Download or read book Measurements and Modeling of the Mean and Turbulent Flow Structure in High Speed Rough Wall Non Equilibrium Boundary Layers written by and published by . This book was released on 2010 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt: The response of a supersonic high Reynolds number turbulent boundary layer flow subjected to mechanical distortions was experimentally examined. Local disturbances were introduced via small-scale wall patterns, and global distortions were induced through streamline curvature driven pressure gradients. Local surface topologies included k-type diamond and d-type square elements; a smooth wall was examined for comparison purposes. Three global distortions were studied with each of the three surface topologies. Measurements included planar contours of the mean and fluctuating velocity pressure sensitive paint and schlieren photography. The velocity data were acquired with sufficient resolution to characterize the mean and turbulent flow structure and to examine interactions between the local surface roughness distortions and the imposed pressure gradients on the turbulence production. A strong response to both the local and global distortions was observed with the diamond elements, where the effect of the elements extended into the outer-regions of the boundary layer. It was shown that the primary cause for the observed response was the result of local shock and expansion waves modifying the turbulence structure and production. By contrast, the square elements showed a less pronounced response to local flow distortions as the waves were significantly weaker. However, the frictional losses were higher for the blunter square roughness elements. Detailed quantitative characterizations of the turbulence flow structure and the associated production mechanisms are described herein. These experiments demonstrate fundamental differences between supersonic and subsonic rough-wall flows, and the new understanding of the underlying mechanisms provides a scientific basis to systematically modify the mean and turbulence flow structure all the way across supersonic boundary layers.
Download or read book Experimental Investigation of High Speed Boundary Layers with Wall Roughness written by and published by . This book was released on 2001 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive investigation of the influence of surface roughness on the mean and turbulent flow properties of a high-speed turbulent boundary layer flow was performed. Six wall topologies, including a smooth and five rough surfaces consisting of three random sand-grain plates and two uniformly machined plates (k = 0 - 1.7 mm), were tested at three high Reynolds number (Re/m = 2 x lO (exp 7) Mach numbers (0.22, 0.65 and 2.75) . Mean flow measurements included surveys of the velocity and density. Turbulence quantities included measurements of the kinematic velocity turbulence intensities, mass flux turbulence intensities, kinematic Reynolds shear stress, compressible Reynolds shear stress, density-transverse-velocity fluctuation correlation, velocity spectra, auto-correlations, micro- and integral-scales and turbulent structure angles. Numerical simulations included evaluating three algebraic turbulence models with a boundary layer program. A three-year program was performed.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 836 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Near wall Turbulent Flows written by Ronald M. C. So and published by Elsevier Publishing Company. This book was released on 1993 with total page 1072 pages. Available in PDF, EPUB and Kindle. Book excerpt: Knowledge of near-wall turbulence from experimental, theoretical and numerical sources is accumulating at an ever increasing rate. An overview of the latest important developments is reported and discussed in depth in this volume with the goal of stimulating closer dialogue between researchers in all areas of near-wall turbulence. The full text of 95 contributed papers cover a broad range of topics in near-wall turbulent flows that includes boundary layers, coherent structures, drag reduction, experimental methods, high speed flows, numerical simulations, transition and turbulent modeling. The innovativeness of the contributions demonstrates that near-wall turbulence remains a vital and dynamically evolving field with important technological consequences for the future.
Download or read book Open Channel Turbulent Boundary Layers and Wall Jets on Rough Surfaces written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: For many industrial and environmental flows, the momentum and convective heat transfer rates at the surface are determined by the turbulence structure in the near-wall region. Although many flows of practical interest occur on rough surfaces, our understanding and ability to predict rough wall turbulent flows lags far behind the corresponding technology for smooth surfaces. This provides reasonable grounds for additional refined rough wall measurements with the expectation of improving our physical understanding of practically relevant turbulent flows. This thesis reports an experimental investigation of wall roughness effects on the characteristics of turbulent boundary layers and wall jets. The measurements are obtained for smooth wall and three different roughness elements using a laser-Doppler anemometer. An insightful presentation of the results requires that the correct scaling laws must be used. In the case of the turbulent boundary layer, the appropriateness of the log law proposed by Millikan (1938) to model the overlap region of the mean flow and the power laws proposed by Barenblatt (1993) and George and Castillo (1997) is compared. The boundary layer results show that the theory proposed by George and Castillo (1997) has important advantages over the log law in modeling the mean velocity profiles as well as predicting the wall shear stress. The results also show that wall roughness increases the turbulence fluctuations and transport terms, which suggests that rough wall turbulence models must explicitly account for roughness effects in order to predict the mixing characteristics accurately. This promises to provide significant challenges to rough wall turbulence models. The wall jet results show that wall roughness increases the inner layer thickness but the jet half-width does not show any important sensitivity to surface roughness. The spread rates for the jet half-width are higher than the values obtained in earlier measurements. This may be attribute.
Download or read book The Thermal and Hydrodynamic Behavior of Thick Rough wall Turbulent Boundary Layers written by P. M. Ligrani and published by . This book was released on 1979 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thick, fully rough, and transitionally rough turbulent boundary layers were studied in order to investigate the differences between fully rough and transitionally rough behavior and to observe how downstream development affects these flows as the boundary layers become very thick. Measurements included Stanton numbers, skin friction coefficients, mean temperature and velocity profiles, Reynolds stress tensor component profiles, and spectra of the longitudinal velocity fluctuations. Predictions of wall heat transfer, wall shear, and mean profiles were made using a mixing-length and turbulent Prandtl number closure scheme which accounted for the effects of wall roughness in the boundary layer equations. The turbulent layers were artificially thickened using an array of solid obstacles which produced a two-dimensional equilibrium flow field with properties representative of natural bounday layers, at least up to the level of the turbulent correlations on a smooth wall, and to the level of the spectra of longitudinal velocity fluctuations on a rough wall. A rough-wall boundary layer environment was provided in which all measurements of lower order than the turbulence correlations could be discussed regarding the influence of roughness, and considered to have properties representative of natural behavior. (Author).
Download or read book Numerical Simulations of Rough wall Turbulent Boundary Layers written by and published by . This book was released on 2015 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt: At sufficiently high Reynolds number, all surfaces are rough, and roughness affects most flows in engineering and the natural sciences. Examples range from atmospheric boundary layers over buildings and canopies, to engineering surfaces with erosion, deposits, etc. To study the roughness effects, we take a high-resolution approach to capture the flow around individual roughness elements using direct and large-eddy simulations (DNS and LES); the goal is to elucidate phenomena which have been difficult to access using physical experiments, and to help develop engineering correlations and models. First, most experiments and turbulence models are based on a standardized type of roughness, sand-grain roughness, which can be described using a single length scale. The relationship between the geometry of an arbitrary surface and the canonical one must be known, to predict critical flow parameters such as the drag, using either experimental correlations or turbulence models. Using numerical experiments, we relate this length-scale to the roughness geometry, and propose a guideline for its prediction in the industrial setting. Next, to explain the dependence of drag on the topographical details, we examine the role of the wake of the roughness elements in the drag generation of a rough surface. The wake field is found to promote vertical momentum transfer and near-wall instability; it might provide a link between geometry details and the engineering modeling of roughness effects. Lastly, we focus on a more realistic flow scenario -- the one with freestream accelerations -- and study the combined effects of roughness and acceleration, a phenomenon widely present in engineering flows over airfoils or complex landscapes. It is first shown, by comparing equilibrium accelerating flows obtained in the present study with the non-equilibrium flows in the literature, that the roughness and acceleration effects are interdependent and depend on the flow equilibrity. Then, using DNS data of a spatially developing flat-plate boundary layer, it is found that the effect coupling develops as the roughness affects the turbulence time scale and thus the flow susceptibility of the acceleration stabilization, while acceleration changes the wake velocity and ultimately the roughness destabilization level.
Download or read book Analysis of Turbulent Boundary Layers written by Tuncer Cebeci and published by Elsevier. This book was released on 2012-12-02 with total page 423 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Turbulence Measurements and Flow Modeling written by C.J. Chen and published by Springer. This book was released on 1987-03 with total page 888 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Constructive Modeling of Structural Turbulence and Hydrodynamic Instabilities written by Oleg Mikhailovich Belotserkovskii and published by World Scientific. This book was released on 2009 with total page 489 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book provides an original approach in the research of structural analysis of free developed shear compressible turbulence at high Reynolds number on the base of direct numerical simulation (DNS) and instability evolution for ideal medium (integral conservation laws) with approximate mechanism of dissipation (FLUX dissipative monotone OC upwindOCO difference schemes) and does not use any explicit sub-grid approximation and semi-empirical models of turbulence. Convective mixing is considered as a principal part of conservation law.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1972 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Origin of Turbulence in Near Wall Flows written by A.V. Boiko and published by Springer Science & Business Media. This book was released on 2002-01-22 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents a comprehensive survey of the origin of turbulence in near-wall shear layer flows. Instead of going too far into details modern approaches to the problem are discussed in a conceptual treatment. The transition from laminar to turbulent flows in shear layers is described including the generation of flow perturbations, their amplification and development, the breakdown of the initial laminar state, and transformation to a turbulent regime. This book also presents new approaches to boundary-layer transitions with strong external-flow perturbations and to the prediction and control of the presented near-wall transitions to turbulence. This book is addressed to researchers, lecturers and students in engineering, physics and mathematics.
Download or read book Some Characteristics of Turbulent Boundary Layers in Rapidly Accelerated Flows written by Paul F. Brinich and published by . This book was released on 1971 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book The Effects of Streamwise Concave Curvature on Turbulent Boundary Layer Structure written by Albert H. Jeans and published by . This book was released on 1982 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: Concave curvature has a relatively large, unpredictable effect on turbulent boundary layers. Some, but not all previous studies suggest that a large-scale, stationary array of counter-rotating vortices exists within the turbulent boundary layer on a concave wall. The objective of the present study was to obtain a qualitative model of the flow field in order to increase our understanding of the underlying physics. A large free-surface water channel was constructed in order to perform a visual study of the flow. Streamwise components of mean velocity and turbulence intensity were measured using a hot film anemometer. The upstream boundary was spanwise uniform with a momentum thickness to radius of curvature of 0.05. Compared to flat wall flow, large-scale, randomly distributed sweeps and ejections were seen in the boundary layer on the concave wall. The sweeps appear to suppress the normal mechanism for turbulence production near the wall by inhibiting the bursting process. The ejections appear to enhance turbulence production in the outer layers as the low speed fluid convected from regions near the wall interacts with the higher speed fluid farther out. The large-scale structures did not occur at fixed spanwise locations, and could not be called roll cells or vortices. (Author).
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1998 with total page 920 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Progress in Wall Turbulence 2 written by Michel Stanislas and published by Springer. This book was released on 2015-08-17 with total page 430 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the proceedings of the ERCOFTAC Workshop on Progress in Wall Turbulence: Understanding and Modelling, that was held in Lille, France from June 18 to 20, 2014. The workshop brought together world specialists of near wall turbulence and stimulated exchanges between them around up-to-date theories, experiments, simulations and numerical models. This book contains a coherent collection of recent results on near wall turbulence including theory, new experiments, DNS and modeling with RANS, LES. The fact that both physical understanding and modeling by different approaches are addressed by the best specialists in a single workshop is original.
Download or read book Physics Briefs written by and published by . This book was released on 1993 with total page 1212 pages. Available in PDF, EPUB and Kindle. Book excerpt:
