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| Author | : Douglas J. Lewis |
| Publisher | : |
| Total Pages | : |
| Release | : 1998 |
| Genre | : |
| ISBN | : |
| Author | : |
| Publisher | : |
| Total Pages | : 495 |
| Release | : 1996 |
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The turbulence structure of convective beat transfer was studied experimentally in complex three-dimensional and separating turbulent boundary layers. Three test cases whose fluid dynamics have been well documented were examined. In case 1, time- and spatially-resolved surface heat transfer was measured in the nose region of a wing-body junction formed by a wing and a flat plate. Both the wing and the endwall were heated and held at a constant uniform temperature 20 C above ambient temperature. Heat flux rates were increased up to a factor of 3 over the heat flux rates in the approach boundary layer. The rms of the heat flux fluctuations were as high as 25% of the mean heat flux in the vortex-dominated nose region. Away from the wing, upstream of the time-averaged vortex center, augmentation in the heat flux is due to increased turbulent mixing caused by large-scale unsteadiness of the vortex. Adjacent to the wing the augmentation in heat flux is due to a change in the mean velocity field. In case 2, simultaneous surface heat flux and temperature profiles were measured at 8 locations in the spatially-developing pressure-driven three-dimensional turbulent boundary layer upstream of a wing-body junction. Mean heat transfer was decreased 10% by three-dimensionality. The turbulent Prandtl number in the near-wall region of logarithmic temperature variation was approximately 0.9 at all measurement locations in the three-dimensional boundary layer. Profiles of the skewness factor of temperature fluctuations and conditionally-averaged temperature signals during a sweep/ejection event suggest that the strength of ejections of hot fluid from the near-wall region are decreased by three-dimensionality.
| Author | : P. Bradshaw |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 345 |
| Release | : 2013-06-29 |
| Genre | : Science |
| ISBN | : 3662225689 |
Turbulent transport of momentum, heat and matter dominates many of the fluid flows found in physics, engineering and the environmental sciences. Complicated unsteady motions which mayor may not count as turbulence are found in interstellar dust clouds and in the larger blood vessels. The fascination of this nonlinear, irreversible stochastic process for pure scientists is demonstrated by the contributions made to its understanding by several of the most distinguished mathematical physicists of this century, and its importance to engineers is evident from the wide variety of industries which have contributed to, or benefit from, our current knowledge. Several books on turbulence have appeared in recent years. Taken collectively, they illustrate the depth of the subject, from basic principles accessible to undergraduates to elaborate mathematical solutions representing many years of work, but there is no one account which emphasizes its breadth. For this, a multi-author work is necessary. This book is an introduction to our state of knowledge of turbulence in most of the branches of science which have contributed to that knowledge. It is not a Markovian sequence of unrelated essays, and we have not simply assembled specialized accounts of turbulence problems in each branch; this book is a unified treatment, with the material classified according to phenomena rather than application, and freed as far as possible from discipline-oriented detail. The approach is "applied" rather than "pure" with the aim of helping people who need to under stand or predict turbulence in real life.
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| Total Pages | : 27 |
| Release | : 1995 |
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The turbulence structure of convective heat transfer was studied experimentally in complex three- dimensional and separated turbulent boundary layers. Three test cases whose fluid dynamics have been well documented were examined. In case 1, time resolved surface heat transfer was measured in the nose region of a wing-body junction formed by a wing and a flat plate. Mean, statistical and spectral characteristics of the surface heat transfer are reported. The effects of wing shape were investigated by measuring the surface heat transfer in the nose region of a modified NACA 0020, a streamlined cylinder shape and NACA 0015. The effectiveness of a flow control device to reduce surface heat transfer is reported. In case 2, simultaneous surface heat flux and temperature profiles were measured at 11 locations in the spatially-developing pressure-driven three-dimensional turbulent boundary layer upstream of the wing-body junction. In case 3, simultaneous surface heat flux and temperature profiles were measured at 18 stream-wise locations in a mean 2-dimensional adverse-pressure gradient separating turbulent boundary layer. Mean, statistical and spectral heat flux and temperature data are reported. Mean ejection frequencies, turbulence length scales, inclination angles of the turbulence structure. and coherency between the inner and outer regions of the flow were examined from these results. Several useful correlations between surface heat transfer and velocity are reported.
| Author | : O. Sendstad |
| Publisher | : |
| Total Pages | : 130 |
| Release | : 1992 |
| Genre | : Simulation methods |
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| Total Pages | : 16 |
| Release | : 1996 |
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Almost all practical turbulent flows include three dimensional boundary layers (3DTBL's), and in many cases, the 3DTBL is the dominant feature of the flow. A boundary layer is defined as a thin layer adjacent to the surface in which the velocity drops rapidly from the freestream value to zero at the wall. A 3D boundary layer is one in which the flow direction also changes rapidly approaching the wall. This change in the flow direction called skewing is caused by transverse pressure gradients, centrifugal forces, or motion of the surface. Most research on turbulent boundary layers has been done in simple two dimensional flows in carefully controlled wind tunnels. Such boundary layers are now well understood, and excellent models are available describing both the fluid mechanics and heat transfer behavior. Recent fluid mechanics studies have shown that skewing can have a pronounced effect on the boundary layer turbulence. Models based on eddy-viscosity concepts fail, and more complex stress transport models cannot capture the reduction of turbulent mixing that usually accompanies skewing. It was unknown prior to the present study what effect the skewing might have on turbulent heat transfer. It was suspected that turbulent heat transport would be reduced in analogy to the reductions of turbulent shear stress. It was also unknown how the skewing would effect the turbulent Prandtl number, a quantity which is embedded in most turbulent heat transfer prediction schemes. The objectives of the present study were then to study the surface heat transfer rate and the turbulent heat flux in a simple three dimensional boundary layer. In particular, the research addressed the heat transfer from a heated disk rotating in an otherwise quiescent environment.
| Author | : Jean Piquet |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 767 |
| Release | : 2013-04-17 |
| Genre | : Technology & Engineering |
| ISBN | : 3662035596 |
obtained are still severely limited to low Reynolds numbers (about only one decade better than direct numerical simulations), and the interpretation of such calculations for complex, curved geometries is still unclear. It is evident that a lot of work (and a very significant increase in available computing power) is required before such methods can be adopted in daily's engineering practice. I hope to l"Cport on all these topics in a near future. The book is divided into six chapters, each· chapter in subchapters, sections and subsections. The first part is introduced by Chapter 1 which summarizes the equations of fluid mechanies, it is developed in C~apters 2 to 4 devoted to the construction of turbulence models. What has been called "engineering methods" is considered in Chapter 2 where the Reynolds averaged equations al"C established and the closure problem studied (§1-3). A first detailed study of homogeneous turbulent flows follows (§4). It includes a review of available experimental data and their modeling. The eddy viscosity concept is analyzed in §5 with the l"Csulting ~alar-transport equation models such as the famous K-e model. Reynolds stl"Css models (Chapter 4) require a preliminary consideration of two-point turbulence concepts which are developed in Chapter 3 devoted to homogeneous turbulence. We review the two-point moments of velocity fields and their spectral transforms (§ 1), their general dynamics (§2) with the particular case of homogeneous, isotropie turbulence (§3) whel"C the so-called Kolmogorov's assumptions are discussed at length.
| Author | : Stanford University. Thermosciences Division |
| Publisher | : |
| Total Pages | : 390 |
| Release | : 1987 |
| Genre | : Turbulent boundary layer |
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| Author | : Manuel D. Salas |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 402 |
| Release | : 1999-04-30 |
| Genre | : Science |
| ISBN | : 9780792355908 |
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.
| Author | : Olav Sendstad |
| Publisher | : |
| Total Pages | : 146 |
| Release | : 1992 |
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| ISBN | : |
