共查询到20条相似文献,搜索用时 15 毫秒
1.
L. W. Morland 《Transport in Porous Media》2010,81(1):161-179
The flow of a viscous fluid through a porous matrix undergoing only infinitesimal deformation is described in terms of intrinsic
variables, namely, the density, velocity and stress occurring in coherent elements of each material. This formulation arises
naturally when macroscopic interfaces are conceptually partitioned into area fractions of fluid–fluid, fluid–solid, and solid–solid
contact. Such theory has been shown to yield consistent jump conditions of mass, momentum and energy across discontinuities,
either internal or an external boundary, unlike the standard mixture theory jump conditions. In the previous formulation,
the matrix structure has been considered isotropic; that is, the area fractions are independent of the interface orientation.
Here, that is not assumed, so in particular, the cross-section area of a continuous fluid tube depends on its orientation,
which influences the directional fluxes, and in turn the directional permeability, anisotropy of the structure. The simplifications
for slow viscous flow are examined, and particularly for an isotropic linearly elastic matrix in which area partitioning induces
anisotropic elastic response of the mixture. A final specialization to an incompressible fluid and stationary matrix leads
to potential flow, and a simple plane flow solution is presented to illustrate the effects of anisotropic permeability. 相似文献
2.
C.G. Speziale 《Theoretical and Computational Fluid Dynamics》1999,13(3):161-166
A resent extension of the nonlinear K–ε model is critically discussed from a basic theoretical standpoint. While it was said in the paper that this model was formulated
to incorporate relaxation effects, it will be shown that the model is incapable of describing one of the most basic such turbulent
flows as is obvious but is described for clarity. It will be shown in detail that this generalized nonlinear K–ε model yields erroneous results for the Reynolds stress tensor when the mean strains are set to zero in a turbulent flow
– the return-to-isotropy problem which is one of the most elementary relaxational turbulent flows. It is clear that K–ε type models cannot describe relaxation effects. While their general formalism can describe relaxation effects, the nonlinear
K–ε model – which the paper is centered on – cannot. The deviatoric part of the Reynolds stress tensor is predicted to be zero
when it actually only gradually relaxes to zero. Since this model was formulated by using the extended thermodynamics, it
too will be critically assessed. It will be argued that there is an unsubstantial physical basis for the use of extended thermodynamics
in turbulence. The role of Material Frame-Indifference and the implications for future research in turbulence modeling are
also discussed.
Received 19 February 1998 and accepted 23 October 1998 相似文献
3.
H. Ramkissoon 《Applied Scientific Research》1977,33(3-4):243-257
This paper examines the Stokes' flow due to an axially symmetric body rotating about its axis of symmetry in a micropolar fluid which sustains anti-symmetric stress and couple stress. General solutions are obtained to the coupled differential equations governing such a flow and the special case of a sphere is deduced. Then, with the aid of a concentrated couple, a simple formula for the couple experienced by a body is derived in terms of the angular velocity of the flow field. 相似文献
4.
Weakly nonlinear stability analysis of a falling film with countercurrent gas–liquid flow has been investigated. A normal
mode approach and the method of multiple scales are employed to carry out the linear and nonlinear stability solutions for
the film flow system. The results show that both supercritical stability and subcritical instability are possible for a film
flow system when the gas flows in the countercurrent direction. The stability characteristics of the film flow system are
strongly influenced by the effects of interfacial shear stress when the gas flows in the countercurrent direction. The effect
of countercurrent gas flow in a falling film is to stabilize the film flow system. 相似文献
5.
In the present paper it is shown that the elastic range in the second Piola–Kirchhoff stress space can be chosen in a hyperplane
which is through the origin of Lagrangian stress space and perpendicular to the normal of the constraint manifold at the plastic
configuration, if the determinate stress response of the elastic–plastic material with simple internal constraints with some
condition is correctly chosen, otherwise, it is in general in a hypersurface and the normal flow rule by Il yushin’s postulate
will have an indeterminate part. The choice of determinate stress response is probable because of its indeterminacy. Therefore
the yield function should be a function of the second Piola–Kirchhoff stress lying in the hyperplane so that it is more simple
and the back stress as the geometric center of the elastic range in general is inside the elastic range. Finally some examples
are concerned.
The project supported by the National Natural Science Foundation of China (10272055). 相似文献
6.
S. Hormozi K. Wielage-Burchard I.A. Frigaard 《ournal of non Newtonian Fluid Mechanics》2011,166(5-6):262-278
We present results of a computational study of visco-plastically lubricated plane channel multi-layer flows, in which the yield stress fluid layers are unyielded at the interface. We demonstrate that symmetric 3-layer flows may be established for wide ranges of viscosity ratio (m), Bingham number (B) and interface position (yi), for Reynolds numbers Re ≤ 100. Here an inner Newtonian layer is sandwiched between 2 layers of Bingham fluid. Results are presented illustrating the variation of development length with the main dimensionless parameters and for different inlet sizes. We also show that these flows may be initiated by injecting either fluid into a steady flow of the other fluid. The flows are established quicker when the core fluid is injected into a channel already full of the outer fluid. In situations where the inner fluid flow rate is dominant we observed inertial symmetry breaking in the symmetric start-up flows as Re was increased. Asymmetry is also observed in studying temporal nonlinear stability of these flows, which appear stable up to moderate Re and significant amplitudes. In general the flows destabilize at lower Re and perturbation amplitudes than do the analogous core-annular pipe flows, but 1–1 comparison is hard. When the flow is stable the decay characteristics are very similar to those of the pipe flows. In the final part of the paper we explore more exotic flow effects. We show how flow control could be used to position layers asymmetrically within the flow, and how this effect might be varied transiently. We demonstrate that more complex layered flows can be stably achieved, e.g. a 7-layered flow is established. We also show how a varying inlet position can be used to “write” in the yield stress fluid: complex structures that are advected with the flow and encapsulated within the unyielded fluid. 相似文献
7.
Axisymmetric free film flows are encountered in many technological processes [1] associated with the atomization of liquids.
The transversely symmetric flow produced by an atomizer consisting of two coaxial disks rotating at the same speed and arranged
to form an annular gap is considered.
Moscow. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 23–29, September–October, 1988 相似文献
8.
Using the fact that for simple fluids the most general constitutive equation in constant stretch history flows for the extra
stress tensor τ is known in an explicit form, the Giesekus fluid model is cast into this (ω–D) form for two-dimensional flows. The three material functions needed to characterize τ are listed. The explicit results for
simple shear and planar elongation reveal that the parameter α should be restricted to values less than 0.5. It is demonstrated
that in this explicit form the constitutive equation is free from thermodynamic objections and can thus be used as a starting
point for numerical calculations of general, but steady, two-dimensional flows.
Received: 9 November 1998 Accepted: 20 May 1999 相似文献
9.
The Characterization of the effects of surface wettability and geometry on pressure drop of slug flow in isothermal horizontal
microchannels is investigated for circular and square channels with hydraulic diameter (D
h
) of 700 μm. Flow visualization is employed to characterize the bubble in slug flow established in microchannels of various
surface wettabilities. Pressure drop increases with decrease in surface wettability, while the channel geometry influences
slug frequency. It is observed that the gas–liquid contact line in advancing and receding interfaces of bubble change with
surface wettability in slug flows. Flow resistance, where capillary force is important, is estimated using Laplace–Young equation
considering the change of dynamic contact angles of bubble. The experimental study also demonstrates that the liquid film
presence elucidates the pressure drop variation of slug flows at various surface wettabilities due to diminishing capillary
effect. 相似文献
10.
A. M. Lipanov S. A. Karskanov 《Journal of Applied Mechanics and Technical Physics》2008,49(3):354-361
Results of a parametric study of steady asymmetric flows are analyzed. Three-dimensional unsteady equations of hydromechanics
for a compressible medium are solved by a time-dependent method. The range of the characteristic Reynolds number Re = 60–350 is considered. It is shown that a symmetric flow becomes asymmetric at Re = 90. This value can be considered as a threshold value for air. In the examples considered, the upper separation region
is always smaller than the lower separation region owing to flow asymmetry in the vicinity of the left boundary of the domain
of integration. The dependence of the separation region size on the Reynolds number is found.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 11–19, May–June, 2008. 相似文献
11.
The effect of viscoelasticity on stress fields within polyethylene melt flow for a cross-slot and contraction–expansion slit geometry 总被引:1,自引:1,他引:0
The sensitivity of the principal stress difference (PSD) profiles to material viscoelasticity is demonstrated for two flow
geometries using three different polyethylenes. Studies were performed using both experimental optical techniques and computational
simulations, in the latter case to evaluate the ability to model these complex flows. The materials were characterised using
linear and extensional rheology which was fitted to a multimode POM-POM model implemented in the Lagrangian–Eulerian code
flowSolve. A contraction–expansion (CE) slit geometry was used to create a mixed, but primarily simple shear flow, whilst a cross-slot
geometry provided a region of high extensional shear and high strain. In both flows, the PSD developed from an initial Newtonian
profile to increasing levels of asymmetry between the inlet and the outlet flow. More specific phenomena, such as downstream
stress fangs in the CE slit and the formation of centreline cusps and “W”-shaped cusps in the cross-slot, were also observed.
The simulations of PSD development within the CE slit geometry quantitatively captured the experimental results. In the case
of the cross-slot geometry, the qualitative features of the PSD development were well captured, although the results were
quantitatively less accurate. 相似文献
12.
Shifang Han 《Acta Mechanica Sinica》2007,23(2):149-158
A continuum constitutive theory of corotational derivative type is developed for the anisotropic viscoelastic fluid–liquid
crystalline (LC) polymers. A concept of anisotropic viscoelastic simple fluid is introduced. The stress tensor instead of
the velocity gradient tensor D in the classic Leslie–Ericksen theory is described by the first Rivlin–Ericksen tensor A and a spin tensor W measured with respect to a co-rotational coordinate system. A model LCP-H on this theory is proposed and the characteristic
unsymmetric behaviour of the shear stress is predicted for LC polymer liquids. Two shear stresses thereby in shear flow of
LC polymer liquids lead to internal vortex flow and rotational flow. The conclusion could be of theoretical meaning for the
modern liquid crystalline display technology. By using the equation, extrusion–extensional flows of the fluid are studied
for fiber spinning of LC polymer melts, the elongational viscosity vs. extension rate with variation of shear rate is given
in figures. A considerable increase of elongational viscosity and bifurcation behaviour are observed when the orientational
motion of the director vector is considered. The contraction of extrudate of LC polymer melts is caused by the high elongational
viscosity. For anisotropic viscoelastic fluids, an important advance has been made in the investigation on the constitutive
equation on the basis of which a series of new anisotropic non-Newtonian fluid problems can be addressed.
The project supported by the National Natural Science Foundation of China (10372100, 19832050) (Key project). The English
text was polished by Yunming Chen. 相似文献
13.
Hot-wire anemometry is a measuring technique that is widely employed in fluid mechanics research to study the velocity fields
of gas flows. It is general practice to calibrate hot-wire sensors against velocity. Calibrations are usually carried out
under atmospheric pressure conditions and these suggest that the wire is sensitive to the instantaneous local volume flow
rate. It is pointed out, however, that hot wires are sensitive to the instantaneous local mass flow rate and, of course, also
to the gas heat conductivity. To calibrate hot wires with respect to mass flow rates per unit area, i.e., with respect to
(ρU), requires special calibration test rigs. Such a device is described and its application is summarized within the (ρU) range 0.1–25 kg/m2 s. Calibrations are shown to yield the same hot-wire response curves for density variations in the range 1–7 kg/m3. The application of the calibrated wires to measure pulsating mass flows is demonstrated, and suggestions are made for carrying
out extensive calibrations to yield the (ρU) wire response as a basis for advanced fluid mechanics research on (ρU) data in density-varying flows. 相似文献
14.
V. P. Bushlanov 《Fluid Dynamics》1999,34(1):133-135
An approximate solution of the axially symmetric problem of the flow of a viscous incompressible fluid in the vicinity of
the point of contact between a uniformly moving plunger and a channel wall is obtained.
Tomsk (Tomsk Branch of the Institute of Structural Macrokinetics, Russian Academy of Sciences). Translated from Izvestiya
Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 157–160, January–February, 1999. 相似文献
15.
A “curvature correction”, in the sense used herein, is model fragment that is intended to account for some proportion of the
error that is introduced into explicit algebraic Reynolds-stress models as a consequence of ignoring the convective transport
of stress anisotropy within a framework in which the velocity vector and stress tensor are represented in terms of Cartesian
components in highly-curved flow conditions. The present paper examines the ability of such corrections to represent this
error, based on a-priori investigations of representative 2-D and 3-D massively separated flows for which the ‘exact’ level of the stress transport
is known. In essence, the corrections reflect the assumption that the convection of the Reynolds-stress components, or the
associated strain-tensor components, expressed in terms of curvature-oriented coordinates, is negligible. The analysis shows,
first, that in general recirculating flows, the contribution of anisotropy transport to the stress balance is generally small,
so that any form of related correction is of little consequence. Second, the variants of curvature correction examined correlate
poorly with the real anisotropy convection. Thus, while these curvature corrections are useful in very particular conditions,
such as flow in highly-curved ducts, they are not generality effective – indeed, possibly counterproductive – and cannot be
recommended for inclusion in general numerical schemes. 相似文献
16.
Manish K. Tiwari Alexander V. Bazilevsky Alexander L. Yarin Constantine M. Megaridis 《Rheologica Acta》2009,48(6):597-609
Rheological behavior of concentrated suspensions of chemical vapor deposition carbon nanotubes in uniaxial elongation and
simple shear is studied experimentally and theoretically. Nanotubes are suspended in viscous host liquids—castor oil or its
blends with n-decane. The elongational measurements are performed by analyzing self-thinning (due to surface tension effect) liquid threads
of nanotube suspensions. A quasi-one-dimensional model is used to describe the self-thinning process, whereas corrections
accounting for thread nonuniformity and necking are introduced a posteriori. The effects of nanotube concentration and aspect
ratio, viscosity of the suspending liquid, and initial diameter of the self-thinning thread in uniaxial elongation are elucidated.
The results for uniaxial elongation are compared with those for simple shear. The correspondence in the results of the shear
and elongational measurements is addressed and interpreted. The results conform to the Herschel–Bulkley rheological constitutive
equation (i.e., power law fluids with yield stress). However, the yield stress in elongation is about 40% higher than in simple
shear flow, which suggests that the original Herschel–Bulkley model need modification with the yield stress being a function
of the second invariant of the deviatoric stress tensor. The present effort is the first to study capillary self-thinning
of Herschel–Bulkley liquids, which are exemplified here by suspensions of carbon nanotubes. 相似文献
17.
M. I. Muchnaya 《Fluid Dynamics》1986,21(6):860-866
Simplified Navier-Stokes equations have found application as an alternative to the complete Navier-Stokes equations for the
simulation of viscous gas flows in regions of large dimensions, when there is a predominant direction of the flow [1–4]. In
the present paper, flows in wind tunnel nozzles are investigated on the basis of this model. Flows in conical and profiled
axisymmetric hypersonic nozzles are calculated in a wide range of Mach and Reynolds numbers. Good agreement with the experiment
is obtained. The important role of viscous-inviscid interaction in nozzles for large hypersonic Mach numbers is shown.
Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 20–26, November–December, 1986.
The representation of the nature of flows in hypersonic nozzles given here arose as a result of repeated discussions of the
results of the calculations with my colleagues: V. N. Vetlutskii, V. L. Ganimedov, G. P. Klemenkov, Yu. G. Korobeinikov, and
V. I. Pinchukov, for which the author is deeply grateful to them. 相似文献
18.
Chun-Lang Yeh 《Heat and Mass Transfer》2008,44(3):275-280
The performances of three linear eddy viscosity models (LEVM) and one algebraic Reynolds stress model (ARSM) for the simulation
of turbulent flow inside and outside pressure-swirl atomizer are evaluated by comparing the interface position with available
experimental data and by comparing the turbulence intensity profiles at the atomizer exit. It is found that the turbulence
models investigated exhibit zonal behaviors, i.e. none of the models investigated performs well throughout the entire flow
field. The turbulence intensity has a significant influence on the global characteristics of the flow field. The turbulence
models with better predictions of the turbulence intensity, such as Gatski-Speziale’s ARSM model, can yield better predictions
of the global characteristics of the flow field, e.g. the reattachment lengths for the backward-facing step flow and the sudden
expansion pipe flow, or the discharge coefficient, film thickness and the liquid sheet outer surface position for the atomizer
flows. The standard k–ε model predicts stronger turbulence intensity as compared to the other models and therefore yields smaller film thickness
and larger liquid sheet outer surface position. In average, the ARSM model gives both quantitatively and qualitatively better
results as compared to the standard k–ε model and the low Reynolds number models. 相似文献
19.
B. N. Elemesova 《Journal of Applied Mechanics and Technical Physics》1999,40(1):28-35
The plane-parallel unsteady-state shear gas flow in a narrow channel of constant cross section is considered. The existence
theorem of solutions in the form of simple waves of a set of equations of motion is proved for a class of isentropic flows
with a monotone velocity profile over the channel depth. The exact solution described by incomplete beta-functions is found
for a polytropic equation of state in a class of isentropic flows.
Lavrent'ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 1, pp. 36–43, January–February, 1999. 相似文献
20.
It is shown, analytically and numerically, that if there are no external force fields and the hydraulic resistance is low,
sustained thermoconvective subsonic flows may exist in a closed channel of variable cross section, in the wider part of which
the medium is heated while in the narrower part it is cooled. The flow parameters depend on the equation of state of the medium,
the channel geometry and the amount of heat transferred by the flow from the heated to the cooled part. Steady thermoconvective
flows exist up to a certain critical value of the thermal power transported by the flow. The relation between the results
obtained and the mechanism by which the motion of the medium is sustained in natural convection is discussed.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 11–17, March–April, 1994. 相似文献