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1.
Consideration of the requirements for robust, high-fidelity subgrid closure of large-eddy simulations of multiphysics turbulent flows indicates the need for a spatially and temporally resolved representation of fine-scale physical and chemical processes that are coupled to fluid motion. One-Dimensional Turbulence (ODT), a potentially cost-effective approach for this purpose, captures these couplings by means of a stochastic simulation implemented on a one-dimensional domain. A subgrid implementation of ODT is formulated and its potential advantages and limitations are assessed.  相似文献   

2.
Many large eddy simulation (LES) techniques have been developed for stationary computational meshes. This study applies a single equation LES to Arbitrary Lagrangian-Eulerian (ALE) simulations of Rayleigh-Taylor instability and investigates its effects. Behavior of LES is similar for Eulerian and ALE simulations for the test problem studied. However, the motion of the mesh can be tied to the subgrid scale model in the form of a relaxation weight based on subgrid scale energy. This increases mesh resolution in areas of high subgrid scale energy.  相似文献   

3.
We present detailed analysis of a lattice Boltzmann approach to model time-dependent Newtonian flows. The aim of this study is to find optimized simulation parameters for a desired accuracy with minimal computational time. Simulation parameters for fixed Reynolds and Womersley numbers are studied. We investigate influences from the Mach number and different boundary conditions on the accuracy and performance of the method and suggest ways to enhance the convergence behavior.  相似文献   

4.
Many two-dimensional incompressible inviscid vortex flows can be simulated very efficiently by means of the contour dynamics method. Several applications require the use of a hierarchical-element method (HEM), which is a modified version of the classical contour dynamics scheme based on the fast multipole method. The HEM can be used, for example, to study the large-scale motion of coherent structures in idealized geophysical fluid dynamics where the flow can be modelled as the motion in a thin layer of fluid in the presence of a non-uniform background rotation. Nevertheless, such simulations require a substantial computational effort, even when the HEM is used. In this article it is shown that the acceleration of contour dynamics simulations can be increased further by parallelizing the HEM algorithm. Speed-up, load balance and scalability are parallel performance features which are studied for several representative cases. The HEM has been parallelized using the OpenMP interface and is tested with up to 16 processors on an Origin 3800 CC-NUMA computer.  相似文献   

5.
In this work we assess the quality and performance of several novel dissipative particle dynamics integration schemes that have not previously been tested independently. Based on a thorough comparison we identify the respective methods of Lowe and Shardlow as particularly promising candidates for future studies of large-scale properties of soft matter systems.  相似文献   

6.
A high-accuracy numerical approach is introduced for three-dimensional, time-dependent simulations of variable density and viscosity, miscible flows in a circular tube. Towards this end, the conservation equations are treated in cylindrical coordinates. The spatial discretization is based on a mixed spectral element/Fourier spectral scheme, with careful treatment of the singularity at the axis. For the temporal discretization, an efficient semi-implicit method is applied to the variable viscosity momentum equation. This approach results in a constant coefficient Helmholtz equation, which is solved by a fast diagonalization method. Numerical validation data are presented, and simulations are conducted for the three-dimensionally evolving instability resulting from an unstable density stratification in a vertical tube. Some preliminary comparisons with corresponding experiments are undertaken.  相似文献   

7.
Results of a numerical simulation of the flow in a model of the human nasal cavity using an AUSM-based method of second-order accuracy on a multi-block structured grid are presented and compared with experimental data. Computations are performed for inspiration and expiration at rest with Reynolds numbers Re=1560 and Re=1230 at the nostril, respectively. The comparison shows good agreement with experimental findings.  相似文献   

8.
A two-dimensional Eulerian hydrodynamic method for the numerical simulation of inviscid compressible axisymmetric multi-material flow in external force fields for the situation of pure fluids separated by macroscopic interfaces is presented. The method combines an implicit Lagrangian step with an explicit Eulerian advection step. Individual materials obey separate energy equations, fulfill general equations of state, and may possess different temperatures. Material volume is tracked using a piecewise linear volume-of-fluid method. An overshoot-free logically simple and economic material advection algorithm for cylinder coordinates is derived, in an algebraic formulation. New aspects arising in the case of more than two materials such as the material ordering strategy during transport are presented. One- and two-dimensional numerical examples are given.  相似文献   

9.
The semi-Lagrangian method using the hybrid-cubic-rational interpolation function [M. Ida, Comput. Fluid Dyn. J. 10 (2001) 159] is modified to a conservative method by incorporating the concept discussed in [R. Tanaka et al., Comput. Phys. Commun. 126 (2000) 232]. In the method due to Tanaka et al., not only a physical quantity but also its integrated quantity within a computational cell are used as dependent variables, and the mass conservation is achieved by giving a constraint to a forth-order polynomial used as an interpolation function. In the present method, a hybrid-cubic-rational function whose optimal mixing ratio was determined theoretically is employed for the interpolation, and its derivative is used for updating the physical quantity. The numerical oscillation appearing in results by the method due to Tanaka et al. is sufficiently eliminated by the use of the hybrid function.  相似文献   

10.
In this paper we consider a variety of schemes for performing interpolation in space and time to allow particle trajectories to be integrated from a velocity field given only on a discrete collection of data points in space and time. Using a widely-studied model of chaotic advection as a test case we give a method for quantifying the quality of interpolation methods and apply this to a variety of interpolation schemes in space only and in both space and time. It is shown that the performance of a method when interpolating in space is not a reliable predictor of its performance when interpolation in time is added. It is demonstrated that a method using bicubic spatial interpolation together with third-order Lagrange polynomials in time gives excellent accuracy at very modest computational expense compared to other methods.  相似文献   

11.
A method for the localization of small scales in turbulent velocity fields is proposed. The method is based on the definition of a function f of the velocity and vorticity fields that reproduces a normalized form of the twisting-stretching term of the Helmholtz equation. By means of this method the equations of motion can be selectively filtered in regions that are rich in small scale motions. The method is applied through a criterion built on a statistical link between the function f and a local property of the turbulence that was derived from the analysis a homogeneous and isotropic high Reynolds number (Reλ=280) turbulence field. The localization criterion is independent of the subgrid scale model used in a possible Large Eddy Simulation carried out after the small scale localization is obtained. This extends the typology of possible applications to the analysis of experimental laboratory data. In case of compressible regimes, a second sensor that depends on the local pressure variation and divergence can be associated to the previous one in order to determine the eventual emergence of shocks. The capture of shocks is made possible by suppressing the subgrid terms where this second sensor indicates the presence of a shock.A priori tests were carried out on the turbulent channel flow, Reλ=180 and 590, to validate the localization procedure in a highly inhomogeneous flow configuration. A second set of a priori test was carried out on a turbulent time decaying jet which initiates its evolution at Mach 5 and which reproduces a few hydrodynamical properties of high Reynolds number hypersonic jets which exist in the Universe.  相似文献   

12.
An efficient swap algorithm for the lattice Boltzmann method   总被引:1,自引:0,他引:1  
During the last decade, the lattice-Boltzmann method (LBM) as a valuable tool in computational fluid dynamics has been increasingly acknowledged. The widespread application of LBM is partly due to the simplicity of its coding. The most well-known algorithms for the implementation of the standard lattice-Boltzmann equation (LBE) are the two-lattice and two-step algorithms. However, implementations of the two-lattice or the two-step algorithm suffer from high memory consumption or poor computational performance, respectively. Ultimately, the computing resources available decide which of the two disadvantages is more critical. Here we introduce a new algorithm, called the swap algorithm, for the implementation of LBE. Simulation results demonstrate that implementations based on the swap algorithm can achieve high computational performance and have very low memory consumption. Furthermore, we show how the performance of its implementations can be further improved by code optimization.  相似文献   

13.
A numerical method is proposed to evaluate gradients on non-uniform, non-orthogonal, three-dimensional structured meshes of hexahedra, as commonly used by finite volume methods. The method uses isoparametric transforms on tetrahedra to evaluate the gradient on a regular mesh and transform it back to the general mesh. It provides second-order accuracy, even on highly non-orthogonal meshes. Results of stationary three-dimensional numerical simulations of a direct current plasma torch, making use of the proposed method, are presented.  相似文献   

14.
An efficient and robust approach is proposed in order to conduct numerical simulations of collisional particle dynamics in the Lagrangian framework. Clusters of particles are made of particles that interact or may interact during the next global time-step. Potential collision partners are found by performing a test move, that follows the patterns of a hard-sphere model. The clusters are integrated separately and the collisional forces between particles are given by a soft-sphere collision model. However, the present approach also allows longer range inter-particle forces. The integration of the clusters can be done by any one-step ordinary differential equation solver, but for dilute particle systems, the variable step-size Runge-Kutta solvers as the Dormand and Prince scheme [J. Comput. Appl. Math. 6 (1980) 19] are superior. The cluster integration method is applied on sedimentation of 5000 particles in a two-dimensional box. A significant speed-up is achieved. Compared to a traditional discrete element method with the forward Euler scheme, a speed-up factor of three orders of magnitude in the dilute regime and two orders of magnitude in the dense regime were observed. As long as the particles are dilute, the Dormand and Prince scheme is ten times faster than the classical fourth-order Runge-Kutta solver with fixed step size.  相似文献   

15.
We investigate the spontaneous fluctuation in a real-coded lattice gas (RLG) model by studying the density correlation function. In particular, the dynamic structure factor obtained from RLG is in agreement with the Rayleigh-Brillouin spectrum, a spectrum which can also be measured from a real fluid at the continuum limit. We also work out the analytic form of the static structure factor for the RLG model, which is supported by the numerical results.  相似文献   

16.
17.
We present an overview of recent advances in numerical simulations of the 2+1-dimensional Kuramoto–Sivashinsky equation, describing the flame-front deformation in a combustion experiment. Algorithmic development includes a second-order unconditionally A-stable Crank–Nicolson scheme, using distributed approximating functionals (DAFs) for well-tempered, highly accurate, representation of the physical quantity and its derivatives. The simulator reproduces a multitude of patterns observed in experiments-in-the-wild, including rotating 2-cell, 3-cell, hopping 3-cell, stationary 2, 3, 4, 5-cell, stationary 5/1, 6/1, 7/1, 8/2 two-ring patterns, etc. The numerical observation of hopping flame patterns – characterized by non-uniform rotations of a ring of cells, in which individual cells make abrupt changes in their angular positions while they rotate around the ring – is the first outside of physical experiments. We show modal decomposition analysis of the simulated patterns, via the singular value decomposition (SVD), which exposes the spatio-temporal behavior in which the overall temporal dynamics is similar to that of equivalent experimental states. Symmetry-based arguments are used to derive normal form equations for the temporal behavior, and a bifurcation analysis of the associated normal form equations quantifies the complexity of hopping patterns. Conditions for their existence and their stability are also derived from the bifurcation analysis. Further, we study the effects of thermal noise in a stochastic formulation of the Kuramoto–Sivashinsky equation. Numerical integration reveals that the presence of noise increases the propensity of dynamic cellular states, which seems to explain the generic behavior of related laboratory experiments. Most importantly, we also report on observations of certain dynamic states, homoclinic intermittent states, previously only observed in physical experiments.  相似文献   

18.
A discrete random number (DRN) generator for stochastic differential equations is proposed. The generator has exactly 8 states and thus 10 DRN's can be obtained from a single 32-bit random variable. This is advantageous when large numbers of DRN's are needed, as for example in fluctuating lattice-Boltzmann models. The moments of the discrete distribution match those of a Gaussian distribution (zero mean and unit variance) up to 5th order. Numerical tests show that satisfactory statistical properties can be obtained with several 32-bit pseudo random number (PRN) generators.  相似文献   

19.
We present a code for the simulation of laser-plasma interaction processes relevant for applications in inertial confinement fusion. The code consists of a fully nonlinear hydrodynamics in two spatial dimensions using a Lagrangian, discontinuous Galerkin-type approach, a paraxial treatment of the laser field and a spectral treatment of the dominant non-local transport terms. The code is fully parallelized using MPI in order to be able to simulate macroscopic plasmas.One example of a fully nonlinear evolution of a laser beam in an underdense plasma is presented for the conditions previewed for the future MegaJoule laser project.  相似文献   

20.
Three dimensional truncated pyramidal quantum dots are simulated numerically to compute the energy states and the wave functions. The simulation of the hetero-structures is realized by using a novel finite volume scheme to solve the Schrödinger equation. The simulation benefits greatly from the finite volume scheme in threefold. Firstly, the BenDaniel-Duke hetero-junction interface condition is ingeniously embedded into the scheme. Secondly, the scheme uses uniform meshes in discretization and leads to simple computer implementation. Thirdly, the scheme is efficient as it achieves second-order convergence rates over varied mesh sizes. The scheme has successfully computed all the confined energy states and visualized the corresponding wave functions. The results further predict the relation of the energy states and wave functions versus the height of the truncated pyramidal quantum dots.  相似文献   

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