ISSN:1061-8562    

DOI:10.1080/10618569908940873

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An experimental and numerical study has been made of transient natural convection of water freezing in a cube-shaped cavity. The effect of the heat transfer through the side walls is studied in two configurations: with the cavity surrounded by air and with the cavity immersed in an external water bath of constant temperature. The experimental data for the velocity and temperature fields are obtained using liquid crystal tracers. The transient development of the ice/water interface is measured. The collected data are used as an experimental benchmark and compared with numerical results obtained from a Finite-difference code with boundary fitted grid generation. The computational model has been adopted to simulate as closely as possible the physical experiment. Hence, fully variable fluid properties are implemented in the code, and, to improve modelling of the thermal boundary conditions, the energy equation is also solved inside the bounding walls. Although the general behaviour of the calculated ice front and its volume matches observations, several details of the flow structure do not. Observed discrepancies between experimental and numerical results indicate the necessity of verifying and improving the usual assumptions for modelling ice formation.

ISSN:1061-8562    

DOI:10.1080/10618569908940874

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A semi-analytic numerical scheme has been developed to solve the one-dimensional, moving boundary phase change problem with time-dependent boundary conditions. Locally analytic, approximate solutions are developed for the position of the moving boundary, and for temperature distribution. Set of discrete equations are obtained by applying these solutions over space-time nodes, and by imposing continuity of temperature and heat flux. Application of this so-called nodal integral approach to the nonlinear Stefan problem shows that the scheme isO(Δx2), and that it predicts the position of the moving boundary and the temperature distribution within the domain very accurately. For example, with as little as two nodes in the spatial domain, the location of the moving boundary for the case of an exponentially increasing surface temperature on the boundary, after one dimensionless time unit, is found with an error of less than 1%. In addition to large size nodes in space, this scheme also allows the use of very large size time steps. Comparison of numerical results with reference solutions is presented.

ISSN:1061-8562    

DOI:10.1080/10618569908940875

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A Computational Fluid Dynamics (CFD) model is presented for the uniform viscous two dimensional flow past an oscillating cylinder at low Reynolds number. Numerical simulations are made to study the effect of differing forced induced oscillation mechanisms with a large range of cylinder forcing frequencies. In the first case sinusoidal velocity slip boundary conditions are adopted for the cylinder surface to simulate cylinder oscillation. The implication suggests that no modification or additional term need to be added to the Navier-Stokes equations. In the second case this time extra body force terms which are assumed to account for velocity effects due to cylinder movement are included in the Navier-Stokes equations with the imposition of same boundary conditions. Drag and lift coefficients are extracted from present numerical results and other detailed computations of these coefficients are made at a Reynolds number of 80 and an amplitude-to diameter ratio 0.14. The results are found to be in agreement with each other at low force driving frequencies below and near lock-in. However, differences are found at higher frequencies above lock-in. Agreement are also found with experimental results at some frequency ranges.

ISSN:1061-8562    

DOI:10.1080/10618569908940876

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The effectivity of vent hole designs of a bulk container for seed potatoes concerning water vapour transfer is investigated using a numerical model based on the Lattice Boltzmann technique. The model describes the heat and water vapour transport driven by natural convection in the potato container. By numerical study we have found an effective vent hold design which maintains the keeping quality of the potatoes by preventing water condensation.

ISSN:1061-8562    

DOI:10.1080/10618569908940877

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A standardh-adaptive finite element procedure based ona-posteriorierror-estimation is described. The pure advection equation is solved (in both steady and transient states) using the SUPG (streamline upwind Petrov-Galerkin) formulation of the finite element method. Applied to standard benchmark problems (of uniform flow advecting discontinuous functions) the SUPG method on its own is insufficient to resolve the sharp discontinuities present when used with a uniform mesh of insufficient refinement. The amount of false diffusion is also seen to be related to the degree of mesh refinement. An iterativeh-adaptive procedure used in combination with the SUPG formulation (with a discontinuity capturing term) produces a near perfect solution of the steady state benchmark problem. The transient benchmark problem (rotating cosine hill) shows that the adaptive Galerkin FEM in combination with central difference time integration produces solutions indistinguishable from the corresponding adaptive SUPG solution. This result clearly indicates that at least for transient problems correct mesh refinement with GFEM can overcome the wiggle problems associated with using GFEM with central difference time integration for advection problems. So in effect adaptivity in addition to providing the expected benefits of selective mesh refinement also acts as awiggle suppressentfor an otherwise highly oscillatory GFEM/Central Difference combination. This result is even more interesting in view of the fact that when SUPG is used it does not improve significantly on the quality of the adaptive GFEM/CD solution.

ISSN:1061-8562    

DOI:10.1080/10618569908940878

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Bifurcations of central symmetry breaking and stability of nonsymmetric states of buoyancy-driven convection in laterally heated cavities are studied numerically. The calculations are carried out using two independent numerical approaches. Stability and weakly nonlinear analysis of the calculated bifurcations are studied by the spectral Galerkin method. Time-marching calculations are carried out using the finite volume method. By applying two independent numerical approaches the subcritical steady flows, their stability, the transitions between different states and flows at small and large supercriticalities are comprehensively investigated. It is shown how these numerical techniques can be applied for interpreting a particular experimental result.

ISSN:1061-8562    

DOI:10.1080/10618569908940879

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The issue of turbine lifetime is an important one, particularly for modern turbines operating at high temperature regimes. A cooling design such as ribs may achieve an improved lifetime and complex mechanisms of heat transfer need to be well studied. In this paper, a Direct Numerical Simulation (DNS) is presented for a 3-D channel flow with two square ribs on the lower wall. The full unsteady compressible Navier-Stokes equations are solved with an original hybrid finite difference/finite element scheme. The Reynolds number of the simulation is 7 000 based on the bulk velocity at the inlet and the channel height. The present study is mainly devoted to understand the mechanism of heat transfer at the wall through the topological analysis of the flow and the temperature flux. Results show that the large-scale structures generated by obstacles splash onto the lower surface and induce longitudinal vortices which enhance heat transfer at the wall. A comprehensive data base including 56 correlations was set up for testing and improving turbulence models for this complex, separated flow.

ISSN:1061-8562    

DOI:10.1080/10618569908940880

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An adaptive finite-volume method which maps the time-dependent, curvilinear geometry of annular liquid jets into a unit square is developed to study the fluid dynamics and heat transfer of these jets once combustion within the volume that they enclose ceases. The method employs a strong-conservation law form for the governing equations, upwind and central differences for the convective and diffusive fluxes, respectively, and is conservative and implicit. It is shown that the cooling of annular liquid jets is characterized by thin, thermal boundary layers at the jet's interfaces and rapid pressure and temperature variations initially, whose accurate resolution demands the use of very small time steps and grid sizes. It is also shown that the pressure of the gases enclosed by the jet and The temperature and heat flux at the jet's inner interface drop steeply initially and that the steepness of this drop increases as the Weber number is decreased and as the nozzle exit angle decreases from outwardly to inwardly directed flows. The effects of the initial pressure and temperature, jet's thickness-to-mean radius ratio at the nozzle exit, Froude, Reynolds and thermal Péclet numbers, gas specific heat ratio, and liquid-to-gas specific heat and density ratios on the cooling of annular liquid jets are also analyzed.

ISSN:1061-8562    

DOI:10.1080/10618569908940881

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper numerically investigates the interaction between the Marangoni convection, the double diffusive convection and the intrusion force a multi-cavity system. The model consists of a two-cavity rectangular system in which the smaller cavity is located at the top left corner of the larger one. The larger cavity is filled with hot salty fluid while the smaller one contains cold fresh fluid. This problem is solved for the case of the fresh water intruding into the salty water. The interaction between the Marangoni (thermal and solutal) and the double diffusive regimes is investigated, for different solutal Rayleigh number, in detail. Finite element modelling results indicate that salinity induces stronger convection than the thermal ones and the thermal and solutal Marangoni convection further enhances the strength of the cellular flow. Numerical results indicate that surface force should be taken into consideration during the analysis and that the intruding force played an important role in the flow behaviour.

ISSN:1061-8562    

DOI:10.1080/10618569908940882

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor