摘要:

A computational method is presented to predict the time evolution of the velocity field and of the interface position of a thin liquid layer where its motion is driven by surface tension gradients. It is based on a spectral-like collocation technique, utilizes a grid adapting to the moving free interface at which a prescribed tangential stress is compensated by viscous stresses and uses a singular value decomposition treatment to balance the weight of governing equations. The solution is fully closed

ISSN:1061-8562    

DOI:10.1080/10618569908940887

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Large eddy simulation (LES) has been carried out to investigate the oblique transition process of a flat-plate boundary layer at a free-stream Mach number of M∞= 4.5 and a Reynolds number of 10,000 based on the free-stream velocity and inflow displacement thickness. The numerical simulation is performed using a spatial approach to solve a full compressible Navier-Stokes system in the curvilinear coordinates. A compact sixth-order central difference scheme (Lele, 1992) is applied to the wall-normal direction and streamwise direction, the pseudo-spectral method is used in the spanwise direction. A compact storage third order Runge-Kutta scheme (Wray, 1986) is adopted for lime-integration. The sub-grid scales are formulated according to the filtered structure function model (Ducroset al., 1996). A pair of oblique first-mode perturbation is imposed on the inflow boundary. Several stages of transition process can be identified, i.e., the linear and weak nonlinear growth of disturbance, the appearance of staggered A-vortex pattern, the evolution of A-vortex into hairpin vortex, and the break-down of hairpin vortical structures. The organized motions during the transition are discussed in detail. The vortical and the shear layer structures are compared with the results obtained by Adams and Kleiser (1996) in their direct numerical simulation based on a temporal approach. The evolution of the averaged quantities, such as the boundary layer thickness are studied. The skin friction coefficient and the turbulent mean velocity profile obtained from the simulation agree well with the flat-plate theory of Van Driest (1956).

ISSN:1061-8562    

DOI:10.1080/10618569908940888

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A method for changing the relaxation coefficients in the course of the solution of a CFD problem is presented. The aim of the method is to provide, with as little input from the user as possible, the fastest possible (hopefully) approach lo convergence. The method draws on elements borrowed from fuzzy-logic theory, which provides an appropriate framework for establishing and applying systematic rules for changing the values of the variables that control a system as a function of the values of some other system variables. The method is tested on several simple but yet typical CFD cases, including Cartesian and curvilinear coordinates, single and multiphase problems, laminar and turbulent flows, inert- and chemically-reacting fluids, and one- to three-dimensional geometries. For these cases, the method is generally well behaved (e.g., non-oscillatory), and provides faster convergence than the use of constant relaxation coefficients for the whole calculation.

ISSN:1061-8562    

DOI:10.1080/10618569908940889

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A computational method is presented for the analysis of interaction between a thin, flexible filament and wind flow around it. Restricting the computational domain to the two dimensional vertical plane, the filament is discretized by truss elements. A geometrically nonlinear dynamic analysis method is applied to the motion of the filament. The ALE finite element method is employed for the flow analysis. A simple staggered algorithm to solve the filament motion and the flow alternatively was unstable unless the density of the filament is sufficiently large. An improved algorithm, where the excessive acceleration of the filament due to the excessive fluid force is reduced by introducing an inner iteration algorithm during each time integration step, was found effective to simulate a wind-induced flutter of the filament stably.

ISSN:1061-8562    

DOI:10.1080/10618569908940890

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A 3-D incompressible unsteady flow solver based on simple finite elements with adaptive remeshing and grid movement for both moving and deforming surfaces is described. We demonstrate the combination of adaptive remeshing techniques with the incompressible flow solver with the computation of flow past an eel in 2-D and a blue-fin tuna in 3-D. The flow past a swimming tuna was computed for two extreme cases of the caudal fin frequency and swimming speed. A grid refinement study was performed and a grid converged solution for the force produced by the caudal fin was obtained.

ISSN:1061-8562    

DOI:10.1080/10618569908940891

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Multilayer seepage model is proposed instead of three dimensional model. Optimum theory based on multilayer finite element formulation is applied to planning the efficient flow rate and pumping well layout. The Sakawa-Shindo method is used for the optimum control calculation. As a numerical example, calculations are carried out to determine an optimum pumping flow for use where a cut-off wall and pumping wells are combined.

ISSN:1061-8562    

DOI:10.1080/10618569908940892

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor