Study of the Structure of Turbulence in Accelerating Transitional Boundary Layers PDF Download
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Author: Michael F. Blair Publisher: ISBN: Category : Languages : en Pages : 219
Book Description
A combined experimental and analytical program has been conducted to examine transitional, accelerating boundary layer flows with high levels of freestream turbulence. An earlier program focused on measurement of transitional heat transfer distributions for four combinations of streamwise acceleration and freestream turbulence. The present program was designed to document the boundary layer turbulence structure and spectral distributions for the same four test conditions. The results from the present program have shown that transition in accelerating flows consists of an acceleration dominated stage of slowly developing intermittency followed by a second stage with the same general characteristics as zero-pressure-gradient transition. Conditionally sampled fluctuating velocity profile measurements indicated that the boundary layer turbulence was highly anisotropic in the early stages of transition. Conditionally sampled mean velocity measurements showed that within the intermittent turbulent patches the mean velocity profiles were very similar to those of an equilibrium turbulent boundary layer. Spectral distribution data indicated that preferred amplification of the most unstable (as predicted by linear stability theory) frequencies occurred upstream of the onset of transitional bursting. In addition to the experimental portion of this investigation, numerical experiments were undertaken to assess the ability of currently existing methods to predict heat transfer during transition in accelerating flows.
Author: Michael F. Blair Publisher: ISBN: Category : Languages : en Pages : 219
Book Description
A combined experimental and analytical program has been conducted to examine transitional, accelerating boundary layer flows with high levels of freestream turbulence. An earlier program focused on measurement of transitional heat transfer distributions for four combinations of streamwise acceleration and freestream turbulence. The present program was designed to document the boundary layer turbulence structure and spectral distributions for the same four test conditions. The results from the present program have shown that transition in accelerating flows consists of an acceleration dominated stage of slowly developing intermittency followed by a second stage with the same general characteristics as zero-pressure-gradient transition. Conditionally sampled fluctuating velocity profile measurements indicated that the boundary layer turbulence was highly anisotropic in the early stages of transition. Conditionally sampled mean velocity measurements showed that within the intermittent turbulent patches the mean velocity profiles were very similar to those of an equilibrium turbulent boundary layer. Spectral distribution data indicated that preferred amplification of the most unstable (as predicted by linear stability theory) frequencies occurred upstream of the onset of transitional bursting. In addition to the experimental portion of this investigation, numerical experiments were undertaken to assess the ability of currently existing methods to predict heat transfer during transition in accelerating flows.
Author: William S. Saric Publisher: ISBN: Category : Languages : en Pages : 34
Book Description
Detailed experiments were performed for boundary layers undergoing transition to turbulence. The experiments utilized multiple hot wire anemometer techniques in combination with recently developed flow visualization and computational techniques. The use of a phase-correlated and conditionally sampled measurements permitted the study of the origin and evolution of the characteristic of transitional boundary layers. Fundamental transition mechanisms and the receptivity of the boundary layer to external disturbances that led to transition were studied.
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: Publisher: ISBN: Category : Languages : en Pages : 62
Book Description
The effects of elevated free-stream turbulence and streamwise acceleration on flow and thermal structures in transitional boundary layers have been investigated experimentally on a heated flat plate. The effects on the turbulent Prandtl number and Reynolds analogy were included in this study. The free-stream turbulence levels ranged from 0.5 to 7%, and the acceleration strengths, based on K, ranged from 0.39xl0 to the minus 6th power to 4.lxl0 to the minus 6th power. A three-wire probe was used to measure the detailed momentum and thermal boundary layer structures, including the streamwise and cross-stream velocity fluctuations, the temperature fluctuation, the Reynolds stresses, the Reynolds heat fluxes, the eddy viscosity, the turbulent thermal diffusivity and the turbulent Prandtl number. The results show that elevated free-stream turbulence values result in an earlier onset of transition and reduced length of transition, whereas streamwise acceleration delays the onset of transition and lengthens the transition region, even at elevated FSTI. Compared to streamwise acceleration, FSTI is the more dominant factor on flow and thermal structure in transitional boundary layers; however, streamwise acceleration significantly reduces the turbulent spot formation rate.
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: Paul F. Brinich Publisher: ISBN: Category : Boundary layer Languages : en Pages : 36
Book Description
An analysis of time-mean-turbulent boundary layer velocity profiles measured in a rapidly accelerating flow suggests that the outer region of the velocity profiles consists of essentially inviscid, rotational flow. The extent of this inviscid outer region was observed in some cases to exceed 90 percent of what is ordinarily thought of as the turbulent boundary layer thickness. On the other hand, the inner frictional region of these velocity profiles appears to have turbulent characteristics similar to those of more conventional turbulent boundary layers. Hence, the outer edge boundary condition for this inner region is more properly the external rotational flow region than the free stream.
Author: M.Y. Hussaini Publisher: Springer Science & Business Media ISBN: 9401110328 Category : Science Languages : en Pages : 394
Book Description
These two volumes contain the proceedings of the Workshop on Transition, Turbulence and Combustion, sponsored by the Insti tute for Computer Applications in Science and Engineering (ICASE) and the NASA Langley Research Center (LaRC), during June 7 to July 2, 1993. Volume I contains the contributions from the transi tion research, and Volume II contains the contributions from both the turbulence and combustion research. This is the third workshop in the series on the subject. The first was held in 1989, the second in 1991, and their proceedings were published by Springer-Verlag under the titles "Instability and Transition" (edited by M. Y. Hussaini and R. G. Voigt) and "Instability, Transition and Turbulence" (edited by M. Y. Hussaini, A. Kumar and C. L. Streett) respectively. The objectives of these workshops are to expose the academic community to current technologically important issues of transition, turbulence and combustion, and to acquaint the academic commu nity with the unique combination of theoretical, computational and experimental capabilities at LaRC. It is hoped these will foster con tinued interactions, and accelerate progress in elucidating the funda mental phenomena of transition, turbulence and combustion. The research areas of interest in transition covered the full range of the subject: linear and nonlinear stability, direct and large-eddy simulation and phenomenological modeling of the transition zone.
Author: Bo-Jang Tu Publisher: ISBN: Category : Languages : en Pages : 137
Book Description
An experimental investigation is described in which emphasis is given to revealing the structure of turbulence near the wall in a boundary layer. Measurements made include space-time correlations between the fluctuating wall pressure and the span-wise velocity component w, and between the various velocity components. The velocity correlations include measurements of the space-time correlation of the streamwise component of the fluctuating wall shear stress. Experiments have been conducted in a thick (5 in.) turbulent boundary layer with zero pressure gradient which is produced by natural transition on a smooth surface. Sufficient data have been obtained to allow the proposal of a qualitative model for the structure of turbulence near the wall. The proposed model outlines the sequence of events that results in the production of intense pressure and velocity fluctuations by stretching of the vorticity after it is produced by viscous stresses within and near the edge of the viscous sublayer. The measurements are in qualitative agreement with the model. Qualitative agreement means that the size and shape of the contours of constant correlation and the sign of the measured correlations are in agreement with the proposed model for the turbulent structure. (Author).
Author: Michael F. Blair
Author: Michael F. Blair
Author: William S. Saric
Author: Robert Edward Mayle
Author: 
Author: 
Author: Tuncer Cebeci
Author: Pablo Hidalgo Ardana
Author: Paul F. Brinich
Author: M.Y. Hussaini
Author: Bo-Jang Tu