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Three physical mechanisms which may affect dispersion of particle's motion in wall-bounded turbulent flows,
including the effects of turbulence, wall roughness in particle-wall collisions, and inter-particle collisions, are numerically investigated in this study.
Parametric studies with different wall roughness extents and with different mass loading ratios of particles are performed in fully developed channel flows with the Eulerian-Lagrangian approach.
A low-Reynolds-number $k-\epsilon$ turbulence model is applied for the solution of the carrier-flow field,
while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion.
It is shown that the mechanism of inter-particle collisions should be taken into account in the modeling except for the flows laden with sufficiently low mass loading ratios of particles.
Influences of wall roughness on particle dispersion due to particle-wall collisions are found to be considerable in the bounded particle-laden flow.
Since the investigated particles are associated with large Stokes numbers, i.e., larger than $\mathcal{O}(1)$, in the test problem,
the effects of turbulence on particle dispersion are much less considerable, as expected, in comparison with another two physical mechanisms investigated in the study. 相似文献
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Nai‐Ning Wang 《Particle & Particle Systems Characterization》2001,18(1):26-32
Based on light scattering theory, an optical method is presented for measuring the concentration and particle size distribution of the dispersed phase in two‐phase flows. A prototype was also constructed. Comprehensive computer simulation and numerical calculations were carried out to calibrate the correctness of this method. An experimental study was also performed in gas–solid and gas–liquid two‐phase flows. The results of the measurements are given and discussed in detail. 相似文献
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Hans‐Joachim Schmid Susanne Veith Heinz Umhauer 《Particle & Particle Systems Characterization》2002,19(3):203-215
An optical measuring technique is presented allowing the exact in‐situ measurement of local particle flux densities in a confined channel flow by counting single particles penetrating an optically well defined measuring volume. This enables a precise flux determination up to the direct vicinity of planar walls. The measurement set‐up and its calibration as well as the whole test facility are described in detail. This measurement technique is used to study the particle transport in electrostatic precipitators. Exemplarily, results of particle flux profiles as well as precipitation, as gained from balances of parts of the precipitator channel, are presented. Furthermore, the possibility to determine particle velocity fluctuations is demonstrated. 相似文献
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An efficient numerical modal calculation method for an axially symmetric optical fiber is presented using a numerical Galerkin's method. By decomposing the transverse electric field of a guided wave with Bessel functions of the first kind in cylindrical polar coordinates, we have shown that dispersion characteristics of an optical fiber can be obtained very easily. In order to illustrate the effectiveness of this suggested method, numerical examples are given for a step index fiber, a W-shape depressed inner cladding fiber, and a dispersion-flattened fiber. 相似文献
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The spray cone emerging during an extended metal atomization process (called spray forming) has been investigated in order to quantify the influence of highly concentrated multiphase flows on phase‐Doppler‐anemometry (PDA) measurements. Using this non‐intrusive, optical measurement technique not only the local particle size and velocity distributions of the spray can be obtained but also additional information about the mass flux in the multiphase flow. Since standard phase‐Doppler systems can be easily applied to low concentrated particle systems (spherical particles with smooth surfaces and an optical transparent continuous phase taken for granted) the application of this measurement technique to highly concentrated multiphase flows is more complex. Both the laser light propagating from the PDA device to the probe volume and the scattered one going backward to the PDA receiving system are disturbed by passing the highly concentrated multiphase flow. The resulting significant loss in signal quality especially concerns the measurement of the smaller particles of the spray because of their reduced silhouette (in comparison with the bigger ones). Thus, the detection of the smallest particles becomes partially impossible leading to measurement of a distorted diameter distribution of the entire particle collective. In this study the distortions of the measured distributions dependent on the particle number concentration as well as on the path length of the laser light are discussed. 相似文献
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改进WKB方法与相移值的修正 总被引:4,自引:0,他引:4
利用非均匀波导的多层分割法,对传统WKB法的相称值进行修正,导出了改进的WKB计算公式,并给出相移修正值的计算公式。对常见的典型折射率剖面(指数型、高斯型、余误差型、截断线型)的数值计算表明,该方法所得公式的精度远高于传统的WKB近似,在接近截止时仍与精确数值十分吻合。 相似文献
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Xiuping Li Jianjun Gao Choi Look Law Sheel Aditya Georg Boeck 《International Journal of Infrared and Millimeter Waves》2003,24(10):1759-1766
An improved on-wafer measurement method by using coaxial calibration instead of on-wafer calibration for PHEMT modeling is proposed in this paper. The advantage is that S-parameters of PHEMT device can be measured on wafer without impedance standard substrate (ISS) after the S-parameters of the microprobes have been determined. Excellent agreement is obtained between on-wafer calibration measurement and coaxial calibration measurements, respectively. 相似文献
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Christof Grüner Wolfgang Kanther Sren Gtz Karl Strauß 《Particle & Particle Systems Characterization》2004,21(3):219-227
The behavior of the particulate phase in a highly turbulent gas flow has been investigated in a vertical channel. Variations of the flow configuration (1. Flow past a cylinder, 2. flow past a wall‐mounted obstacle and 3. flow around a horizontally injected jet) have been subject to both experiments and numerical simulations. The velocity vector field of the solid phase has been measured by digital particle image velocimetry (DPIV). The measurements have been focused on particle‐obstacle collisions and crossflow in the vicinity of the jet nozzle using the lately developed twinpeak detection method. By application of this method regions of highly inhomogeneous particle behavior could be detected mainly upstream of the flow perturbation. Numerical results have been obtained by an Eulerian‐Lagrangian method on boundary‐fitted grids. Particle‐particle interactions as well as interphase exchange of momentum have been taken into account. The simulation results showed to be well in accordance with the experimental results. 相似文献
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This paper presents a numerical method directed towards the simulation of flows with mass transfer due to changes of phase. We use a volume of fluid (VOF) based interface tracking method in conjunction with a mass transfer model and a model for surface tension. The bulk fluids are viscous, conducting, and incompressible. A one-dimensional test problem is developed with the feature that a thin thermal layer propagates with the moving phase interface. This test problem isolates the ability of a method to accurately calculate the thermal layers responsible for driving the mass transfer in boiling flows. The numerical method is tested on this problem and then is used in simulations of horizontal film boiling. 相似文献
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光全散射颗粒测量法中需求解第一类Fredholm积分方程。在不知道被测颗粒的尺寸范围的情况下如何确定积分方程的上下限、即测量范围,迄今仍是个问题。本文针对此问题提出了一种自适应非独立模式算法。该算法可根据双参数颗粒分布函数的分布参数K自动确定积分的上下限.数值模拟和实验都证实了此算法。 相似文献
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The amplitudes of incipient fault signals are similar to health state signals, which increases the difficulty of incipient fault diagnosis. Multi-scale reverse dispersion entropy (MRDE) only considers difference information with low frequency range, which omits relatively obvious fault features with a higher frequency band. It decreases recognition accuracy. To defeat the shortcoming with MRDE and extract the obvious fault features of incipient faults simultaneously, an improved entropy named hierarchical multi-scale reverse dispersion entropy (HMRDE) is proposed to treat incipient fault data. Firstly, the signal is decomposed hierarchically by using the filter smoothing operator and average backward difference operator to obtain hierarchical nodes. The smoothing operator calculates the mean sample value and the average backward difference operator calculates the average deviation of sample values. The more layers, the higher the utilization rate of filter smoothing operator and average backward difference operator. Hierarchical nodes are obtained by these operators, and they can reflect the difference features in different frequency domains. Then, this difference feature is reflected with MRDE values of some hierarchical nodes more obviously. Finally, a variety of classifiers are selected to test the separability of incipient fault signals treated with HMRDE. Furthermore, the recognition accuracy of these classifiers illustrates that HMRDE can effectively deal with the problem that incipient fault signals cannot be easily recognized due to a similar amplitude dynamic. 相似文献
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Peyman Bashi Shahabi Hamid Niazmand Mohammad Reza Modarres Razavi 《Particle & Particle Systems Characterization》2012,29(4):253-262
Exhaust Gas Recirculation (EGR) method has already shown its benefits on controlling NOx emissions in internal combustion engines. An important issue associated with this method is homogeneous cylinder‐to‐cylinder distribution of the recirculating gas. Any maldistribution leads to power reduction and increase of other pollutants, which are strictly limited by recent emission laws. In addition to EGR, these limitations force the engine manufacturers to recycle blowby gases into the cylinders as homogeneous as possible. Since geometrical parameters and injection locations of EGR/blowby have substantial effects on homogenous cylinder‐to‐cylinder distribution of EGR/blowby gases, any developments in identifying the injecting locations with the least EGR/blowby maldistribution are of great practical importance. The existing experimental and numerical methods for evaluating the EGR/blowby maldistribution are based on the injection of air with different temperature or of different gas (mostly CO2) from the main air stream. However, these methods are time consuming due to the large number of possible injection locations. It has been shown that the most uniform distribution cannot be obtained by just a single injection point; therefore, the study of simultaneous injection points becomes inevitable. Clearly, such a study is practically impossible with the present methods. In this research a new method based on particle tracking is proposed, which greatly reduces the time and effort to find the injection locations with the least maldistribution, especially when multiple injections are considered. 相似文献
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In this work the semiclassical potential for plasma particles pair interactions, which takes into account the diffraction effects due to the uncertainty principle in two‐component plasma (the region of temperatures 104K < T < 108K and densities 1021cm–3 < n ≤ 1024cm–3), was proposed. The values of this potential were numerically calculated and an interpolation formula was obtained (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献