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Experimental and Numerical Investigation of Developing Turbulent Flow Over a Wavy Wall

Author : Vinicius Martins Segunda

Publisher :

Page : 0 pages

File Size : 12,76 MB

Release : 2017

Category :

ISBN :

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Book Description

Turbulent flow over a wavy wall in a horizontal channel is investigated by experimental and numerical methods. The thorough problem understanding can advance turbulent flow physics knowledge for separating and reattaching flows. Another important consideration is the performance evaluation of mathematical models used in computational fluid dynamics (CFD) codes to predict the flow characteristics. This study explores numerical models because they are critically important to the design and performance evaluation of engineering systems. The experimental data are obtained to provide repository data and more insights into the flow physics considering both the flow development and fully periodic regions. A channel with a wavy bottom wall is considered for this study, and its main characteristic is a value of 10 for the ratio between the wave length and wave amplitude. A high-resolution particle image velocimetry (PIV) system is used to obtain detailed measurements of velocity at Reynolds number of 5040, 8400, 10700 and 13040 in both the developing and fully periodic regions. The numerical simulations are performed with a commercial CFD code using four eddy viscosity turbulence models and three Second-Moment Closure (SMC) turbulence models. This work assessed the predictive accuracy of a total of seven turbulence models. The experimental study covered a lack of data for the flow development within the waves, prior the periodic condition region, and it supported the turbulence models evaluation. The experiments provided features of the flow such as the recirculation regions, Reynolds stresses, and turbulent kinetic energy production at different channel locations. A comprehensive comparison between models and experimental data revealed a significant dependency on the turbulence model formulation and on the wall treatment selection for the flow development and fully periodic regions predictions.







The Origin of Turbulence in Near-Wall Flows

Author : A.V. Boiko

Publisher : Springer Science & Business Media

Page : 273 pages

File Size : 28,29 MB

Release : 2013-03-09

Category : Technology & Engineering

ISBN : 3662047659

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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.







Near-wall Turbulent Flows

Author : Ronald M. C. So

Publisher : Elsevier Publishing Company

Page : 1072 pages

File Size : 49,93 MB

Release : 1993

Category : Mathematics

ISBN :

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Book Description

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.







Annular Two-Phase Flow

Author : Geoffrey Hewitt

Publisher : Elsevier

Page : 327 pages

File Size : 37,33 MB

Release : 2013-10-22

Category : Technology & Engineering

ISBN : 1483285235

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Book Description

Annular Two-Phase Flow presents the wide range of industrial applications of annular two-phase flow regimes. This book discusses the fluid dynamics and heat transfer aspects of the flow pattern. Organized into 12 chapters, this book begins with an overview of the classification of the various types of interface distribution observed in practice. This text then examines the various regimes of two-phase flow with emphasis on the regions of occurrence of the annular flow regime. Other chapters consider the single momentum and energy balances, which illustrate the differences and analogies between single- and two-phase flows. This book discusses as well the simple modes for annular flow with consideration to the calculation of the profile of shear stress in the liquid film. The final chapter deals with the techniques that are developed for the measurement of flow pattern, entrainment, and film thickness. This book is a valuable resource for chemical engineers.