摘要:

An accurate numerical solution of diffusion problems containing large local gradients can be obtained with a significant reduction in computational time by using a multi-grid computational scheme. The spatial domain is covered with sets of uniform square grids of different sizes. The finer grid patterns overlap the coarse grid patterns. The finite-difference expressions for each grid pattern are solved Independently by iterative techniques. Two interpolation methods were used to establish the values of the potential function on the fine grid boundaries with information obtained from the coarse grid solution. The accuracy and computational requirements for solving a test problem by a simple multigrid and a multilevel-multigrid method were compared. The multilevel-multigrid method combined with a Taylor series interpolation scheme was found to be best.

ISSN:0149-5720    

DOI:10.1080/01495728408961824

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A “front-tracking” finite-element method has been developed for the study of inverse one-dimensional conduction heat transfer problems with phase change. The method can be used to determine the transient position of the change of phase interface and the thermal history in the solid region from information concerning the temperature history at two arbitrary points in the solid region. This technique can be employed in the control and experimental evaluation of practical heat transfer problems with phase change, such as welding. The accuracy of the method is illustrated through numerical experimentation and found to depend on a typical dimensionless Fourier number.

ISSN:0149-5720    

DOI:10.1080/01495728408961825

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Solutions for the periodic fully developed regime in an annulus of axially varying cross section were obtained numerically. The annular duct considered here has stream wise-periodic variations of the cross-sectional area, and its dimensions were those of an actual double-pipe heat exchanger (a reflux condenser). The calculations were performed for laminar flow in the Reynolds number range from SO to 1000. In the heat transfer analysis, two boundary conditions were investigated-uniform wall temperature and uniform wall heat flux. The Prandtl number of the fluid was varied from 2 to 10, with liquid water in mind. On the basis of the computed heat transfer coefficients and pressure drops, the periodic annulus appears to be an attractive enhancement configuration relative to the annulus of axially unchanging cross section. For example, at the largest Reynolds and Prandtl numbers investigated (Re ≃. 1000, Pr = 10), the Nusselt number values for the periodic annulus exceed those for the uniform annulus by about a factor of 4, with an increase in the pressure drop of only about a factor of 2. The differences between the Nusselt numbers for the two boundary conditions studied were moderate, typically on the order of 10%, with localized extreme deviations of 15% occurring at the largest investigated Re and Pr.

ISSN:0149-5720    

DOI:10.1080/01495728408961826

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A finite-difference numerical scheme is used to study combined free- and forced-convection boundary-layer flow in a porous medium near a vertical wall. The model results show that the inertial and viscous effects have a significant influence on the velocity profiles and heat transfer rate at the surface. The dimensionless parameters Pr, Gr/Re, and Re all have a marked effect on the velocity and temperature distributions within the boundary layer. Consideration is also given to the effects of porosity variation and of low blowing velocities at the surface. It is found that while porosity variation has a negligible effect on the results, blowing at the walls produces large changes in the velocity and temperature distributions.

ISSN:0149-5720    

DOI:10.1080/01495728408961827

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Steady three-dimensional conjugate natural convection heat transfer from a horizontal isothermal cylinder with infinitely large transverse nonisothermal fins is studied numerically. The complete Navier-Stokes equations are solved using a vorticity-vector potential approach. Results are obtained for a Rayleigh number of 103and a Prandtl number of 5. Effects of the variation of fin spacing and fin conduction are studied. Two limits of this problem at a large fin spacing are an infinitely long isothermal free cylinder and an infinitely large vertical conducting plate fin with a circular isothermal heat source. Results are compared against both limits and the latter limit is used to develop a correlation for the local heat transfer from the fin. It is found that heat is transferred from the fluid to the fin in a sector adjacent to the plume above the heated cylinder. With alt other conditions held fixed, there exists an optimum fin spacing at which the total heat transfer per unit length of cylinder is a maximum.

ISSN:0149-5720    

DOI:10.1080/01495728408961828

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A numerical study was performed on die Reynolds-stress turbulence closure for separating, reattaching, recirculating, and redeveloping flow. The calculations were made for two different closure models of pressure-strain correlation. The results were compared with experimental data. Furthermore, the remits were compared with computations made by using the one-layer and three-layer treatments of the k-ε turbulence model that were developed in the authors' earlier work. Generally, die computation with the Reynolds-stress model gave better results than were obtained with the k-ε model; in particular, some improvement was noticed in the redeveloping region of the separating and reattaching flow in a pipe with sudden expansion.

ISSN:0149-5720    

DOI:10.1080/01495728408961829

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A theoretical and experimental study has been conducted to Investigate the turbulent separated flows behind a rotating cone. Measurements of the pressure, mean velocity, and turbulence intensity were made with a micromanometer and a hot-wire anemometer. As a theoretical part of the study, a general finite-difference calculation procedure was developed for heat transfer prediction of the axisymmetric turbulent separated flows with a nonzero tangential velocity component. A special effort was made to deal with irregular boundaries. The calculations performed with the present numerical method and the k-ε turbulence model are compared extensively with experimental data obtained for various apex angles, free-stream velocities, and angular velocities.

ISSN:0149-5720    

DOI:10.1080/01495728408961830

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor