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Author: J. P. Gostelow Publisher: ISBN: Category : Boundary layer Languages : en Pages : 0
Book Description
Boundary layer transition has been investigated experimentally under low, moderate, and high free-stream turbulence levels and varying adverse pressure gradients. Under high turbulence levels and adverse pressure gradients a pronounced sub-transition was present. A strong degree of similarity in intermittency distributions was observed, for all conditions, when the Narasimha procedure for determination of transition inception was used. Effects of free-stream turbulence on the velocity profile are particularly strong for the laminar boundary layer upstream of the transition region. This could reflect the influence of the turbulence on the shear stress distribution throughout the layer and this matter needs further attention. The velocity profiles in wall coordinates undershoot the turbulent wall layer asymptote near the wall over most of the transition region. The rapidity with which transition occurs under adverse pressure gradients produces strong lag effects on the velocity profile; the starting turbulent boundary layer velocity profile may depart significantly from local equilibrium conditions. The practice of deriving integral properties and skin friction for transitional boundary layers by a linear combination of laminar and turbulent values for equilibrium layers is inconsistent with the observed lag effects. The velocity profile responds sufficiently slowly to the perturbation imposed by transition that much of the anticipated drop in form factor will not have occurred prior to the completion of transition. This calls into question both experimental techniques, which rely on measured form factor to characterize transition, and boundary layer calculations, which rely on local equilibrium assumptions in the vicinity of transition.
Author: J. P. Gostelow Publisher: ISBN: Category : Boundary layer Languages : en Pages : 0
Book Description
Boundary layer transition has been investigated experimentally under low, moderate, and high free-stream turbulence levels and varying adverse pressure gradients. Under high turbulence levels and adverse pressure gradients a pronounced sub-transition was present. A strong degree of similarity in intermittency distributions was observed, for all conditions, when the Narasimha procedure for determination of transition inception was used. Effects of free-stream turbulence on the velocity profile are particularly strong for the laminar boundary layer upstream of the transition region. This could reflect the influence of the turbulence on the shear stress distribution throughout the layer and this matter needs further attention. The velocity profiles in wall coordinates undershoot the turbulent wall layer asymptote near the wall over most of the transition region. The rapidity with which transition occurs under adverse pressure gradients produces strong lag effects on the velocity profile; the starting turbulent boundary layer velocity profile may depart significantly from local equilibrium conditions. The practice of deriving integral properties and skin friction for transitional boundary layers by a linear combination of laminar and turbulent values for equilibrium layers is inconsistent with the observed lag effects. The velocity profile responds sufficiently slowly to the perturbation imposed by transition that much of the anticipated drop in form factor will not have occurred prior to the completion of transition. This calls into question both experimental techniques, which rely on measured form factor to characterize transition, and boundary layer calculations, which rely on local equilibrium assumptions in the vicinity of transition.
Author: Robert Edward Mayle Publisher: Logos Verlag Berlin GmbH ISBN: 3832545980 Category : Science Languages : en Pages : 418
Book Description
Second Enhanced Edition Suitable for advanced-level courses or an independent study in fluid mechanics, this text by an expert in the field provides the basic aspects of laminar-to-turbulent flow transition in boundary layers. Logically organized into three major parts, the book covers pre- and post-transitional flow, transitional flow, and several advanced topics in periodically disturbed transitional flow. Some of the subjects covered within the book include high-frequency unsteady laminar flow, turbulent flow, natural transition, bypass transition, turbulent spot theory, turbulent spot kinematics and production, correlations for the onset and rate of transition, global and conditional averaging, transitional flow models, wakeinduced transition, multimode transition, and separated-flow transition. Containing some 202 figures (all drawn by the author), 28 tables, 12 appendices, a supplement on tensors, and an extensive bibliography, the 415 page book provides a wealth of data and information about the subject.
Author: Gregory John Walker Publisher: ISBN: Category : Boundary layer Languages : en Pages : 0
Book Description
Existing transition models are surveyed and deficiencies in previous predictions, which seriously overestimate transition length under an adverse pressure gradient, are discussed. A new model for transition in an adverse pressure gradient situation is proposed and experimental results are provided which confirm its validity. A correlation for transition length is advanced which incorporates both Reynolds number and pressure gradient effects. Under low free-stream turbulence conditions the basic mechanism of transition is laminar instability. There are, however, physical differences between zero and adverse pressure gradients. In the former case transition occurs randomly, due to the breakdown of laminar instability waves in sets. For an adverse pressure gradient the Tollmien-Schlichting waves appear more regularly with a well-defined spectral peak. As the adverse pressure gradient is increased from zero to the separation value the flow evolves continuously from random to periodic behavior and the dimensionless transition length progressively decreases.
Author: Hal L. Moses Publisher: ISBN: Category : Boundary layer Languages : en Pages : 85
Book Description
The problem of predicting the behavior of the incompressible turbulent boundary layer in an adverse pressure gradient is re-examined. An outline of the problem is given along with a brief summary of the work that has already been done, including both experimental investigation are presented for a separating turbulent boundary layer with various pressure distributions. An approximate theory is developed in which the momentum integral equation is satisfied for each half of the boundary layer. The velocity profiles used in the analysis consist of the well known wall and wake regions, resulting in a two-parameter family with the Reynolds number as one parameter. It is assumed, with some experimental justification, that the eddy viscosity can be reasonably approximated from zero pressure gradient experimets. The numerical calculations, using the Runge-Kutta procedure, show good agreement with the experiments. The reliability that can be expected of such approximate methods is discussed. (Author).
Author: Yoshimichi Tanida Publisher: Springer Science & Business Media ISBN: 3642848249 Category : Technology & Engineering Languages : en Pages : 904
Book Description
Over the last decade, flow visualization has advanced in step with the progress in laser and computer technologies. The scope of the International Symposium on Flow Visualiza- tion will be broader than ever, covering the range of infor- mation generally thought of as nonvisual and reflecting the inclusion of computer - aided methodologies. The Sixth In- ternational Symposium on Flow Visualization aims to attract the participation of experts and users of flow viualizing techniques on furthering an advanced philosophy for the de- velopment of the methods and their applications.
Author: G. Bergeles Publisher: Newnes ISBN: 0444600132 Category : Technology & Engineering Languages : en Pages : 932
Book Description
This book presents and discussses new developments in the area of turbulence modelling and measurements, with particular emphasis on engineering-related problems. At present, turbulence is one of the key issues in tackling engineering flow problems. Powerful computers and numerical methods are now available for solving the flow equations, but the simulation of turbulence effects which are nearly always important in practice, is still in an unsatisfactory state and introduces considerable uncertainities in the accuracy of CFD calculations. These and other aspects of turbulence modelling and measurements are dealt with in detail by experts in the field. The resulting book is an up-to-date review of the most recent research in this exciting area.
Author: J. P. Gostelow
Author: J. P. Gostelow
Author: Robert Edward Mayle
Author: Gregory John Walker
Author: 
Author: Hal L. Moses
Author: 
Author: Yoshimichi Tanida
Author: Shimer Zane Pinckney
Author: Ki-Hyeon Sohn
Author: G. Bergeles