bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experiments with several elements for viscous incompressible flows
Authors: Fortin M. , Fortin A. 
Published: August 2005

AbstractWe present a numerical procedure to eliminate internal nodes from elements designed to approximate incompressible flow problems. We compare six elements in academic and industrial like flow problem and we discuss their relative qualities. A surprising conclusion is that richer elements may behave less well than simple ones if a good enforcement of incompressibility is not maintained.
On the numerical computation of laminar boundary layers at a phase‐changing, gas‐liquid interface
Authors: Klotz Stephen P. , Street Robert L. 
Published: August 2005

AbstractThe two‐dimensional, laminar boundary‐layer equations of heat, mass and momentum at a smooth, phase‐changing, gas‐liquid interface are solved numerically by the Keller Box method. The gas and liquid regimes are embedded in a single marching scheme which computes interfacial parameters implicitly. Results of both self‐similar and non‐similar boundary‐layer computations are presented and effects of mild pressure gradient, a mean current in the liquid, and free‐stream vapour concentration on the interfacial parameters are analysed.In order to assess the accuracy of the method, several self‐similar problems are solved by Runge‐Kutta integration and results are compared to those obtained by the finite‐difference scheme. Agreement is excellent in all cases.
Conservative calculations of non‐isentropic transonic flows
Authors: Hafez M. M. , Habashi W. G. , Kotiuga P. L. 
Published: August 2005

AbstractThe classical potential formulation of inviscid transonic flows is modified to account for non‐isentropic effects. The density is determined in terms of the speed as well as the pressure, which in turn is calculated from a second‐order mixed‐type equation derived via differentiating the momentum equations.The present model differs in general from the exact inviscid Euler equations since the flow is assumed irrotational. On the other hand, since the shocks are not isentropic, they are weaker and are placed further upstream compared to the classical potential solution. Furthermore, the streamline leaving the aerofoil does not necessarily bisect the trailing edge.Results for the present conservative calculations are presented for non‐lifting and lifting aerofoils at subsonic and transonic speeds and compared to potential and Euler solutions.
An improved Vorticity–Potential method for three‐dimensional duct flow simulations
Authors: Yang Herong , Camarero Ricardo 
Published: August 2005

AbstractAn improved Vorticity–Potential method is presented for the numerical solutions of three‐dimensional duct flow problems. The solution procedure requires first a potential solution. Then the viscous effects are added through the vorticity transport equation. By using body‐fitted coordinates, the method is applied to simulate the incompressible laminar flows in a square elbow and in a twisted square elbow.
On numerical modelling of embedded subsonic flow
Authors: Davis M. P. , Mace A. C. H. , Markatos N. C. 
Published: August 2005

AbstractAn analytical model has been developed for computing embedded subsonic flow in rocket plumes from underexpanded axisymmetric supersonic nozzles. Numerical procedures based on the analysis have been incorporated in a simplified, non‐reacting exhaust structure program and calculations for representative plume conditions performed. The technique is numerically stable and has provided satisfactory predictions of Mach–disc associated embedded subsonic flow.
An evaluation of eight discretization schemes for two‐dimensional convection‐diffusion equations
Authors: Patel M. K. , Markatos N. C. 
Published: August 2005

AbstractA comparative study of eight discretization schemes for the equations describing convection‐diffusion transport phenomena is presented. The (differencing) schemes considered are the conventional central, upwind and hybrid difference schemes,1,2 together with the quadratic upstream,3,4 quadratic upstream extended4 and quadratic upstream extended revised difference4 schemes. Also tested are the so called locally exact difference scheme5 and the power difference scheme.6 In multi‐dimensional problems errors arise from ‘false diffusion’ and function approximations. It is asserted that false diffusion is essentially a multi‐dimensional source of error. Hence errors associated with false diffusion may be investigated only via two‐ and three‐dimensional problems. The above schemes have been tested for both one‐ and two‐dimensional flows with sources, to distinguish between ‘discretization’ errors and ‘false diffusion’ errors.7 The one‐dimensional study is reported in Reference 7. For 2D flows, the quadratic upstream difference schemes are shown to be superior in accuracy to the others at all Peclet numbers, for the test cases considered. The stability of the schemes and their CPU time requirements are also discussed.
Local pressure oscillation and boundary treatment for the 8‐node quadrilateral
Authors: Carey G. F. , McLay R. 
Published: August 2005

AbstractThe 8‐node (serendipity) velocity basis with C° bilinear pressure is a popular element but has been observed to yield poor pressures. We present some details of numerical experiments that indicate the local nature of the error and the effects of mesh refinement, increasing Reynolds number and regularity of the data. This leads to a strategy for appropriately modifying the data near the corners that is effective in improving the computed pressure approximation.
Rotating disk with uniform suction in streaming flow
Authors: Szeri A. Z. , Lai C. Y. , Kayhan A. A. 
Published: August 2005

AbstractWe investigate the flow as it occurs above a single rotating disk when uniform suction is applied at the disk surface. It has been demonstrated by others that at zero suction repeated branching of the solution occurs as the parameter s is varied, where s is the ratio of the angular velocity of the fluid at infinity to the angular velocity of the disk. We show multiplicity of solution also at −0·82⩽α⩽1·15, where α is the suction parameter; for large absolute values of α the solution fails to turn back on itself and we obtain only the von Karman solution.We then generalize the von Karman solution for flow above a single rotating disk with uniform suction to include non‐axisymmetric solutions due to streaming at infinity. These solutions are continuous in an arbitrary parameter, the streaming velocity at infinity; for zero value of this parameter the asymmetric flow degenerates into the classical von Karman flow. Thus the classical solution is never isolated when considered within the framework of the Navier–Stokes equations: there are asymmetric solutions in every neighbourhood of the von Karman solution.
Simulation of forming processes by FEM with a Bingham fluid model
Authors: Bercovier M. , Engelman M. , Fortin M. , Goldberger N. 
Published: August 2005

AbstractWe model the forming process as a fluid flow. A finite element program, FIDAP, which analyses flow problems, was used to calculate velocity and strain rates at points throughout the material during the deformation process. This allows predictions to be made on the shape and quality of the resulting part. The stress‐strain relation we used models the plastic flow of metals (Bingham fluids). The FEM approximation of such a fluid is tested by comparing results for a simple analytical example. In forming processes provision must be made for friction between dye and workpiece, and the program was modified accordingly. Two classical ring forming simulations are compared to published results.
Numerical simulation of storm surges in Bangladesh using a multi‐level model
Authors: Sinha P. C. , Dube S. K. , Roy G. D. , Jaggi Sunil 
Published: August 2005

AbstractA comparative study with a vertically integrated model and the multi‐level model has shown that the former can remain a good substitute for the latter in the prediction of sea‐surface elevation as long as the bottom friction coefficients in the vertically integrated models are properly specified.
Comparison of iterative and direct solution methods for viscous flow calculations in body‐fitted co‐ordinates
Authors: Braaten M. E. , Shyy W. 
Published: August 2005

AbstractAn investigation has been conducted to study the relative performance between the line iterative and direct sparse matrix solution procedures for viscous flow calculations. A key focus point is to assess the method of speeding up the computation in the context of the body‐fitted co‐ordinate system. A series of test problems has been set up to investigate the effects of mesh skewness, Reynolds number and grid size on the two methods. The fully coupled fully implicit treatment of the equations in the direct sparse matrix method leads to rates of convergence that are much more rapid than the iterative method. Whereas the convergence rate of the iterative method is found to decrease monotonically with increasing global mesh skewness and Reynolds number, the direct method is quite insensitive to these parameters. However, the increased complexity of the equations in curvilinear co‐ordinates causes the storage requirements and the cost per iteration of the direct method to be even higher than in corresponding methods using Cartesian co‐ordinates. Consequently, the total CPU time for the direct method is found to be proportional to N2 (where N is the total number of nodes), which compares unfavourably with the iterative method, where CPU time varies as N.1,5 Hence, increases in grid size penalize both the CPU time and computer storage requirements of the direct method more severely than the iterative method. These findings make the straightforward adoption of the direct sparse matrix method less attractive in the curvilinear co‐ordinate system. However, the importance of the coupling between the equations on speeding up the convergence of the solution procedure is clearly demonstrated, suggesting possible alternatives for achieving code speed‐up.
Numerical solution of the supersonic laminar flow over a two‐dimensional compression corner using an implicit approach
Authors: Madhavan N. S. , Swaminathan V. 
Published: August 2005

AbstractThe use of an implicit numerical scheme, analogous to MacCormack's1, for the supersonic laminar two‐dimensional compression corner flow problem using unsteady Navier–Stokes equations is demonstrated. The technique entails a reduction of about 70 per cent in the computation time for a Courant number of 5, but it is characterized by an increase of approximately 20 per cent in computer memory requirement.
A finite element approximation of the unsteady two‐dimensional Navier–Stokes equations
Authors: Van De Vosse F. N. , Śegal A. , Van Steenhoven A. A. , Janssen J. D. 
Published: August 2005

AbstractIn this paper a penalty finite element solution method for the unsteady Navier–Stokes equations for two‐dimensional incompressible flow is described. The performances of the Euler implicit (EI) and the Crank–Nicolson (CN) time integration methods are analysed. Special attention is payed to the undamped pressure oscillations which can occur when the Crank–Nicolson integration rule is used in combination with the penalty function method. Stability and convergence properties are illustrated by means of the computation of fully developed oscillating flow between two flat plates. Furthermore, the von Karman vortex street past a circular cylinder is computed to demonstrate the behaviour of the time integration schemes for a more complicated flow. It is concluded that the EI method has its advantages over the CN method with respect to the damping of numerical oscillations. However, for flows with an important convective contribution, where physically originated oscillations may be present, the CN method is preferable.
Mesh effects on the computation of non‐linear gravity waves of arbitrary discharge
Authors: Toro E. F. 
Published: August 2005

AbstractNumerical computations of non‐linear gravity waves are presented and the effects of mesh variations on the results are discussed.Waves are regarded as two‐parameter families (λ,A)Q of arbitrary discharge Q, and computations are carried out using a new Kantorovich algorithm.Mesh effects are to a large extent dependent on the particular wave region under consideration. Three such regions are identified and typical examples are computed and discussed.
Orbital flow past a cylinder: A numerical approach
Authors: Borthwick A. 
Published: August 2005

AbstractOrbital flow past a cylinder is relevant to offshore structures. The numerical scheme presented here is based on a finite‐difference solution of the Navier–Stokes equations. Alternating‐directional‐implicit (ADI) and successive‐over‐relaxation (SOR) techniques are used to solve the vorticity‐transport and stream‐function equations. Theoretical simulations to low Reynolds number flows (up to 1000) are discussed for cases involving uniform flow past stationary and rotating cylinders and orbital flow past a cylinder. The separation points for cylinders that are rotating or immersed in an orbital flow are deduced from velocity profiles through the boundary layer using a hybrid mesh scheme. During the initial development of orbital flow surface vorticity on the impulsively started cylinder dominates the flow. A vortex then detaches from behind the cylinder and establishes the flow pattern of the orbit. After some time a collection of vortices circles the orbit and distorts its shape a great deal. These vortices gradually spiral outward as others detach from the cylinder and join the orbital path.
A finite element approximation of steady flow through a rotating non‐aligned straight tube
Authors: Noronha W. P. , Berman J. 
Published: August 2005

AbstractA finite element solution is developed for a penalty function formulation of the equations which govern the steady motion of a Newtonian fluid through a pipe that rotates about an axis not parallel to its own. The motion in this system is driven by the Coriolis acceleration, which has components in the axial direction as well as in the transverse plane of the pipe. The relative magnitudes of these components significantly affect the qualitative and quantitative nature of the primary and secondary flow field. The present results compare favourably with those of previously reported experimental and theoretical studies over a wide range of flow regimes.
Turbulent boundary‐layer analysis using finite elements
Authors: Sharma M. , Carey G. F. 
Published: August 2005

AbstractThe use of finite element methods for turbulent boundary‐layer flow is relatively recent and of limited extent.1 In the present study, we extend the group variable approach of Fletcher and Fleer2,3 to treat turbulent boundary layer flows with heat transfer using a two‐equation turbulence model. The main concepts in the formulations include a Dorodnitsyn‐type transformation which uses a velocity component as the transverse variable, a ‘variational’ formulation for the transformed equations using special test functions and development of a two‐equation turbulence model in terms of the turbulent kinetic energy and turbulence dissipation rate as additional field variables. Several numerical test cases have been examined comparing the results with finite difference calculations and comparing the two‐equation turbulence model with an algebraic turbulence model.
Analysis of lubricated squeezing flow
Authors: Papanastasiou A. C. , Macosko C. W. , Scriven L. E. 
Published: August 2005

AbstractA thin film of low‐viscosity lubricating liquid between a solid wall and a viscous material reduces shear stress on the latter and tends to make it flow as though it were slipping along the wall. The result when the lubricated material is being squeezed out of the gap between approaching parallel plates is flow more nearly irrotational, or extensional, the more effective the lubricating film on the plates. Two Newtonian analyses of this flow situation are reported. One is an approximate, asymptotic analytical solution for Newtonian lubricating flow in the films and combined mixed flow, shear and extension, in the viscous layer. The second is a full two‐dimensional axisymmetric solution of the momentum and continuity equations along with the kinematic condition which governs the motion of the interface. Both analyses indicate that there are two limiting flow regimes, depending on the ratio of the thickness of each of the two phases to radius and on the viscosity ratio of the two liquids. In one limit the flow is parallel squeezing and the lubricant layer slowly thins and persists a long time. In the other the lubricant is expelled preferentially. Implications of the results are discussed for rheological characterization of viscoelastic liquids and for prediction of lubricated or autolubricated flows in processing situations.
Solution of three‐dimensional natural convection about a vertical square rod in a cylindrical enclosure
Authors: Glakpe E. K. , Watkins C. B. , Kurien B. 
Published: August 2005

AbstractThe problem of three‐dimensional laminar natural convection in a vertical enclosure with an inner square rod is treated by a numerical method in boundary‐fitted co‐ordinates. The inner and outer cylinders are heated and cooled, respectively, to maintain different constant surface temperatures. The horizontal enclosure surfaces are maintained at adiabatic conditions. The Prandtl number is that of air, 0·703, and the Rayleigh numbers span the conduction, transition and boundary layer regimes of flow. The radius ratio is 1, and the aspect ratio (cylinder length divided by maximum annular gap) is 1. The results of the study provide data useful in the design and performance assessment of nuclear reactor spent fuel shipping casks.
A spectral method with staggered grid for incompressible Navier‐Stokes equations
Authors: Montigny‐Rannou F. , Morchoisne Y. 
Published: August 2005

AbstractIn order to solve the Navier‐Stokes equations by spectral methods, we develop an algorithm using a staggered grid to compute the pressure. On this grid, an iterative process based on an artificial compressibility matrix associates the pressure with the continuity equation. This method is very accurate and avoids naturally most of the effects of parasite modes appearing in classical spectral methods with a velocity—pressure formulation.
Finite element analysis of flow in a gas‐filled rotating annulus
Authors: Berger M. H. 
Published: August 2005

AbstractLinearized multidimensional flow in a gas centrifuge can be described away from the ends by Onsager's pancake equation. However a rotating annulus results in a slightly different set of boundary conditions from the usual symmetry at the axis of rotation. The problem on an annulus becomes ill‐posed and requires some special attention. Herein we treat axially linear inner and outer rotor temperature distributions and velocity slip. An existence condition for a class of non‐trivial, one‐dimensional solutions is given. New exact solutions in the infinite bowl approximation have been derived containing terms that are important at finite gap width and non‐vanishing velocity slip. The usual one‐dimensional, axially symmetric solution is obtained as a limit. Our previously reported finite element algorithm has been extended to treat this new class of problems. Effects of gap width, temperature and slip conditions are illustrated. Lastly, we report on the compressible, finite length, circular Couette flow for the first time.
A hydrometeorological, three‐dimensional model of thermal energy releases into environmental media
Authors: Markatos N. C. , Pericleous K. , Simitovic R. 
Published: August 2005

AbstractA computer model has been developed to study thermal energy releases into the environment. A typical application of the model is the study of the behaviour of cooling‐tower effluent under different weather and operating conditions. The model employs the full three‐dimensional transport equations describing the conservation of mass, momentum and energy. The flow is treated as single‐phase and the behaviour of any droplets present is calculated indirectly. The model takes into account such hydrometeorological phenomena as the effects of humidity, wind direction and speed, density variations and the presence and precipitation of droplets. Sample results from cooling tower applications are presented and discussed.
Application of conjugate‐gradient‐like methods to a hyperbolic problem in porous‐media flow
Authors: Obeysekare Upul R. B. , Allen Myron B. , Ewing Richard E. , George John H. 
Published: August 2005

AbstractThis paper presents the application of a preconditioned conjugate‐gradient‐like method to a non‐self‐adjoint problem of interest in underground flow simulation. The method furnishes a reliable iterative solution scheme for the non‐symmetric matrices arising at each iteration of the non‐linear time‐stepping scheme. The method employs a generalized conjugate residual scheme with nested factorization as a preconditioner. Model runs demonstrate significant computational savings over direct sparse matrix solvers.
Application of an explicit TVD scheme for unsteady, axisymmetric, muzzle brake flow
Authors: Cooke C. H. 
Published: August 2005

AbstractOperator splitting in the presence of source terms is necessary in order to apply Harten's second‐order accurate, total‐variation‐diminishing (TVD), shock‐capturing scheme to higher‐dimensional problems. By employing Godunov boundary treatment at the muzzle brake, such splitting is applied to the problem of muzzle brake flow simulation for the case of blasts which are impeded, by vertical and slanted baffles, respectively. Results from numerical studies of various types of wall boundary condition treatment which are consistent with Harten's TVD scheme are indicated.
Studies in numerical computations of recirculating flows
Authors: Castro I. P. , Jones J. M. 
Published: August 2005

AbstractThis paper considers the use of various finite differencing schemes for the computation of flows involving regions of recirculation. Standard first‐order hybrid schemes, vector (or skew) schemes and second‐order schemes are used to predict laminar flows in a channel containing a constriction and over a normal flat plate with a downstream splitter plate. In the former case the results are compared with those of other workers and with the implications of analytic theories for the viscous dominated flow around the sharp corner.Attention is concentrated on the effects of errors arising from the use of non‐uniform grids and it is shown that higher‐order differencing schemes are generally much less susceptible to these than the simpler schemes. The major conclusion is that for flows containing regions where pressure gradients largely balance the convective terms in the momentum equations, in addition to other regions where convection and diffusion balance, higher order differencing schemes are likely to be essential if accurate predictions are required on grids without excessive numbers of nodes. It is argued that similar conclusions must hold for high Reynolds number turbulent flows.