共查询到20条相似文献,搜索用时 0 毫秒
1.
Shaoping Quan 《Journal of computational physics》2011,230(13):5430-5448
In multiphase flows, the length scales of thin regions, such as thin films between nearly touching drops and thin threads formed during the interface pinch-off, are usually several orders of magnitude smaller than the size of the drops. In this paper, a number of extra length criteria for adaptive meshes are developed and implemented in the moving mesh interface tracking method to solve these multiple-length-scale problems with high fidelity. A nominal length scale based on the solutions of Laplace’s equations with the unit normal vectors of surfaces as the boundary conditions is proposed for the adaptive mesh refinement in the thin regions. For almost flat interfaces/boundaries which are near to the thin regions, the averaged length of the interior edges sharing the two nodes with the boundary edge is introduced for the mesh adaptation. The averaged length of the interfacial edges is used for the interior elements near the interfaces but outside of the thin regions. For the interior mesh away from the interfaces/boundaries, different averaged length scales based on the initial mesh are employed for the adaptive mesh refining and coarsening. Numerous cases are simulated to demonstrate the capability of the proposed schemes in handling multiple length scales, which include the relaxation and necking of an elongated droplet, droplet–droplet head-on approaching, droplet-wall interactions, and a droplet pair in a shear flow. The smallest length resolved for the thin regions is three orders of magnitude smaller than the largest characteristic length of the problem. 相似文献
2.
《Journal of computational physics》2003,184(1):163-191
We report on the numerical simulation of a two-fluid magnetohydrodynamics problem arising in the industrial production of aluminium. The motion of the two non-miscible fluids is modeled through the incompressible Navier–Stokes equations coupled with the Maxwell equations. Stabilized finite elements techniques and an arbitrary Lagrangian–Eulerian formulation (for the motion of the interface separating the two fluids) are used in the numerical simulation. With a view to justifying our strategy, details on the numerical analysis of the problem, with a special emphasis on conservation and stability properties and on the surface tension discretization, as well as results on tests cases are provided. Examples of numerical simulations of the industrial case are eventually presented. 相似文献
3.
An adaptive version of ghost-cell immersed boundary method for incompressible flows with complex stationary and moving boundaries 总被引:1,自引:0,他引:1
WANG Liang & WU ChuiJie School of Science PLA University of Science Technology Nanjing China State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of Technology Dalian School of Aeronautics Astronautics 《中国科学:物理学 力学 天文学(英文版)》2010,(5)
An adaptive version of immersed boundary method for simulating flows with complex stationary and moving boundaries is presented.The method employs a ghost-cell methodology which allows for a sharp representation of the immersed boundary.To simplify the implementation of the methodology,a volume-of-fluid method is introduced to identify the immersed boundary.In addition,the domain is spatially discretized using a tree-based discretization which is relatively simple to implement a fully flexible adaptive refi... 相似文献
4.
We derive and evaluate high order space Arbitrary Lagrangian–Eulerian (ALE) methods to compute conservation laws on moving meshes to the same time order as on a static mesh. We use a Discontinuous Galerkin Spectral Element Method (DGSEM) in space, and one of a family of explicit time integrators such as Adams–Bashforth or low storage explicit Runge–Kutta. The approximations preserve the discrete metric identities and the Discrete Geometric Conservation Law (DGCL) by construction. We present time-step refinement studies with moving meshes to validate the approximations. The test problems include propagation of an electromagnetic gaussian plane wave, a cylindrical pressure wave propagating in a subsonic flow, and a vortex convecting in a uniform inviscid subsonic flow. Each problem is computed on a time-deforming mesh with three methods used to calculate the mesh velocities: from exact differentiation, from the integration of an acceleration equation, and from numerical differentiation of the mesh position. 相似文献
5.
6.
V. Ya. Rudyak A. V. Minakov A. A. Gavrilov A. A. Dekterev 《Thermophysics and Aeromechanics》2010,17(4):565-576
A method is proposed for modelling fluid flows in microchannels. The method is tested on the known experimental data on studying
the flows in microchannels with the aid of the micro-PIV. The flow regimes in micromixers of the Y- and T-types are studied. The passive and active mixers are considered. The dependence of the mixing efficiency on the Reynolds
and Péclet numbers as well as the possibility of using the hydrophobic and ultra-hydrophobic coatings are analysed. A T-mixer is proposed as an active technique of mixing, in which the flow rate in one of the inlet channels varied according
to the harmonic law. The dependence of the mixing efficiency on the frequency of the variation of the flow rate and its amplitude
is established. 相似文献
7.
8.
The dynamic modification of the computational grid due to element displacement, deformation and edge swapping is described here in terms of suitably-defined continuous (in time) alterations of the geometry of the elements of the dual mesh. This new interpretation allows one to describe all mesh modifications within the arbitrary Lagrangian Eulerian framework, thus removing the need to interpolate the solution across computational meshes with different connectivity. The resulting scheme is by construction conservative and it is applied here to the solution of the Euler equations for compressible flows in two spatial dimensions. Preliminary two dimensional numerical simulations are presented to demonstrate the soundness of the approach. Numerical experiments show that this method allows for large time steps without causing element invalidation or tangling and at the same time guarantees high quality of the mesh elements without resorting to global re-meshing techniques, resulting in a very efficient solver for the analysis of e.g. fluid-structure interaction problems, even for those cases that require large mesh deformations or changes in the domain topology. 相似文献
9.
Samuel K.M. Chenoweth Julio Soria Andrew Ooi 《Journal of computational physics》2009,228(15):5592-5619
Moving least squares interpolation schemes are in widespread use as a tool for numerical analysis on scattered data. In particular, they are often employed when solving partial differential equations on unstructured meshes, which are typically needed when the geometry defining the domain is complex. It is known that such schemes can be singular if the data points in the stencil happen to be in certain special geometric arrangements, however little research has specifically addressed this issue. In this paper, a moving least squares scheme is presented which is an appropriate tool for use when solving partial differential equations in two dimensions, and the precise conditions under which singularities occur are identified. The theory is used to develop a stencil building algorithm which automatically detects singular stencils and corrects them in an efficient manner, while attempting to maintain stencil symmetry as closely as possible. Finally, the scheme is applied in a convection–diffusion equation solver and an incompressible Navier–Stokes solver, and the results are shown to compare favourably with known analytical solutions and previously published results. 相似文献
10.
Ribak EN 《Optics letters》2003,28(8):613-615
Several optical schemes have been proposed to measure the separate contributions of atmospheric layers for astronomical adaptive optics. I show here that simple conjugation of the wave-front sensors to the layers is sufficient. Although a larger camera is required for a larger field of view, only the pixels that sense stars are being read out. The nearly periodic Hartmann data are analyzed by Fourier filtering so that the signals from all stars are added up while most of the noise is excluded. Acoustic Hartmann wave-front sensors [Opt. Lett. 26, 1834 (2001)1 that switch between layers improve flexibility and sensitivity. 相似文献
11.
T. Loarer E. Gravier J. Gunn J. L. Lachambre K. H. Finken M. Lehnen G. Mank S. Jachmich H. Van Goubergen G. Van Oost 《Czechoslovak Journal of Physics》2000,50(12):1441-1450
The superconducting tokamak Tore Supra will be equipped with an actively cooled toroidal pump limiter (TPL), in the framework
of the CIEL (Composants Internes Et Limiteurs) project, dedicated to plasma facing component design for steady state operation.
The TPL is equipped with throats, located only on the high field side, for particle collection allowing the control of plasma
density which is essential for long plasma discharges. The present design work of the CIEL includes a biasing system in order
to enhance the particle pumping. A fluid model, based on the classical fluid equation, is used to estimate the effects of
the electric field on the particle flows in the Scrape-Off Layer (SOL). The modifications of the density, the particle flow
(toroidal and poloidal) and the position of the stagnation point are discussed as a function of the bias voltage. The model
clearly illustrates the different resulting effects on particle pumping for a divertor and a limiter configuration which are
designed respectively for poloidal or parallel particle collection.
The model is used to interpret the ALT-biasing experiments recently carried out on TEXTOR-94. The pumping capability is shown
to be improved by about (15–20)% for positive biasing while the experimental measurements of parallel Mach number are reproduced
as a function of the applied voltage. The e-folding length of the edge density in the SOL is also shown to increase from 1.5
to about 2.0 cm for a biased voltage of −400 to 400 V, respectively, in accordance with the model. Finally, the model is used
to extrapolate the TEXTOR-94 results to CIEL suggesting that pumping speed enhancement of 25 to 30% may be obtained.
Partner in Trilateral Euregio Cluster
Partner in Trilateral Euregio Cluster
Presented at the Workshop on Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June 2000. 相似文献
12.
自适应光学实时大气湍流补偿实验 总被引:18,自引:9,他引:9
本文报道了用自适应光学系统实时探测和校正距地面约15m高的340m水平传输通道上的大气湍流效应的实验.实验结果表明,用自适应光学校正后,对点目标和一定扩展度的扩展目标都可提高成像质量. 相似文献
13.
G. A. Kamalova V. E. Messerle A. Zh. Naimanova A. B. Ustimenko 《Thermophysics and Aeromechanics》2008,15(1):139-151
The spatial combustion of turbulent jets in furnace devices is modelled numerically basing on equations for multi-component
turbulent reacting gaseous mixtures. The dependencies are obtained for the influence of the secondary air velocity and composition
of gaseous components on torch configuration at a diffusion combustion process. The effect of regime parameters on the increase
in torch sizes, which arises at the interaction of secondary air with gaseous components, has been elucidated. 相似文献
14.
Pierre-Henri Maire 《Journal of computational physics》2009,228(7):2391-2425
We present a high-order cell-centered Lagrangian scheme for solving the two-dimensional gas dynamics equations on unstructured meshes. A node-based discretization of the numerical fluxes for the physical conservation laws allows to derive a scheme that is compatible with the geometric conservation law (GCL). Fluxes are computed using a nodal solver which can be viewed as a two-dimensional extension of an approximate Riemann solver. The first-order scheme is conservative for momentum and total energy, and satisfies a local entropy inequality in its semi-discrete form. The two-dimensional high-order extension is constructed employing the generalized Riemann problem (GRP) in the acoustic approximation. Many numerical tests are presented in order to assess this new scheme. The results obtained for various representative configurations of one and two-dimensional compressible fluid flows show the robustness and the accuracy of our new scheme. 相似文献
15.
Stéphane Popinet 《Journal of computational physics》2009,228(16):5838-5866
A method combining an adaptive quad/octree spatial discretisation, geometrical Volume-Of-Fluid interface representation, balanced-force continuum-surface-force surface-tension formulation and height-function curvature estimation is presented. The extension of these methods to the quad/octree discretisation allows adaptive variable resolution along the interface and is described in detail. The method is shown to recover exact equilibrium (to machine accuracy) between surface-tension and pressure gradient in the case of a stationary droplet, irrespective of viscosity and spatial resolution. Accurate solutions are obtained for the classical test case of capillary wave oscillations. An application to the capillary breakup of a jet of water in air further illustrates the accuracy and efficiency of the method. The source code of the implementation is freely available as part of the Gerris flow solver. 相似文献
16.
《Combustion Theory and Modelling》2013,17(2):383-399
Splitting techniques have been used extensively for computing reacting flows with detailed chemistry. Nevertheless, there are still some open questions with respect to efficiency and the error introduced by splitting. In this paper, the accuracy and effectiveness of split-operator methods for computing steady-state reacting flows are determined. A fully coupled scheme is described together with two splitting schemes: a standard Strang-splitting scheme and a consistent-splitting scheme, all with implicit transport computations. The effect of splitting errors on the convergence and solution accuracy is investigated analytically using a one-dimensional scalar equation. The accuracy with respect to the original discretized equations is tested for an H2/O2 burner flame. Finally, consistent splitting is combined with an adaptive chemistry approach to compute three partially premixed laminar methane flames using detailed chemistry (217 reactions). The calculations confirm that HCO radical concentration is an excellent surrogate for heat release rate. 相似文献
17.
This paper presents a second-order accurate adaptive generalized Riemann problem (GRP) scheme for one and two dimensional compressible fluid flows. The current scheme consists of two independent parts: Mesh redistribution and PDE evolution. The first part is an iterative procedure. In each iteration, mesh points are first redistributed, and then a conservative interpolation formula is used to calculate the cell-averages and the slopes of conservative variables on the resulting new mesh. The second part is to evolve the compressible fluid flows on a fixed nonuniform mesh with the Eulerian GRP scheme, which is directly extended to two-dimensional arbitrary quadrilateral meshes. Several numerical examples show that the current adaptive GRP scheme does not only improve the resolution as well as accuracy of numerical solutions with a few mesh points, but also reduces possible errors or oscillations effectively. 相似文献
18.
S.J. Kamkar A.M. Wissink V. Sankaran A. Jameson 《Journal of computational physics》2011,230(16):6271-6298
We develop locally normalized feature-detection methods to guide the adaptive mesh refinement (AMR) process for Cartesian grid systems to improve the resolution of vortical features in aerodynamic wakes. The methods include: the Q-criterion [1], the λ2 method [2], the λci method [3], and the λ+ method [4]. Specific attention is given to automate the feature identification process by applying a local normalization based upon the shear-strain rate so that they can be applied to a wide range of flow-fields without the need for user intervention. To validate the methods, we assess tagging efficiency and accuracy using a series of static vortex-dominated flow-fields, and use the methods to drive the AMR process for several theoretical and practical simulations. We demonstrate that the adaptive solutions provide comparable accuracy to solutions obtained on uniformly refined meshes at a fraction of the computational cost. Overall, the normalized feature detection methods are shown to be effective in driving the AMR process in an automated and efficient manner. 相似文献
19.
Many adaptive optics applications require wavefront corrections with a high stroke, and at a high bandwidth. Often, these two requirements cannot be met by a single wavefront corrector, and, instead, the combination of a low-bandwidth, high-stroke woofer and a high-bandwidth low-stroke tweeter is used in a so-called woofer-tweeter architecture. The optimal (minimum residual phase variance) way to split the correction between the woofer and the tweeter in the context of a linear-quadratic-Gaussian (LQG) controller has been addressed previously. However, the necessity to fold the temporal characteristics of the woofer and tweeter into the LQG controller significantly increases its complexity. In this Letter, this optimal strategy is compared to a simpler, ad hoc approach, which consists in optimizing the LQG controller as if it were controlling a high-bandwidth, high-stroke corrector and splitting the correction using first-order high- and low-pass temporal filters. In the case of tilt correction for NFIRAOS on the Thirty Meter Telescope, it is found that the ad hoc approach, which is already used or planned for several systems, holds the same overall correction performance compared to the optimal strategy. 相似文献
20.
We develop a high order numerical boundary condition for compressible inviscid flows involving complex moving geometries. It is based on finite difference methods on fixed Cartesian meshes which pose a challenge that the moving boundaries intersect the grid lines in an arbitrary fashion. Our method is an extension of the so-called inverse Lax–Wendroff procedure proposed in [17] for conservation laws in static geometries. This procedure helps us obtain normal spatial derivatives at inflow boundaries from Lagrangian time derivatives and tangential derivatives by repeated use of the Euler equations. Together with high order extrapolation at outflow boundaries, we can impose accurate values of ghost points near the boundaries by a Taylor expansion. To maintain high order accuracy in time, we need some special time matching technique at the two intermediate Runge–Kutta stages. Numerical examples in one and two dimensions show that our boundary treatment is high order accurate for problems with smooth solutions. Our method also performs well for problems involving interactions between shocks and moving rigid bodies. 相似文献