meeting of the APS-DFD

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## ‣ On the Motion of a Self-Gravitating Incompressible Fluid with Free Boundary

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/11/2015
Português

Relevância na Pesquisa
47.238467%

We consider the motion of the interface separating a vacuum from an inviscid,
incompressible, and irrotational fluid, subject to the self-gravitational force
and neglecting surface tension, in two space dimensions. The fluid motion is
described by the Euler-Poission system in moving bounded simply connected
domains. A family of equilibrium solutions of the system are the perfect balls
moving at constant velocity. We show that for smooth data which are small
perturbations of size $\epsilon$ of these static states, measured in
appropriate Sobolev spaces, the solution exists and remains of size $\epsilon$
on a time interval of length at least $c\epsilon^{-2},$ where $c$ is a constant
independent of $\epsilon.$ This should be compared with the lifespan
$O(\epsilon^{-1})$ provided by local well-posdness. The key ingredient of our
proof is finding a nonlinear transformation which removes quadratic terms from
the nonlinearity. An important difference with the related gravity water waves
problem is that unlike the constant gravity for water waves, the self-gravity
in the Euler-Poisson system is nonlinear. As a first step in our analysis we
also show that the Taylor sign condition always holds and establish local
well-posedness for this system.; Comment: 73 pages

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## ‣ On the flow of Oldroyd-B fluids with fractional derivatives over a plate that applies shear to the fluid

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/08/2014
Português

Relevância na Pesquisa
47.32259%

The motion of incompressible fractional Oldroyd-B fluids between two parallel
walls perpendicular to a plate that applies time-dependent shear stresses to
the fluid is studied by means of integral transforms. In the special cases of
Newtonian and second grade fluids, these shear stresses reduces to fH(t)sin(wt)
or fH(t)cos(wt). General solutions for velocity are presented as a sum of
Newtonian solutions and the corresponding non-Newtonian contributions. They
reduce to the similar solutions corresponding to the motion over an infinite
plate if the distance between walls tend to infinity and can be easy
particularized to give the similar solutions for ordinary and fractional
Maxwell or second grade fluids performing the same motions. As a check of
general results some known solutions from the literature are recovered as
limiting cases. Finally, the influence of fractional parameters on the fluid
motion and the distance between walls for which the measured value of the
velocity in the middle of the channel is unaffected by their presence (more
exactly, it is equal to the velocity corresponding to the motion over an
infinite plate) are graphically determined.; Comment: 23 pages, 9 figures

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## ‣ To the Fluid Motion Dynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/05/2006
Português

Relevância na Pesquisa
57.32259%

A fluid motion through the flow element is presented in the kind of an
autooscillating system with the distributed parameters: mass, elasticity,
viscosity. The system contains a self-excited oscillator and possesses a
self-regulation on base of the intrinsic voluntary negative servo output
feedback. The interaction dynamics of the submerged jet, out-flowing out of a
flow element, with the homogeneous for it surrounding medium as well as
dynamics of evolution of the spiral-vortex structures, appearing at the
relative motion of fluids, are described for the first time. The conceptual
model of a flow in the kind of the completed system of the cause and effect
relationship, that presents the fluid motion process as a result in interaction
of the motive power, applied from without, and the internal wave mechanism,
selfregulating the flow structure and its intensity, is created.; Comment: 20 pages, 15 figures

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## ‣ Rheological fluid motion in tube by metachronal wave of cilia

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 16/08/2013
Português

Relevância na Pesquisa
47.28577%

The purpose of this paper is a theoretical study of a non-linear problem of
rheological fluid transport in an axisymmetric tube by cilium. However, an
attempt has been made to explain the role of cilia motion on the transport of
fluid through the ductus efferentes of the male reproductive tract. Ostwald-de
Waele power law viscous fluid has been considered to represent the rheological
fluid to analyze pumping by means of a sequence of beat of cilia from row to
row of cilia in a given row of cells and from one row of cells to the next
(metachronal wave movement) under conditions for which the corresponding
Reynolds number is small enough for inertial effects to be negligible and the
wavelength to diameter ratio is large enough for the pressure to be considered
uniform over the cross-section. Analyses and computations of the detailed fluid
motions reveal that the time-averaged flow rates are directly dependent on
epsilon, a non-dimensional measure involving the mean radius R of the tube and
the cilia length. Thus, flow rate significantly varies with the cilia length.
Moreover, the flow rate has been reported close to the estimated value 0.006
ml/h in human ductus efferentes when epsilon is near by 0.5. The estimated
value was suggested by Lardner and Shack [4] in human based on the experimental
observations on the flow rates in the ductus efferentes in the other animals...

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## ‣ Fluid Motion Physics: The Total Head Vector of the Real Fluid Stream

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
57.19718%

The overcoming of a mechanics problem on origin of secondary jet flows, on
dynamics of its development and interaction with the main stream of the viscous
fluid is reached by means of elucidation of the energy distribution in the
stream at its interaction with the flow system walls and a body surface. In
contrast to a traditional conception on a total head of a fluid stream in a
pipe as a sum of a velocity head and a static pressure, it is ascertained that
this sum is only longitudinal component of the stream total head vector. It is
stated a new conception and it is produced the expressions for quantitative
evaluation of radial and tangential components of the stream total head vector
and for angle of its deflection from the stream axis. The new approach has
allowed rationally to explain the causes of origin of the secondary jet flows
and dynamics of its interaction with the main stream in various cases. Thereby
with the taking into account of previous articles of the author the necessary
theoretical preconditions has been created for a working out of the modern
physically valuable apparatus for mathematical modeling of the real - viscous -
fluid motion in any problems of hydromechanics and gas dynamics.; Comment: 14 pages, 1 figure

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## ‣ Three-dimensional fluid motion in Faraday waves: creation of vorticity and generation of two-dimensional turbulence

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 31/03/2014
Português

Relevância na Pesquisa
57.293867%

We study the generation of 2D turbulence in Faraday waves by investigating
the creation of spatially periodic vortices in this system. Measurements which
couple a diffusing light imaging technique and particle tracking algorithms
allow the simultaneous observation of the three-dimensional fluid motion and of
the temporal changes in the wave field topography. Quasi-standing waves are
found to coexist with a spatially extended fluid transport. More specifically,
the destruction of regular patterns of oscillons coincides with the emergence
of a complex fluid motion whose statistics are similar to that of
two-dimensional turbulence. We reveal that a lattice of oscillons generates
vorticity at the oscillon scale in the horizontal flow. The interaction of
these vortices explain how 2D turbulence is fueled by almost standing waves.
Remarkably, the curvature of Lagrangian trajectories reveals a "footprint" of
the forcing scale vortices in fully developed turbulence. 2D Navier-Stokes
turbulence should be considered a source of disorder in Faraday waves. These
findings also provide a new paradigm for vorticity creation in 2D flows.

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## ‣ Volumetric 3-component velocimetry measurements of the flow around a Rushton turbine: A fluid dynamics video

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 13/10/2009
Português

Relevância na Pesquisa
47.15717%

This article describes a video uploaded to the APS DFD Annual Meeting 2009
Gallery of Fluid Motion. The video contains both animations and still images
from a three-dimensional volumetric velocimetry measurement set acquired in the
flow around a Rushton turbine.; Comment: Description of a fluid dynamics video uploaded for the APS DFD Annual
Meeting 2009 Gallery of Fluid Motion

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## ‣ von K\`arm\`an--Howarth and Corrsin equations closure based on Lagrangian description of the fluid motion

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
57.10177%

A new approach to obtain the closure formulas for the von K\'arm\'an--Howarth
and Corrsin equations is presented, which is based on the Lagrangian
representation of the fluid motion, and on the Liouville theorem associated to
the kinematics of a pair of fluid particles. This kinematics, characterized by
the finite--scale separation vector, is assumed to be statistically independent
from the velocity field. Such assumption is justified by the hypothesis of
fully developed turbulence and by the property that this vector varies much
more rapidly than the velocity field. This formulation leads to the closure
formulas of von K\'arm\'an--Howarth and Corrsin equations in terms of
longitudinal velocity and temperature correlations following a demonstration
completely different and more concise with respect to the previous works. Some
of the properties and the limitations of the closed equations are discussed. In
particular, the times of evolution of the developed kinetic energy and
temperature spectra are shown to be finite quantities which depend on the
initial conditions.; Comment: 28 pages, 2 figures

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