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1.
Lattice Boltzmann method was used to numerically investigate the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio. The transient impulse model of 3D collisions between particles and between particle and wall is proposed. The numerical results are qualitatively in agreement with and quantitatively comparable to the experiment data. The results show that the increases of both the cylindrical particle to pipe size ratio and the particle aspect ratio decrease the rotation about all axes. All rotations of cubic particles decrease with increasing the particle concentration. The cubic particles, rotating more drastically in the flow with large Reynolds number, rotate faster than the cylindrical particles with the same size. The cylindrical particles align with the flow direction more obviously with decreasing Reynolds numbers. However, the orientations of cubic particles are spread all over the range with no significant difference in magnitude, and the Reynolds numbers have no obvious effect on the orientations of cubic particles. 相似文献
2.
纤维滤料新模型的阻力数值模拟研究 总被引：1，自引：0，他引：1
利用流体力学开源代码OpenFOAM验证了单圆柱体周围的流体特性（包括流型和阻力）,表明Open-FOAM能够用于模拟低Re数流,并发现Shaw的解析解是斯托克斯悖论的一种解.通过对纤维滤料进行试验以及对Tronville-Rivers二维纤维随机分布滤料新模型的阻力特性进行数值模拟,发现Kuwabara模型比Hap-pel模型更能精确预测纤维滤料的阻力,而且试验阻力值介于纤维表面为无滑移和全滑移边界条件下的数值模拟值之间. 相似文献
3.
INTRODUCTIONPlanewakeflowisonetypeoffreeshearflowandexistswidelyinnatureandmanyengi neeringsystems.Tounderstandthekineticchar acterofthelarge scalecoherentvortexstructuresandparticledispersioninplanewakeflowishelpfulforimprovingmanyprocessesinenergyengineering,chemicalengineeringandmaterialengineering .LargeeddysimulationinvolvesbothdirectsimulationandReynolds averagedapproaches.MethodshavebeendevelopedinrecentyearstosolvetheproblemofinstantaneousgasflowfieldandtosimulatehighReynoldsnumb… 相似文献
4.
INTRODUCTION Turbulent gas-particle flows are frequently found in natural phenomena and industrial processes.Cases of cylinders in cross flows with particles occur in heat exchange equipment,including the convective zone of a fluidized-bed combustor,and in the primary superheaters,reheaters,and economizers of coal-fired boilers.Coherent structures often occur in the above-mentioned gas-particle flow,and have great effect on such different systems,while some features of tur-bulent multiphas… 相似文献
5.
To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particle-laden wake flow. The well-known Sub-grid Scale mode introduced by Smagorinsky was employed to simulate the gas flow field and Lagrangian approach was used to trace the particles. The results showed that the typical large-scale vortex structures exhibit a stable counter rotating arrangement of opposite sign, and alternately form from the near wall region, shed and move towards the downstream positions of the wake with the development of the flow. For particle dispersion, the Stokes number of particles is a key parameter. At the Stokes numbers of 1.4 and 3.8 the particles concentrate highly in the outer boundary regions. While the particles congregate densely in the vortex core regions at the Stokes number of 0.15, and the particles at Stokes number of 15 assemble in the vortex braid regions and the rib regions between the adjoining vortex structures. 相似文献
6.
Gas-solid two-phase turbulent plane jet is applied to many natural situations and in engineering systems. To predict the particle
dispersion in the gas jet is of great importance in industrial applications and in the designing of engineering systems. A
large eddy simulation of the two-phase plane jet was conducted to investigate the particle dispersion patterns. The particles
with Stokes numbers equal to 0.0028, 0.3, 2.5, 28 (corresponding to particle diameter 1 μm, 10μm, 30μm, 100μm, respectively)
inRe=11 300 gas flow were studied. The simulation results of gas phase motion agreed well with previous experimental results.
And the simulation results of the solid particles motion showed that particles with different Stokes number have different
spatial dispersion; and that particles with intermediate Stokes number have the largest dispersion ratio.
Project (No. G19990222) supported by the Special Funds for Major State Basic Research of China 相似文献
7.
WAN Zhan-hong SUN Zhi-lin YOU Zhen-jiang 《浙江大学学报(A卷英文版)》2007,8(9):1435-1442
The linear stability of fiber suspensions between two concentric cylinders rotating independently is studied. The modified stability equation is obtained based on the fiber orientation model and Hinch-Leal closure approximation. The primary instabilities and bicritical curves have been calculated numerically. The critical Reynolds number,wavenumber and wave speeds of fiber suspensions as functions of the aspect ratio,volume concentration of the fibers and the gap width of cylinders are obtained. 相似文献
8.
Fu-you Tian Lian-feng Huang Li-wu Fan Hong-liang Qian Jia-xi Gu Zi-tao Yu Ya-cai Hu Jian Ge Ke-fa Cen 《浙江大学学报(A卷英文版)》2016,17(2):89-100
The pressure drop over a packed bed with sintered ore particles was studied experimentally. The sintered ore particles were characterized to determine their equivalent particle diameter, bed voidage, and sphericity. The pressure drop experiments were performed on unsorted and sieved particles with various size distributions for a superficial velocity up to 2.4 m/s, covering flow regimes from laminar to turbulent. It was shown that the Ergun equation underestimates the pressure drop for such highly irregular-shaped particles by about 40%. The measured modified friction factor was well correlated to a scaled Ergun equation, which was verified to be valid for the modified particle Reynolds number up to 12 000 toward design and optimization of vertically arranged sinter coolers for waste heat recovery. 相似文献
9.
A micro-sized tube heat exchanger(MTHE) was fabricated, and its performance in heat transfer and pressure drop was experimentally studied. The single-phase forced convection heat transfer correlation on the sides of the MTHE tubes was proposed and compared with previous experimental data in the Reynolds number range of 500—1 800. The average deviation of the correlation in calculating the Nusselt number was about 6.59%. The entrance effect in the thermal entrance region was discussed. In the same range of Reynolds number, the pressure drop and friction coefficient were found to be considerably higher than those predicted by the conventional correlations. The product of friction factor and Reynolds number was also a constant, but much higher than the conventional. 相似文献
10.
Given the definition of the reference Knudsen number for micro gas journal bearings, the range in the number is related to the viscosity of air at different temperatures. A modified Reynolds equation for micro gas journal bearings based on Burgdorfer＇s first-order slip boundary condition is proposed that takes into account the gas rarefaction effect. The finite difference method （FDM） is adopted to solve the modified Reynolds equation to obtain the pressure profiles, load capacities and attitude angles for micro gas journal bearings at different reference K_nudsen numbers, bearing numbers and journal eccentricity ratios. Numerical analysis shows that pressure profiles and non-dimensional load capacities decrease markedly as gas rarefaction increases. Attitude angles change conversely, and when the eccentricity ratio is less than 0.6, the attitude angles rise slightly and the influence of the reference Knudsen number is not marked. In addition, the effect of gas rarefaction on the non-dimensional load capacity and attitude angle decreases with smaller bearing numbers. 相似文献
11.
Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized
bed process, pneumatic conveying process, chemical process, drying process, etc. This paper focuses on the influence of the
presence of particles on the heat transfer between a tube and gas-solid suspension. The presence of particles causes positive
enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the
case of very low solid loading ratio (M
s of less than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle size and flow Reynolds number
was derived from experimental data. In addition, thek-∈ two-equation model and the Fluctuation-Spectrum-Random-Trajectory Model (FSRT Model) are used to simulate the flow field
and heat transfer of the gasphase and the solid-phase, respectively. Through coupling of the two phases the model can predict
the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement
due to particles loading the model predictions agreed well with experimental data.
Project supported by National Natural Science Foundation for Distinguished Young Scholars (No. 50025618) 相似文献
12.
作者从前文 [ ]已得到的脉动流速微分方程 [10 ]出发 ,对于粘性二元平行流动这一类流动模式 ,进行分析、研究并得到了脉动尺度、脉动流速及雷诺应力的物理方程。在封闭的条件下 ,求解了所设定流动模式下的雷诺方程 ,解析得到沿边界法线方向的流速分布公式。希望本文的工作对湍流的半经验理论的理性化进展有所帮助。 相似文献
13.
推导了两光滑平板间干气密封微尺度流动场的非线性雷诺方程,应用PH线性化方法、迭代法对非线性雷诺方程近似求解,得到气膜压力的近似解析式;利用极坐标下的流线方程,通过Maple程序求解压力方程和流线方程得到流线,此流线就是符合条件的拟合曲线。对拟合曲线槽干气密封气膜刚度进行计算与测试,并与螺旋槽进行比较。研究结果表明：在相同工况下,拟合曲线槽干气密封气膜刚度比螺旋槽大,且气膜刚度比螺旋槽稳定,这在工程实践中具有重要意义和应用价值。 相似文献
14.
In this paper, the characteristics of two-dimensional viscous flow over two dams were numerically investigated. The results show that the behavior of the vortices is closely related to the space between two dams, water depth, Fr number and Reynolds number. In addition, the flow properties behind each dam are different, and the changes over two dams are more complex than over one dam. Finally, the relevant turbulent characteristics were analyzed. 相似文献
15.
We presented a numerical examination of the effect of microtexturing negative rings’ structure on the tribological performance of parallel bearing couples’ cell. Three mcirotexturing rings, which are circle, square and ellipse, were chosen and the analysis model were established. We used the Reynolds equation coupled with finite difference method and successive over relaxation Gauss-Seidel iterative method to solve the Newtonian flow’s hydrodynamics within a bearing couple. The effect of texture density and radius ratio (thickness) of the microtexturing rings were investigated on the tribological performance under the similar operating conditions. The numerical simulation reveals that: 1) The microtexturing rings’ structure can homogenize the local pressure much uniformly within the bearing cell. 2) The tribological performance is determined mainly by the microtexturing rings’ geometry and texture density, and the thickness of the rings’ structure can help to change the quantitative values. 3) The square and circle rings’s microtexturing surface can slightly improve the frictional performance with the bearing cells’ gap, while the ellipse ring’s surface may decrease the frictional performance. 4) The ellipse rings’ microtexturing surface can achieve the minimum spacing gap but the maximum friction coefficient of the bearing couple, and then the circle and square rings’ structure take the second and third place, respectively 相似文献
16.
Car following model is one of microscopic models for describing traffic flow. Through linear stability analysis, the neutral stability lines and the critical points are obtained for the different types of car following models and two modified models. The singular perturbation method has been used to derive various nonlinear wave equations, such as the Korteweg-de-Vries (KdV) equation and the modified Korteweg-de-Vries (mKdV) equation, which could describe different density waves occurring in traffic flows under certain conditions. These density waves are mainly employed to depict the formation of traffic jams in the congested traffic flow. The general soliton solutions are given for the different types of car following models, and the results have been used to the modified models efficiently. 相似文献
17.
New numerical solution for self-acting gas journal bearings 总被引：1，自引：0，他引：1
Taking a small pressure change in the gas film of self-acting gas-lubricated journal bearings into account, the corresponding nonlinear Reynolds equation is linearized through appropriate approximation and a modified Reynolds equation is derived and solved by means of the finite difference method （FDM）. The gas film pressure distribution of a self-acting gas-lubricated journal bearing is attained and the load capacity is calculated. The numerical solution has a better agreement with experimental data than a direct numerical solution for different values of the bearing number. It is of interest to note that the eccentricity ratio, at which the new numerical solution is in better agreement with experimental data, is different when the bearing number is changing. The new numerical solution is slightly larger when the eccentricity ratio is smaller, and becomes slightly smaller when the eccentricity ratio is larger. 相似文献
18.
In this paper, the hydrodynamically generated noise by the flow over an open cavity is studied. First, aeroacoustic theories
and computational aeroacoustic (CAA) methodologies are reviewed in light of hydrodynamic acoustics, based on which, a hybrid
method is presented. In the coupling procedure, the unsteady cavity flow field is computed using large-eddy simulation (LES),
while the radiated sound is calculated by the Ffowcs Williams-Hawkings (FW-H) acoustic analogy with acoustic source terms
extracted from the time-dependent solutions of the unsteady flow. The hybrid LES-FW-H acoustic analogy method is tested with
an open cavity flow at Mach number of 0.006 and Reynolds number of 105. Following the reflection theorem of Powell, the contributions from different source terms are quantified, and the terms
involving wall-pressure fluctuations are found to account for most of the radiated intensity. The radiation field is investigated
in the frequency domain. For the longitudinal direction, the sound propagates with a dominant radiation downstream the cavity
in the near-field and a flatter directivity in the far-field, while for the spanwise direction, the acoustic waves have a
similar propagation along +z and −z directions, with no visible directivity. 相似文献
19.
The lattice Boltzmann method (LBM) is employed to simulate the uniform flow past a circular cylinder. The performance of the two-dimensional LBM model on the prediction of force coefficients and vortex shedding frequency is investigated. The local grid refinement technique and second-order boundary condition for curved walls are applied in the calculations. It is found that the calculated vortex shedding frequency, drag coefficient and lift coefficient are consistent with experimental results at Reynolds nu... 相似文献
20.
In this paper, to study the characteristics of the flow in a laminar regime, an immersed boundary-lattice Boltzmann flux solver (IB-LBFS) is applied to numerically simulate the unsteady viscous flows around two fixed and rotating circular cylinders in side-by-side arrangement. This method applies finite volume discretization to solve the macroscopic governing equations with the flow variables defined at cell centers. At the cell interface, numerical fluxes are physically evaluated by a local lattice Boltzmann solution. In addition, the no-slip boundary condition is accurately imposed by using the implicit boundary condition-enforced immersed boundary method. Due to the simplicity and high efficiency of IB-LBFS on non-uniform grids, it is suitable for simulating fluid flows with complex geometries and moving boundaries. Firstly, numerical simulations of laminar flow past two side-by-side cylinder are performed with different gap spacings at Reynolds numbers of 100 and 200. The simulation results show that a small gap spacing induces a biased flow and forms an irregular big wake behind two cylinders at a low Reynolds number. As the gap spacing increases, an in-phase or anti-phase flow is observed. Then, the effects of the main important parameters on flow characteristics are analyzed for flow past two side-by-side rotating cylinders, including the rotational speed, Reynolds number, and gap spacing. As the rotational speed is increased, the numerical results illustrate that unsteady wakes are suppressed and the flow becomes steady. As the gap spacing is increased, two separate vortex streets behind each cylinder are formed with a definite phase relationship and single shedding frequency. 相似文献