Journal ArticleDOI
On nonlinear K-l and K-ε models of turbulence
TLDR
In this paper, a nonlinear K-l and K-e model is proposed to predict the normal Reynolds stresses in turbulent channel flow much more accurately than the linear model, and the nonlinear model is shown to be capable of predicting turbulent secondary flows in non-circular ducts.Abstract:
The commonly used linear K-l and K-e models of turbulence are shown to be incapable of accurately predicting turbulent flows where the normal Reynolds stresses play an important role. By means of an asymptotic expansion, nonlinear K-l and K-e models are obtained which, unlike all such previous nonlinear models, satisfy both realizability and the necessary invariance requirements. Calculations are presented which demonstrate that this nonlinear model is able to predict the normal Reynolds stresses in turbulent channel flow much more accurately than the linear model. Furthermore, the nonlinear model is shown to be capable of predicting turbulent secondary flows in non-circular ducts - a phenomenon which the linear models are fundamentally unable to describe. An additional application of this model to the improved prediction of separated flows is discussed briefly along with other possible avenues of future research.read more
Citations
More filters
Journal ArticleDOI
Investigation of diesel engine performance and emissions by multi-dimensional modeling
TL;DR: In this article, a development combustion model Extended Coherent Flame Models 3 Zones (ECFM-3Z) was used to predict in-cylinder combustion behavior, effects of turbulence levels, flow structures and emission modeling.
Epistemic Uncertainty Quantification of RANS Turbulence Models
Vahid Esfahanian,Iman Rahbari +1 more
TL;DR: In this article, a new and efficient method to quantify this type of uncertainty is presented, in which RANS equations with and without modeling are balanced so that, the sources of introduced uncertainty in Reynolds stress tensor can be found.
Book ChapterDOI
Burners for reformers and cracking furnaces
TL;DR: In this paper, the authors discuss the furnaces and burners used in reforming and cracking processes, including general design principles such as metering the fuel and air, mixing the fuel, maintaining ignition, molding the flame, and minimizing pollution emissions, as well as specific types used in reformers and crackers.
Book ChapterDOI
High Performance Computing of Turbulent Flows
TL;DR: The quest for unlimited geometric flexibility as a prerequisite to the integration of CFD into the design cycle for real engineering components has led to the development of flexible three-dimensional multi-block and unstructured-grid schemes supported by sophisticated gridgeneration techniques.
Journal ArticleDOI
二次元後方ステップ流れに対するK-ε,K-Tモデルの評価・検討
Abstract: The capability of two-equation K-e and K- T models to predict separated flows is investigated from the computational standpoint. The flow over a backward-facing step is chosen as a test problem. A method of lines approach is adopted as a numerical method. The spatial derivatives are discretized by the second order central and upwind difference approximations. As a time integration scheme a rational Runge-Kutta method is used. In the first place, a variety of low-Raynolds number K-e and K-T (Launder-Sharma, Lam-Bremhorst, Speziale) models are tested. It is found that the Launder-Sharma model predicts the reattachment length more closely to the experimentally measured value than the other two models, and that the dumping function used in the Lam-Bremhorst or Speziale model is not appropriate for separated flows. In the next place, it is found that the use of the anisotropic eddy-viscosity models predicts normal stress better than the isotropic model, whereas the computed reattachment length and mean-velocity profile are not greatly improved by the use of the anisotropic models.
References
More filters
Journal ArticleDOI
Progress in the development of a Reynolds-stress turbulence closure
TL;DR: In this article, the authors developed a model of turbulence in which the Reynolds stresses are determined from the solution of transport equations for these variables and for the turbulence energy dissipation rate E. Particular attention is given to the approximation of the pressure-strain correlations; the forms adopted appear to give reasonably satisfactory partitioning of the stresses both near walls and in free shear flows.
Journal ArticleDOI
A numerical study of three-dimensional turbulent channel flow at large Reynolds numbers
TL;DR: In this article, the three-dimensional, primitive equations of motion have been integrated numerically in time for the case of turbulent, plane Poiseuille flow at very large Reynolds numbers.
Journal ArticleDOI
Numerical investigation of turbulent channel flow
Parviz Moin,John Kim +1 more
TL;DR: In this article, a large-scale flow field was obtained by directly integrating the filtered, three-dimensional, time dependent, Navier-Stokes equations, and small-scale field motions were simulated through an eddy viscosity model.
Book ChapterDOI
Computational Modeling of Turbulent Flows
TL;DR: In this article, it is shown that direct simulation is not an alternative for practical computation and that the various sophisticated closures suffer from essentially the same problems as the direct simulations and therefore, are limited to homogeneous situations.
Journal ArticleDOI
A Reynolds stress model of turbulence and its application to thin shear flows
Kemal Hanjalic,Brian Launder +1 more
TL;DR: In this paper, the authors provided a model of turbulence which effects closure through approximated transport equations for the Reynolds stress tensor the turbulence energy κ and e.g., the turbulent shear stress does not vanish where the mean rate of strain goes to zero.