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1.
Yongbin Zhang 《Theoretical and Computational Fluid Dynamics》2009,23(4):255-269
The present paper is the subsequent research of the first part (Theor Comput Fluid Dyn, 2009). It investigates the boundary
film shear elastic modulus effect in a hydrodynamic contact in different operating conditions. The hydrodynamic contact is
one-dimensional, composed of two parallel plane surfaces, which are respectively rough rigid with rectangular micro projections
in profile periodically distributed on the surface and ideally smooth rigid. The whole contact consists of cavitated area
and hydrodynamic area. The hydrodynamic area consists of many micro Raleigh bearings which are discontinuously and periodically
distributed in the contact. The hydrodynamic contact in a micro Raleigh bearing consists of boundary film area and fluid film
area which, respectively, occur in the outlet and inlet zones. In boundary film area, the film slips at the upper contact
surface due to the limited shear stress capacity of the film–contact interface, while the film does not slip at the lower
contact surface due to the shear stress capacity of the film–contact interface large enough. In boundary film area, the viscosity,
density, and shear elastic modulus of the film are varied across the film thickness due to the film–contact interactions,
and their effective values are used in modeling which depends on the film thickness. In fluid film area, the film does not
slip at either of the contact surfaces, and the shear elastic modulus of the film is neglected. It is found from the simulation
results that the boundary film shear elastic modulus influences are normally negligible on the mass flow through the contact,
the carried load of the contact and the overall film thickness of the contact, and the boundary film shear elastic modulus
would normally influence the local film thickness in an elastic contact when the local film thickness is on the film molecule
diameter scale. It is also found that the boundary film shear elastic modulus effect has the tendency of being increased with
the reduction of the width of a micro contact. It is increased with the reduction of the boundary film–contact interfacial
shear strength or with the increase of the critical boundary film thickness, while it is strongest at certain values of the
contact surface roughness, the width ratio of fluid film area to boundary film area, and the lubricant film shear elastic
modulus.
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2.
O. V. Voinov 《Journal of Applied Mechanics and Technical Physics》2000,41(4):666-669
We consider the creeping motion of a thin layer of a nonvolatile viscous fluid spreading due to capillary forces over a rigid
surface covered by a thin homogeneous film (microfilm). The influence of van der Waals forces on the asymptotic slope of the
free boundary of the layer is studied in the region of large thickness, where capillary forces dominate. A solution of the
problem of the slope angle is obtained for the entire possible range of the microfilm thickness. In the limit of small thickness
of the microfilm, this solution is in agreement with the well-known solution of the problem of the dynamics of wetting of
a dry surface in the presence of a precursory film and van der Waals forces. The role of the condition at the end of the precursory
film is studied.
Institute of Mechanics of Multiphase Systems, Siberian Division, Russian Academy of Sciences. Tyumen' 625000. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika. Vol. 41, No. 4, pp. 101–105, July–August. 2000. 相似文献
3.
Yongbin Zhang 《Theoretical and Computational Fluid Dynamics》2009,23(4):239-254
Boundary film shear elastic modulus effect is analyzed in a hydrodynamic contact. The contact is one-dimensional composed
of two parallel plane surfaces, which are, respectively, rough rigid with rectangular micro projections in profile periodically
distributed on the surface and ideally smooth rigid. The whole contact is consisted of cavitated area and hydrodynamic area.
The hydrodynamic area consists of many micro Raleigh bearings which are discontinuously and periodically distributed in the
contact. Analysis is thus carried out for a micro Raleigh bearing in this contact. The hydrodynamic contact in this micro
Raleigh bearing consists of boundary film area and fluid film area which, respectively, occur in the outlet and inlet zones.
In boundary film area, the film slips at the upper contact surface due to the limited shear stress capacity of the film–contact
interface, while the film does not slip at the lower contact surface due to the shear stress capacity large enough at the
film–contact interface. In boundary film area, the viscosity, density and shear elastic modulus of the film are varied across
the film thickness due to the film–contact interactions, and their effective values are used in modeling, which depend on
the film thickness. The analytical approach proposed by Zhang (J Mol Liq 128:60–64, 2006) and Zhang et al. (Int J Fluid Mech
Res 30:542–557, 2003) is used for boundary film area. In fluid film area, the film does not slip at either of the contact
surfaces, and the shear elastic modulus of the film is neglected. Conventional hydrodynamic analysis is used for fluid film
area. The present paper presents the theoretical analysis and a typical solution. It is found that for the simulated case
the boundary film shear elastic modulus effects on the mass flow through the contact, the overall film thickness of the contact
and the carried load of the contact are negligible but the boundary film shear elastic modulus effect on the local film thickness
of the contact may be significant when the boundary film thickness is on the 1 nm scale and the contact surfaces are elastic.
In Part II will be presented detailed results showing boundary film shear elastic modulus effects in different operating conditions.
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4.
We explore the effects of fluid films of variable depths on droplets impacting into them. Corresponding to a range of fluid
“film” depths, a non-dimensional parameter—H*, defined as the ratio of the film thickness to the droplet diameter—is varied in the range 0.1≤H*≤10. In general, the effect of the fluid film imposes a dramatic difference on the dynamics of the droplet–surface interaction
when compared to a similar impact on a dry surface. This is illustrated by the size distribution and number of the splash
products. While thin fluid films (H*≈0.1) promote splashing, thicker films (1≤H*≤10) act to inhibit it. The relative roles of surface tension and viscosity are investigated by comparison of a matrix of
fluids with low and high values of these properties. Impingement conditions, as characterized by Reynolds and Weber numbers,
are varied by velocity over a range from 1.34 to 4.22 m/s, maintaining a constant droplet diameter of 2.0 mm. The dependence
of splashing dynamics, characterized by splash product size and number, on the fluid surface tension and viscosity and film
thickness are discussed. 相似文献
5.
V. A. Chugunov L. D. Eskin S. L. Tonkonog 《Journal of Applied Mechanics and Technical Physics》2000,41(2):267-272
The problem of exhaustion of a thin film of a non-Newtonian fluid with a power rheological law from a slotted orifice is solved
with account of film slipping relative to the underlying surface. By the method of group analysis with transformation of the
parameters entering the problem, an asymptotic formula for the film profile is obtained and a law of motion of the film edge
with small slipping is derived.
Kazan' State University, 420008 Kazan'. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp.
71–76, March–April, 2000. 相似文献
6.
S. N. Samatov O. Yu. Tsvelodub 《Journal of Applied Mechanics and Technical Physics》1999,40(4):630-637
A thin film of a viscous fluid flowing down a vertical plane in a gravitational field is considered. The plane executes harmonic
oscillations in the direction normal to itself. An equation that describes the evolution of surface disturbances at small
fluid flow rates is obtained. Some solutions of this equation are found.
Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 4, pp. 90–98, July–August, 1999. 相似文献
7.
The process of contact melting of the solid phase change material (PCM) around a hot sphere, which is driven by the temperature
difference between the PCM and the sphere, is analyzed in this paper. Considering the difference of the normal angle between
the sphere surface and the solid–liquid interface of the melting PCM, the fundamental equations of the melting process are
derived with the film theory. The new film thickness and pressure distribution inside the liquid film and the variation law
of the normal angle of the solid–liquid interface and the melting velocity of the sphere are also obtained. It is found that
(1) while normal angle at sphere surface φ is within a certain value φ0, which is related to Ste number and the outside force F, it has no obvious effect on the pressure distribution inside the liquid film and the numerical results by the present model
are in accordance with the analytical results in the published literature, (2) the film thickness at φ = ±90° is constringent
to a certain value and not the infinity, (3) the analytical results can be employed approximately to analyze the contact melting
process except for the film thickness at φ = ±90°. 相似文献
8.
An analytical solution to the problem of condensation by natural convection over a thin porous substrate attached to a cooled
impermeable surface has been conducted to determine the velocity and temperature profiles within the porous layer, the dimensionless
thickness film and the local Nusselt number. In the porous region, the Darcy–Brinkman–Forchheimer (DBF) model describes the
flow and the thermal dispersion is taken into account in the energy equation. The classical boundary layer equations without
inertia and enthalpyterms are used in the condensate region. It is found that due to the thermal dispersion effect, the increasing
of heat transfer is significant. The comparison of the DBF model and the Darcy–Brinkman (DB) one is carried out. 相似文献
9.
V. P. Ryabchenko 《Journal of Applied Mechanics and Technical Physics》2008,49(2):267-276
This paper considers a two-dimensional linear unsteady problem of rigid-stamp indentation on an elastic layer of finite thickness
lying on the surface of a compressible fluid of infinite depth. The Lamé equations holds for the elastic layer, and the wave
equation for the fluid velocity potential. Using the Laplace and Fourier transforms, the problem is reduced to determining
the contact stresses under the stamp from the solution of an integral equation of the first kind, whose kernel has a logarithmic
singularity. An asymptotic solution of the problem is constructed for large times of interaction.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 131–142, March–April, 2008. 相似文献
10.
In order to evaluate characteristics of the liquid film flow and their influences on heat and mass transfer, measurements
of the instantaneous film thickness using a capacitance method and observation of film breakdown are performed. Experimental
results are reported in the paper. Experiments are carried out at Re = 250–10000, T
in = 20–50°C and three axial positions of vertically falling liquid films for film thickness measurements. Instantaneous surface
waveshapes are given by the interpretation of the test data using the cubic spline method. The correlation of the mean film
thickness versus the film Reynolds number is also given by fitting the test data. It is revealed that the surface wave has
nonlinear behavior. Observation of film breakdown is performed at Re = 1.40 × 103–1.75 × 104 and T
in = 85–95°C. From experimental results, the correlation of the film breakdown criterion can be obtained as follows: Bd = 1.567 × 10−6
Re
1.183 相似文献
11.
Chyong Za Bin' 《Fluid Dynamics》1986,21(6):934-939
A phenomenological theory is proposed to describe the equilibrium of a thin structured film of magnetic fluid on the surface
of another non-magnetic fluid in the absence of an external magnetic field. The stability of a semi-infinite plane magnetic
film is considered on the basis of the theory proposed. The result obtained can serve as a qualitative explanation of experiments
performed on thin films of magnetic fluid.
Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 105–110, November–December, 1986.
The author is grateful to L. I. Sedov and V. V. Gogosov for useful discussions and their interest in his work. 相似文献
12.
Chien-Hsin Chen 《Heat and Mass Transfer》2003,39(8-9):791-796
In this paper the problem of momentum and heat transfer in a thin liquid film of power-law fluid on an unsteady stretching
surface has been studied. Numerical solutions are obtained for some representative values of the unsteadiness parameter S and the power-law index n for a wide range of the generalized Prandtl number, 0.001 ≤ Pr ≤ 1000. Typical temperature and velocity profiles, the dimensionless film thickness, free-surface temperature, and the surface
heat fluxes are presented at selected controlling parameters. The results show that increasing the value of n tends to increase the boundary-layer thickness and broadens the temperature distributions. The free-surface temperature of
a shear thinning fluid is larger than that of a Newtonian fluid, but the opposite trend is true for a shear thickening fluid.
For small generalized Prandtl numbers, the surface heat flux increases with a decrease in n, but the impacts of n on the heat transfer diminish for Pr greater than a moderate value (approximately 1 ≤ Pr ≤ 10, depending on the magnitude of S). 相似文献
13.
A. E. Bukatov 《Fluid Dynamics》1994,29(4):549-555
The nonlinear interaction of periodic traveling waves of the first and second harmonics in a constant-depth uniform fluid
covered with broken ice is considered. Uniform asymptotic expansions up to third-order values for the velocity potential of
the fluid and the elevation of the basin surface are found by means of the multivariable expansion procedure. The dependence
of the wave perturbations on the thickness of the ice and the interacting-harmonic characteristics is analyzed.
Sevastopol. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 136–143, July–August,
1994. 相似文献
14.
V. É. Borzykh G. G. Volokitin S. K. Karandashov A. M. Shilyaev 《Journal of Applied Mechanics and Technical Physics》1998,39(6):875-880
The behavior of a liquid layer moving in a mass-force field on the inner surface of a rotating vertical cylinder is studied
experimentally. Free-surface profiles of the liquid moving under these conditions are constructed. An empirical dependence
for the mean thickness of the film is obtained in criterial forms. The presence of a hydraulic jump in the lower part of the
cylinder behind the entrance of the liquid onto the vertical surface is revealed.
Tomsk, State Architectural-Building University, Tomsk 634003. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika,
Vol. 39, No. 6, pp. 65–71, November–December, 1998. 相似文献
15.
A thin liquid sheet present in the shear layer of a compressible gas jet is investigated using an Eulerian approach with mixed-fluid
treatment for the governing equations describing the gas–liquid two-phase flow system, where the gas is treated as fully compressible
and the liquid as incompressible. The effects of different topological configurations, surface tension, gas pressure and liquid
sheet thickness on the flow development of the gas–liquid two-phase flow system have been examined by direct solution of the
compressible Navier–Stokes equations using highly accurate numerical schemes. The interface dynamics are captured using volume
of fluid and continuum surface force models. The simulations show that the dispersion of the liquid sheet is dominated by
vortical structures formed at the jet shear layer due to the Kelvin–Helmholtz instability. The axisymmetric case is less vortical
than its planar counterpart that exhibits formation of larger vortical structures and larger liquid dispersion. It has been
identified that the vorticity development and the liquid dispersion in a planar configuration are increased at the absence
of surface tension, which when present, tends to oppose the development of the Kelvin–Helmholtz instability. An opposite trend
was observed for an axisymmetric configuration where surface tension tends to promote the development of vorticity. An increase
in vorticity development and liquid dispersion was observed for increased liquid sheet thickness, while a decreasing trend
was observed for higher gas pressure. Therefore surface tension, liquid sheet thickness and gas pressure factors all affect
the flow vorticity which consequently affects the dispersion of the liquid.
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16.
Many fish depend primarily on their tail beat for propulsion. Such a tail is commonly modeled as a two-dimensional flapping
foil. Here we demonstrate a novel experimental setup of such a foil that heaves and pitches in a soap film. The vortical flow
field generated by the foil correlates with thickness variations in the soap film, which appear as interference fringes when
the film is illuminated with a monochromatic light source (we used a high-frequency SOX lamp). These interference fringes
are subsequently captured with high-speed video (500 Hz) and this allows us to study the unsteady vortical field of a flapping
foil. The main advantage of our approach is that the flow fields are time and space resolved and can be obtained time-efficiently.
The foil is driven by a flapping mechanism that is optimized for studying both fish swimming and insect flight inside and
outside the behavioral envelope. The mechanism generates sinusoidal heave and pitch kinematics, pre-described by the non-dimensional
heave amplitude (0–6), the pitch amplitude (0°–90°), the phase difference between pitch and heave (0°–360°), and the dimensionless
wavelength of the foil (3–18). We obtained this wide range of wavelengths for a foil 4 mm long by minimizing the soap film
speed (0.25 m s−1) and maximizing the flapping frequency range (4–25 Hz). The Reynolds number of the foil is of order 1,000 throughout this
range. The resulting setup enables an effective assessment of vortex wake topology as a function of flapping kinematics. The
efficiency of the method is further improved by carefully eliminating background noise in the visualization (e.g., reflections
of the mechanism). This is done by placing mirrors at an angle behind the translucent film such that the camera views the
much more distant and out-of-focus reflections of the black laboratory wall. The resulting high-quality flow visualizations
require minimal image processing for flow interpretation. Finally, we demonstrate the effectiveness of our setup by visualizing
the vortex dynamics of the flapping foil as a function of pitch amplitude by assessing the symmetry of the vortical wake. 相似文献
17.
18.
O. Yu. Tsvelodub V. Yu. Shushenachev 《Journal of Applied Mechanics and Technical Physics》2005,46(3):365-374
The flow of a thin film of a nonlinearly viscous fluid whose stress tensor is modeled by a power law, flowing down a vertical
plane in the field of gravity, is considered. For the case of low flow rates, an equation that describes the evolution of
surface disturbances is derived in the long-wave approximation. The domain of linear stability of the trivial solution is
found, and weakly nonlinear, steady-state travelling solutions of this equation are obtained. The mechanism of branching of
solution families at the singular point of the neutral curve is described.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 3, pp. 73–84, May–June, 2005. 相似文献
19.
The problem of convective instability of a fluid in a system consisting of two horizontal porous strata with different permeabilities
and a permeable common boundary is considered. The problem is investigated in parametric form as a function of the stratum
thickness ratio and stratum permeabilities. As distinct from a uniform stratum, in this case the neutral curve can have one
or two minima depending on the relationship between the parameters. The case of two minima is characterized by the condition
of loss of stability of the fluid in the system as a whole and in the thinner stratum with greater permeability. These minima
correspond to significantly different wave numbers.
Makhachkala. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 165–169, January–February,
1999. 相似文献
20.
Absorber is an important component in absorption machines and its characteristics have significant effects on the overall
efficiency of absorption machines. This article reports a model of simultaneous heat and mass transfer process in absorption
of refrigerant vapor into a lithium bromide solution of water––cooled vertical plate absorber in the Reynolds number range
of 5 < Re < 150. The boundary layer assumptions were used for the transport of mass, momentum and energy equations and the fully implicit
finite difference method was employed to solve the governing equations in the film flow. Dependence of lithium bromide aqueous
properties to the temperature and concentration and film thickness to vapor absorption was employed. This model can predict
temperature, concentration and properties of aqueous profiles as well as the absorption heat and mass fluxes, heat and mass
transfer coefficients, Nusslet and Sherwood number of absorber. An analysis for linear distribution of wall temperature condition
carries out to investigation the reliability of the present numerical method through comparing with previous investigation. 相似文献