共查询到20条相似文献,搜索用时 46 毫秒
1.
Viscous potential flow analysis of Kelvin-Helmholtz instability with heat and mass transfer has been studied. A dispersion relation has been obtained. Stability criterion is given by a critical value of relative velocity. It has been found that heat and mass transfer has destabilizing effect on relative velocity when lower fluid viscosity is low while it has stabilizing effect when lower fluid viscosity is high. Various graphs have been plotted for relative velocity and growth rate. In statically unstable situation viscosity has stabilizing effect while in statically stable situation it has destabilizing effect. 相似文献
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The system for Particle Image Velocimetry (PIV) measurements in the flow with superimposed pulsations of the fluid (air) has been developed. Measurements of velocity and vorticity fields in a smooth duct in certain phases of superimposed pulsations have been performed. Statistics of a turbulent pulsating flow: velocity profiles, turbulent pulsations, and Reynolds stresses has been obtained. 相似文献
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A DGV system using a continuous wave Argon laser and an optical arrangement with a single intensified camera has been set
up at the ISL blow-down supersonic wind tunnel. The first tests have been performed over a 12.5° 2D wedge at a freestream
Mach number of 2. A mean velocity field has been calculated from 28 individual measurements. When compared to the theoretical
velocity distribution, deviations of 8 % to 15 % have been obtained. Preliminary tests have also been performed on a missile-like
model equipped with a lateral jet system. Individual as well as mean velocity fields are presented. 相似文献
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O. A. Novodvorsky O. D. Khramova E. O. Filippova C. Wenzel J. W. Bartha 《Optics and Lasers in Engineering》1999,32(5):449
The laser plasma plume expansion induced by UV nanosecond irradiation from metallic Nb and Ta targets has been studied using Langmuir probe time-of-flight measurements. The ion current shape was measured as a function of the laser radiation flux at various probe-to-target distances. The ion velocity distribution and the ion energy spectra have been determined by measuring the time of flight of ions reaching the Langmuir probe. A multi-mode velocity distribution of ions has been revealed. The dependence of the amplitudes of the plume energy components on the plume scatter time and on the laser radiation flux has been investigated. The experimental time-of-flight data have been compared with a Maxwell velocity distribution. The threshold values of the laser intensity were determined for different distribution modes in the ion energy spectrum. 相似文献
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耐蚀合金Au3Cu高温冷却过程中能量及结构转变的分子动力学模拟 总被引:2,自引:1,他引:1
用分子动学模拟方法对液态Au3Cu冷却过程进行了研究,考察了不同冷却速度下Au3Cu结构变化特点,原子间相互作用势采用F-S多体势,结构分析采用键取向序和对分析技术。计算结果表明,冷却速度对液态Au3Cu能量及结构转变有重要影响,给出了不同冷却速度下液态Au3Cu结构转变的微观信息。 相似文献
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A C Biswas 《Pramana》1988,30(3):L255-L257
It has been shown that when the root-mean-square of the gradient of phase fluctuation exceeds the inverse of the coherence
length a system of superfluid rotating with angular velocity exceeding the critical angular velocity has an instability. 相似文献
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A. I. Frank P. Geltenbort M. Jentschel D. V. Kustov G. V. Kulin A. N. Strepetov 《JETP Letters》2011,93(7):361-365
The results of a new experiment on the observation of the effect of accelerating matter in neutron optics are reported. It has been shown that the velocity of neutrons periodically varies when they pass through a harmonically moving refractive sample. The idea of the experiment is based on time focusing, i.e., on the fact that the periodic modulation of the velocity of neutrons leads to the oscillation of the flux density at the observation point. The magnitude of the effect is in reasonable agreement with the theoretical predictions. The experiment has been carried out with ultracold neutrons and a change of ±1 cm/s has been detected in the neutron velocity. 相似文献
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A new instability predicte by theory to occur in rotating shallow water in which the rotation velocity has a discontinuity, in a regime where the flow velocity exceeds the characteristics velocity of the waves, has been found experimentally. The instability develops when the radial gradient of the angular velocity across the discontinuity is negative; such an instability is likely to be responsible for the formation of the spiral structure in galaxies which have a similar rotational velocity profile. 相似文献
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Phase and group velocities of plane waves may have different directions in a linear and homogeneous medium. This difference may lead to interesting situations such as the phase reversal propagation and the orthogonal phase velocity. Although the former has been analyzed in depth and it has found many applications, the latter has been left as a hypothesis. Actually, due to our best knowledge there is no evidence of such media where the phase velocity is orthogonal to the group velocity. In this paper we discuss this situation thoroughly. We show that a plane wave with orthogonal phase velocity cannot possess linear momentum. Moreover, we show that a plane wave without the linear momentum cannot propagate at all, so the orthogonality of the phase velocity does not take place in reality for electromagnetic plane waves. 相似文献
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The group velocity of gamma radiation scattered in the forward direction by a nuclear lambda scheme experiencing level mixing induced transparency, which shows some similarity to optical EIT, has been investigated. The equations for the nuclear coherences governing the group velocity have been solved. The group velocity decreases with the density of the resonant nuclei and with a decrease in the intensity of the mixing interaction. A comparison between the group velocity of the gamma radiation and the probe radiation in “classical” optical EIT conditions has been made. 相似文献
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A theory of the excitation of surface waves by a fast charged particle moving in a thin homogeneous metal film surrounded
by a dielectric medium has been proposed. The Cherenkov effect for the surface waves has been shown to occur at the velocity
of particles one or two orders of magnitude lower than the respective velocity in a homogeneous medium. 相似文献
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Maxwell’s equations for an electromagnetic field propagating in an array of carbon nanotubes have been considered in the case when the velocity of the incident pulse is greater than the speed of light in the medium. The equation for the vector potential of the electromagnetic field has been derived and solved numerically. The dependence of the pulse on its velocity at the entrance to the array of carbon nanotubes has been revealed. 相似文献
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本文对垂直低温两相流管底部液氮汽泡的上升速度运用高速摄像机进行了可视化实验研究,对所采集的实时图像进行处理.在Cole和Mendelson汽泡上升速度经验公式的基础上,通过对液氮汽泡的上升速度的分析,提出了圆管管路底部液氮汽泡的上升速度的拟合公式,分析研究其变化规律,为进一步探求圆管内液氮弹状汽泡的生成机理提供依据. 相似文献
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The problem about the average velocity of electrons in the cathode fall region of a glow discharge during nitriding has been solved theoretically and verified experimentally. The technique and analytical apparatus for practical calculations of the average electron velocity have been presented. 相似文献
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The problem of determining the nonstationary nonlinear velocity field of a viscous incompressible liquid excited by the surface of tangentially vibrating cylinder has been solved numerically in the 2D approximation. It has been shown that the vibrating solid surface generates 2D viscous waves and a displacement flow. The trajectories of propagation of viscous waves and their velocities have been determined. The interaction of a viscous wave with the displacement flow has been analyzed in the first approximation; as a result of this interaction, the velocity field can not only be suppressed with increasing distance from the surface, but also enhanced. 相似文献
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Local variation in surface skimming longitudinal wave (SSLW) velocity has been measured using a scanning acoustic microscope. A very narrow width electrical impulse has been used to excite the transducer of the acoustic lens. This permits the separation of the SSLW signal from the direct reflected signal in the time domain. A simple method of measuring the time delay between the directly reflected signal and the SSLW signal at two defocuses has been utilized for the local measurement of SSLW velocity. The variation in the SSLW velocity measured over an area of the sample is scaled and presented as an image. The method has been implemented to image the variation of the SSLW velocity around a crack tip in a sample of Ti-6Al-4V. Since the SSLW velocity is known to change linearly with the stress, the SSLW velocity image is considered as a representation of the image of stress around the crack tip. Local stress variation in the same region of the crack tip is directly measured using x-ray diffraction. The SSLW velocity image is compared with the x-ray diffraction stress image. The contrast in the two images, spatial resolution, and the penetration depth into the sample of acoustic waves and x rays are discussed. 相似文献
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A calculation has been carried out for the drift velocity of electrons in the highfield region under the condition of impact ionization in III–V semiconductor compounds.The energy-balance equation of the one-electron model has been solved considering alloy scattering and carrier-carrier interaction, in addition to optical phonon and ionization scattering. Fairly good agreement is obtained for GaAs with the available experimental and Monte-Carlo results. Graphs for the high-field drift velocity has also been plotted for Ga1–x
InxAs (x = 0.53) at different ratios of ionization mean-free path and optical phonon mean-free path. The plot of high-field drift velocity versus ionization rate reveals that the high-field drift velocity strongly depends on the ionization rate of carriers, and vice versa. 相似文献
20.
Spray characteristics and their spatial distribution have been investigated experimentally for sprays generated by the breakup of thin liquid sheets in co‐flowing air streams. The spray characteristics such as droplet mean and fluctuation velocity and Sauter mean diameter have been measured by using phase Doppler anemometry under various liquid and air flow conditions at the nozzle exit. The results show that at a given spray cross section the droplet axial mean velocity has a maximum value at the spray center, and decreases towards the edge of the spray; whereas the Sauter mean diameter has a minimum value at the center and increases monotonically towards the spray periphery. Data analysis indicates that sufficiently downstream of the nozzle exit the droplet mean velocity attains a jet‐like self‐similar distribution in the transverse direction, and such universal distribution is also observed for the turbulent fluctuation velocity and turbulent intensity, although it is achieved further downstream compared to the mean velocity profile. The Sauter mean diameter at the spray center has a complex variation in the downstream direction due to secondary atomization at high air velocity near the nozzle exit and droplet entrainment, migration and possible coalescence farther downstream. 相似文献