摘要:

AbstractA comparison between solutions from simulations of a non‐linear density current test problem was made in order to study the behaviour of a variety of numerical methods. The test problem was diffusion‐limited so that a grid‐converged reference solution could be generated using high spatial resolution. Solutions of the test problem using several different resolutions were computed by the participants of the ‘Workshop on Numerical Methods for Solving Nonlinear Flow Problems’, which was held on 11–13 September 1990 at the National Center for Supercomputing Applications (NCSA). In general, it was found that when the flow was adequately resolved, all of the numerical schemes produced solutions that contained the basic physics as well as most of the flow detail of the reference solution. However, when the flow was marginally resolved, there were significant differences between the solutions produced by the various models. Finally, when the flow was poorly resolved, none of the models performed very well. While higher‐order and spectral‐type schemes performed best for adequately and marginally resolved flow, solutions made with these schemes were virtually unusable for poorly resolved flow. In contrast, the monotonic schemes provided the most coherent and smooth solutions for poorly resolved flow, however with noticeable amplitude and phase speed errors, even at fi

ISSN:0271-2091    

DOI:10.1002/fld.1650170103

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA finite‐element model has been used to study steady‐state turbulent flow through bifurcated submerged‐entry nozzles with oversized ports typical of those used in the continuous casting of steel. Both 2D and 3D simulations have been performed with the commercial code FIDAP, using the standardK–ϵ turbulence model. Predicted velocities from 3D simulations compare reasonably with experimental measurements using a hot‐wire anemometer conducted in a physical water model, where severe turbulent fluctuations are present. Results show that a 2D simulation can also capture the main flow characteristics of the jet existing the nozzle and requires two orders of magnitude less computer time than the 3D simulation. A model combining the nozzle and mould was set up to study the effect of the outlet boundary conditions of the nozzle on the jet characteristics. This modelling technique will assist in the design of submerged‐entry nozzles, especially as applied to enhance steel quality in the continuous casting process. Further, the model will provide appropriate inlet boundary conditions for a separate numerical model

ISSN:0271-2091    

DOI:10.1002/fld.1650170104

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe time evolution of finite amplitude axisymmetric perturbations (Taylor cells) to the purely azimuthal, viscoelastic, cylindrical Couette flow was numerically simulated. Two time integration numerical methods were developed, both based on a pseudospectral spatial approximation of the variables, efficiently implemented using fast Poisson solvers and optimal filtering routines. The first method, applicable for finiteRenumbers, is based on a time‐splitting integration with the divergence‐free condition enforced through an influence matrix technique. The second one, is based on a semi‐implicit time integration of the constitutive equation with both the continuity and the momentum equations enforced as constraints. Stability results for an upper convected Maxwell fluid were obtained for the supercritical bifurcations, either steady or time‐periodic, developed after the onset of instabilities in the primary flow. At small elasticity values, ϵ ≡De/Re, the time integration of finite amplitude disturbances confirms the stability of the single branch of steady Taylor cells. At intermediate ϵ values the rotating wave family of time‐periodic solutions developed at the onset of instability is stable, whereas the standing wave is found to be unstable. At high ϵ values, and in particular for the limit of creeping flow (ϵ = ∞), the present study shows that the rotating wave family is unstable and the standing (radial) wave is stable, in agreement with previous finite‐element investigations. It is thus shown that spectral techniques provide a robust and computationally efficient method for the simulation of complex, non‐linear, time‐depen

ISSN:0271-2091    

DOI:10.1002/fld.1650170105

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAn approach for simultaneously assessing numerical accuracy and extracting physical information from multidimensional calculations of complex (engineering) flows is proposed and demonstrated. The method is based on global balance equations, i.e. volume‐integrated partial differential equations for primary or derived physical quantities of interest. Balances can be applied to the full computational domain or to any subdomain down to the single‐cell level. Applications to in‐cylinder flows in reciprocating engines are used for illustration. It is demonstrated that comparison of the relative magnitude of the terms in the balances provides insight into the physics of the flow being computed. Moreover, for quantities that are not conserved at the cell or control volume level in the construction of the numerical scheme, the imbalance allows a direct assessment of numerical accuracy in a single run using a single mesh. The mean kinetic energy imbalance is shown to be a particularly sensitive indicator of numerical accuracy. This simple and powerful diagnostic approach can be implemented for finite‐difference, finite‐volume or finite‐elem

ISSN:0271-2091    

DOI:10.1002/fld.1650170106

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650170102

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY