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Author: J. D. A. Walker Publisher: ISBN: Category : Fluid dynamics Languages : en Pages : 47
Book Description
"The prediction of the influence of freestream turbulence on boundary layer properties such as wall heat transfer, skin friction and the integral thicknesses is investigated using the model of McDonald, Fish and Kreskovsky; the model is critically discussed in detail. In addition, an assessment is made both of the overall performance of the model and of the numerical finite difference procedures used to implement the model in a current UTRC prediction code. Detailed comparisons are made with recently obtained experimental data, taken over a wide range of freestream turbulence and pressure gradient conditions. In an overall sense, the turbulence model provided good predictions for the skin friction and integral boundary layer properties in fully developed zero pressure gradient flows; relatively good qualitative levels of the solutions were encountered. For favorable pressure gradient flows, the behavior in the transition zone was only captured qualitatively. Generally, it is concluded that the model provides a reasonable basis for further development to accurately account for mainstream turbulence effects in boundary layers; however, in view of difficulties encountered in using the code, a need to revise the numerical procedures is indicated."--Abstract.
Author: J. D. A. Walker Publisher: ISBN: Category : Fluid dynamics Languages : en Pages : 47
Book Description
"The prediction of the influence of freestream turbulence on boundary layer properties such as wall heat transfer, skin friction and the integral thicknesses is investigated using the model of McDonald, Fish and Kreskovsky; the model is critically discussed in detail. In addition, an assessment is made both of the overall performance of the model and of the numerical finite difference procedures used to implement the model in a current UTRC prediction code. Detailed comparisons are made with recently obtained experimental data, taken over a wide range of freestream turbulence and pressure gradient conditions. In an overall sense, the turbulence model provided good predictions for the skin friction and integral boundary layer properties in fully developed zero pressure gradient flows; relatively good qualitative levels of the solutions were encountered. For favorable pressure gradient flows, the behavior in the transition zone was only captured qualitatively. Generally, it is concluded that the model provides a reasonable basis for further development to accurately account for mainstream turbulence effects in boundary layers; however, in view of difficulties encountered in using the code, a need to revise the numerical procedures is indicated."--Abstract.
Author: Kanika Gakhar Publisher: ISBN: Category : Languages : en Pages : 201
Book Description
This thesis describes an analysis of the effect of freestream turbulence (FST) on turbulent boundary layer loss generation. A relation has been derived between a turbulence parameter, which characterizes the FST, and the increase in boundary layer dissipation coefficient. The relation gives guidelines for trade studies, for example between combustor turbulence properties and turbine performance in a typical gas turbine engine. Based on the FST length-scale, two regimes of FST influence have been defined, with consequent different functional dependencies between FST parameters and boundary layer dissipation coefficient. In one regime, characterized by self-similarity of mean velocity and turbulence production profiles, the dissipation coefficient is a function of local parameters, and can be determined using measurement data for effects of FST on skin-friction. In the second regime, the boundary layer deviates from equilibrium due to the lag between the rate of turbulence production and dissipation. For this latter case, a method has been developed to estimate the effect of FST on dissipation using a modified shear-lag model, based on the conservation of turbulent kinetic energy. This thesis shows that the increase in boundary layer loss due to local FST can be as high as 73%, and that non-equilibrium effects can result in an additional increase in boundary layer loss as high as 8%. Finally, the framework developed in this thesis has also been applied to an industry relevant situation, quantifying the effect of combustor turbulence on high pressure turbine (HPT) performance. Example trade studies show that increasing the size of dilution ports, increasing the length of the combustor, and rearranging or re-orienting the dilution jets in cross-flow in the combustor all can help decrease HPT profile loss generation, and potentially increase stage efficiency up to 0.5%.
Author: M. F. Blair Publisher: ISBN: Category : Languages : en Pages : 193
Book Description
In an earlier funded investigation, experimental research was conducted to deterine the influence of free-stream turbulence on turbulent boundary layer heat transfer and mean profile development. The data obtained under this earlier contract indicated that both the skin friction and the heat transfer increased significantly with increased free-stream turbulence level. Under the present investigation, detailed boundary layer turbulence structural data and turbulent heat transfer data were obtained for experimental test conditions and profile locations selected from the earlier test matrix. Numerious measurements assured that the present test conditions (boundary layer development and free-stream turbulence distributions) duplicated those of the earlier contract. The purposes for making these present detailed boundary layer turbulence measurements were: to provide data to which current finite-difference boundary layer turbulence models could be compared, and to generate a data base for the development of new analytical models for bondary layer heat transfer prediction. With the completion of the experimental portion of this investigation, a theoretical effort was made to assess the capability of a finite difference boundary layer computer program, ABLE (Analysis of the Boundary Layer Equations) for predicting the effect of free-stream turbulence on momentum and thermal boundary layers.
Author: A.V. Boiko Publisher: Springer Science & Business Media ISBN: 3662047659 Category : Technology & Engineering Languages : en Pages : 273
Book Description
The Origin of Species Charles Darwin The origin of turbulence in fluids is a long-standing problem and has been the focus of research for decades due to its great importance in a variety of engineering applications. Furthermore, the study of the origin of turbulence is part of the fundamental physical problem of turbulence description and the philosophical problem of determinism and chaos. At the end of the nineteenth century, Reynolds and Rayleigh conjectured that the reason of the transition of laminar flow to the 'sinuous' state is in stability which results in amplification of wavy disturbances and breakdown of the laminar regime. Heisenberg (1924) was the founder of linear hydrody namic stability theory. The first calculations of boundary layer stability were fulfilled in pioneer works of Tollmien (1929) and Schlichting (1932, 1933). Later Taylor (1936) hypothesized that the transition to turbulence is initi ated by free-stream oscillations inducing local separations near wall. Up to the 1940s, skepticism of the stability theory predominated, in particular due to the experimental results of Dryden (1934, 1936). Only the experiments of Schubauer and Skramstad (1948) revealed the determining role of insta bility waves in the transition. Now it is well established that the transition to turbulence in shear flows at small and moderate levels of environmental disturbances occurs through development of instability waves in the initial laminar flow. In Chapter 1 we start with the fundamentals of stability theory, employing results of the early studies and recent advances.
Author: Tuncer Cebeci Publisher: Elsevier ISBN: 0323151051 Category : Technology & Engineering Languages : en Pages : 423
Book Description
Analysis of Turbulent Boundary Layers focuses on turbulent flows meeting the requirements for the boundary-layer or thin-shear-layer approximations. Its approach is devising relatively fundamental, and often subtle, empirical engineering correlations, which are then introduced into various forms of describing equations for final solution. After introducing the topic on turbulence, the book examines the conservation equations for compressible turbulent flows, boundary-layer equations, and general behavior of turbulent boundary layers. The latter chapters describe the CS method for calculating two-dimensional and axisymmetric laminar and turbulent boundary layers. This book will be useful to readers who have advanced knowledge in fluid mechanics, especially to engineers who study the important problems of design.
Author: Jafar Mehdi Hassan Publisher: Bentham Science Publishers ISBN: 1681088126 Category : Science Languages : en Pages : 303
Book Description
Turbulent Flow and Boundary Layer Theory: Selected Topics and Solved Problems explains fundamental concepts of turbulent flow with boundary layer analysis. A general introduction to turbulent flow familiarizes the reader with the mechanics of turbulence in fluid flow in both nature and engineering applications. The book also explains related concepts including transient flow, methods for controlling transients, turbulent models and dynamic equations for unsteady flow through closed conduits. The contents of the book are designed to help both students and teachers in carrying out turbulent flow analysis and solving problems in engineering and hydraulic applications. Key Features - all the basic concepts in turbulent flow are clearly identified and presented in a simple manner with illustrative and practical examples. - includes a self-contained approach to the subject, indicating prerequisite materials and information needed from courses. - each chapter also has a set of questions and problems to test the student’s power of comprehending the topics. - provides an exhaustive appendix on interesting examples Turbulent Flow and Boundary Layer Theory: Selected Topics and Solved Problems a useful textbook for students of engineering. It also serves as a quick reference for professionals, researchers and project consultants involved with processes that require turbulent flow and boundary layer methods analysis.
Author: Angel Nicolas Menendez Publisher: ISBN: Category : Turbulent boundary layer Languages : en Pages : 226
Book Description
A turbulent boundary layer, subjected to a free-stream velocity which changes sinusiodally in time under a zero time mean pressure gradient, is studied both experimentally and analytically. Using a two-component Laser Doppler Anemometer and a Heat Flux Gage, detailed and high quality information is obtained on the instantaneous velocity distribution and wall shear stress, respectively, at various stations. An asymptotic theory, for large Reynolds numbers, is developed for the oscillatory motion. It is valid for both boundary layers at arbitrary time-mean pressure gradients and fully developed pipe and channel flow, and is successfully applied to the present and previous available experimental information. The theory identifies two frequency parameters, in terms of which four different frequency regimes are defined. Similarity laws are identified for each one of these frequency regimes. All the experimental data have been archived on magnetic tape. (Author).
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Experimental research has been conducted to determine the influence of free-stream turbulence on zero pressure gradient fully turbulent boundary layer flow. During this period convective heat transfer coefficients, boundary layer mean velocity and temperature profile data, and wall static pressure distribution data were obtained for five flow conditions of constant free-stream velocity and free-stream turbulence intensities ranging from approximately 1/4% to 7%. Free-stream multi-component turbulence intensity, longitudinal integral scale, and spectral distributions were obtained for the various turbulence levels. The test results with 1/4% free-stream turbulence indicate that these data are in excellent agreement with classic two-dimensional low free-stream turbulence, turbulent boundary layer correlations, thus establishing the absolute accuracy of the experiment. The data obtained for the test cases with higher free-stream turbulence indicate that the turbulence has a significant effect on turbulent boundary layer skin friction and heat transfer. It has been shown that these effects are a function of the free-stream turbulence intensity, the turbulence length scale, and the boundary layer momentum thickness Reynolds number. Suggested correlations for the influence of free-stream turbulence on skin friction, heat transfer, and Reynolds analogy factor are given. Also during this period, a boundary layer prediction method has been assessed as to its ability to predict free-stream turbulence effects on flat plate heating and skin friction. Comparisons with the experimental data obtained here showed that adequate predictions can be made for this case with an existing turbulence model. (Author).
Author: J. D. A. Walker
Author: J. D. A. Walker
Author: Kanika Gakhar
Author: M. F. Blair
Author: A.V. Boiko
Author: Tuncer Cebeci
Author: Jafar Mehdi Hassan
Author: Rodney C. Schmidt
Author: Angel Nicolas Menendez
Author: 
Author: James Liburdy