bluuebunny/crossref_metadata_2025_split huggingface dataset:
A boundary element method for a non‐linear free surface problem
Authors: Campana E. , Lalli F. , Bulgarelli U. 
Published: August 2005

AbstractIn this paper a numerical method to compute the wave resistance of a body submerged in a free stream of finite and infinite depth is presented. Non‐linear effects on the free surface are taken into account by an iterative procedure; the solution is in the form of a single‐layer potential. For the 2D problem, results are shown for both the cases of finite and infinite depth of the fluid domain, with special emphasis on the supercritical flow in which the consistency of the scheme is pointed out. The method is also extended to the 3D case of a spheroid submerged in deep water. All the results presented are compared with experimental data and analytical solutions available in the literature.
An efficient algorithm for compressible flows with real gases
Authors: Glaister P. 
Published: August 2005

AbstractAn efficient algorithm is presented for the solution of the Euler equations of gas dynamics with a general convex equation of state. The scheme is based on solving linearized Riemann problems approximately, and in more than one dimension incorporates operator splitting. In particular, only one function evaluation in each computational cell is required by using a local parametrization of the equation of state. The scheme is applied to two standard test problems in gas dynamics for some specimen equations of state.
Comments on a recent paper by W. Zijl
Authors: Greenside H. S. 
Published: August 2005

AbstractA recent paper by W. Zijl, which reformulated the Navier–Stokes and Boussinesq equations in terms of Clebsch potentials, has an error that greatly reduces the generality of the results. Some other recent efforts to use such potentials in fluid and plasma dynamics are briefly discussed.
A comparison of primitive variables and streamfunction–vorticity for fem depth‐averaged modelling of steady flow
Authors: DeVantier Bruce A. 
Published: August 2005

AbstractThe governing equations for depth‐averaged turbulent flow are presented in both the primitive variable and streamfunction–vorticity forms. Finite element formulations are presented, with special emphasis on the handling of bottom stress terms and spatially varying eddy viscosity. The primitive variable formulation is found to be preferable because of its flexibility in handling spatial variation in viscosity, variability in water surface elevations, and inflow and outflow boundaries. The substantial reduction in computational effort afforded by the streamfunction–vorticity formulation is found not to be sufficient to recommend its use for general depth‐averaged flows. For those flows in which the surface can be approximated as a fixed level surface, the streamfunction–vorticity form can produce results equivalent to the primitive variable form as long as turbulent viscosity can be estimated as a constant.
A numerical study of heat and momentum transfer for tube bundles in crossflow
Authors: Chang Yeon , Beris Antony N. , Michaelides Efstathios E. 
Published: August 2005

AbstractA numerical scheme is developed to predict the heat transfer and pressure drop coefficients in flow through rigid tube bundles. The scheme uses the Galerkin finite element technique. The conservation equations for laminar steady‐state flow are cast in the form of streamfunction and vorticity equations. A Picard iteration method is used for the solution of the resulting system of non‐linear algebraic equations. Results for the heat transfer and pressure drop coefficients are obtained for tube arrays of pitch ratios of 1·5 and 2·0. Very good agreement of the present results and experimental data obtained in the past is observed up to Reynolds numbers of 1000. It is also observed that the results of the present method show better agreement with the experimental data and that they are applicable for higher Reynolds numbers than results of other studies.
Probabilistic approach for transport of contaminants through porous media
Authors: Roco M. C. , Khadilkar J. , Zhang J. 
Published: August 2005

AbstractThe channels formed between individual particles in porous media have variable dimensions and orientations. The porosity, permeability and its anisotropy exhibit random spatial distributions. The probabilistic approach can effectively describe the transport of contaminants through porous media and is analysed in this paper. Numerical results are obtained by considering (I) random dispersion coefficients without and with spatial structure, (II) random time distribution of concentration at the inlet boundary, (III) random velocity distribution in the flow field without and (IV) with variable dispersion coefficient, (V) non‐linearity of the governing equation and (VI) anisotropy of the dispersion coefficient. Two methods are used for probabilistic predictions: (1) Gaussian field approach in conjunction with Monte Carlo method and (2) random walk method. The input random parameters are assumed to have normal and log‐normal distributions according to available experimental data. The probability distribution functions of the contaminant concentration at different locations within the flow domain are calculated and compared with the input distributions as a function of the mean and fluctuation Peclet numbers. The one‐dimensional case is analysed in detail and the illustrative numerical predictions are compared with analytical and experimental results. The extension to a two‐dimensional domain is discussed in the last part of this paper.
High‐order axisymmetric Navier–Stokes code: Description and evaluation of boundary conditions
Authors: Sørensen J. N. , Loc Ta Phuoc 
Published: August 2005

AbstractA description is given of a high‐order solution algorithm for the solution of the unsteady axisymmetric Navier–Stokes equations. The method consists of a combination of fourth‐order and second‐order accurate finite difference schemes, where the approximated equations are solved by an alternating direction implicit (ADI) method. Special attention is paid to the boundary conditions. Results are compared with measurements for the cases of rotating flow within a closed cylinder (rotating driven cavity), developing axial flow in a stationary pipe and developing flow in a rotating pipe.
Large eddy simulation of a developing turbulent boundary layer at a low Reynolds number
Authors: Tsai H. M. , Leslie D. C. 
Published: August 2005

AbstractA spectral code has been used to simulate a developing turbulent boundary layer at low Reynolds number Reθ (based on free stream velocity and momentum thickness) between 353 and 576. The starting field was generated by allowing a step change of temperature to diffuse outwards from one wall in a fully developed channel flow. The thermal boundary layer so created was conditionally sampled to convert it into a momentum boundary layer with an irrotational free stream region, a process which is justified by appeal to experiments. This initial field was allowed to develop until the momentum boundary layer thickness δ995 had grown to about 1·5 times its original thickness.The results of the simulation have been compared with a wide range of experimental data. The outcome of this comparison is generally very satisfactory; the main trends of the experiments are well reproduced and our simulation supplements and extends the existing sets of experimental data. The simulation also gives pressure statistics which cannot be obtained experimentally. In particular, it gives the contribution of pressure diffusion to the balance equations for the Reynolds stress and indicates the error produced by omitting this term.
A stable fast marching scheme for computational fluid mechanics
Authors: Behnia M. , Wolfshtein M. , De Vahl Davis G. 
Published: August 2005

AbstractA stable fast marching scheme has been developed for the solution of coupled parabolic partial differential equations such as the Navier–Stokes equations. The scheme was developed with the aid of a stability analysis. The implementation of the method in standard alternating direction implicit algorithms is straightforward. The scheme was tested on the problem of natural convection in a square cavity. The number of iterations required for convergence was significantly reduced compared to conventional methods.
A computational method for simulating transient motions of an incompressible inviscid fluid with a free surface
Authors: Nakayama Tsukasa 
Published: August 2005

AbstractA new numerical method has been developed for the analysis of unsteady free surface flow problems. The problem under consideration is formulated mathematically as a two‐dimensional non‐linear initial boundary value problem with unknown quantities of a velocity potential and a free surface profile. The basic equations are discretized spacewise with a boundary element method and timewise with a truncated forward‐time Taylor series. The key feature of the present paper lies in the method used to compute the time derivatives of the unknown quantities in the Taylor series.The use of the Taylor series expansion has enabled us to employ a variable time‐stepping method. The size of time increment is determined at each time step so that the remainders of the truncated Taylor series should be equal to a given small error limit. Such a variable time‐stepping technique has made a great contribution to numerically stable computations.A wave‐making problem in a two‐dimensional rectangular water tank has been analysed. The computational accuracy has been verified by comparing the present numerical results with available experimental data. Good agreement is obtained.
A finite difference self‐adaptive mesh solution of flow in a sedimentation tank
Authors: Casonato Marco , Gallerano Francesco 
Published: August 2005

AbstractA new numerical model has been developed to evaluate the removal efficiency of primary sedimentation clarifiers operating at neutral density condition. The velocity and concentration fields as well as the development in time and space of the settled particle bed thickness are simulated. The main difficulties in simulation of velocity and concentration fields are related to (1) numerical instabilities produced by the prevalence of convective terms in the unknown variable high‐gradient regions and (2) turbulence effects on the suspension of solid particles from the settled bed. The need to overcome the numerical instabilities without the upwind difference approximation, which introduces high numerical viscosity, suggests the use of non‐uniform grids of calculation.The velocity field is obtained by solving the motion equations in the vorticity and streamfunction formulation by means of a new numerical method based upon a dynamically self‐adjusting calculation grid. These grids allow for a finer mesh following the evolution of the unknown quantities. A k–ϵ model is used to simulate turbulence phenomena.The sedimentation field is found by solving the diffusion and transport equation of the solid particle concentration. Boundary conditions on the bottom line are imposed relating the amount of turbulence flux and sedimentation flux to the actual concentration and the reference concentration. Such an approach makes it possible to represent the solid particle suspension from the bottom, taking into account its dependence on (1) the characteristics and the evolution in time of the settled bed, (2) the velocity component parallel to the bottom line and (3) the turbulence structure.
Boundary node correction and superconvergence in the FEM
Authors: Yao M. , Malkus D. S. 
Published: August 2005

AbstractConvergence improvement and superconvergence behaviour, obtained by the simple boundary node correction (BNC) procedure for certain stress‐like variables of smoothed FEM solutions, are reported in this paper. The effectiveness of BNC is shown through three examples of steady flow problems, and a posterior error analysis based on the multiple‐mesh extrapolation technique has been used for estimating the convergence rates.
Finite volume method for prediction of fluid flow in arbitrarily shaped domains with moving boundaries
Authors: Demirdžić I. , Perić M. 
Published: August 2005

AbstractIn this paper a method is presented that can be used for both the Lagrangian and the Eulerian solution of the Navier–Stokes equations in a domain of arbitrary shape, bounded by boundaries which move in any prescribed time‐varying fashion. The method uses the integral form of the governing equations for an arbitrary moving control volume, with pressure and Cartesian velocity components as dependent variables. Care is taken to also satisfy the space conservation law, which ensures a fully conservative computational procedure. Fully implicit temporal differencing makes the method stable for any time step.A detailed description is provided for the discretization in two dimensions, with a collocated arrangement of variables. Central differences are used to evaluate both the convection and diffusion fluxes. The well known SIMPLE algorithm is employed for pressure–velocity coupling. The resulting algebraic equation systems are solved iteratively in a sequential manner. Results are presented for a flow in a channel with a moving indentation; they show favourable agreement with experimental observations.
Internal three‐dimensional viscous flow solutions using the vorticity‐potential method
Authors: Yang Herong , Camarero Ricardo 
Published: August 2005

AbstractA numerical solution procedure for internal three‐dimensional viscous flow is proposed in this paper. The formulation is based on the non‐primitive variables, the vorticity and potentials, on a curvilinear grid. A new upwind difference scheme is introduced to overcome the convective instabilities arising in the central difference scheme for the vorticity transport equations, while keeping false diffusion to a minimum level. Developing flows in both straight and curved square ducts are simulated to validate the procedure. The results are compared with both experimental measurements and analytical solutions.
A higher‐order eulerian scheme for coupled advection‐diffusion transport
Authors: Yang Guolu , Belleudy Philippe , Temperville André 
Published: August 2005

AbstractA new accurate high‐order numerical method is presented for the coupled transport of a passive scalar (concentration) by advection and diffusion.Following the method of characteristics, the pure advection problem is first investigated. Interpolation of the concentration and its first derivative at the foot of the characteristic is carried out with a fifth‐degree polynomial. The latter is constructed by using as information the concentration and its first and second derivatives at computational points on current time level t in Eulerian co‐ordinates. The first derivative involved in the polynomial is transported by advection along the characteristic towards time level t + Δt in the same way as is the concentration itself. Second derivatives are obtained at the new time level t + Δt by solving a system of linear equations defined only by the concentrations and their derivatives at grid nodes, with the assumption that the third‐order derivatives are continuous. The approximation of the method is of sixth order.The results are extended to coupled transport by advection and diffusion. Diffusion of the concentration takes place in parallel with advection along the characteristic. The applicability and precision of the method are demonstrated for the case of a Gaussian initial distribution of concentrations as well as for the case of a steep advancing concentration front. The results of the simulations are compared with analytical solutions and some existing methods.
Numerical aspects of calculation of confined swirling flows with internal recirculation
Authors: Durst F. , Wennerberg D. 
Published: August 2005

AbstractPredictions were performed for two different confined swirling flows with internal recirculation zones. The convection terms in the elliptic governing equations were discretized using three different finite differencing schemes: hybrid, quadratic upwind interpolation and skew upwind differencing. For each flow case, calculations were carried out with these schemes and successively refined grids were employed. For the turbulent flow case the k‐ε turbulence model was used. The predicted cases were a laminar swirling flow investigated by Bornstein and Escudier, and a turbulent low‐swirl case studied by Roback and Johnson. In both cases an internal recirculation zone was present. The laminar case is well predicted when account is taken of the estimated radial velocity component at the chosen inlet plane. The quadratic upwind interpolation and skew upwind schemes predict the main features of the internal recirculation zone also with a coarse grid. The turbulent case is well predicted with the coarse as well as the finer grids, the skew upwind and quadratic upwind interpolation schemes yielding results very close to the measurements. It is concluded that the skew upwind scheme reaches grid independence slightly before the quadratic upwind scheme, both considerably earlier than the hybrid scheme.
Vortex simulation of the intake flow in a planar piston‐chamber device
Authors: Martins Luis‐Filipe , Ǵhoniem Ahmed F. 
Published: August 2005

AbstractA numerical scheme based on the application of the vortex method to update the vorticity field and the implementation of the finite element method to satisfy the normal velocity boundary condition inside a complex time‐dependent geometry is applied to simulate the flow produced by a piston sliding out of a chamber equipped with single or multiple intakes. This unsteady confined vortex flow is of interest in many applications. We use the idealization that the flow is incompressible, two‐dimensional and planar and we analyse the results to study the flow during the intake process inside a model of an engine cylinder. The chamber top is fitted with an inlet channel, an inlet port or an inlet valve. In all cases when the intake channel axis coincides with that of the chamber, the flow in each side of the chamber consists essentially of two large counter‐rotating eddies of almost the same size. The computed structures of these flows resemble qualitatively those which have been observed experimentally. The fluid motion is also computed for the case of a chamber equipped with an intake whose axis is not aligned with the chamber axis. In this case the flow at the end of the stroke is dominated by a single large eddy produced by the merging of the two eddies forming on the sides of the port.
Acceleration of convergence by shifting the spectrum of implicit finite difference operators associated with the equations of gas dynamics
Authors: Cheer A. , Saleem M. 
Published: August 2005

AbstractEigensystem analysis techniques are applied to finite difference formulations of the Navier‐Stokes equations in one dimension. Spectra of the resulting implicit difference operators are computed. The largest eigenvalues are calculated by using a combination of the Frechet derivative of the operators and Arnoldi's method. The accuracy of Arnoldi's method is tested by comparing the rate of convergence of the iterative method with the dominant eigenvalue of the original iteration matrix.On the basis of the pattern of eigenvalue distributions for various flow configurations, a shifting of the implicit operators in question is devised. The idea of shifting is based on the power method of linear algebra and is very simple to implement. This procedure has improved the rates of convergence of CFD codes (developed at NASA Ames Research Center) by 20%–50%. The sensitivity of the computed solution with respect to the shift is also studied. Finally, an adaptive shifting of the spectrum together with Wynn's acceleration algorithm are discussed. It turns out that the shifting process is a preconditioner for Wynn's method.
Finite element modelling of quasi‐three‐dimensional nearly horizontal flow
Authors: Utnes Torbjørn 
Published: August 2005

AbstractA quasi‐three‐dimensional numerical model is presented and applied to some test problems with constant density. The numerical technique is based on a finite element formulation and the three‐dimensional problem is factorized into one‐ and two‐dimensional subproblems. The non‐linear advection is treated by use of a weak formulation of the characteristics method and the equations are transformed to ‘sigma’ coordinates.
Cavitating flows through a cascade of flat plates
Authors: Wen X. , Ingham D. B. 
Published: August 2005

AbstractThe purpose of this research is to consider the flow through a cascade of bluff bodies, behind which there exist cavities, by using the free streamline theory. When the wake extends to infinity, both the free surface and the velocity on the free surface are unknown and the cavitation number cannot be specified arbitrarily. Given the geometry of the cascade, a numerical method is described in which we obtain the shape of the free surface and the cavitation number. We obtain the relationship between the contraction coefficient, cavitation number and drag coefficient.
A two‐phase, two‐component model for natural convection in a porous medium
Authors: Forsyth P. A. , Simpson R. B. 
Published: August 2005

AbstractA numerical study of natural convection in a two‐phase, two‐component flow in a porous medium heated from below is presented. Interphase mass and energy transfer, latent heat and bouyancy effects are major physical features. This study extends earlier studies of natural convection based on single‐phase, saturated porous medium models. The appearance of two‐phase heat pipe zones in the flow has a marked effect on the fluid and heat flows as well as on the performance of the numerical methods. The numerical techniques for handling phase change, Jacobian construction and time step selection are discussed.
Three‐dimensional streamlined finite elements: Design of extrusion dies
Authors: Ellwood Kevin R. J. , Papanastasiou T. C. , Wilkes J. O. 
Published: August 2005

AbstractA method to determine three‐dimensional die shapes from extrudate swell and vice versa is presented using a three‐dimensional Galerkin finite element method based on a streamlined formulation with the fluid velocities and pressures represented by triquadratic and trilinear basis functions respectively. The three‐dimensional streamlined method, an extension of the two‐dimensional formulation, uses successive streamsurfaces to form a boundary‐conforming co‐ordinate system. This produces a fixd, computational domain leaving the spatial location of the elements as unknowns to be determined with the standard primary variables (u, v, w, p). The extrudate produced by a die of a given shape is considered for moderate Reynolds numbers. Finally, the method is extended to address the problem of die design, where a die profile is sought to produce a target extrudate shape.