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B.R.: Thin-film flow in open helically-wound channels
- In M. Behnia, W. Lin, G.D. McBain (eds), 15th Australian Fluid Mechanics Conference (CSROM), 2004, Paper AFMC00187
"... The study of flow in open helically-wound channels has appli-cation to many natural and industrial flows, including those in static spiral separators. The flow consists of a primary axial component and a secondary cross flow and, in spiral separators, the fluid depth is typically small making experi ..."
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The study of flow in open helically-wound channels has appli-cation to many natural and industrial flows, including those in static spiral separators. The flow consists of a primary axial component and a secondary cross flow and, in spiral separators, the fluid depth is typically small making experimental investiga-tion difficult. Mathematical models are therefore of great value for determining how such flows are influenced by fluid proper-ties and geometrical parameters and, hence, for predicting and improving the performance of these separators. A thin-film ap-proximation is appropriate and yields an explicit expression for the fluid velocity in terms of the free-surface shape. The latter satisfies an interesting non-linear ordinary differential equation that can easily be solved numerically and in some cases analyt-ically. The semi-analytic predictions of the thin-film model are found to be in good agreement with much more computation-ally expensive solutions of the Navier–Stokes equations.
Unsteady flows in pipes with finite curvature
, 2007
"... Motivated by the study of blood flow in a curved artery, we consider fluid flow through a curved pipe of uniform curvature, δ, driven by a prescribed oscillatory axial pressure gradient. The curved pipe has finite (as opposed to asymptotically small) curvature, and we determine the effects of both t ..."
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Motivated by the study of blood flow in a curved artery, we consider fluid flow through a curved pipe of uniform curvature, δ, driven by a prescribed oscillatory axial pressure gradient. The curved pipe has finite (as opposed to asymptotically small) curvature, and we determine the effects of both the centrifugal and Coriolis forces on the flow. In addition to δ, the flow is parameterized by the Dean number, D, the Womersley number, α, and a secondary streaming Reynolds number, Rs. Asymptotic solutions are developed for the case when δ 1, α 1 and the magnitude of the axial pressure gradient is small, using regular perturbation techniques. For intermediate values of the governing parameters, a pseudospectral code is used to obtain numerical solutions. For flows driven by a sinusoidal pressure gradient (D=0), we identify three distinct classes of stable solutions: 2π-periodic symmetric, 2π-periodic asymmetric, and asymmetric solutions that are either quasi-periodic, or periodic with period 2πk for k ∈ . The transition between solutions is dependent on the value of δ; thus pipes with finite curvature may exhibit qualitatively different transitions between the solution classes as the governing parameters are varied from those of curved pipes
Global computational modeling of cardiovascular blood flow
- Proceedings of RIKEN Symposium-Computational Biomechanics-, RIKEN
, 2000
"... Abstract The cardiovascular system is an internal flow network with multiple branches in which three-dimensional and pulsatile blood flow circulates. We propose a new paradigm of simulation-based biomedical engineering, which is designed as a useful means for predictive medicine. In order to achieve ..."
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Abstract The cardiovascular system is an internal flow network with multiple branches in which three-dimensional and pulsatile blood flow circulates. We propose a new paradigm of simulation-based biomedical engineering, which is designed as a useful means for predictive medicine. In order to achieve this paradigm a global computational modeling of cardiovascular blood flow is highlighted and some preliminary results are presented. 1.
IOS Press Arterial bends: The development and decay of helical flows
"... Abstract. The macrocirculation is modelled by incompressible Newtonian flow through a rigid network of pipes for which possible simplifications are discussed. The common assumptions of two-dimensionality or axisymmetry can be generalised to helical symmetry, and in the first part of the paper, the t ..."
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Abstract. The macrocirculation is modelled by incompressible Newtonian flow through a rigid network of pipes for which possible simplifications are discussed. The common assumptions of two-dimensionality or axisymmetry can be generalised to helical symmetry, and in the first part of the paper, the three-dimensionality of arterial bends is considered by varying the curvature and torsion of a section of a helical pipe. The torsion is found to impart a preferential twist to the cross-sectional flow. This loss of symmetry ensures that flow separation is less severe for a helical bend than for a toroidal bend. The effects of variations in body size are examined using allometric scaling laws. In the second part of the paper, the approach to “fully developed ” Dean or Womersley flow is considered in an attempt to quantify the regions of validity of idealised models. A perturbation approach, akin to hydrodynamic stability theory, is used. It is argued that often potential flows are more suitable for describing the rapid interactions between geometry and pulsatility rather than the eventual fully developed state so that, for example, the first 100 ◦ of the aortic arch may be considered irrotational. Helical potential flows are found to develop faster than the corresponding toroidal flows, but slower than those in a straight pipe. The presence of vorticity in the core also retards the development of symmetric flows. It is concluded that while idealised flows can occur at some points in the body, in general experimental observation is needed to justify their use. Particular caution is recommended when interpreting calculations with Poiseuille input. 1. Mathematical simplifications in haemodynamics
DYNAMO ACTION IN STEADY HELICAL PIPE FLOW
"... Summary The steady, pressure-driven flow of a conducting fluid down a helical pipe of rectangular cross-section is shown to drive a kinematic dynamo at moderate values of the magnetic Reynolds number, R m . The asymptotic structure of the growing modes is analysed as Rm → ∞. This is the first lamin ..."
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Summary The steady, pressure-driven flow of a conducting fluid down a helical pipe of rectangular cross-section is shown to drive a kinematic dynamo at moderate values of the magnetic Reynolds number, R m . The asymptotic structure of the growing modes is analysed as Rm → ∞. This is the first laminar, pressure-driven dynamo to be found.
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"... Any use of trade, product, or finn names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government ..."
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Any use of trade, product, or finn names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government
This work is dedicated to my father and mother,
, 2005
"... I would like to express my most sincere gratitude to Dr. Don P. Giddens, the supporter and advisor throughout my career at Tech, for his foresight, erudite and patient in my research works because the major ideas of the research have been discussing results with him over long period of times, and fi ..."
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I would like to express my most sincere gratitude to Dr. Don P. Giddens, the supporter and advisor throughout my career at Tech, for his foresight, erudite and patient in my research works because the major ideas of the research have been discussing results with him over long period of times, and finally he updated all the words of the thesis. I would like to acknowledge the fruitful support and advice of Dr. John Oshinski for providing all the MRI measurements that were the fundamental materials for the research. I am grateful to Dr. W. Robert Taylor for offering me the chance to attend the NIH project that ensured the completion of this research. works. In addition, I thank Dr. Ramond P. Vito for all his help and advice in my study and Last, I must say thanks to all the members of Dr. Giddens group for promotion and friendship. iv
Endoscopic PIV in a helical pipe coil
"... In recent years curvature effects on the wall turbulence structure have been the subject of an intense research. At present, these topics are being investigated both numerically and experimentally at the Dipartimento di Ingegneria Aerospaziale, Politecnico di Milano. This work deals with an experime ..."
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In recent years curvature effects on the wall turbulence structure have been the subject of an intense research. At present, these topics are being investigated both numerically and experimentally at the Dipartimento di Ingegneria Aerospaziale, Politecnico di Milano. This work deals with an experimental research project about the properties of the turbulent flow in a helical coil. The facility consists of a reinforced rubber circular duct, filled with water, which is wrapped on a cylindrical core (the core diameter is 10 times the pipe diameter) in such a way that the coils are tightly in touch. An endoscopic PIV system has been developed in order to investigate mean flow and wall turbulence properties on planes both normal and parallel to the duct axis. Suitable endoscopic optical devices for lighting and image acquisition, a continuous Argon Ion Laser 2W green laser and a fast gated image intensifier, are employed. Fluorescent particles and narrow-band optical filters will be used to achieve a better signal-to-noise ratio in the region very close to the wall. 1.
