摘要:

AbstractWe consider the use of accelerated gradient‐type iterative methods for solution of Newtonian and certain non‐Newtonian (power‐law and Bingham models) viscous flow problems. The formulations are based on penalty and mixed finite element methods, and such factors as the effect of the penalty parameter, asymmetry, continuation and preconditioning are exa

ISSN:0271-2091    

DOI:10.1002/fld.1650090202

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA numerical analysis of the flow pattern in the inlet region of a circular pipe rotating steadily about an axis parallel to its own is presented. Both finite cell and finite element methods are used to analyse the problem and they give qualitatively similar results which show that a swirling fluid motion is induced in the pipe inlet region. The analyses show that the direction of swirl is opposite to that of the pipe rotation when viewed along the flow axis and that its magnitude depends on the speed of pipe rotation and throughflow Reynolds number. Neither numerical analysis predicts the marked upturn in friction factor (or pressure drop) which has been observed experimentally. However, a dependence on the pipe inlet boundary conditions is demonstrated.

ISSN:0271-2091    

DOI:10.1002/fld.1650090203

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractNumerical studies of turbulent flow in an axisymmetric 45° expansion combustor and bifurcated diffuser are presented. The Navier‐Stokes equations incorporating ak–ϵ model were solved in a non‐orthogonal curvillinear co‐ordinate system. A zonal grid method, wherein the flow field was divided into several subsections, was developed. This approach permitted different computational schemes to be used in the various zones. In addition, grid generation was made a more simple task. However, treatment of the zonal boundaries required special handling. Boundary overlap and interpolating techniques were used and an adjustment of the flow variables was required to assure conservation of mass flux. Three finite differencing methods—hybrid, quadratic upwind and skew upwind—were used to represent the convection terms. Results were compared with existing experimental data. In general, good agreement between predicted and measured values

ISSN:0271-2091    

DOI:10.1002/fld.1650090204

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA collocation‐type boundary element method based on bilinear B‐splines is used for the numerical solution of the Stokes Dirichlet problem in bounded domainsD⊂R3. The computation of the influence matrix requires the numerical evaluation of weakly singular integrals on the domain boundary if the usual double‐layer potentialansatzis chosen. Here mostly standard methods with disjoint grids for collocation and integration are used. We develop a special integration scheme based on triangular co‐ordinates near the singularity and show its efficiency compared with the method mentio

ISSN:0271-2091    

DOI:10.1002/fld.1650090205

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractNine finite difference schemes using primitive variables on various grid arrangements were systematically tested on a benchmark problem of two‐dimensional incompressible Navier–Stokes flows. The chosen problem is similar to the classical lid‐driven cavity flow, but has a known exact solution. Also, it offers the reader an opportunity to thoroughly evaluate accuracies of various conceptual grid arrangements.Compared to the exact solution, the non‐staggered grid scheme with higher‐order accuracy was found to yield an accuracy significantly better than others. In terms of ‘overall performance’, the so‐called 4/1 staggered grid scheme proved to be the best. The simplicity of this scheme is the primary benefit. Furthermore, the scheme can be changed into a non‐staggered grid if the pressure is replaced by the pressure gradient as a field variable.Finally, the conventional staggered grid scheme developed by Harlow and Welch also yields relatively high accuracy and demonstrates satisfactory ov

ISSN:0271-2091    

DOI:10.1002/fld.1650090206

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractPreconditioning techniques based on incomplete Gaussian elimination for large, sparse, non‐symmetric matrix systems are described. A certain level of fill‐in may be specified in the incomplete factorizations. All methods considered may be applied to matrices with arbitrary sparsity patterns, for instance those associated with the general preprocessor algorithms or adaptive mesh techniques. The preconditioners have been combined with five conjugate gradient‐like methods and tested on finite element discretized scalar convection‐diffusion equations in 2D and 3D. It is found from numerical experiments that an amount of fill‐in corresponding to about 50% of the number of original non‐zero matrix entries is the optimal choice for this class of preconditioners. The preconditioners show almost no sensitivity to grid distortion. In problems with significantly variable coefficients or anisotropy the preconditioners stabilize the basic iterative schemes in addition to reducing the computational work substantially, mostly by more than 90%. The modified preconditioning technique, where fill‐in is added on the main diagonal, performs in general better than the standard incomplete LU factorization, but is inferior to the latter in 3D problems and for matrix systems with complicated spar

ISSN:0271-2091    

DOI:10.1002/fld.1650090207

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractRational strategies are considered for the specification of the intermediate boundary condition at an inflow boundary where process splitting (fractional steps) is adopted in solving the advection–dispersion equation. Three lowest‐order methods are initially considered and evaluation is based on comparisons with an analytical solution. For flow and dispersion parameter ranges typical of rivers and estuaries, the given boundary condition for the complete advection–dispersion equation at the end of the complete time step provides a satisfactory estimate of the intermediate boundary value. This was further confirmed by the development and evaluation of two higher‐order methods. These required non‐centred discrete approximations for spatial derivatives, which offset any special advantages from the higher truncation er

ISSN:0271-2091    

DOI:10.1002/fld.1650090208

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650090209

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650090210

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650090201

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY