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181.
Near-field flow and flame dynamics of LOX/methane shear-coaxial injector under supercritical conditions 总被引:2,自引:0,他引:2
The mixing and combustion of liquid oxygen (LOX) and gaseous methane of a shear coaxial injector operating under supercritical pressures have been numerically investigated. The near-field flow and flame dynamics are examined in depth, with emphasis placed on the flame-stabilization mechanisms. The model accommodates the full conservation laws and real-fluid thermodynamics and transport phenomena over the entire range of fluid states of concern. The injector flowfield is characterized by the evolution of the three mixing layers originating from the trailing edges of the two concentric tubes of the injector. As a consequence of the strong inertia of the oxygen stream and light density of methane, a diffusion-dominated flame is anchored in the wake of the LOX post and propagates downstream along the boundary of the oxygen stream. The large-scale vortices shedding from the outer rim of the LOX postengulf methane into the wake recirculation region to react with gasified oxygen. The frequencies of vortex shedding match closely those of the flow over a rear-facing step, mainly due to the large density disparity between LOX and gaseous methane. The effects of the momentum-flux ratio of the two streams are also examined. A higher-momentum methane stream enhances mixing and shortens the potential cores of both the LOX and methane jets. 相似文献
182.
A theory is presented for the onset of shear thickening in colloidal suspensions of particles, stabilized by an electrostatic
repulsion. Based on an activation model, a critical shear stress can be derived for the onset of shear thickening in dense
suspensions for a constant potential and a constant charge approach of the spheres. Unlike previous models, the total interaction
potential is taken into account (sum of attraction and repulsion). The critical shear stress is related to the maximum of
the total interaction potential scaled by the free volume per particle. A comparison with experimental investigations shows
the applicability of the theory. 相似文献
183.
First of all the deformation is considered of two infinitesimal material line elements lying along vectors M,N emanating from a particle at X in a body. For all M,N lying in a given plane, an identity is derived relating the stretches along M,N and the angles of the pair of infinitesimal material line elements before and after deformation. Then, the deformation is
considered of three non-coplanar infinitesimal material line elements lying along vectors M,N,P emanating from a particle at X in a body. An identity is derived relating the stretches along M,N,P and the angles between the three pairs of infinitesimal material line elements before and after deformation. The identity
is factored leading to easy interpretation. The special case of infinitesimal strain is considered.
相似文献
184.
This paper describes a novel measuring system for investigating the influence of pressure and temperature on the mechanical
properties of time-dependent polymer materials. The system can measure the volume and the shear relaxation moduli of solid
polymer specimens simultaneously subjected to temperatures from −50 to +120°C with a precision of ±0.01°C, and pressures from
atmospheric to 500 MPa with a precision of ±0.1 MPa. The paper demonstrates the measuring capabilities of the apparatus. For
poly(vinyl) acetate (PVAc) are presented sample measurements of the shear relaxation modulus as function of time, pressure
and temperature; specific volume; the bulk creep compliance; the coefficient of thermal expansion; the bulk modulus; and the
pressure drop experiments which simulate conditions to which a material is exposed during the injection molding process. The
shear moduli may be measured in the range from 1 to 4,000 MPa with the relative error of 3%.The error of volumetric measurements
is 0.05%, which corresponds to 0.00005 cm3/g. In all cases results are shown as measured, no additional smoothing or filtering was employed.
This paper is dedicated to Professor Nicholas W. Tschoegl on the occasion of his 87th birthday, for his contributions to the
field of time-dependent bulk properties of polymeric materials. 相似文献
185.
This paper presents an experimental study of vortex-induced-vibration (VIV) of a curved flexible free-hanging cylinder in exponential shear flows. The emphasis is on previously unexplained phenomena in our early research and in some cases offers insights on the mode transition of nonlinear vibration behavior of long flexible cylinders. The experimental results illustrate that the cylinder undergoes multi-frequency response and the dominant frequency varies spatially. The IL and CF response and transition are out-of-sync. In the second (2nd) mode response, the spanwise response exhibits a mixed pattern with standing wave and traveling wave. The contribution of traveling wave becomes greater as the reduced velocity increases. Only two distinct branches of response, namely the initial and lower branches, are observed in each mode. The lower branches of the first (1st) and 2nd modes present the same normalized frequency. A phase jump around 180°occurs at the transition between initial branches and lower branches, accompanying with a switch between 2S 2P or P+S vortex shedding modes. 相似文献
186.
C. W. Lim C. M. Wang S. Kitipornchai 《Archive of Applied Mechanics (Ingenieur Archiv)》1997,67(3):179-190
Summary This paper presents the exact relationships between the deflections and stress resultants of Timoshenko curved beams and
that of the corresponding Euler-Bernoulli curved beams. The curved beams considered are of rectangular cross sections and
constant radius of curvature. They may have any combinations of classical boundary conditions, and are subjected to any loading
distribution that acts normal to the curved beam centreline. These relationships allow engineering designers to directly obtain
the bending solutions of Timoshenko curved beams from the familiar Euler-Bernoulli solutions without having to perform the
more complicated shear deformation analysis.
Accepted for publication 26 July 1996 相似文献
187.
H. Saraf K. T. Ramesh A. M. Lennon A. C. Merkle J. C. Roberts 《Experimental Mechanics》2007,47(3):439-449
Traditionally, Kolsky bars are used to study the dynamic response of hard materials in uniaxial compression, tension or torsion.
We present modifications to the technique that allow loading of a soft tissue specimen in (a) hydrostatic compression and
(b) simple shear. The first modification is designed to determine the pressure vs. volume behavior of each material, and thence
to extract a measure of the dynamic compressibility or equivalently of the bulk modulus. The second modification is designed
to develop the shear stress versus shear strain behavior for a near-simple shear experiment. The critically important questions
of the proper acquisition of human tissue samples and protocols for appropriate experimentation have also been addressed.
The experimental techniques and the results are discussed in detail and the results compared to finite element simulations.
We present examples of the dynamic response of typical tissue simulants as well as human liver and stomach tissues. 相似文献
188.
P. V. Makarov I. Y. Smolin I. P. Prokopinsky 《Theoretical and Applied Fracture Mechanics》1998,29(1):302
Analyzed numerically are the localized strain of polycrystalline materials subjected to quasi-static loading. The objective is to study the peculiarities associated with the deformation process close to the stress concentrators such as holes, notches and interfaces of internal structure. Analytical results show that geometry and/or heterogeneous internal structure of material together with the action of maximum shear result in the development of a system of plastically deformed shear bands. Shears and rotations in the regions of strain localization are found to be higher than in other parts of the specimen while rotations are more sensitive to localization. 相似文献
189.
Experiments were conducted in which multiwalled carbon nanotubes were subjected to uniaxial compression and shell-buckling
loads were measured. A comparison with existing theoretical models shows that the predictions are about 40–50% smaller than
the experimentally measured buckling loads. This is in contrast to the classical elastic shell studies in which the experimental
values were always substantially lower than the predicted values due to imperfection sensitivity. It is proposed that the
discrepancy between the predicted and measured value might be due to imperfections in the multiwalled nanotubes in the form
of sp
3 bonds between the tube walls, which introduce shear coupling between them. An analytical model is presented to estimate the
effect of the shear coupling on the critical buckling strain, which shows that the contribution from shear coupling increases
linearly with the effective shear modulus between the walls. Further, this contribution increases with the number of walls;
the increment from each additional wall progressively decreases. 相似文献
190.
Experimental results concerning the pressure oscillations induced by a grazing flow over a deep cavity like a Helmholtz resonator are presented. The study deals with the forcing of the neck shear layer instability in an opened-loop control scheme by means of pulsed micro-jets. The effects of the frequency and amplitude are investigated. It is found that efficient attenuation of the pressure oscillations can be reached when the forcing frequency is larger than the cavity resonance frequency. Then the shear layer is locked with the forcing and resonance with the cavity is lost, inducing a significant decrease of the acoustic pressure level in the cavity. Effects of the jet amplitude are weak, a very small amplitude being capable of forcing the shear layer. By contrast, when the forcing frequency is lower than the cavity resonance frequency (the forcing wave length is greater than twice the neck length) the forcing is ineffective. 相似文献