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基于Smagorinsky涡黏模型以及颗粒动理学理论,建立了气固两相流双大涡模拟模型。考虑大涡模拟中过滤尺度的影响,给出颗粒相亚格子压力和热传导系数计算模型。考虑颗粒聚团对两相作用的影响,给出了考虑颗粒聚团作用的气固两相多尺度曳力系数模型。数值模拟了提升管内气固两相流动特性,合理地预测出了提升管内气固两相环-核流动结构。模拟结果与Knowlton等实测结果相吻合。 相似文献
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本文采用双流体模型,引入颗粒动力学理论,对提升管内的稠密气粒两相流动进行了大涡模拟。采用改进的分步投影法对滤波后的方程进行显式求解,小尺度量采用Smagorinsky亚格子模式模拟。模拟结果给出的颗粒相速度分布、浓度分布与实验值基本吻合,气固两相存在速度滑移。模拟结果合理预报出了提升管内的环-核流动结构。 相似文献
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给出求解双向耦合可压缩气固两相流的间断有限元方法,对所得到的气固两相流方程组不需要采用分裂的方法离散,对气相、颗粒相方程及其对流部分和源项可以统一处理,两相都采用基于近似Riemann解的数值通量.数值模拟低压含尘激波管内的两相非平衡流动,并与平衡流、冻结流的结果进行比较.分析颗粒相的存在对气体运动的影响,及激波后松弛区域内两相间相互作用规律.发现颗粒质量比决定两相平衡后的最终状态,而颗粒直径决定两相流从非平衡到平衡的过渡过程,即不同尺寸颗粒对应的驰豫时间、松弛距离不同.结果表明:本文提出的计算方法对求解可压缩气固两相流是可行的,为研究复杂的气固两相流动问题奠定了基础. 相似文献
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A three-dimensional numerical framework is presented that examines the burning of aluminized solid propellants. The numerical solver accounts for heat conduction in the solid, combustion in the gas phase, and coupling of these by means of a level set method. The aluminium particles are treated as heat conducting solid spheres. The aluminium particle detachment process is modelled using level sets, but once the particle becomes free from the surface, its subsequent motion in the gas phase is governed by particle dynamics. Some preliminary calculations of the three-dimensional combustion field supported by a pack with embedded aluminium particles are presented. 相似文献
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A multiscale hybrid method for coupling the direct simulation Monte Carlo (DSMC) method to the nonequilibrium molecular dynamics (NEMD) method is introduced. The method addresses Knudsen layer type gas flows within a few mean free paths of an interface or about an object with dimensions of the order of a few mean free paths. It employs the NEMD method to resolve nanoscale phenomena closest to the interface along with coupled DSMC simulation of the remainder of the Knudsen layer. The hybrid DSMC/NEMD method is a particle based algorithm without a buffer zone. It incorporates a new, modified generalized soft sphere (MGSS) molecular collision model to improve the poor computational efficiency of the traditional generalized soft sphere GSS model and to achieve DSMC compatibility with Lennard-Jones NEMD molecular interactions. An equilibrium gas, a Fourier thermal flow, and an oscillatory Couette flow, are simulated to validate the method. The method shows good agreement with Maxwell–Boltzmann theory for the equilibrium system, Chapman–Enskog theory for Fourier flow, and pure DSMC simulations for oscillatory Couette flow. Speedup in CPU time of the hybrid solver is benchmarked against a pure NEMD solver baseline for different system sizes and solver domain partitions. Finally, the hybrid method is applied to investigate interaction of argon gas with solid surface molecules in a parametric study of the influence of wetting effects and solid molecular mass on energy transfer and thermal accommodation coefficients. It is determined that wetting effect strength and solid molecular mass have a significant impact on the energy transfer between gas and solid phases and thermal accommodation coefficient. 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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We describe a numerical method for modeling temperature-dependent fluid flow coupled to heat transfer in solids. This approach to conjugate heat transfer can be used to compute transient and steady state solutions to a wide range of fluid–solid systems in complex two- and three-dimensional geometry. Fluids are modeled with the temperature-dependent incompressible Navier–Stokes equations using the Boussinesq approximation. Solids with heat transfer are modeled with the heat equation. Appropriate interface equations are applied to couple the solutions across different domains. The computational region is divided into a number of sub-domains corresponding to fluid domains and solid domains. There may be multiple fluid domains and multiple solid domains. Each fluid or solid sub-domain is discretized with an overlapping grid. The entire region is associated with a composite grid which is the union of the overlapping grids for the sub-domains. A different physics solver (fluid solver or solid solver) is associated with each sub-domain. A higher-level multi-domain solver manages the entire solution process. 相似文献
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Wei-Xi Huang Cheong Bong Chang Hyung Jin Sung 《Journal of computational physics》2011,230(12):5061-5079
An improved penalty immersed boundary (pIB) method has been proposed for simulation of fluid–flexible body interaction problems. In the proposed method, the fluid motion is defined on the Eulerian domain, while the solid motion is described by the Lagrangian variables. To account for the interaction, the flexible body is assumed to be composed of two parts: massive material points and massless material points, which are assumed to be linked closely by a stiff spring with damping. The massive material points are subjected to the elastic force of solid deformation but do not interact with the fluid directly, while the massless material points interact with the fluid by moving with the local fluid velocity. The flow solver and the solid solver are coupled in this framework and are developed separately by different methods. The fractional step method is adopted to solve the incompressible fluid motion on a staggered Cartesian grid, while the finite element method is developed to simulate the solid motion using an unstructured triangular mesh. The interaction force is just the restoring force of the stiff spring with damping, and is spread from the Lagrangian coordinates to the Eulerian grids by a smoothed approximation of the Dirac delta function. In the numerical simulations, we first validate the solid solver by using a vibrating circular ring in vacuum, and a second-order spatial accuracy is observed. Then both two- and three-dimensional simulations of fluid–flexible body interaction are carried out, including a circular disk in a linear shear flow, an elastic circular disk moving through a constricted channel, a spherical capsule in a linear shear flow, and a windsock in a uniform flow. The spatial accuracy is shown to be between first-order and second-order for both the fluid velocities and the solid positions. Comparisons between the numerical results and the theoretical solutions are also presented. 相似文献
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A second-order hybrid level set-volume constraint method (HLSVC) for numerically simulating deforming boundaries is presented. We combine the HLSVC interface advection algorithm with a two phase flow solver in order to numerically capture deforming bubbles and drops whose actual volume (s) fluctuate about fixed “target” volume (s). Three novel developments are described: (1) a new method for enforcing a volume constraint in which the number of bubbles and drops can change due to merging or splitting, (2) a new, second order, semi-lagrangian narrow band level set reinitialization algorithm, and (3) validation of a two-phase flow numerical method by comparison with linear stability analysis results for a co-flowing liquid jet in gas. The new interface capturing method is tested on benchmark problems in which the velocity is prescribed (passive advection of interfaces) and in which the velocity is determined by the incompressible Navier–Stokes equations for two-phase flow. The error in interface position when using the hybrid level set-volume constraint method is reported for many benchmark problems in polar coordinates, cylindrical coordinates, and on an adaptive grid in which one criteria of adaptivity is the magnitude of the interface curvature. 相似文献
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Hesameddin Fatehi Mário Costa Xue-Song Bai 《Proceedings of the Combustion Institute》2021,38(3):3909-3917
In this paper, the interaction between different organic and inorganic K/S/Cl compounds in the solid structure of biomass is studied and a model is presented to predict the temporal release of Kg, HCl, CH3Cl, KCl, KOH, K2SO4 and SO2 from biomass devolatilization. Four types of pulverized biomass are chosen from literature, two of which have no chlorine content and two with chlorine content in lower stoichiometry to potassium. The results of the model are compared with the experimental measurements. In the presence of chlorine, KCl, HCl and Kg were found to be the dominant chlorine and potassium species. In the absence of chlorine, Kg dominates the release of potassium. KOH and K2SO4 release into the gas phase towards the end of devolatilization due to the overlapping with char combustion. SO2 is the main sulfur species released into the gas phase. The model is coupled with a CFD solver where the gas phase chemistry of the K/S/Cl system can be studied using available chemical mechanisms for these species. 相似文献
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Jean-Fran?ois Lemieux Bruno Tremblay Jan Sedlá?ek Paul Tupper Stephen Thomas David Huard Jean-Pierre Auclair 《Journal of computational physics》2010,229(8):2840-2852
We have implemented the Jacobian-free Newton–Krylov (JFNK) method to solve the sea ice momentum equation with a viscous-plastic (VP) formulation. The JFNK method has many advantages: the system matrix (the Jacobian) does not need to be formed and stored, the method is parallelizable and the convergence can be nearly quadratic in the vicinity of the solution. The convergence rate of our JFNK implementation is characterized by two phases: an initial phase with slow convergence and a fast phase for which the residual norm decreases significantly from one Newton iteration to the next. Because of this fast phase, the computational gain of the JFNK method over the standard solver used in existing VP models increases with the required drop in the residual norm (termination criterion). The JFNK method is between 3 and 6.6 times faster (depending on the spatial resolution and termination criterion) than the standard solver using a preconditioned generalized minimum residual method. Resolutions tested in this study are 80, 40, 20 and 10 km. For a large required drop in the residual norm, both JFNK and standard solvers sometimes do not converge. The failure rate for both solvers increases as the grid is refined but stays relatively small (less than 2.3% of failures). With increasing spatial resolution, the velocity gradients (sea ice deformations) get more and more important. Nonlinear solvers such as the JFNK method tend to have difficulties when there are such sharp structures in the solution. This lack of robustness of both solvers is however a debatable problem as it mostly occurs for large required drops in the residual norm. Furthermore, when it occurs, it usually affects only a few grid cells, i.e., the residual is small for all the velocity components except in very localized regions. Globalization approaches for the JFNK solver, such as the line search method, have not yet proven to be successful. Further investigation is needed. 相似文献
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Prabal Talukdar D. Trimis 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(4):527-537
This paper deals with the heat transfer analysis of a 2-D rectangular porous radiant burner. Combustion in the porous medium is modelled as a spatially dependent heat generation zone. The gas and the solid phases are considered in non-local thermal equilibrium, and separate energy equations are used for the two phases. The solid phase is assumed to be absorbing, emitting and scattering, while the gas phase is considered transparent to radiation. The radiative part of the energy equation is solved using the collapsed dimension method. The alternating direction implicit scheme is used to solve the transient 2-D energy equations. Effects of various parameters on the performance of the burner are studied. 相似文献
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A Schur complement formulation that utilizes a linear iterative solver is derived to solve a free-boundary, Stefan problem describing steady-state phase change via the Isotherm–Newton approach, which employs Newton’s method to simultaneously and efficiently solve for both interface and field equations. This formulation is tested alongside more traditional solution strategies that employ direct or iterative linear solvers on the entire Jacobian matrix for a two-dimensional sample problem that discretizes the field equations using a Galerkin finite-element method and employs a deforming-grid approach to represent the melt–solid interface. All methods demonstrate quadratic convergence for sufficiently accurate Newton solves, but the two approaches utilizing linear iterative solvers show better scaling of computational effort with problem size. Of these two approaches, the Schur formulation proves to be more robust, converging with significantly smaller Krylov subspaces than those required to solve the global system of equations. Further improvement of performance are made through approximations and preconditioning of the Schur complement problem. Hence, the new Schur formulation shows promise as an affordable, robust, and scalable method to solve free-boundary, Stefan problems. Such models are employed to study a wide array of applications, including casting, welding, glass forming, planetary mantle and glacier dynamics, thermal energy storage, food processing, cryosurgery, metallurgical solidification, and crystal growth. 相似文献