Showing papers on "Hele-Shaw flow published in 2010"
TL;DR: In this article, a method is introduced that is able to extract dynamic information from flow fields that are either generated by a (direct) numerical simulation or visualized/measured in a physical experiment.
Abstract: The description of coherent features of fluid flow is essential to our understanding of fluid-dynamical and transport processes. A method is introduced that is able to extract dynamic information from flow fields that are either generated by a (direct) numerical simulation or visualized/measured in a physical experiment. The extracted dynamic modes, which can be interpreted as a generalization of global stability modes, can be used to describe the underlying physical mechanisms captured in the data sequence or to project large-scale problems onto a dynamical system of significantly fewer degrees of freedom. The concentration on subdomains of the flow field where relevant dynamics is expected allows the dissection of a complex flow into regions of localized instability phenomena and further illustrates the flexibility of the method, as does the description of the dynamics within a spatial framework. Demonstrations of the method are presented consisting of a plane channel flow, flow over a two-dimensional cavity, wake flow behind a flexible membrane and a jet passing between two cylinders.
4,150 citations
TL;DR: In this article, the authors studied the issues of uniform flow distribution for general application in fuel cells, fuel processing chemical reactors, and other industrial devices, and proposed a novel method for uniform flow distributions, in which multiple levels of flow channel bifurcations were considered to uniformly distribute a flow into 2 n flow channels at the final stage.
133 citations
TL;DR: In this paper, a polynomial expression, like Forchheimer law, was used to describe the dependence of pressure drop on flow rate for non-linear fluid flow through rough fractures.
118 citations
TL;DR: In this article, an analysis of published data on a gas-liquid two-phase flow in capillaries of various shapes is given, which makes it possible to systematize the collected body of information.
Abstract: Capillary hydrodynamics has three considerable distinctions from macrosystems: first, there is an increase in the ratio of the surface area of the phases to the volume that they occupy; second, a flow is characterized by small Reynolds numbers at which viscous forces predominate over inertial forces; and third, the microroughness and wettability of the wall of the channel exert a considerable influence on the flow pattern. In view of these differences, the correlations used for tubes with a larger diameter cannot be used to calculate the boundaries of the transitions between different flow regimes in microchannels. In the present review, an analysis of published data on a gas-liquid two-phase flow in capillaries of various shapes is given, which makes it possible to systematize the collected body of information. The specific features of the geometry of a mixer and an inlet section, the hydraulic diameter of a capillary, and the surface tension of a liquid exert the strongest influence on the position of the boundaries of two-phase flow regimes. Under conditions of the constant geometry of the mixer, the best agreement in the position of the boundaries of the transitions between different hydrodynamic regimes in capillaries is observed during the construction of maps of the regimes with the use of the Weber numbers for a gas and a liquid as coordinate axes.
100 citations
TL;DR: The electro-osmotic flow of a viscoelastic fluid between parallel plates is investigated analytically and equations for the critical shear rates and maximum electrical potential that can be applied to maintain a steady fully developed flow are derived and discussed.
93 citations
TL;DR: In this paper, the authors measured the streamwise component of the turbulence intensity in a fully developed pipe flow at Reynolds numbers up to 145 000 and showed that the magnitude of the near-wall peak is invariant with Reynolds number in location and magnitude.
Abstract: New measurements of the streamwise component of the turbulence intensity in a fully developed pipe flow at Reynolds numbers up to 145 000 indicate that the magnitude of the near-wall peak is invariant with Reynolds number in location and magnitude. The results agree with previous pipe flow data that have sufficient spatial resolution to avoid spatial filtering effects, but stand in contrast to similar results obtained in boundary layers, where the magnitude of the peak displays a prominent Reynolds number dependence, although its position is fixed at the same location as in pipe flow. This indicates that the interaction between the inner and outer regions is different in pipe flows and boundary layers.
91 citations
TL;DR: In this article, two versions of a second-order characteristic-based split scheme are developed in the framework of incremental projection method for the solution of incompressible flow problem, and numerical results show that, at sufficiently small and large s, the range of which is different for different α, the flow interference is dominated by proximity and wake effect, respectively.
91 citations
TL;DR: In this article, the authors review the range of flows that may be created within thin cylindrical or annular cavities due to the rotation of one of the confining disks and show that at low Reynolds numbers, the rotation gives rise to an axisymmetric, radially outward motion near the rotor with a return flow along the stationary disk.
Abstract: This article reviews the range of flows that may be created within thin cylindrical or annular cavities due to the rotation of one of the confining disks. At low Reynolds numbers, the rotation gives rise to an axisymmetric, radially outward motion near the rotor with a return flow along the stationary disk. As the Reynolds number is raised, this base flow gives way to a shear flow populated by discrete vortices, whether of cylindrical or spiral form, near both the rotating and stationary disks. At Reynolds numbers high enough for turbulent flow to occur, in the twentieth century both experimental and computational studies treated the flow as axisymmetric and steady. Recent research has shown, however, that complex organized structures also persist in the turbulent regime.
91 citations
Abstract: The mutual interaction of laminar-turbulent transition and mean flow evolution is studied in a pressure-induced laminar separation bubble on a flat plate. The flat-plate boundary layer is subjected to a sufficiently strong adverse pressure gradient that a separation bubble develops. Upstream of the bubble a small-amplitude disturbance is introduced which causes transition. Downstream of transition, the mean flow strongly changes and, due to viscous-inviscid interaction, the overall pressure distribution is changed as well. As a consequence, the mean flow also changes upstream of the transition location. The difference in the mean flow between the forced and the unforced flows is denoted the mean flow deformation. Two different effects are caused by the mean flow deformation in the upstream, laminar part: a reduction of the size of the separation region and a stabilization of the flow with respect to small, linear perturbations. By carrying out numerical simulations based on the original base flow and the time-averaged deformed base flow, we are able to distinguish between direct and indirect nonlinear effects. Direct effects are caused by the quadratic nonlinearity of the Navier-Stokes equations, are associated with the generation of higher harmonics and are predominantly local. In contrast, the stabilization of the flow is an indirect effect, because it is independent of the Reynolds stress terms in the laminar region and is solely governed by the non-local alteration of the mean flow via the pressure. © 2010 Cambridge University Press.
91 citations
TL;DR: In this article, large-eddy simulations (LES) and Reynolds-averaged numerical simulations (RANS) were carried out and compared with experiments of the flow through a strongly bent laboratory flume.
Abstract: In order to unravel the main flow and secondary flow characteristics and the role of turbulence in a curved single-bend open-channel flow, large-eddy simulations (LES) and Reynolds-averaged numerical simulations (RANS) were carried out and compared with experiments of the flow through a strongly bent laboratory flume. Turbulence was found to play an important role with respect to processes that are important in natural rivers. The strength of the curvature-induced secondary flow in the core of the flow domain, which is the most typical feature of curved open-channel flow, depends on the turbulence. Turbulence is especially important in the flow regions near the banks. Only the LES model is able to resolve accurately the boundary layer detachment and the formation of an internal shear layer at the inner bank as well as the outer-bank cell of secondary flow, whereas the RANS model is unable to reproduce these processes. Turbulence also conditions the magnitude of the bed shear stress, as indicated by the co...
89 citations
TL;DR: In this article, a new type of microfluidic rectifier was proposed to achieve high anisotropic flow resistance between the two flow directions, which is able to operate efficiently under creeping flow conditions.
Abstract: In this work we propose a new type of microfluidic rectifier, which is able to operate efficiently under creeping flow conditions. The flow of Newtonian and non-Newtonian fluids was investigated experimentally in different microchannels with triangular (nozzle/diffuser) and hyperbolic shapes in order to achieve high anisotropic flow resistance between the two flow directions. The Newtonian fluid used was de-ionized water and the viscoelastic fluids were aqueous solutions of polyacrylamide and polyethylene oxide with different molecular weights. Pressure drop measurements were performed in addition to visualizations of the flow patterns by streak line photography for a wide range of flow rates. For the Newtonian flows, inertia leads to the appearance of recirculations for both flow directions, but no significant rectification effects appear. For the viscoelastic fluids, two distinct behaviors are identified: at low flow rates, the pressure drops are similar in both flow directions; above a critical flow rate (or Deborah number), the flow patterns become quite different, leading to different flow rates in the forward and backward flow directions for the same pressure drop, i.e., rectification effects emerge. In particular, the viscoelastic fluid flow becomes unsteady in the forward direction, due to the presence of elastic instabilities, which leads to a significant increase in the flow resistance. Flow resistance ratios greater than three were achieved for the hyperbolic rectifier, clearly in excess of the value for the triangular-shaped rectifier and for other geometries proposed in the literature for operation in creeping flow conditions. This high diodicity is associated with the distinct nature of the extensional flows in the forward and backward directions of the hyperbolic-type microgeometry.
TL;DR: In this article, Couette flow states in a span-wise rotating frame of reference have been mapped experimentally in the parameter space spanned by the Reynolds number and rotation rate.
Abstract: Flow states in plane Couette flow in a spanwise rotating frame of reference have been mapped experimentally in the parameter space spanned by the Reynolds number and rotation rate. Depending on the ...
TL;DR: In this paper, the scaling of the torque with Reynolds numbers at various angular velocity ratios (Rotation numbers) and the behavior of the wall shear stress when varying the Rotation number at high Reynolds numbers were investigated.
Abstract: We experimentally study the turbulent flow between two coaxial and independently rotating cylinders. We determined the scaling of the torque with Reynolds numbers at various angular velocity ratios (Rotation numbers) and the behavior of the wall shear stress when varying the Rotation number at high Reynolds numbers. We compare the curves with particle image velocimetry analysis of the mean flow and show the peculiar role of perfect counter-rotation for the emergence of organized large scale structures in the mean part of this very turbulent flow that appear in a smooth and continuous way: the transition resembles a supercritical bifurcation of the secondary mean flow.
TL;DR: Direct observation of the decay of turbulent states in Taylor-Couette flow with lifetimes spanning five orders of magnitude suggests that for a range of Reynolds numbers characteristic decay times increase superexponentially with increasing Reynolds number but remain bounded in agreement with the most recent data from pipe flow.
Abstract: Recent studies have brought into question the view that at sufficiently high Reynolds number turbulence is an asymptotic state. We present direct observation of the decay of turbulent states in Taylor-Couette flow with lifetimes spanning five orders of magnitude. We also show that there is a regime where Taylor-Couette flow shares many of the decay characteristics observed in other shear flows, including Poisson statistics and the coexistence of laminar and turbulent patches. Our data suggest that for a range of Reynolds numbers characteristic decay times increase superexponentially with increasing Reynolds number but remain bounded in agreement with the most recent data from pipe flow. Our data are also consistent with recent theoretical predictions of lifetime scaling in transitional flows.
TL;DR: In this paper, the fundamental physical mechanisms of a finger formation or the interface evolution between immiscible fluids are described in terms of the relative importance of viscous forces, surface tension, and gravity, which are quantifiable via the dimensionless quantities, namely, capillary number, Bond number and viscosity ratio between displaced fluid and displacing fluid.
TL;DR: In this article, the effects of gap to diameter ratio, Reynolds number and flat seabed roughness for a given boundary layer thickness of the inlet flow upstream of the cylinder have been investigated.
TL;DR: In this article, the effects of topological flow patterns on the wake properties are revealed and discussed, and the Strouhal number of vortex shedding, turbulence in the wake, and wake width present drastically different behaviors in different characteristic flow regimes.
TL;DR: This work investigates the possibility of using nominally second-order-accurate techniques for resolving flow about solid boundaries as a means of improving accuracy and reducing grid resolution requirements in pore-scale simulations, using an LBGK method to calculate flow in several geometries of increasing complexity.
TL;DR: In this paper, the authors used CTAC/NaSal (cetyltrimethyl ammonium chloride/sodium salicylate) solutions of aqueous solutions of surfactant to create the peculiar chaotic fluid motions in several specially designed microchannels in which flows with curvilinear streamlines can be generated.
TL;DR: In this paper, a series of wind tunnel tests was performed to investigate the effects of Reynolds number on the aerodynamic characteristics of hemispherical dome in smooth and turbulent boundary layer flows.
TL;DR: In this paper, LDA measurements are reported on the turbulent velocity fields in vessels agitated by a Rushton turbine and containing Newtonian as well as non-Newtonian, shear-thinning fluids.
Abstract: LDA measurements are reported on the turbulent velocity fields in vessels agitated by a Rushton turbine and containing Newtonian as well as non-Newtonian, shear-thinning fluids. Ten different liquids were investigated, with flow indices varying from 1.00 down to 0.56. Experiments were performed in three vessel sizes, viz. 28.6, 44.1, and 62.7 cm in diameter, at various impeller speeds. The main issue of the paper is the question whether or not, and if so to what extent, turbulent flow of shear-thinning fluids differs from that of Newtonian liquids, or – in other words – whether and when turbulent flow of shear-thinning liquids exhibits Reynolds number similarity. The experimental data presented comprise profiles of the mean velocity components and the rms fluctuating velocity components as a function of the radial position in the tank at the height of the impeller disc as well as similar profiles in the impeller outflow near to the impeller tip. The effects – if any – of both Reynolds number and flow index on these profiles are assessed. Fit equations are presented for the various profiles in the various liquids. These fit equations are claimed to be valid throughout the ranges of Reynolds numbers and flow indices covered by the experiments presented. The idea is that these fit equations may be used to validate Computational Fluid Dynamics (CFD) simulations of the Reynolds Averaged Navier–Stokes (RANS) type for agitated shear-thinning liquids, even for liquids and conditions not investigated in this study as long as falling within the Reynolds number and flow index ranges investigated. © 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
TL;DR: In this article, the influence of the Reynolds number on coherent flow structures generated over a gravel bed by assessing the importance of effective bed roughness has been quantified through the application of particle imaging velocimetry, which allows study of the downstream and vertical components of velocity over the entire flow field.
Abstract: [1] Turbulent flows moving over a gravel bed develop large-scale, macroturbulent flow structures that are initiated at anchor clasts in the bed and grow and dissipate as they move upward through the flow depth. This paper extends previous research in which we investigated the influence of the Reynolds number on coherent flow structures generated over a gravel bed by assessing the importance of effective bed roughness. Here, we report on flume experiments in which flows over beds of decreasing surface roughness have been quantified through the application of digital particle imaging velocimetry, which allows study of the downstream and vertical components of velocity over the entire flow field. These results indicate that as the effective roughness increases (1) the visual distinctiveness of the coherent flow structures becomes more defined throughout the flow depth, (2) the upstream angle of slope of the coherent flow structure increases, and (3) the reduction in streamwise flow velocity and turbulence intensity toward the upstream side of the structure becomes greater. Applying standard scaling laws, these structures appear shear-generated and form through a combination of both wake flapping and the reattachment of localized shear layers associated with flow separation around individual topographic protrusions. As the effective protrusion decreases, the scale of these coherent flow structures also decreases.
TL;DR: In this article, a perturbation analysis is carried out to give effective equations for Darcy-Brinkman flow through a porous channel with slightly corrugated walls, where the corrugations are periodic sinusoidal waves of small amplitude.
Abstract: A perturbation analysis is carried out to the second order to give effective equations for Darcy–Brinkman flow through a porous channel with slightly corrugated walls. The flow is either parallel or normal to the corrugations, and the corrugations of the two walls are either in phase or half-period out of phase. The present study is based on the assumptions that the corrugations are periodic sinusoidal waves of small amplitude, and the channel is filled with a sparse porous medium so that the flow can be described by the Darcy–Brinkman model, which approaches the Darcian or Stokes flow limits for small or large permeability of the medium. The Reynolds number is also assumed to be so low that the nonlinear inertia can be ignored. The effects of the corrugations on the flow are examined, quantitatively and qualitatively, as functions of the flow direction, the phase difference, and the wavelength of the corrugations, as well as the permeability of the channel. It is found that the corrugations will have greater effects when it is nearer the Stokes’ flow limit than the Darcian flow limit, and when the wavelength is shorter. For the same wavelength and phase difference, cross flow is more affected than longitudinal flow by the corrugations. Opposite effects can result from 180° out-of-phase corrugations, depending on the flow direction, the wavelength, as well as the permeability.
TL;DR: In this paper, the effect of the vortex generators on the near-wake flow structure of a circular cylinder was experimentally investigated using particle image velocimetry (DPIV) measurements in a large circulating water tunnel facility at a Reynolds number of 41,300.
Abstract: The effect of the streamwise vortex generators on the near-wake flow structure of a circular cylinder was experimentally investigated. Digital particle image velocimetry (DPIV) measurements were performed in a large circulating water tunnel facility at a Reynolds number of 41,300 where the flow around a bare cylinder was expected to be at the sub-critical flow state. In order to capture various flow properties and to provide a detailed wake flow topology, the DPIV images were analysed with three different but complementary flow field decomposition techniques which are Reynolds averaging, phase averaging and proper orthogonal decomposition (POD). The effect of the vortex generators was clearly demonstrated both in qualitative and in quantitative manner. Various topological features such as vorticity and stress distribution of the flow fields as well as many other key flow characteristics including the length scales and the Strouhal number were discussed in the study. To the best of the authors’ knowledge, the study presents the first DPIV visualization of the near-wake flow of a circular cylinder fitted with the vortex generators in the open literature.
TL;DR: In this article, the authors proposed an energy gradient method for studying the flow instability and turbulent transition in annulus flow and derived the critical flow rate and critical Reynolds number for various radius ratios.
TL;DR: In this article, a flow configuration devised for investigation of active control of separated airfoil flows using synthetic jets is presented, which consists of a flat plate, with an elliptic leading edge and a blunt trailing edge, at zero incidence in a free stream.
Abstract: A novel flow configuration devised for investigation of active control of separated airfoil flows using synthetic jets is presented. The configuration consists of a flat plate, with an elliptic leading edge and a blunt trailing edge, at zero incidence in a free stream. Flow separation is induced on the upper surface of the airfoil at the aft-chord location by applying suction and blowing on the top boundary of the computational domain. Typical separated airfoil flows are generally characterized by at least three distinct frequency scales corresponding to the shear layer instability, the unsteadiness of the separated region and the vortex shedding in the wake, and all these features are present in the current flow. Two-dimensional Navier-Stokes simulations of this flow at a chord Reynolds number of 6 104 have been carried out to examine the nonlinear dynamics in this flow and its implications for synthetic-jet-based separation control. The results show that there is a strong nonlinear coupling between the various features of the flow, and that the uncontrolled as well as the forced flow is characterized by a variety of lock-on states that result from this nonlinear coupling. The most effective separation control is found to occur at the highest forcing frequency for which both the shear layer and the separated region lock on to the forcing frequency. The effects of the Reynolds number on the scaling of the characteristic frequencies of the separated flow and its subsequent control are studied by repeating some of the simulations at a higher Reynolds number of 1 105. © 2010 Cambridge University Press.
TL;DR: In this paper, the authors investigated the effect of the first normal stress difference on the transition from one pair to two pairs of vortices and showed that the negative second normal stress change has the opposite effect on this transition and can stabilize the flow.
Abstract: This paper investigates the inertial and creeping flow of a second-order fluid in a curved duct with a square cross-section. Numerical modeling is employed to analyze fluid flow, and the governing equations are discretized using the finite difference method on a staggered mesh. The marker-and-cell method is employed to allocate the parameters on the staggered mesh, and static pressure is calculated using the artificial compressibility approach. The effect of centrifugal force due to the curvature of the duct and the opposing effects of the first and second normal stress difference on the flow field are investigated. In addition, the order-of-magnitude technique is used to derive the force balance relations for the core region of flow. Based on these relations, the performance mechanism of centrifugal force and normal stress differences on the generation of secondary flows is considered. We also present an analytical relation for the axial velocity profile and flow resistance ratio of creeping flow. For this kind of flow, previous studies have investigated the effect of the first normal stress difference on the transition from one pair to two pairs of vortices while we show that the negative second normal stress difference has the opposite effect on this transition and can stabilize the flow.
TL;DR: A new methodology for CFD simulation of airflow in the human bronchopulmonary tree is presented, and results show excellent agreement with the fully resolved geometry, while reducing the mesh size and computational cost by up to an order of magnitude.
Abstract: A new methodology for CFD simulation of airflow in the human bronchopulmonary tree is presented. The new approach provides a means for detailed resolution of the flow features via three-dimensional Navier–Stokes CFD simulation without the need for full resolution of the entire flow geometry, which is well beyond the reach of available computing power now and in the foreseeable future. The method is based on a finite number of flow paths, each of which is fully resolved, to provide a detailed description of the entire complex small-scale flowfield. A stochastic coupling approach is used for the unresolved flow path boundary conditions, yielding a virtual flow geometry that allows accurate statistical resolution of the flow at all scales for any set of flow conditions. Results are presented for multigenerational lung models based on the Weibel morphology and the anatomical data of Hammersley and Olson (1992, “Physical Models of the Smaller Pulmonary Airways,” J. Appl. Physiol., 72(6), pp. 2402–2414). Validation simulations are performed for a portion of the bronchiole region (generations 4–12) using the flow path ensemble method, and compared with simulations that are geometrically fully resolved. Results are obtained for three inspiratory flowrates and compared in terms of pressure drop, flow distribution characteristics, and flow structure. Results show excellent agreement with the fully resolved geometry, while reducing the mesh size and computational cost by up to an order of magnitude.
TL;DR: In this article, the velocity of an incompressible fluid between two parallel lel plates, initially induced by a constant pressure gradient, is studied in the context of a couple stress flui d.
Abstract: Consider the flow of an incompressible fluid between two paral lel plates, initially induced by a constant pressure gradient. After st eady state is attained, the pressure gradient is suddenly with drawn while the plates are impulsively started simultaneously. The arising flow is referred to as run up flow a nd the present paper aims at studying this flow in the context of a couple stress flui d. Using Laplace transform technique, the expression for velocity is obtained in Lapla ce transform domain which is later inverted to the space time domain using a numerical approach. The variation of velocity with respect to various flow parameters is presente d through graphs.
TL;DR: Using these two flow arrangements the amount of stretch and compression near the stagnation point can be varied, providing further insights on the viscoelastic flow instability mechanisms in extensionally dominated flows with an interior stagnation point.
Abstract: Creeping and low Reynolds number flows of an upper-convected Maxwell (UCM) fluid are investigated numerically in a three-dimensional orthogonal cross-slot geometry. We analyze two different flow configurations corresponding to uniaxial extension and biaxial extension, and assess the effects of extensional flow type, Deborah and Reynolds numbers on flow dynamics near the interior stagnation point. Using these two flow arrangements the amount of stretch and compression near the stagnation point can be varied, providing further insights on the viscoelastic flow instability mechanisms in extensionally dominated flows with an interior stagnation point. The uniaxial extensional flow arrangement leads to the onset of a steady flow asymmetry, followed by a second purely elastic flow instability that generates an unsteady flow at higher flow rates. On the other hand, for the biaxial extension flow configuration a symmetric flow is observed up to the critical Deborah number when the time-dependent purely elastic instability sets in, without going through the steady symmetric to steady asymmetric transition.