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1.
For numerical analysis of shock wave propagation in gas-particle mixtures, drag coefficients of a sphere in steady flows are
generally used. However, it is shown both experimentally and numerically that a shock loaded solid sphere experiences unsteady
drag forces. The paper describes a model of unsteady drag force and its effect on the structure of the non-equilibrium region
behind a shock front traveling in a dusty gas. The results are compared with those obtained by using a steady drag coefficient
and are discussed. It is demonstrated that the large drag force at the early stage of the interaction between shock-wave induced
flow and a solid particle affects the flow structure that is obtained with a steady drag force.
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2.
Rafael Cortell 《Theoretical and Computational Fluid Dynamics》2007,21(6):435-446
In this paper, a numerical analysis of the momentum and heat transfer of an incompressible fluid past a parallel moving sheet
based on composite reference velocity U is carried out. A single set of equations has been formulated for both momentum and thermal boundary layer problems containing
the following parameters: r the ratio of the free stream velocity to the composite reference velocity, σ (Prandtl number) the ratio of the momentum diffusivity
of the fluid to its thermal diffusivity, and E
c
(E
ck
) (Eckert number). The present study has been carried out in the domain 0 ≤ r ≤ 1. It is found that the direction of the wall shear changes in such an interval and an increase of the parameter r yields an increase in temperature.
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3.
Gas-particle two-phase turbulent flow in a vertical duct 总被引:5,自引:0,他引:5
Two-phase gas-phase turbulent flows at various loadings between the two vertical parallel plates are analyzed. A thermodynamically consistent turbulent two-phase flow model that accounts for the phase fluctuation energy transport and interaction is used. The governing equation of the gas-phase is upgraded to a two-equation low Reynolds number turbulence closure model that can be integrated directly to the wall. A no-slip boundary condition for the gas-phase and slip-boundary condition for the particulate phase are used. The computational model is first applied to dilute gas-particle turbulent flow between two parallel vertical walls. The predicted mean velocity and turbulence intensity profiles are compared with the experimental data of Tsuji et al. (1984) for vertical pipe flows, and good agreement is observed. Examples of additional flow properties such as the phasic fluctuation energy, phasic fluctuation energy production and dissipation, as well as interaction momentum and energy supply terms are also presented and discussed.
Applications to the relatively dense gas-particle turbulent flows in a vertical channel are also studied. The model predictions are compared with the experimental data of Miller & Gidaspow and reasonable agreement is observed. It is shown that flow behavior is strongly affected by the phasic fluctuation energy, and the momentum and energy transfer between the particulate and the fluid constituents. 相似文献
4.
V. Svetsov 《Shock Waves》2001,11(3):229-244
A new nonstationary regime of the flow around a step and a cylinder was found to exist at high free-stream Mach numbers for
gas specific heat ratios below 1.2. The main features of the flow are strong vortices in the shock-compressed region with
supersonic reversal velocities at the body face. The bow shock wave takes on a complicated shape, fluctuating in time. The
vortical regimes can result from local heterogeneities in the free stream. The case of the heterogeneity is studied in this
paper in the form of a thin thermal layer of limited length. The vortical regime remains in existence after the source of
disturbances is removed. The results have been obtained through computer simulations through the use of Eulerian hydrodynamic
equations and by way of several numerical methods: FLIC, Godunov's scheme, TVD, and PPM. The influence of viscosity on the
development of the vortical regime has been studied by computer solving the Navier–Stokes equations.
Received 21 August 1998 / Accepted 6 June 2001 相似文献
5.
6.
In this paper, Euler-Lagrange type equations are used to describe the jet flow of a mixture of pulverized-coal and gas, which
is an unsteady axisymmetric two-phase flow. By means of the finite-difference method, the coal particle's distribution, velocity
and trajectory in the flow field are obtained. The coal particles are represented by a finite number of computational particles.
Each particle's diameter is randomly assigned according to a given distribution. The states of the computational particles
are different from each other. Turbulence is accounted for in a stochastic model. Explicit time-splitting scheme is used to
calculate the strongly coupling interphase term. The numerical results are reasonable. The comparison between the numerical
results and the experiment data for the case of the oil droplet injection shows good agreement. This numerical technique can
be extended to the calculation of other two-phase flows of dilute particles or a droplet system.
Mr. Mei Renwei also participated in the work of this paper. 相似文献
7.
Hua-Shu Dou Boo Cheong Khoo Nhan Phan-Thien Khoon Seng Yeo Rong Zheng 《Rheologica Acta》2007,46(4):427-447
The simulation of fibre orientation in dilute suspension with front moving is carried out using the projection and level-set
methods. The motion of fibres is described using the Jeffery equation, and the contribution of fibres to the flow is accounted
for by the configuration-field method. The dilute suspension of short fibres in Newtonian fluids is considered. The governing
Navier–Stokes equation for the fluid flow is solved using the projection method with finite difference scheme, while the fibre-related
equations are directly solved with the Runge–Kutta method. In the present study for fibres in dilute suspension flow for injection
molding, the effects of various flow and material parameters on the fibre orientation, the velocity distributions and the
shapes of the leading flow front are found and discussed. Our findings indicate that the presence of fibre motion has little
influence on the front shape in the ranges of fibre parameters studied at the fixed Reynolds number. Influence of changing
fibre parameters only causes variation of front shape in the region near the wall, and the front shape in the central core
area does not vary much with the fibre parameters. On the other hand, the fibre motion has strong influence on the distributions
of the streamwise and transverse velocities in the fountain flow. Fibre motion produces strong normal stress near the wall
which leads to the reduction of transversal velocity as compared to the Newtonian flow without fibres, which in turn, leads
to the increased streamwise velocity near the wall. Thus, the fibre addition to the flow weakens the strength of the fountain
flow. The Reynolds number has also displayed significant influence on the distribution of the streamwise velocity behind the
flow front for a given fibre concentration. It is also found that the fibre orientation is not always along the direction
of the velocity vector in the process of mold filling. In the region of the fountain flow, the fibre near the centreline is
more oriented across the streamwise direction compared to that in the region far behind the flow front. This leads to the
fact that the fibre near the centreline in the region of fountain flow is more extended along the transverse direction. As
the fibre orientation in the suspension flow and the shape of the flow front have great bearing on the quality of the product
made from injection molding, this study has much implications for engineering applications. These results can also be useful
in other fields dealing with fibre suspensions. 相似文献
8.
Numerical simulations of unsteady radiative-convective heat transfer in a turbulent flow of a mixture of gases and solid particles
past a semi-transparent plate are performed. An ablation process is demonstrated to occur on the plate surface in the case
of intense radiative heating of the plate by an external source with emission in a limited spectral range. Temperature fields
and distributions of heat fluxes in the boundary layer and in the plate are calculated. Calculation results are presented,
which allow determining the effect of ablation and reflecting properties of the plate surface on the thermal state of the
medium in the system containing the boundary layer and the plate under conditions of plate heating by a high-temperature source
of radiation.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 140–146, May–June, 2009. 相似文献
9.
运动物体与运动激波干扰流场特性数值研究 总被引:1,自引:0,他引:1
用数值方法求解非定常可压缩Navier—Stokes方程,模拟了运动物体分别以超声速和亚声速穿越激波的全过程。在这两种情况下,激波都是从高压区运动到低压区,阻力急剧地减小,但在亚声速情况下,会在物体上产生不对称力和力矩,导致运动物体的不稳定。 相似文献
10.
A digital tracer technique is applied to reconstruct the velocity fields in a convective flow developing in a rectangular cavity filled with a layer of fluid and having a bottom consisting of two heat exchangers kept at different temperatures. The upper boundary of the fluid is free. The structure of the secondary flows in the form of streamwise helicoidal rolls generated in the boundary layer over a hot plate is studied. It is shown that the centers of roll rotation coincide with temperature minima in the boundary layer, while the roll shape and dimensions vary with the distance from the temperature jump. With increase in the temperature difference the roll dimensions decrease but the velocity of their rotation increases. 相似文献
11.
In this paper, the steady boundary layer flow and heat transfer of a micropolar fluid on an isothermal continuously moving plane surface is studied analytically. It is assumed that the microinertia density is variable and the viscous dissipation effect is taken into account. The system of nonlinear ordinary differential equations is solved analytically using the homotopy analysis method (HAM) and the results are obtained for various flow and heat transfer characteristics. By using HAM, accurate analytic series solutions are obtained in the whole spatial region. Also, a new suggestion for choosing the proper value of the auxiliary parameter ? in the convergence region is proposed. It is observed that the present solutions have higher accuracy when the residual error is obtained. The present results show that this algorithm is effective and can be similarly applied to other nonlinear equations. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
12.
In this work we have experimentally measured the apparent wall slip velocity in open channel flow of neutrally buoyant suspension of non-colloidal particles. The free surface velocity profile was measured using the tool of particle imaging velocimetry (PIV) for two different channels made of plane and rough walls. The rough walled channel prevents wall slip, whereas the plane wall showed significant wall slip due to formation of slip layer. By comparing the velocity profiles from these two cases we were able to determine the apparent wall slip velocity. This method allows characterization of wall slip in suspension of large sized particles which cannot be performed in conventional rheometers. Experiments were carried out for concentrated suspensions of various particle volume concentrations and for two different sizes of particles. It was observed that wall slip velocity increases with particle size and concentration but decreases with increase in the viscosity of suspending fluid. The apparent wall slip velocity coefficients are in qualitative agreement with the earlier measurements. The effect of wall slip on free surface corrugation was also studied by analyzing the power spectral density (PSD) of the refracted light from the free surface. Our results indicate that free surface corrugation is a bulk flow response and it does not arise from boundary problem such as development of slip layer. 相似文献
13.
I. I. Lipatov 《Fluid Dynamics》2006,41(5):725-735
Local flows in a laminar boundary layer flowing over surface heating elements are investigated. Mathematical models of disturbed flows are constructed on the basis of an asymptotic analysis and the similarity parameters are determined. The time-dependent local heating regimes ensuring control of separation and flow stability in the boundary layer are studied. The results of a numerical and analytic analysis are obtained. 相似文献
14.
A. A. Verevkin Yu. M. Tsirkunov 《Journal of Applied Mechanics and Technical Physics》2008,49(5):789-798
An unsteady gas-particle flow in a hypersonic shock tunnel is studied numerically. The study is performed in the period from
the instant when the diaphragm between the high-pressure and low-pressure chambers is opened until the end of the transition
to a quasi-steady flow in the test section. The dispersed phase concentration is extremely low, and the collisions between
the particles and their effect on the carrier gas flow are ignored. The particle size is varied. The time evolution of the
particle concentration in the test section is obtained. Patterns of the quasi-steady flow of the dispersed phase in the throat
of the Laval nozzle and the flow around a model (sphere) are presented. Particle concentration and particle velocity lag profiles
at the test-section entrance are obtained. The particle-phase flow structure and the time needed for it to reach a quasi-steady
regime are found to depend substantially on the particle size.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 5, pp. 102–113, September–October, 2008. 相似文献
15.
The effect of the nonparallelism of the boundary layer flow over a flat plate on its stability characteristics has been investigated
by several authors, and it was claimed that the results of the theoretical calculations are already in good agreement with
the experimental observations. However, this is not true. In this paper, this problem is reinvestigated, using two different
methods. It is found that within the framework of linear theory, the theoretical results are in fact not in good agreement
with the experimental observations. To settle this problem, nonlinear effect must be taken into consideration.
Projects Supported by the Science Fund of the Chinese Academy of Sciences 相似文献
16.
17.
The results of an investigation of the dynamics of hard particles and liquid drops in the flow behind a transmitted shock wave are presented. From the equation of motion of a particle in the shock wave, relations for the displacement, velocity and acceleration as functions of time and certain velocity-relaxation parameters taking into account the properties of the gas and the aerodynamic drag of the particles are obtained for unsteady flow around the particles at an acceleration of 103–104 m/s2. It is shown that the velocity-relaxation parameters are universal. Approaches to finding the aerodynamic drag of freely-accelerating bodies from the dynamics of their acceleration after being suddenly exposed to the flow are considered. It is established that under these conditions the drop dynamics observed can be well described in terms of the same velocity-relaxation parameters with account for linear growth of the transverse drop size. All the kinematic functions obtained are confirmed experimentally. 相似文献
18.
The formation of a secondary shock wave behind a shock wave diffracting at a convex corner 总被引:3,自引:0,他引:3
This paper deals with the formation of a secondary shock wave behind the shock wave diffracting at a two-dimensional convex
corner for incident shock Mach numbers ranging from 1.03 to 1.74 in air. Experiments were carried out using a 60 mm 150 mm shock tube equipped with holographic interferometry. The threshold incident shock wave Mach number () at which a secondary shock wave appeared was found to be = 1.32 at an 81° corner and = 1.33 at a 120° corner. These secondary shock waves are formed due to the existence of a locally supersonic flow behind
the diffracting shock wave. Behind the diffracting shock wave, the subsonic flow is accelerated and eventually becomes locally
supersonic. A simple unsteady flow analysis revealed that for gases with specific heats ratio the threshold shock wave Mach number was = 1.346. When the value of is less than this, the vortex is formed at the corner without any discontinuous waves accompanying above the slip line. The
viscosity was found to be less effective on the threshold of the secondary shock wave, although it attenuated the pressure
jump at the secondary shock wave. This is well understood by the consideration of the effect of the wall friction in one-dimensional
duct flows. In order to interpret the experimental results a numerical simulation using a shock adaptive unstructured grid
Eulerian solver was also carried out.
Received 1 May 1996 / Accepted 12 September 1996 相似文献
19.
The interaction of a planar shock wave with a loose dusty bulk layer has been investigated both experimentally and numerically.
Experiments were conducted in a shock tube. The incident shock wave velocity and particle diameters were measured with the
use of pressure transducers and a Malvern particle sizer, respectively. The flow fields, induced by shock waves, of both gas
and granular phase were visualized by means of shadowgraphs and pulsed X-ray radiography with trace particles added. In addition,
a two-phase model for granular flow presented by Gidaspow is introduced and is extended to describe such a complex phenomenon.
Based on the kinetic theory, such a two-phase model has the advantage of being able to clarify many physical concepts, like
particulate viscosity, granular conductivity and solid pressure, and deduce the correlative constitutive equations of the
solid phase. The AUSM scheme was employed for the numerical calculation. The flow field behind the shock wave was displayed
numerically and agrees well with our corresponding experimental results.
相似文献
20.
Tang Guiming 《Acta Mechanica Sinica》1998,14(2):139-146
An experimental study was conducted on shock wave turbulent boundary layer interactions caused by a blunt swept fin-plate
configuration at Mach numbers of 5.0, 7.8, 9.9 for a Reynolds number range of (1.0∼4.7)×107/m. Detailed heat transfer and pressure distributions were measured at fin deflection angles of up to 30° for a sweepback
angle of 67.6°. Surface oil flow patterns and liquid crystal thermograms as well as schlieren pictures of fin shock shape
were taken. The study shows that the flow was separated at deflection of 10° and secondary separation were detected at deflection
of ϑ≥20°. The heat transfer and pressure distributions on flat plate showed an extensive plateau region followed by a distinct
dip and local peak close to the fin foot. Measurements of the plateau pressure and heat transfer were in good agreement with
existing prediction methods, but pressure and heating peak measurements atM≥6 were significantly lower than predicted by the simple prediction techniques at lower Mach numbers.
The project supported by China Academy of Launch Vehicle Technology 相似文献