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21.
The low Reynolds number turbulent flow and mixing in a confined impinging jet reactor 总被引:1,自引:0,他引:1
Florian Schwertfirm Johannes Gradl Hans C. Schwarzer Wolfgang Peukert Michael Manhart 《International Journal of Heat and Fluid Flow》2007,28(6):1429-1442
Turbulent mixing takes an important role in chemical engineering, especially when the chemical reaction is fast compared to the mixing time. In this context a detailed knowledge of the flow field, the distribution of turbulent kinetic energy (TKE) and its dissipation rate is important, as these quantities are used for many mixing models. For this reason we conduct a direct numerical simulation (DNS) of a confined impinging jet reactor (CIJR) at Re = 500 and Sc = 1. The data is compared with particle image velocimetry (PIV) measurements and the basic flow features match between simulation and experiment. The DNS data is analysed and it is shown that the flow is dominated by a stable vortex in the main mixing duct. High intensities of turbulent kinetic energy and dissipation are found in the impingement zone which decrease rapidly towards the exit of the CIJR. In the whole CIJR the turbulence is not in equilibrium. The strong mixing in the impingement zone leads to a rapid development of a monomodal PDF. Due to the special properties of the flow field, a bimodal PDF is generated in cross-sections downstream the impingement zone, that slowly relaxes under relaminarising conditions. The time required for meso-mixing is dominating the overall mixing performance. 相似文献
22.
As alternative to the usual assumptions of Boussinesq, we propose, for heated gases, a new approximation called polytropic approximation. With this approximation the quantities of corresponding state are related by a polytropic law of exponent χ of which we neglect the variability in space-time derivations in the equations governing the flow considered. As application, we used this new proposition to solve numerically a heated gas flow in an annular cavity of rotor-stator type. We expose here the numerical method and some results of the polytropic approximation with comparison to results of Boussinesq approximations. To cite this article: S. Benjeddou et al., C. R. Mecanique 332 (2003). 相似文献
23.
The mechanical behaviour of the upper layers of a sandy loam soil was studied under standard triaxial compression and direct shear box tests. Variations of soil material properties were investigated at four different initial dry bulk densities of 1410, 1520, 1610 and 1670 kg/m3. Soil deformation and volume change under the triaxial compression loading were also studied at these bulk densities. Results from the two tests showed increases in the soil mechanical properties with the initial dry bulk density. The internal friction angle values measured with the triaxial compression apparatus exceeded those measured with the direct shear box. In contrast, the soil cohesion values measured with the direct shear box exceeded those measured with the triaxial compression apparatus. Under the triaxial compression test, the loose soil samples underwent contraction and volume reduction, whereas the dense samples swelled and failure cracks appeared clearly at various planes. The soil contraction for the former case characterizes the occurrence of soil compaction, whereas the cracks propagation and volume increase in the latter case characterizes the breaking up and loosening of soil during tillage operations. For the loose and moderately compacted states, the engineering Poisson's ratio increased with the axial strain until loading was completed. It also increased at the compacted and very compacted states until reaching given loading stages, after which its value started to decrease. This shifting in the engineering Poisson's ratio during loading may provide another identification of the moment of soil failure occurrence, in addition to that of the maximum shear stress. 相似文献
24.
Qing Cao Kausik Sarkar Ajay K. Prasad 《International Journal of Multiphase Flow》2004,30(12):1485-1508
Two-dimensional simulations of flow instability at the interface of a two-layer, density-matched, viscosity-stratified Poiseuille flow are performed using a front-tracking/finite difference method. We present results for the small-amplitude (linear) growth rate of the instability at small to medium Reynolds number for varying thickness ratio n, viscosity ratio m, and wavenumber. We also present results for large-amplitude non-linear evolution of the interface for varying viscosity ratio and interfacial tension. For the linear case, the interfacial mode is neutrally stable for as predicted by analysis. The growth rate is proportional to Reynolds number for small Re, and increases with viscosity ratio. The growth rate also increases when the thickness of the more viscous layer is reduced. Strong non-linear behavior is observed for relatively large initial perturbation amplitude. The higher viscosity fluid is drawn out as a finger that penetrates into the lower viscosity layer. The simulated interface shape compares well with previously reported experiments. Increasing interfacial tension retards the growth rate of the interface as expected, whereas increasing the viscosity ratio enhances it. Drop formation at the small Reynolds number considered in this study is precluded by the two-dimensional nature of the calculations. 相似文献
25.
26.
在选矿车间的狭小范围内,用控爆技术拆除大型构筑物的基础是一大难题。本文针对大型设备基础的爆破实践,简述了复杂环境下控爆拆除方案及使用不同爆破参数和装药结构的设计,并对预裂切割爆破的特点及爆破效果进行了评述。 相似文献
27.
In this paper, the direct method is used to find the first integrals and two new solvable cases of the Euler–Poisson equations are given. 相似文献
28.
Zhu?He Zhaohui?LiuEmail author Sheng?Chen Lei?Weng Chuguang?Zheng 《Acta Mechanica Sinica》2005,21(2):112-120
Direct numerical simulations were conducted to investigate the behavior of heavy particles in homogeneous isotropic turbulence. The present study focused on the effect of particle inertia and drift on the autocorrelations of the particle velocity and the fluid seen by particles and the dispersion characteristics of particles. The Lagrangian integral time scale of particles monotonically increased as the magnitude of the particle response time increased, while that of the fluid seen by particles remained relatively constant; it reached a maximum when the particle response time was close to the Kolmolgorov time scale of the flow. Particle dispersion increased as the particle inertia increased for small particles, while for larger particles, it decreased as particle inertia increased; particle eddy diffusion coefficient was maximal, and greater than that of the fluid by about 30%, at the preferential concentration. The concentration field of the particles with τp/τk≈1.0 showed that particles tend to collect in regions of low vorticity (high strain) due to preferential concentration. As the drift velocity of a particle is increased it crosses the paths of fluid elements more rapidly and will tend to lose correlation with its previous velocity faster than a fluid element will. And the correlation of particle velocities along the drift direction is more persistent than that perpendicular to the direction of drift. Simulations also showed that the continuity effect and the crossing-trajectory effect are weakened for particles with infinite inertia. 相似文献
29.
爆炸荷载作用下钢筋混凝土梁的动力响应及破坏形态分析 总被引:15,自引:0,他引:15
对基于Timoshenko梁理论建立的非线性动力有限元法作了改进。根据压区理论得到混凝土的平均剪应力和平均剪应变关系,建立了能反映箍筋的抗剪作用的材料模型;此外,对结构在爆炸荷载作用下可能出现的各种响应现象进行了描述,以准确地预测梁破坏时不同位置截面上钢筋和混凝土的受力、变形及破坏情况。应用改进的材料模型,对爆炸荷载作用下的五个钢筋混凝土试验梁的动力响应和破坏形态进行了数值模拟,结果表明,该数值方法能较好地模拟钢筋混凝土梁的弯曲、弯剪和剪切等破坏形态。 相似文献
30.
Direct simulations of macromolecular fluids are carried out for flows between parallel plates and in expanding and contracting channels. The macromolecules are modeled as FENE dumbbells with soft disks or Lennard-Jones dumbbell-dumbbell interactions. The results are presented in terms of profiles and contour plots of velocity, pressure, temperature, density, and flow fields. In addition the data for potential energy, shear stress, and the normal components of the stress tensor are collected. In general, an excellent agreement is found between the simulated profiles and the well-known flow structures, such as flow separation and formation of viscous eddies, indicating that micro-hydrodynamics is a viable tool in linking macroscopic phenomena with the underlying physical mechanisms. The simulations are performed in the Newtonian regime, for medium-size systems comprising up to 3888 dumbbells. This number is sufficiently large to control boundary and particle number effects. The flow is induced by gravity. The traditional stochastic (thermal) and periodic boundary conditions are employed. Also, diffusive boundary conditions, which could include a stagnant fluid layer and repulsive potential walls, are developed. The scaling problems, which are related to the application of a large external force in a microscopic system (of the size of the order 100 Å), result in extreme pressure and temperature gradients. In addition, the viscosity and thermal conductivity coefficients obtained from velocity and temperature profiles of the channel flow are presented. These results are confirmed independently from modeling of Couette flow by the SLLOD equations of motion and from the Evans algorithm for thermal conductivity. 相似文献