共查询到20条相似文献,搜索用时 9 毫秒
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《Comptes Rendus de l'Académie des Sciences》2001,329(9):687-692
Calculations of the reaction zone of the detonation of gaseous nitromethane, either pure or diluted with oxygen, in the range of equivalence ratio Φ between 0.1 and 1.75, show that for 1.75⩾Φ⩾1.3 the chemical energy is released in two main successive reaction steps characterized by very different induction times. These results corroborate the experimental observations of two levels of cellular structures in the same range of equivalence ratios. To our knowledge this work is the first which deals with the problem of nonmonotonous chemical energy release behind the leading shock of a detonation wave. 相似文献
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We propose a resolution of d’Alembert’s Paradox comparing observation of substantial drag/lift in fluids with very small viscosity
such as air and water, with the mathematical prediction of zero drag/lift of stationary irrotational solutions of the incompressible
inviscid Euler equations, referred to as potential flow. We present analytical and computational evidence that (i) potential
flow cannot be observed because it is illposed or unstable to perturbations, (ii) computed viscosity solutions of the Euler
equations with slip boundary conditions initiated as potential flow, develop into turbulent solutions which are wellposed
with respect to drag/lift and which show substantial drag/lift, in accordance with observations. 相似文献
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Abdelkader Djehiche Vladimir Canseco Aziz Omari Henri Bertin 《Comptes Rendus Mecanique》2009,337(9-10):682-692
This study deals with colloid transport in porous media which applications are found in subsurface water, petroleum engineering or civil engineering. An experimental study of colloidal polystyrene Latex particles deposition in a consolidated porous medium is presented. The influence of ionic strength of the colloid suspension and the flow rate on particle deposition is investigated. We see first that beyond a critical salt concentration, the total collector efficiency increases with the ionic strength. Moreover, such collector efficiency decreases as the flow rate increases according to theory. In other respects, using a γ ray attenuation technique allows us to measure local porosity fluctuation due to particles deposition. By this way deposition kinetics may be followed locally and precisely. Nevertheless when considering the thickness of the adsorbed layer over large scales, obtained results using the γ rays attenuation technique are found in good agreement with those obtained by means of an usual technique especially at latest stages of adsorption process. To cite this article: A. Djehiche et al., C. R. Mecanique 337 (2009). 相似文献
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《Comptes Rendus de l'Académie des Sciences》2001,329(7):541-548
We propose here a lift coefficient modeling in a turbulent bubbly boundary layer under the assumption of bidimensional stationary and vertical upward fully developed flow. The basic frame of this approach is to consider that the volumetric flux of bubbles is composed of the convective flux by the liquid, the contribution by the gravitational field and those of the lift force and the bubble dispersion terms. A discussion of results completes this study. 相似文献
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《Comptes Rendus de l'Académie des Sciences》2000,328(8):619-624
The effect of tiny asperities covering a wall on a flow governed by Stokes equations with Fourier boundary conditions is investigated. We calculate the limit flow and we give estimates of the deviations of the drag, velocity field and pressure, in terms of the size ε of the asperities. In the particular case of a plate, the limit drag is larger than the drag of the smooth wall, in contrast with the situation found for Dirichlet boundary conditions. 相似文献
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《Comptes Rendus de l'Académie des Sciences》2000,328(7):531-539
We study the induction of an explosion in a homogeneous substance solicited by a shock resulting from the impact of a planar autonomous detonation. We obtain the explosion time and a condition for initiation as a constraint on the length of the detonating charge. 相似文献
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《Comptes Rendus de l'Académie des Sciences》2000,328(10):741-747
In the present study, we propose a wall friction modeling in a vertical upward bubbly flow under the assumptions of bidimensional stationary and fully developed flow. This approach is based on the two-fluid model and on the hypothesis that the averaged flow is parallel to the wall. The turbulence modeling is an essential part in this model. Comparison with experimental data (presently available) exhibits satisfactory agreement. Other experimental studies, especially at a high void fraction, are desirable to examine further the model validity. 相似文献
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《Comptes Rendus de l'Académie des Sciences》2001,329(7):535-540
In order to study the evolution of damage in a delaminated structure, the assemblage of plates is considered under dynamic loading. Using a general result of the thermodynamic coupling approach, with the Hamiltonian formulation in the general case, the energy release rate associated with the propagation of the delamination is presented as a heat source. 相似文献
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《Comptes Rendus de l'Académie des Sciences》2001,329(1):53-59
Distribution of electrical potential is investigated for two kinds of flames: Bunsen burner and counterflow flames. Different electrode materials have been tested to determine these potentials. Measurable potentials and organized structures are found. Premixed Bunsen burner flames show a zero potential cone at their base just under the most intense potential region. One-dimensional counterflow diffusion flames are characterized by the stretch rate. The potential reaches its minimum value in the reaction zone and its absolute value decreases when stretch increases. 相似文献
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《Comptes Rendus Mecanique》2017,345(10):706-711
The study presented in the present paper deals with the modeling of the rotation effects on a homogeneous turbulence evolving without a mean velocity gradient. The developed model results from a modification of the second order model of Haworth and Pope. This modification is expressed as a function of the rotation rate, of the component of the Reynolds tensor and of the characteristic length scale in the direction of the rotation axis. The obtained results have evidenced the great capacity of the present model to describe the rotation effects on the time evolution of the homogeneous decaying turbulence. 相似文献
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《Comptes Rendus de l'Académie des Sciences》2001,329(10):753-760
The ductile failure of porous metallic materials is studied here using both Limit Analysis (LA) methods, a problem treated by Gurson with his famous kinematic approach in 1977. The present work is devoted to determining the strength of porous materials with long circular cylindrical cavities in the case of plane stress. The numerical methods developed here use the Hill–Mandel method based on the homogenization theory of heterogeneous media within the LA framework. The use of kinematic and static approaches gave an excellent estimation of the yield criterion for all the cases studied. The numerical results based on LA methods have been compared with analytical and semi-analytical yield domain expressions proposed by different authors. The results show that the Richmond model was the most accurate in terms of our predictions. 相似文献
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《Comptes Rendus de l'Académie des Sciences》2000,328(10):727-732
For materials exhibiting a non-linear behaviour (instantaneous elasticity and viscid non-linearities), strain-localization is associated with the occurrence of dynamic effects, even at slow loadings. A criterion is proposed for testing the relevance of the usual equilibrium hypothesis associated with slow loadings; at its fulfilment, the boundary problem is treated as dynamic, leading, by combination of inertia and viscosity terms, to localization. A 1D example of this approach is eventually given. 相似文献