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1.
The paper examines a water hammer in an elastic pipeline through which a liquid containing solid particles flows. The effect
of the particle phase on the pressure jump in the liquid-particle mixture is studied.
S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika,
Vol. 35, No. 10, pp. 80–86, October, 1999. 相似文献
2.
Prediction of separation flows around a 6:1 prolate spheroid using RANS/LES hybrid approaches 总被引:2,自引:0,他引:2
Zhixiang Xiao Yufei Zhang Jingbo Huang Haixin Chen Song Fu 《Acta Mechanica Sinica》2007,23(4):369-382
This paper presents hybrid Reynolds-averaged Navier–Stokes (RANS) and large-eddy-simulation (LES) methods for the separated
flows at high angles of attack around a 6:1 prolate spheroid. The RANS/LES hybrid methods studied in this work include the
detached eddy simulation (DES) based on Spalart–Allmaras (S–A), Menter’s k–ω shear-stress-transport (SST) and k–ω with weakly nonlinear eddy viscosity formulation (Wilcox–Durbin+, WD+) models and the zonal-RANS/LES methods based on the
SST and WD+ models. The switch from RANS near the wall to LES in the core flow region is smooth through the implementation
of a flow-dependent blending function for the zonal hybrid method. All the hybrid methods are designed to have a RANS mode
for the attached flows and have a LES behavior for the separated flows. The main objective of this paper is to apply the hybrid
methods for the high Reynolds number separated flows around prolate spheroid at high-incidences. A fourth-order central scheme
with fourth-order artificial viscosity is applied for spatial differencing. The fully implicit lower–upper symmetric-Gauss–Seidel
with pseudo time sub-iteration is taken as the temporal differentiation. Comparisons with available measurements are carried
out for pressure distribution, skin friction, and profiles of velocity, etc. Reasonable agreement with the experiments, accounting
for the effect on grids and fundamental turbulence models, is obtained for the separation flows.
The project supported by the National Natural Science Foundation of China (10502030 and 90505005). 相似文献
3.
Understanding turbulence kinetic energy (TKE) budget in gas–liquid two-phase bubbly flows is indispensable to develop and
improve turbulence models for the bubbly flows. In this study, a molecular tagging velocimetry based on photobleaching reaction
was applied to turbulent bubbly flows with sub-millimeter bubbles in a vertical square duct to examine the applicability of
the k–ε models to the bubbly flows. Effects of bubbles on TKE budget are discussed and a priori tests of the standard and low Reynolds
number k–ε models are carried out to examine the applicability of these models to the bubbly flows. The conclusions obtained are as
follows: (1) The photobleaching molecular tagging velocimetry is of use for validating turbulence models. (2) The bubbles
increase the liquid velocity gradient in the near wall region, and therefore, enhance the production and dissipation rates
of TKE. (3) The k–ε models can reasonably evaluate the production rate of TKE in the bubbly flows. (4) The modulations of diffusion due to the
bubbles have different characteristics from the diffusion enhancement due to shear-induced turbulence. Hence, the k–ε models fail in evaluating the diffusion rate in the near wall region in the bubbly flows. (5) The k–ε models represent the trends of the production, dissipation, and diffusion rates of ε in the bubbly flow, although more accurate
experimental data are required for quantitative validation of the ε equation. 相似文献
4.
Novel accelerator applications favor free-surface liquid–metal flows, in which the liquid acts both as a target producing
secondary particles but also to remove efficiently the heat deposited. A crucial aspect for the operation is the continuous
monitoring of both shape and position of the liquid’s surface. This demands, in a nuclear environment, a non-intrusive measurement
technique with high temporal and spatial resolution. In this context, the double-layer projection (DLP) technique based on
geometric optics has been developed, allowing one to detect either point-wise or area-wise the shape and position of the nearly
totally reflecting liquid–metal surface. The DLP technique employs a laser beam projected through a coplanar glass plate to
the surface from which it is reflected to the plate again. Beam locations captured by means of a camera permit the position
and shape of the surface to be reconstructed. The parameters affecting the resolution and performance of the DLP technique
are discussed. Additionally, validation studies using static and moving objects of pre-defined shape are conducted, exhibiting
spatial and temporal resolutions of 300 μm and 100 Hz, respectively. Finally, the DLP system is applied to perform measurements
of a circular hydraulic jump (CHJ) in a liquid metal. The DLP system has proved the capability to measure the jump both qualitatively
and quantitatively. Additionally, the experiments identified, at high Reynolds numbers, the existence of a two-step jump.
The analysis of spectral data of the DLP surface measurements shows clearly that, at the outer radius, gravity waves occur.
Also, contributions from the pump oscillations were found, demonstrating the high performance of the DLP system. 相似文献
5.
Through an improved ε transport equation, a major quality enhancement of the cubic k–ε model, earlier developed in[13], is obtained. The ε-equation of [13],yielding good results for wall-bounded and rotating
flows, is combined with the one derived by Shih et al. [20], which produces good results for free shear flows (e.g. the plane
jet–round jet anomaly is resolved).Results are presented for the following flows: fully developed stationary and rotating
channel and pipe, backward-facing step, sudden pipe expansion, smooth channel expansion and contraction, plane and round jet.
Heat transfer predictions in turbulent impinging jets are also discussed. Accurate results are obtained for the mean flow
quantities for all test cases, without case dependent model tuning.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
The concepts of subcritical and supercritical flows are introduced for the long-wave approximation model describing stationary
free-boundary rotational flows of an ideal incompressible fluid. Shear flows of a fluid layer above an uneven bottom are analyzed.
Exact solutions describing different flow regimes are constructed, and the flow properties are studied as a function of the
flow regime. Flows with backward streamlines are considered.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 4, pp. 26–38, July–August, 2006.
An erratum to this article is available at . 相似文献
7.
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
8.
Hiva Shamsborhan Olivier Coutier-Delgosha Guy Caignaert Fadi Abdel Nour 《Experiments in fluids》2010,49(6):1359-1373
This paper presents measurements of the speed of sound in two-phase flows characterized by high void fraction. The main objective
of the work is the characterization of wave propagation in cavitating flows. The experimental determination of the speed of
sound is derived from measurements performed with three pressure transducers, while the void fraction is obtained from analysis
of a signal obtained with an optical probe. Experiments are first conducted in air/water mixtures, for a void fraction varying
in the range 0–11%, in order to discuss and validate the methods of measurement and analysis. These results are compared to
existing theoretical models, and a nice agreement is obtained. Then, the methods are applied to various cavitating flows.
The evolution of the speed of sound according to the void fraction α is determined for α varying in the range 0–55%. In this
second configuration, the effect of the Mach number is included in the spectral analysis of the pressure transducers’ signals,
in order to take into account the possible high flow compressibility. The experimental data are compared to existing theoretical
models, and the results are then discussed. 相似文献
9.
Viscous dissipation effect on heat transfer characteristics of a rectangular microchannel is studied. Flow is governed by the Navier–Stokes equations with the slip flow and temperature jump boundary conditions. Integral transform technique is applied to derive the temperature distribution and Nusselt number. The velocity distribution is taken from literature. The solution method is verified for the case where viscous dissipation is neglected. It is found that, the viscous dissipation is negligible for gas flows in microchannels, since the contribution of this effect on Nu number is about 1%. However, this effect should be taken into account for much more viscous flows, such as liquid flows. Neglecting this effect for a flat microchannel with an aspect ratio of 0.1 for Br=0.04 underestimates the Nu number about 5%. 相似文献
10.
S. K. Betyaev 《Journal of Applied Mechanics and Technical Physics》2007,48(2):192-199
A planar analog of conical flows is considered: an inviscid incompressible fluid flow around a wedge tip. A class of conical
flows is found where vorticity is transported along streamlines by the potential component of velocity. Problems of a wave
“locked” in the corner region and of a flow accelerating along the rib of a dihedral angle are considered. By analogy with
an axisymmetric quasi-conical flow, a planar quasi-conical flow of the fluid is determined, namely, the flow inside and outside
the region bounded by tangent curves described by a power law. Conditions are found where vorticity and swirl produce a significant
effect. An approximate solution of the problem of the fluid flow inside a “zero” angle is obtained.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 57–65, March–April, 2007. 相似文献
11.
A two-scale model of ion transfer in a porous medium is obtained for one-dimensional horizontal flows under the action of
a pressure gradient and an external electric field by the method of homogenization. Steady equations of electroosmotic flows
in flat horizontal nano-sized slits separated by thin dielectric partitions are averaged over a small-scale variable. The
resultant macroequations include Poisson’s equation for the vertical component of the electric field and Onsager’s relations
between flows and forces. The total horizontal flow rate of the fluid is found to depend linearly on the pressure gradient
and external electric field, and the coefficients in this linear relation are calculated with the use of microequations.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 4, pp. 162–173, July–August, 2008. 相似文献
12.
A. A. Chesnokov 《Journal of Applied Mechanics and Technical Physics》2006,47(6):800-811
The problem of the decay of an arbitrary discontinuity for the equations describing plane-parallel shear flows of an ideal
fluid in a narrow channel is considered. The class of particular solutions corresponding to fluid flows with piecewise constant
vorticity is studied. In this class, the existence of self-similar solutions describing all possible unsteady wave configurations
resulting from the nonlinear interaction of the specified shear flows is established.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 6, pp. 34–47, November–December, 2006. 相似文献
13.
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
14.
Three modes of propagation of a traveling-wave front over a noncold gas with different propagation velocities are found using
one thermodynamic model. When the indicated velocity is low, transition from constant values of the gas parameters on both
sides of the traveling-wave front proceeds continuously. An increase in the traveling-wave velocity leads to an isothermal
jump: the density and velocity of the gas undergo a strong discontinuity whereas the temperature varies continuously. With
a further increase in the traveling-wave velocity, the isothermal jump disappears and the flow becomes continuous again.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 4, pp. 15–25, July–August, 2006. 相似文献
15.
Based on the exact spectral presentation of the “rapid” part of the pressure-strain rate correlations, semi-empirical approximations
used for these correlations within the framework of the second-order closures are analyzed. Simple inequalities relating the
values of the model constants, mean velocity parameters, and Reynolds tensor invariants are derived. For certain types of
flows, in contrast to conditions of realizability, these inequalities allow verification of the approximations before solving
differential equations. It is demonstrated that some models cannot be considered as sufficiently precise ones to describe
flows with high degrees of anisotropy. In particular, the condition of non-negative determinacy of the spectral matrix is
violated in a considerable region of the physically admissible range of parameters. The boundaries of this region are calculated
for an irrotational three-dimensional distortion and for an arbitrary two-dimensional distortion of turbulence in channel
flows. Simple constraints on model constants are obtained, which allow these violations to be avoided.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 29–39, March–April, 2008. 相似文献
16.
A. A. Chesnokov 《Journal of Applied Mechanics and Technical Physics》1999,40(3):420-430
A mathematical model of the vortex motion of an ideal two-layer fluid in a narrow straight channel is considered. The fluid
motion in the Eulerian-Lagrangian coordinate system is described by quasilinear integrodifferential equations. Transformations
of a set of the equations of motion which make it possible to apply the general method of studying integrodifferential equations
of shallow-water theory, which is based on the generalization of the concepts of characteristics and the hyperbolicity for
systems with operator functionals, are found. A characteristic equation is derived and analyzed. The necessary hyperbolicity
conditions for a set of equations of motion of flows with a monotone-in-depth velocity profile are formulated. It is shown
that the problem of sufficient hyperbolicity conditions is equivalent to the solution of a certain singular integral equation.
In addition, the case of a strong jump in density (a heavy fluid in the lower layer and a quite lightweight fluid in the upper
layer) is considered. A modeling that results in simplification of the system of equations of motion with its physical meaning
preserved is carried out. For this system, the necessary and sufficient hyperbolicity conditions are given.
Novosibirsk State University, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40,
No. 3, pp. 68–80, May–June, 1999. 相似文献
17.
A new type of flow in a magnetic fluid has been experimentally detected and investigated. The interaction between an alternating
nonuniform magnetic field and a magnetic fluid leads to the parametric excitation of traveling capillary-gravitational waves
which are the direct cause of the average flow. A necessary condition of formation of hydrodynamic flows in an alternating
field is also the presence of time-dependent harmonics with multiple frequencies synchronized with the first harmonic, so
that the time dependence of the ponderomotive force is generally pulsed. It is shown that for plane vibrational flows the
classical theory cannot explain the high intensity of the average flows observed. It is suggested that the high intensity
of magnetovibrational flows is related to the violation of the cylindrical symmetry of the traveling capillary-gravitational
waves and the transition to a three-dimensional motion.
Perm’. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 124–133, January–February,
1998. 相似文献
18.
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
19.
V. K. Baev A. V. Fedorov V. M. Fomin T. A. Khmel' 《Journal of Applied Mechanics and Technical Physics》2006,47(1):36-46
Gas flows inside and around rapidly rotating bodies made of cellular-porous materials are studied numerically and experimentally.
Within the framework of the previously proposed physicomathematical model, an appropriate numerical algorithm is developed
and tested. Internal flows and a conjugate problem with the external flow are considered. The calculated moment and dynamic
pressure are in good agreement with experimentally measured characteristics of a rotating porous disk on a solid substrate.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 46–57, January–February, 2006. 相似文献
20.
A new approach for solving the laminar flow problem above a porous medium is presented here, using an apparent interface for
which both superficial velocity and intrinsic shear stress are continuous. The derivation of this approach is based on a detailed
investigation of the Ochoa-Tapia and Whitaker (Int. J. Heat Mass Transfer 38:2635–2646, 1995a) jump condition and its sensitivity
to the value of β (the jump condition coefficient) and to an error in the interface location. While the value of the jump
condition coefficient is highly sensitive to the interface location, the new apparent interface approach does not require
an a priori information about the location of the interface. This approach can be easily used knowing only one measurable
parameter—the maximum velocity or the flow rate. Validation of the apparent interface approach against measurements from other
works shows that it can be successfully used to predict the velocity profile for different geometrical models. 相似文献