bluuebunny/crossref_metadata_2025_split huggingface dataset:
Buoyancy‐driven instability in a vertical cylinder: Binary fluids with Soret effect. Part I: General theory and stationary stability results
Authors: Hardin G. R. , Sani R. L. , Henry D. , Roux B. 
Published: August 2005

AbstractBuoyancy‐driven instability of a monocomponent or binary fluid which is completely contained in a vertical circular cylinder is investigated, including the influence of the Soret effect for the binary mixture. The Boussinesq approximation is used, and the resulting linear stability problem is solved using Galerkin's technique. The analysis considers various types of fluid mixtures, ranging from gases to liquid metals, in cylinders with a variety of radius‐to‐height ratios. The flow structure is found to depend strongly on both the cylinder aspect ratio and the magnitude of the Soret effect. Comparisons are made with experiments and other theories, and the predicted stability limits are shown to agree closely with observations.
Finite element solutions of axisymmetric Euler equations for an incompressible and inviscid fluid
Authors: Saiac Jacques‐Herve 
Published: August 2005

AbstractIn this paper we present a finite element method for the numerical solution of axisymmetric flows. The governing equations of the flow are the axisymmetric Euler equations. We use a streamfunction angular velocity and vorticity formulation of these equations, and we consider the non‐stationary and the stationary problems.For industrial applications we have developed a general model which computes the flow past an annular aerofoil and a duct propeller. It is able to take into account jumps of angular velocity and vorticiy in order to model the flow in the presence of a propeller. Moreover, we compute the complete flow around the after‐body of a ship and the interaction between a ducted propeller and the stern. In the stationary case we have developed a simple and efficient version of the characteristics/finite element method. Numerical tests have shown that this last method leads to a very fast solver for the Euler equations. The numerical results are in good agreement with experimental data.
A composite grid approach for the Euler equations
Authors: Reggio Marcelo , Trepanier Jean‐Yves , Camarero Ricardo 
Published: August 2005

AbstractA zonal grid methodology has been developed for the calculation of compressible fluid flows. The domain subdivision is based on patched grid systems composed of zones or blocks within which a distinct curvilinear grid is generated. The flow simulation is then carried out with a modified scheme based on the Euler finite volume solver of Ni. This scheme uses a distribution procedure that provides an easy and accurate way for the transfer of information from one block to another. This method results in a naturally conservative computation at the interfaces. It is analysed and developed for the treatment of embedded grids with a grid point common to more than four blocks.
A design method for turbomachinery blading in three‐dimensional flow
Authors: Ghaly W. S. 
Published: August 2005

AbstractA mixed spectral finite element scheme for the implementation of a design method for turbomachinery blading in three‐dimensional subcritical compressible flow is presented. The method gives the detailed blade shape that would produce a prescribed tangential mean swirl schedule, given the hub and shroud profiles, the number of blades and their stacking position. After a presentation of the mathematical formulation of the design theory, the current numerical approach is described. It is then applied to the design of blading for radial inflow turbine impellers in three‐dimensional flow.
Numerical solution of plane and axially symmetric jet flow problems based on the variational inequality formulation
Authors: Lee Han‐Yong , Kim Moon‐Uhn 
Published: August 2005

AbstractThe numerical analysis of plane and axially symmetric jet flows of an incompressible inviscid fluid is treated. A new formulation of the variational inequality type is developed from the variational principle associated with jet problems. A successive approximation method is formulated by the combined use of variational inequality and the finite element method. Numerical examples based on the iterative method are presented. The results obtained agree well with those by other methods.
Cascade aerodynamic gust response including steady loading effects
Authors: Chiang Hsiao‐Wei D. , Fleeter Sanford 
Published: August 2005

AbstractTo predict the unsteady convected gust aerodynamic response of a cascade comprised of arbitrary thick and cambered aerofoils in an incompressible, inviscid, flow field, a complete first‐order model is formulated. The flow is analysed by considering a periodic flow channel. The velocity potential is separated into steady and unsteady harmonic components, each described by a Laplace equation. The strong dependence of the unsteady aerodynamics on the steady effects of aerofoil and cascade geometry and incidence angle is manifested in the coupling of the unsteady and steady flow fields through the unsteady boundary conditions. Analytical solutions in individual grid elements of a body‐fitted computational grid are then determined, with the complete solution obtained by assembly of these local solutions. The validity and capabilities of this model and solution technique are then demonstrated by analysing the steady and unsteady aerodynamics of both theoretical and experimental cascade configurations.
Combined radiation and natural convection in a rectangular cavity with a transparent wall and containing a non‐participating fluid
Authors: Behnia M. , Reizes J. A. , De Vahl Davis G. 
Published: August 2005

AbstractThis paper describes a numerical method for the study of combined natural convection and radiation in a rectangular, two‐dimensional cavity containing a non‐participating (i.e. transparent) fluid.One wall of the cavity is isothermal, being heated either by solar radiation or independently. The opposite wall is partially transparent, permitting radiation exchanges between the cavity and its surroundings and/or the Sun; that wall also exchanges heat by convection from its external surface to the surroundings. The other two walls are adiabatic: convection and radiation there are balanced, so that there is no heat transfer through those walls.The equations of motion and energy are solved by finite difference methods. Coupled to these equations are the radiative flux boundary conditions which are used to determine the temperature distribution along the non‐isothermal walls. A two‐band radiation model has been employed.Results are presented for a square cavity with a vertical hot wall at 150 °C, the ambient at 20 °C and 104 ⩽ Ra ⩽ 3 × 105, in the absence of direct insolation. The effects on the flow and heat transfer in the cavity of radiation and external convection have been examined. More extensive results will be presented in subsequent papers.
A proper orthogonal decomposition of a simulated supersonic shear layer
Authors: Kirby M. , Boris J. P. , Sirovich L. 
Published: August 2005

AbstractThe Karhunen–Loève procedure is applied to the analysis of an ensemble of snapshots obtained from a conditionally sampled localized shear layer simulation. The computed set of optimal basis functions is used to economically characterize sampled flow realizations. Pictorially it is seen that the essential features (and roughly 80% of the energy) of typical flows are captured by retaining roughly 10–20 parameters in the expansion. Smaller‐scale features are resolved by retaining more terms in the series.
An iterative implementation of the Uzawa algorithm for 3‐D fluid flow problems
Authors: Robichaud Michel P. , Tanguy Philippe A. , Fortin M. 
Published: August 2005

AbstractA new iterative algorithm for the solution of the three‐dimensional Navier–Stokes equations by the finite element method is presented. This algorithm is based on a combination of the Uzawa and the Arrow–Hurwicz algorithms and uses a preconditioning technique to enhance convergence. Numerical tests are presented for the cubic cavity problem with two elements, namely the linear brick Q1−P0 and the enriched linear brick Q1+ − P1. It is shown that the proposed methodology is optimal with the enriched element and that the CPU time varies as NEQ1·44, where NEQ is the number of equations.
Finite element solution of the Navier–Stokes equations by a velocity–vorticity method
Authors: Guevremont G. , Habashi W. G. , Hafez M. M. 
Published: August 2005

AbstractA velocity–vorticity formulation of the Navier–Stokes equations is presented as an alternative to the primitive variables approach. The velocity components and the vorticity are solved for in a fully coupled manner using a Newton method. No artificial viscosity is required in this formulation. The pressure is updated by a method allowing natural imposition of boundary conditions. Incompressible and subsonic results are presented for two‐dimensional laminar internal flows up to high Reynolds numbers.
Solution of viscous fluid flows on a distributed memory concurrent computer
Authors: Braaten Mark E. 
Published: August 2005

AbstractA concurrent algorithm for the solution óf the Navier–Stokes equations expressed in curvilinear co‐ordinates has been developed for execution on a distributed memory parallel computer. This algorithm offers the ultimate promise of near‐supercomputer performance on relatively low‐cost parallel computers. The new algorithm is based on an existing serial pressure‐correction‐based algorithm, and uses domain decomposition to partition the problem onto the processors. The algorithm is demonstrated on an Intel iPSC for a complicated two‐dimensional laminar flow problem, for various grid sizes and numbers of processors. Initial results based on straightforward domain decomposition showed that the speed‐up per iteration approached 100% parallel efficiency as the grid size was increased, but that the convergence rate of the algorithm deteriorated relative to the original serial algorithm as the number of processors was increased, limiting the speed‐up achieved. This degradation in convergence rate was traced to a poorer solution of the pressure correction equation in the concurrent procedure. The addition of a global block correction procedure, implemented via efficient global communications routines, remedied this problem, making the convergence rate of the concurrent procedure equivalent to the serial algorithm. The maximum speed‐up achieved with the revised concurrent algorithm was a factor of 12·3 with 16 processors, representing a parallel efficiency of 77%.
Adaptive grid computation of three‐dimensional natural convection in horizontal high‐pressure mercury lamps
Authors: Chang P. Y. , Shyy W. 
Published: August 2005

AbstractA three‐dimensional model has been developed to compute the thermofluid transport within a discharge arctube. The model has proved very useful for guiding the choice of design parameters to optimize the lamp performance. However, uncertainties exist with respect to quantitative aspects of the physical model, especially those related to radiation heat transfer. In the present work a grid refinement procedure and an adaptive grid method are used to improve the quantitative accuracy of the model and to help improve the physical modelling. The adaptive grid method, based on the multiple one‐dimensional equidistribution concept, can responsively redistribute the grids to optimize the grid resolutions. Adaptive grid solutions modify the predicted maximum gas temperature, the buoyancy‐induced convection strength, the location of the high‐temperature core, and the wall temperature profiles. The adaptive grid solutions show more consistent trends when compared to the measurements. On the basis of the quantitatively more definite information, adjustments can be made with regard to the uncertainties of the physical model.
An implicit characteristic‐flux‐averaging method for the euler equations for real gases
Authors: Drikakis D. , Tsangaris S. 
Published: August 2005

AbstractA formulation of an implicit characteristic‐flux‐averaging method for the unsteady Euler equations with real gas effects is presented. Incorporation of a real gas into a general equation of state is achieved by considering the pressure as a function of density and specific internal energy. The Ricmann solver as well as the flux‐split algorithm are modified by introducing the pressure derivatives with respect to density and internal energy. Expressions for calculating the values of the flow variables for a real gas at the cell faces are derived. The Jacobian matrices and the eigenvectors are defined for a general equation of state. The solution of the system of equations is obtained by using a mesh‐sequencing method for acceleration of the convergence. Finally, a test case for a simple form of equation of state displays the differences from the corresponding solution for an ideal gas.
A general numerical method for the solution of gravity wave problems. Part 1: 2D steep gravity waves in shallow water
Authors: Liao S. J. 
Published: August 2005

AbstractIn this paper, 2D steep gravity waves in shallow water are used to introduce and examine a new kind of numerical method for the solution of non‐linear problems called the finite process method (FPM). On the basis of the velocity potential function and the FPM, a numerical method for 2D non‐linear gravity waves in shallow water is described which can be applied to solve 3D problems, e.g. the wave resistance of a ship moving in deep or shallow water. The convergence is examined and a comparison with the results of other authors is made.The FPM can successfully avoid the use of iterative methods and therefore can overcome the disadvantages and limitations of such methods. In contrast to iterative methods, the FPM is insensitive to the selection of the initial solution and the number of unknowns. The basic idea of the FPM can be used to solve other non‐linear problems. Its disadvantage is that much more CPU time is needed to obtain a sufficiently accurate result.
Numerical computation of fluid pressure transients in pumping installations with air entrainment
Authors: Lee T. S. 
Published: August 2005

AbstractIn pumping installations such as sewage pumping stations, where gas content and air entrainment exist, the computation of fluid pressure transients in the pipelines becomes grossly inaccurate when constant wave speed and constant friction are assumed. A numerical model and computational procedure have been developed here to better compute the fluid pressure transient in a pipeline by including the effects of air entrainment and gas evolution characteristics of the transported fluid. Free and dissolved gases in the fluid and cavitation at the fluid vapour pressure are modelled. Numerical experiments show that entrained, entrapped or released gases amplify the pressure peak, increase surge damping and produce asymmetric pressure surges. The transient pressure shows a longer period for down‐surge and a shorter period for up‐surge. The up‐surge is considerably amplified and the down‐surge marginally reduced when compared with the gas‐free case. These observations are consistent with the experimental observations of other investigators. Numerical experiments also show that the use of a variable loss factor in the pressure transient analysis produces marginally higher maximum and lower minimum pressure transients when compared with the constant‐loss‐factor model for pipelines where the pressures are above the fluid vapour pressure.
Three‐dimensional desingularized boundary integral methods for potential problems
Authors: Cao Yusong , Schultz William W. , Beck Robert F. 
Published: August 2005

AbstractThe concept of desingularization in three‐dimensional boundary integral computations is re‐examined. The boundary integral equation is desingularized by moving the singular points away from the boundary and outside the problem domain. We show that the desingularization gives better solutions to several problems. As a result of desingularization, the surface integrals can be evaluated by simpler techniques, speeding up the computation. The effects of the desingularization distance on the solution and the condition of the resulting system of algebraic equations are studied for both direct and indirect versions of the boundary integral method. Computations show that a broad range of desingularization distances gives accurate solutions with significant savings in the computation time. The desingularization distance must be carefully linked to the mesh size to avoid problems with uniqueness and ill‐conditioning. As an example, the desingularized indirect approach is tested on unsteady non‐linear three‐dimensional gravity waves generated by a moving submerged disturbance; minimal computational difficulties are encountered at the truncated boundary.
Dynamics of liquid membranes. I: Non‐adaptive finite difference methods
Authors: Ramos J. I. , Pitchumani R. 
Published: August 2005

AbstractA non‐adaptive method and a Lagrangian‐Eulerian finite difference technique are used to analyse the dynamic response of liquid membrancs to imposed pressure variations. The non‐adaptive method employs a fixed grid and upwind differences for the convection terms, whereas the Lagrangian‐Eulerian technique uses operator splitting and decomposes the mixed convection‐diffusion system of equations into a sequence of convection and diffusion operators. The convection operator is solved exactly by means of the method of characteristics, and its results are interpolated onto the fixed (Eulerian) grid used to solve the diffusion operator. It is shown that although the method of characteristics eliminates the numerical diffusion associated with upwinding the convection terms in a fixed Eulerian grid, the Lagrangian‐Eulerian method may yield overshoots and undershoots near steep flow gradients or when rapid pressure gradients are imposed, owing to the interpolation of the results of the convection operator onto the fixed grid used to solve the diffusion operator. This interpolation should be monotonic and positivity‐preserving and should satisfy conservation of mass and linear momentum. It is also shown that both the non‐adaptive and Lagrangian‐Eulerian finite difference methods produce almost identical (within 1%) results when liquid membranes are subjected to positive and negative step and ramp changes in the pressure coefficient. However, because of their non‐adaptive character, these techniques require an estimate of the (unknown) length of the membrane and do not use all the grid points in the calculations. The liquid membrane dynamic response is also analysed as a function of the Froude number, convergence parameter and nozzle exit angle for positive and negative step and ramp changes in the pressure coefficient.
Dynamics of liquid membranes. II: Adaptive finite difference methods
Authors: Ramos J. I. 
Published: August 2005

AbstractTwo domain‐adaptive finite difference methods are presented and applied to study the dynamic response of incompressible, inviscid, axisymmetric liquid membranes subject to imposed sinusoidal pressure oscillations. Both finite difference methods map the time‐dependent physical domain whose downstream boundary is unknown onto a fixed computational domain. The location of the unknown time‐dependent downstream boundary of the physical domain is determined from the continuity equation and results in an integrodifferential equation which is non‐linearly coupled with the partial differential equations which govern the conservation of mass and linear momentum and the radius of the liquid membrane. One of the finite difference methods solves the non‐conservative form of the governing equations by means of a block implicit iterative method. This method possesses the property that the Jacobian matrix of the convection fluxes has an eigenvalue of algebraic multiplicity equal to four and of geometric multiplicity equal to one. The second finite difference procedure also uses a block implicit iterative method, but the governing equations are written in conservation law form and contain an axial velocity which is the difference between the physical axial velocity and the grid speed. It is shown that these methods yield almost identical results and are more accurate than the non‐adaptive techniques presented in Part I. It is also shown that the actual value of the pressure coefficient determined from linear analyses can be exceeded without affecting the stability and convergence of liquid membranes if the liquid membranes are subjected to sinusoidal pressure variations of sufficiently high frequencies.
A solution for the vertical variation of stress, rather than velocity, in a three‐dimensional circulation model
Authors: Luettich Richard A. , Westerink Joannes J. 
Published: August 2005

AbstractA simple technique is presented that allows a numerical solution to be sought for the vertical variation of shear stress as a substitute for the vertical variation of velocity in a three‐dimensional hydrodynamic model. In its most general form the direct stress solution (DSS) method depends only upon the validity of an eddy viscosity relation between the shear stress and the vertical gradient of velocity. The rationale for preferring a numerical solution for shear stress to one for velocity is that shear stress tends to vary more slowly over the vertical than velocity, particularly near boundaries. Consequently, a numerical solution can be obtained much more efficiently for shear stress than for velocity. When needed, the velocity profile can be recovered from the stress profile by solving a one‐dimensional integral equation over the vertical. For most practical problems this equation can be solved in closed form.Comparisons are presented between the DSS technique, the standard velocity solution technique and analytical solutions for wind‐driven circulation in an unstratified, closed, rectangular channel governed by the linear equations of motion. In no case was the computational effort required by the velocity solution competitive with the DSS when a physically realistic boundary layer was included.The DSS technique should be particularly beneficial in numerical models of relatively shallow water bodies in which the bottom and surface boundary layers occupy a significant portion of the water column.
An algorithm that accelerates convergence rates for incompressible Navier‐Stokes problems
Authors: Shih T. M. , Hwang B. C. 
Published: August 2005

AbstractAn algorithm, called the Algebraic Continuity Equations Solver (ACES), is developed based on the concept that two algebraic equations (three for 3D problems) can be generated from rearranging the discretized continuity equations. These rearranged equations are used to re‐compute the two velocity components (three for 3D problems), whose values are already obtained from solving the momentum equations. When written in a Navier‐Stokes computer code, this algorithm is equivalent to a fairly concise set of statements and can be implemented immediately after the computation of the continuity equation. In our analysis, ACES is used in conjunction with a grid having nodal velocity components at the vertices and the nodal pressure at the centre of each computational cell.With the aid of ACES, correction of velocity components during the iteration can be inexpensively made, leading to faster convergence rates or rendering otherwise divergent computations convergent.Test problems include benchmark problems such as lid‐driven cavity flows and buoyancy‐driven cavity flows of various parametric values and grid sizes. A 3D time‐dependent flow in an irregular geometry is also investigated. Discussions are presented to clarify some relevant issues. A possible reason why we think ACES is capable of improving the convergence rates is also given.