共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Mizzi R. W. Barber D. R. Emerson J. M. Reese S. K. Stefanov 《Continuum Mechanics and Thermodynamics》2007,19(5):273-283
This paper presents a new technique that combines Grad’s 13-moment equations (G13) with a phenomenological approach to rarefied
gas flows. This combination and the proposed solution technique capture some important non-equilibrium phenomena that appear
in the early continuum-transition flow regime. In contrast to the fully coupled 13-moment equation set, a significant advantage
of the present solution technique is that it does not require extra boundary conditions explicitly; Grad’s equations for viscous
stress and heat flux are used as constitutive relations for the conservation equations instead of being solved as equations
of transport. The relative computational cost of this novel technique is low in comparison to other methods, such as fully
coupled solutions involving many moments or discrete methods. In this study, the proposed numerical procedure is tested on
a planar Couette flow case, and the results are compared to predictions obtained from the direct simulation Monte Carlo method.
This test case highlights the presence of normal viscous stresses and tangential heat fluxes that arise from non-equilibrium
phenomena, which cannot be captured by the Navier–Stokes–Fourier constitutive equations or phenomenological modifications.
相似文献
2.
V. M. Agranat 《Fluid Dynamics》1986,21(6):983-985
The nonisothermal Blasius problem for a gas suspension is considered on the basis of the equations of a quasiequilibrium two-phase
laminar boundary layer [1–3]. Approximate analytical expressions are obtained for the friction and heat transfer coefficients
and their region of applicability is estimated; the Reynolds analogy between friction and convective heat transfer processes
[4] is extended to the case of a dusty quasiequilibrium laminar boundary layer.
Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 160–162, November–December, 1986. 相似文献
3.
The forced convection heat transfer with water vapor condensation is studied both theoretically and experimentally when wet
flue gas passes downwards through a bank of horizontal tubes. Extraordinarily, discussions are concentrated on the effect
of water vapor condensation on forced convection heat transfer. In the experiments, the air–steam mixture is used to simulate
the flue gas of a natural gas fired boiler, and the vapor mass fraction ranges from 3.2 to 12.8%. By theoretical analysis,
a new dimensionless number defined as augmentation factor is derived to account for the effect of condensation of relatively
small amount of water vapor on convection heat transfer, and a consequent correlation is proposed based on the experimental
data to describe the combined convection–condensation heat transfer. Good agreement can be found between the values of the
Nusselt number obtained from the experiments and calculated by the correlation. The maximum deviation is within ±6%. The experimental
results also shows that the convection–condensation heat transfer coefficient increases with Reynolds number and bulk vapor
mass fraction, and is 1∼3.5 times that of the forced convection without condensation. 相似文献
4.
E. N. Vasil'ev D. A. Nesterov 《Journal of Applied Mechanics and Technical Physics》2005,46(6):773-779
A two-dimensional computational model is proposed to calculate radiative-convective heat transfer in gas flows with large
gradients of physical properties. The model is based on the numerical solution of the unsteady dynamic equations for a compressible
inviscid gas and the radiative transfer equations. Flow calculations for the magnetogasdynamic channel of a rail accelerator
show that the dynamics of the process is substantially affected by the flow in the discharge region and hydrodynamic instability,
resulting in the nonstationarity and nonuniformity of the flow and discharge structure. During the process, the discharge
can exist both in the form of several current-carrying channels and in the form of a unified plasma formation. Results of
the numerical calculations agree qualitative with experimental data.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 5–13, November–December, 2005. 相似文献
5.
V. I. Zinchenko A. S. Yakimov 《Journal of Applied Mechanics and Technical Physics》1999,40(4):697-703
New methods of controlling thermal regimes in a high-enthalpy spatial flow around a body are considered. They are related
to gas injection from the blunted surface and heat overflow in the material of the shell. The effect of injection is analyzed
for different thermal conductivities. It is shown that highly heat-conducting materials can be successfully used to decrease
the maximum temperatures at the windward side due to intense heat removal to the region of a porous spherical bluntness.
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 4, pp. 162–169, July–August, 1999. 相似文献
6.
On the Chaotic Dynamics of a Spherical Pendulum with a Harmonically Vibrating Suspension 总被引:1,自引:0,他引:1
The equations of motion for a lightly damped spherical pendulum are considered. The suspension point is harmonically excited
in both vertical and horizontal directions. The equations are approximated in the neighborhood of resonance by including the
third order terms in the amplitude. The stability of equilibrium points of the modulation equations in a four-dimensional
space is studied. The periodic orbits of the spherical pendulum without base excitations are revisited via the Jacobian elliptic
integral to highlight the role played by homoclinic orbits. The homoclinic intersections of the stable and unstable manifolds
of the perturbed spherical pendulum are investigated. The physical parameters leading to chaotic solutions in terms of the
spherical angles are derived from the vanishing Melnikov–Holmes–Marsden (MHM) integral. The existence of real zeros of the
MHM integral implies the possible chaotic motion of the harmonically forced spherical pendulum as a result from the transverse
intersection between the stable and unstable manifolds of the weakly disturbed spherical pendulum within the regions of investigated
parameters. The chaotic motion of the modulation equations is simulated via the 4th-order Runge–Kutta algorithms for certain
cases to verify the analysis. 相似文献
7.
Supersonic viscous homogeneous gas flow past axisymmetric smooth nonpointed bodies is analyzed numerically for widely varying
Mach and Reynolds numbers and flow geometry. The initial equations of a viscous shock layer are solved by the stabilization
method. The effect of the determining parameters on the flow character and the heat transfer distribution along the surface
is analyzed. The accuracy and domain of applicability of several approximate approaches to the solution of the problem are
estimated.
Tomsk. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 107–117, January–February,
1999.
This research was carried out with financial support from the Russian Foundation for Basic Research (project No. 98-01-00298). 相似文献
8.
We present the theory of space–time elasticity and demonstrate that it is the extended reversible thermodynamics and gives the coupled model of thermoelasticity and heat conductivity and involves traditional thermoelasticity. We formulate the generally covariant variational model’s dynamic thermoelasticity and heat conductivity in which the basic kinematic and static variables are unified tensor objects (subject, matter). Variation statement defines the whole set of the initial-boundary problems for the 4D vector governing equation (Euler equation), the spatial projections of which define motion equations and the time projection gives the heat conductivity equation. We show that space–time elasticity directly implies the Fourier and the Maxwell–Cattaneo laws of heat conduction. However, space–time elasticity is richer than classical thermoelasticity, and it advocates its own equations of motion for coupled thermoelasticity. Moreover, we establish that the Maxwell–Cattaneo law and Fourier law can be defined for the reversible processes as compatibility equations without introducing dissipation. We argue that the present framework of space–time elasticity should prove adequate to describe the thermoelastic phenomena at low temperatures for interpreting the results of molecular simulations of heat conduction in solids and for the optimal heat and stress management in the microelectronic components and the thermoelectric devices. 相似文献
9.
Hydrogen is a renewable and clean source of energy, and it is a good replacement for the current fossil fuels. Nevertheless,
hydrogen should be stored in high-pressure reservoirs to have sufficient energy. An in-house code is developed to numerically
simulate the release of hydrogen from a high-pressure tank into ambient air with more accuracy. Real gas models are used to
simulate the flow since high-pressure hydrogen deviates from ideal gas law. Beattie–Bridgeman and Abel Noble equations are
applied as real gas equation of state. A transport equation is added to the code to calculate the concentration of the hydrogen–air
mixture after release. The uniqueness of the code is to simulate hydrogen in air release with the real gas model. Initial
tank pressures of up to 70 MPa are simulated. 相似文献
10.
Heterogeneous catalysis is of paramount importance in many areas of gas conversion and processing in chemical engineering
industries. In porous pellets, the catalytic reactions may be affected by diffusional limitations such that the global rate
can be different from the intrinsic reaction rate. In the literature, a number of multicomponent diffusion flux closures have
been applied to characterize the diffusion process within different units in chemical process plants. The main purpose of
this paper is to outline the derivation of the different diffusion flux models: the rigorous Maxwell–Stefan and dusty gas
models, and the simpler Wilke and Wilke–Bosanquet models. Usually the diffusion fluxes are derived and presented with respect
to the molar average velocity definition. In this study, also the diffusion flux closures with respect to the mass average
velocity definition is outlined. Thus, if the temperature equation and the momentum equation are used in the pellet model,
a consistently closed set of pellet equations is obtained on mass basis holding only the mass average velocity. On the other
hand, for the closed set of pellet equations on molar basis, the component balances hold the molar averaged velocity whereas
the temperature and momentum equations hold the mass average velocity due to the physical laws applied deriving these fundamental
balances. Nevertheless, the Maxwell–Stefan and dusty gas models are manipulated and put on the convenient Fickian form. The
second purpose of this article is the evaluation of the diffusion flux closures derived. For this purpose, a transient model
is developed to describe the evolution of the species composition, pressure, velocity, temperature, total concentration, and
fluxes within a spherical pellet. The catalyst problem has been simulated for the methanol dehydration process producing dimethyl
ether (DME), with computed efficiency factor values in the range 0.06–0.6 for pellet pore diameters of 0.1–100 nm. Identical
results are expected for the mole and mass based pellet equations. However, deviations are obtained in the component fractions
comparing the mass and mole based pellet model formulations where the mass fluxes were described according to the Wilke and
Wilke–Bosanquet models. On the other hand, the rigorous Maxwell–Stefan and dusty gas models gave identical results. 相似文献
11.
The paper investigates the chaotic flexural oscillations of the spinning nanoresonator. The influence of cubic nonlinearity
arising from the van der Waals interactions between two neighboring layers of carbon nanotubes on the structural oscillations
of the system is considered. The integral–differential equations describing the flexural displacements of the nanoresonator
are discretized into two coupled Duffing-type equations using the Galerkin–Ritz procedures. The linear stiffness can be either
positive or negative, depending on the amplitudes of the linear trap rigidity arising from both the van der Waals interactions
and the axial tensile loads. The chaotic flexural oscillations of the appropriately excited spinning nanoresonator are predicted
theoretically. Using the Nayfeh–Mook multiscale perturbation algorithms, the coupled Duffing-type equations with linear positive
stiffness may be transformed into autonomous equations of slowly modulated amplitudes whose equilibrium points and chaotic
dynamics are investigated numerically. The potential chaotic oscillations of the elastic nanoresonator can be determined by
the Melnikov–Holmes–Marsden (MHM) integral associated with the homoclinic/heteroclinic solutions of the disturbed Hamiltonian
systems with linear negative stiffness. The findings are validated through the Poincare sections and Lyapunov exponents. 相似文献
12.
A solution of an initial-boundary-value problem for a system of integrodifferential equations which describes the plane waves
excited in an initially stationary heavy two-layer ideal fluid by a cylinder moving at an angle to the horizontal is investigated.
The homogeneous fluid fractions of different densities are assumed to be separated by an evolving fluid interface (horizontal
plane, if the liquid is at rest). An approximate solution of two problems for the waves excited by a cylinder moving with
a constant acceleration and an oscillating cylinder is constructed analytically.
Nizhnii Novgorod. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 137–152, July–August,
1998. 相似文献
13.
Starting from the Liouville equation, the kinetic equations for a finely dispersed rarefied gas-particle medium are derived.
The size of the suspension particles is assumed to be much less than the free path of the gas molecules, while their density
is so small that interaction between the particles can be neglected. It is shown that in general the dynamics of this gas
suspension can be described by a system of two kinetic equations, which differ radically from the Boltzmann equations.
Novosibirsk. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 165–171, March–April,
1994. 相似文献
14.
The aim of this paper is to develop a numerical procedure for simulating a simplified mathematical model of underwater explosion
phenomena. The Euler set of equations is selected as the governing equations and the ideal gas and Tammann equations of state
(EOS) are used to obtain pressure in the gas bubble and the surrounding water zone, respectively. The modified Schmidt EOS
is used to simulate the cavitation regions. An arbitrary Lagrangian–Eulerian method is used to integrate the governing equations
over an unstructured moving grid. A mesh adapting technique is applied to increase the accuracy as well as for better capturing
of flow physics. Moreover, a least-square smoother is employed to moderate the undesirable effects of gas–water interface
irregularities. The numerical results verify that the proposed method is capable of predicting complex physics involved in
a spherical underwater explosion. The method also shows a very good performance in smoothing the interface while minimizing
the loss of mass and momentum in two-dimensional problems. 相似文献
15.
V. M. Teshukov 《Journal of Applied Mechanics and Technical Physics》2007,48(3):303-309
The classical shallow-water equations describing the propagation of long waves in flow without a shear of the horizontal velocity
along the vertical coincide with the equations describing the isentropic motion of a polytropic gas for a polytropic exponent
γ = 2 (in the theory of fluid wave motion, this fact is called the gas-dynamic analogy). A new mathematical model of long-wave
theory is derived that describes shear free-boundary fluid flows. It is shown that in the case of one-dimensional motion,
the equations of the new model coincide with the equations describing nonisentropic gas motion with a special choice of the
equation of state, and in the multidimensional case, the new system of long-wave equations differs significantly from the
gas motion model. In the general case, it is established that the system of equations derived is a hyperbolic system. The
velocities of propagation of wave perturbations are found.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 3, pp. 8–15, May–June, 2007. 相似文献
16.
P. Taheri A. S. Rana M. Torrilhon H. Struchtrup 《Continuum Mechanics and Thermodynamics》2009,21(6):423-443
Four basic flow configurations are employed to investigate steady and unsteady rarefaction effects in monatomic ideal gas
flows. Internal and external flows in planar geometry, namely, viscous slip (Kramer’s problem), thermal creep, oscillatory
Couette, and pulsating Poiseuille flows are considered. A characteristic feature of the selected problems is the formation
of the Knudsen boundary layers, where non-Newtonian stress and non-Fourier heat conduction exist. The linearized Navier–Stokes–Fourier
and regularized 13-moment equations are utilized to analytically represent the rarefaction effects in these boundary-value
problems. It is shown that the regularized 13-moment system correctly estimates the structure of Knudsen layers, compared
to the linearized Boltzmann equation data. 相似文献
17.
CFD modeling and experimental validation of heat and mass transfer in wood poles subjected to high temperatures: a conjugate approach 总被引:1,自引:0,他引:1
R. Younsi D. Kocaefe S. Poncsak Y. Kocaefe L. Gastonguay 《Heat and Mass Transfer》2008,44(12):1497-1509
In this article, a coupling method is presented in the case of high thermal treatment of a wood pole and a three-dimensional
numerical simulation is proposed. The conservation equations for the wood sample are obtained using diffusion equation with
variables diffusion coefficients and the incompressible Reynolds averaged Navier–Stokes equations have been solved for the
flow field. The connection between the two problems is achieved by expressing the continuity of the state variables and their
respective fluxes through the interface. Turbulence closure is obtained by the use of the standard k–ɛ model with the usual
wall function treatment. The model equations are solved numerically by the commercial package ANSYS-CFX10. The wood pole was
subjected to high temperature treatment under different operating conditions. The model validation is carried out via a comparison
between the predicted values with those obtained experimentally. The comparison of the numerical and experimental results
shows good agreement, implying that the proposed numerical algorithm can be used as a useful tool in designing high-temperature
wood treatment processes. A parametric study was also carried out to determine the effects of several parameters such as initial
moisture content, wood aspect ratio and final gas temperature on temperature and moisture content distributions within the
samples during heat treatment. 相似文献
18.
The steady laminar boundary layer flow and heat transfer from a warm, laminar liquid flow to a melting surface moving parallel
to a constant free stream is studied in this paper. The continuity, momentum and energy equations, which are coupled nonlinear
partial differential equations are reduced to a set of two nonlinear ordinary differential equations, before being solved
numerically using the Runge–Kutta–Fehlberg method. Results for the skin friction coefficient, local Nusselt number, velocity
profiles as well as temperature profiles are presented for different values of the governing parameters. Effects of the melting
parameter, moving parameter and Prandtl number on the flow and heat transfer characteristics are thoroughly examined. It is
found that the problem admits dual solutions. 相似文献
19.
Effects of Chemical Reaction and Double Dispersion on Non-Darcy Free Convection Heat and Mass Transfer 总被引:1,自引:0,他引:1
In this article, the effects of chemical reaction and double dispersion on non-Darcy free convection heat and mass transfer
from semi-infinite, impermeable vertical wall in a fluid saturated porous medium are investigated. The Forchheimer extension
(non-Darcy term) is considered in the flow equations, while the chemical reaction power–law term is considered in the concentration
equation. The first order chemical reaction (n = 1) was used as an example of calculations. The Darcy and non-Darcy flow, temperature and concentration fields in this study
are observed to be governed by complex interactions among dispersion and natural convection mechanisms. The governing set
of partial differential equations were non-dimensionalized and reduced to a set of ordinary differential equations for which
Runge–Kutta-based numerical technique were implemented. Numerical results for the detail of the velocity, temperature, and
concentration profiles as well as heat transfer rates (Nusselt number) and mass transfer rates (Sherwood number) are presented
in graphs. 相似文献
20.
M. G. Boyarshinov 《Fluid Dynamics》2000,35(4):534-541
A mathematical continuum model of a stand of forest for assessing the consequences of the movement of a gas cloud, formed
as a result of an accident, industrial gas emission, or production testing, is presented. The Navier-Stokes, continuity and
diffusion equations are used to investigate the accumulation of harmful impurities by the stand and their subsequent removal.
The two-dimensional problem is solved in the natural variables (velocity and pressure) using the Belotserkovskii procedure
and the geometric splitting method.
Perm. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 79–87, July–August, 2000. 相似文献