Download or read book Near wall K epsilon Turbulence Modeling written by and published by . This book was released on 1987 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advanced K Epsilon Modeling of Heat Transfer written by National Aeronautics and Space Adm Nasa and published by . This book was released on 2018-11-19 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes two approaches to low Reynolds-number k-epsilon turbulence modeling which formulate the eddy viscosity on the wall-normal component of turbulence and a length scale. The wall-normal component of turbulence is computed via integration of the energy spectrum based on the local dissipation rate and is bounded by the isotropic condition. The models account for the anisotropy of the dissipation and the reduced mixing length due to the high strain rates present in the near-wall region. The turbulent kinetic energy and its dissipation rate were computed from the k and epsilon transport equations of Durbin. The models were tested for a wide range of turbulent flows and proved to be superior to other k-epsilon models, especially for nonequilibrium anisotropic flows. For the prediction of airfoil heat transfer, the models included a set of empirical correlations for predicting laminar-turbulent transition and laminar heat transfer augmentation due to the presence of freestream turbulence. The predictions of surface heat transfer were generally satisfactory. Kwon, Okey and Ames, Forrest E. AERODYNAMIC HEAT TRANSFER; BOUNDARY LAYER FLOW; COMPUTATIONAL FLUID DYNAMICS; EDDY VISCOSITY; K-EPSILON TURBULENCE MODEL; LOW REYNOLDS NUMBER; TURBULENCE; TURBULENT FLOW; ANISOTROPY; KINETIC ENERGY; MIXING LENGTH FLOW THEORY; NONEQUILIBRIUM FLOW; TURBINE BLADES; WALL FLOW...

Download or read book Modeling Complex Turbulent Flows written by Manuel D. Salas and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 385 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulence modeling both addresses a fundamental problem in physics, 'the last great unsolved problem of classical physics,' and has far-reaching importance in the solution of difficult practical problems from aeronautical engineering to dynamic meteorology. However, the growth of supercom puter facilities has recently caused an apparent shift in the focus of tur bulence research from modeling to direct numerical simulation (DNS) and large eddy simulation (LES). This shift in emphasis comes at a time when claims are being made in the world around us that scientific analysis itself will shortly be transformed or replaced by a more powerful 'paradigm' based on massive computations and sophisticated visualization. Although this viewpoint has not lacked ar ticulate and influential advocates, these claims can at best only be judged premature. After all, as one computational researcher lamented, 'the com puter only does what I tell it to do, and not what I want it to do. ' In turbulence research, the initial speculation that computational meth ods would replace not only model-based computations but even experimen tal measurements, have not come close to fulfillment. It is becoming clear that computational methods and model development are equal partners in turbulence research: DNS and LES remain valuable tools for suggesting and validating models, while turbulence models continue to be the preferred tool for practical computations. We believed that a symposium which would reaffirm the practical and scientific importance of turbulence modeling was both necessary and timely.

Download or read book An Improved K epsilon Model for Near wall Turbulence and Comparison with Direct Numerical Simulation written by and published by . This book was released on 1990 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis of the K Epsilon Turbulence Model written by B. Mohammadi and published by . This book was released on 1994-09-06 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aimed at applied mathematicians interested in the numerical simulation of turbulent flows. Centered around the k-&epsis; model, it also deals with other models such as one equation models, subgrid scale models and Reynolds Stress models. Presents the k-&epsis; method for turbulence in a language familiar to applied mathematicians, but has none of the technicalities of turbulence theory.

Download or read book An Improved k epsilon Model for Near wall Turbulence and Comparison with Direct Numerical Simulation written by T. H. Shih and published by . This book was released on 1990 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A New Time Scale Based K Epsilon Model for Near Wall Turbulence written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-28 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: A k-epsilon model is proposed for wall bonded turbulent flows. In this model, the eddy viscosity is characterized by a turbulent velocity scale and a turbulent time scale. The time scale is bounded from below by the Kolmogorov time scale. The dissipation equation is reformulated using this time scale and no singularity exists at the wall. The damping function used in the eddy viscosity is chosen to be a function of R(sub y) = (k(sup 1/2)y)/v instead of y(+). Hence, the model could be used for flows with separation. The model constants used are the same as in the high Reynolds number standard k-epsilon model. Thus, the proposed model will be also suitable for flows far from the wall. Turbulent channel flows at different Reynolds numbers and turbulent boundary layer flows with and without pressure gradient are calculated. Results show that the model predictions are in good agreement with direct numerical simulation and experimental data. Yang, Z. and Shih, T. H. Glenn Research Center NASA ORDER C-99066-6; RTOP 505-62-21...

Download or read book Kolmogorov Behavior of Near wall Turbulence and Its Application in Turbulence Modeling written by Tsan-Hsing Shih and published by . This book was released on 1992 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A New Time Scale Based K Epsilon Model for Near Wall Turbulence written by National Aeronautics and Space Administration NASA and published by . This book was released on 2018-10-23 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: A k-epsilon model is proposed for wall bonded turbulent flows. In this model, the eddy viscosity is characterized by a turbulent velocity scale and a turbulent time scale. The time scale is bounded from below by the Kolmogorov time scale. The dissipation equation is reformulated using this time scale and no singularity exists at the wall. The damping function used in the eddy viscosity is chosen to be a function of R(sub y) = (k(sup 1/2)y)/v instead of y(+). Hence, the model could be used for flows with separation. The model constants used are the same as in the high Reynolds number standard k-epsilon model. Thus, the proposed model will be also suitable for flows far from the wall. Turbulent channel flows at different Reynolds numbers and turbulent boundary layer flows with and without pressure gradient are calculated. Results show that the model predictions are in good agreement with direct numerical simulation and experimental data. Yang, Z. and Shih, T. H. Glenn Research Center NASA ORDER C-99066-6; RTOP 505-62-21...

Download or read book An Improved K Epsilon Model for Near Wall Turbulence and Comparison with Direct Numerical Simulation written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-08-16 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: An improved k-epsilon model for low Reynolds number turbulence near a wall is presented. The near-wall asymptotic behavior of the eddy viscosity and the pressure transport term in the turbulent kinetic energy equation is analyzed. Based on this analysis, a modified eddy viscosity model, having correct near-wall behavior, is suggested, and a model for the pressure transport term in the k-equation is proposed. In addition, a modeled dissipation rate equation is reformulated. Fully developed channel flows were used for model testing. The calculations using various k-epsilon models are compared with direct numerical simulations. The results show that the present k-epsilon model performs well in predicting the behavior of near-wall turbulence. Significant improvement over previous k-epsilon models is obtained. Shih, T. H. Glenn Research Center NASA-TM-103221, ICOMP-90-16, E-5635, NAS 1.15:103221 NASA ORDER C-99066-G; RTOP 505-62-21...

Download or read book An Improved Near wall K epsilon Model for the Calculation of Wall Bounded Turbulent Flows written by Arup Sarkar and published by . This book was released on 1995 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Critical Evaluation of Two Equation Models for Near Wall Turbulence written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-27 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: A variety of two-equation turbulence models, including several versions of the K-epsilon model as well as the K-omega model, are analyzed critically for near wall turbulent flows from a theoretical and computational standpoint. It is shown that the K-epsilon model has two major problems associated with it: the lack of natural boundary conditions for the dissipation rate and the appearance of higher-order correlations in the balance of terms for the dissipation rate at the wall. In so far as the former problem is concerned, either physically inconsistent boundary conditions have been used or the boundary conditions for the dissipation rate have been tied to higher-order derivatives of the turbulent kinetic energy which leads to numerical stiffness. The K-omega model can alleviate these problems since the asymptotic behavior of omega is known in more detail and since its near wall balance involves only exact viscous terms. However, the modeled form of the omega equation that is used in the literature is incomplete-an exact viscous term is missing which causes the model to behave in an asymptotically inconsistent manner. By including this viscous term and by introducing new wall damping functions with improved asymptotic behavior, a new K-tau model (where tau is identical with 1/omega is turbulent time scale) is developed. It is demonstrated that this new model is computationally robust and yields improved predictions for turbulent boundary layers. Speziale, Charles G. and Abid, Ridha and Anderson, E. Clay Langley Research Center NAS1-18605..

Download or read book The Sensitivity Analysis in K epsilon Turbulence Modeling Applied to Jet Flows written by Farhad Raiszadeh and published by . This book was released on 1984 with total page 368 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Turbulent Flow in a 180 Deg Bend written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-15 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: A low Reynolds number k-epsilon turbulence model was presented which yields accurate predictions of the kinetic energy near the wall. The model is validated with the experimental channel flow data of Kreplin and Eckelmann. The predictions are also compared with earlier results from direct simulation of turbulent channel flow. The model is especially useful for internal flows where the inflow boundary condition of epsilon is not easily prescribed. The model partly derives from some observations based on earlier direct simulation results of near-wall turbulence. The low Reynolds number turbulence model together with an existing curvature correction appropriate to spinning cylinder flows was used to simulate the flow in a U-bend with the same radius of curvature as the Space Shuttle Main Engine (SSME) Turn-Around Duct (TAD). The present computations indicate a space varying curvature correction parameter as opposed to a constant parameter as used in the spinning cylinder flows. Comparison with limited available experimental data is made. The comparison is favorable, but detailed experimental data is needed to further improve the curvature model. Kaul, Upender K. Unspecified Center NAS2-11555...

Download or read book Boundary Layer Theory written by Hermann Schlichting (Deceased) and published by Springer. This book was released on 2016-10-04 with total page 814 pages. Available in PDF, EPUB and Kindle. Book excerpt: This new edition of the near-legendary textbook by Schlichting and revised by Gersten presents a comprehensive overview of boundary-layer theory and its application to all areas of fluid mechanics, with particular emphasis on the flow past bodies (e.g. aircraft aerodynamics). The new edition features an updated reference list and over 100 additional changes throughout the book, reflecting the latest advances on the subject.

Download or read book Modeling of Near wall Turbulence written by T. H. Shih and published by . This book was released on 1990 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advancements in Engineering Turbulence Modeling written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-08-20 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Some new developments in two-equation models and second order closure models are presented. Two-equation models (k-epsilon models) have been widely used in computational fluid dynamics (CFD) for engineering problems. Most of low-Reynolds number two-equation models contain some wall-distance damping functions to account for the effect of wall on turbulence. However, this often causes the confusion and difficulties in computing flows with complex geometry and also needs an ad hoc treatment near the separation and reattachment points. A set of modified two-equation models is proposed to remove the aforementioned shortcomings. The calculations using various two-equation models are compared with direct numerical simulations of channel flow and flat boundary layers. Development of a second order closure model is also discussed with emphasis on the modeling of pressure related correlation terms and dissipation rates in the second moment equations. All the existing models poorly predict the normal stresses near the wall and fail to predict the 3-D effect of mean flow on the turbulence (e.g. decrease in the shear stress caused by the cross flow in the boundary layer). The newly developed second order near-wall turbulence model is described and is capable of capturing the near-wall behavior of turbulence as well as the effect of 3-D mean flow on the turbulence. Shih, T.-H. Glenn Research Center ...