Second Moment Closure Modeling of Complex Turbulent Flows PDF Download
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Author: Sharath Girimaji
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 48
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Book Description
Turbulence subject to unsteady forcing can exhibit novel features that cannot be explained using the well-known steady-turbulence paradigm. Modeling and prediction of such statistically unsteady flows are important in many practical AFOSR applications: turbine flows, wake-flows with vortex shedding, etc. Further, many flow control strategies depend upon the knowledge of unsteady turbulence dynamics to achieve the desired objectives. However, our understanding of unsteadily-forced turbulence dynamics or our ability to predict them is inadequate.
Author: Sharath Girimaji
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 48
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Book Description
Turbulence subject to unsteady forcing can exhibit novel features that cannot be explained using the well-known steady-turbulence paradigm. Modeling and prediction of such statistically unsteady flows are important in many practical AFOSR applications: turbine flows, wake-flows with vortex shedding, etc. Further, many flow control strategies depend upon the knowledge of unsteady turbulence dynamics to achieve the desired objectives. However, our understanding of unsteadily-forced turbulence dynamics or our ability to predict them is inadequate.
Author: Manuel D. Salas
Publisher: Springer Science & Business Media
ISBN: 9401147248
Category : Science
Languages : en
Pages : 385
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Book Description
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: Roger Peyret
Publisher: Springer
ISBN: 3709125901
Category : Science
Languages : en
Pages : 320
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Book Description
This book collects the lecture notes concerning the IUTAM School on Advanced Turbulent Flow Computations held at CISM in Udine September 7–11, 1998. The course was intended for scientists, engineers and post-graduate students interested in the application of advanced numerical techniques for simulating turbulent flows. The topic comprises two closely connected main subjects: modelling and computation, mesh pionts necessary to simulate complex turbulent flow.
Author: Kemal Hanjalić
Publisher: Cambridge University Press
ISBN: 0521845750
Category : Science
Languages : en
Pages : 403
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Book Description
A comprehensive account of advanced RANS turbulence models including numerous applications to complex flows in engineering and the environment.
Author: Kemal Hanjalić
Publisher:
ISBN: 9781139842174
Category : Turbulence
Languages : en
Pages : 379
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Book Description
"Modelling transport and mixing by turbulence in complex flows is one of the greatest challenges for CFD. This highly readable volume introduces the reader to a level of modelling that respects the complexity of the physics of turbulent flows - second-moment closure. Following introductory chapters providing essential physical background, the book examines in detail the processes to be modelled, from fluctuating pressure interactions to diffusive transport, from turbulent time and length scales to the handling of the semi-viscous region adjacent to walls. It includes extensive examples ranging from fundamental homogeneous flows to three-dimensional industrial or environmental applications. This book is ideal for CFD users in industry and academia who seek expert guidance on the modelling options available, and for graduate students in physics, applied mathematics and engineering who wish to enter the world of turbulent flow CFD at the advanced level"--
Author: Brian Edward Launder
Publisher: Cambridge University Press
ISBN: 9780521792080
Category : Mathematics
Languages : en
Pages : 774
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Book Description
Publisher Description
Author: B. E. Launder
Publisher: Cambridge University Press
ISBN: 9780521792080
Category : Mathematics
Languages : en
Pages : 252
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Book Description
Publisher Description
Author: Geoff Hewitt
Publisher: Cambridge University Press
ISBN: 9780521838993
Category : Mathematics
Languages : en
Pages : 366
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Book Description
The prediction of turbulent flows is of paramount importance in the development of complex engineering systems involving flow, heat and mass transfer, and chemical reactions. Arising from a programme held at the Isaac Newton Institute in Cambridge, this volume reviews the current situation regarding the prediction of such flows through the use of modern computational fluid dynamics techniques, and attempts to address the inherent problem of modelling turbulence. In particular, the current physical understanding of such flows is summarised and the resulting implications for simulation discussed. The volume continues by surveying current approximation methods whilst discussing their applicability to industrial problems. This major work concludes by providing a specific set of guidelines for selecting the most appropriate model for a given problem. Unique in its breadth and critical approach, this book will be of immense value to experienced practitioners and researchers, continuing the UK's strong tradition in fluid dynamics.
Author: Naman Jain
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Buoyant shear layers and wakes are encountered in many engineering and environmental applications and have been studied by researchers in the context of experiments and modeling for decades. These flows are typically characterized by high Reynolds and Froude numbers, leading to significant/intractable space-time resolution requirements for turbulence-resolving CFD models of such flows, i.e., Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). Therefore, Reynolds-Averaged Navier-Stokes (RANS) based models are attractive for these configurations, but their accuracy hinges on numerous modeling assumptions. The inherently complex physical mechanisms observed in stratified flows render eddy viscosity-based RANS modeling inappropriate. RANS Second-Moment Closure (SMC) based modeling is more suitable for such complex systems because they account for flow anisotropy by solving the transport equations of important second-moment terms. Also, turbulent density fluctuations and their auto- and velocity cross-correlations are dynamically important in stratified systems, and their dynamics must be adequately captured. Accordingly, in this thesis, Second-Moment Closure is pursued for stratified flows. An eleven-equation SMC model is adopted and improved. Specifically, transport equations for the Reynolds stresses, density fluxes, density/temperature variance, and dissipation transport equations are solved. A range of sub-models for diffusion, pressure strain/scrambling, and dissipation are incorporated, assessed, and improved upon. Although many researchers have pursued SMC over the years, these works have primarily focused on bulk and important second-order statistics. By contrast, in this work, DNS data, produced by the author and his colleagues at Penn State, is used for SMC sub-model assessment and improvement, as these turbulence-resolving simulations provide the exact form of all turbulence statistics and their corresponding SMC models. Also, these data are used to assess the performance of the full RANS closure. This study results in several important recommendations for SMC model improvement. Also, this study has led to the development of a new anisotropic dissipation model, derived and assessed through comparison to DNS data. For the shear layers, the SMC model accurately predicts the growth rate and Reynolds shear stress profiles. In contrast, the stress anisotropy and budgets are captured only qualitatively. Comparing DNS of exact and modeled terms, inconsistencies in model performance and assumptions are observed, including inaccurate prediction of individual statistics, non-negligible pressure diffusion, and dissipation anisotropy. For the stratified shear layer, gradient Richardson number, shear layer growth rates, and stress, flux, and variance decay rates are captured with less accuracy than corresponding flow parameters in the non-stratified shear layer. Detailed analysis of the Reynolds stress budget terms identifies the need to improve turbulence dissipation rate modeling. For the stratified wakes, the SMC models were compared with non-stratified and stratified wake DNS results. A self-consistent RANS-based procedure to initialize SMC simulations is presented to capture the near-wake DNS peak mean defect velocity decay rate. However, over-prediction of wake height and under-prediction of defect velocity, wake width, and turbulent kinetic and potential energies are observed. Also, SMC predicts a near isotropic decay of normal Reynolds stresses in contrast to the anisotropic decay returned by DNS. The DNS data also provide essential physics and modeling insights related to the inaccuracy of the dissipation rate isotropy assumption and the non-negligible size of pressure-diffusion terms. In order to account for the anisotropy in the turbulence dissipation rate tensor induced by stratification, a novel DNS-informed RANS-consistent algebraic model is derived in this work. A generalizable anisotropic dissipation rate model was obtained by invoking tensor representation theory to enrich the model form based on local flow quantities. This is followed by a DNS-informed supervised linear regression algorithm. Finally, a reinforcement machine learning-based strategy was adopted to calibrate the model coefficients to obtain a RANS-consistent model for stratified flows. The proposed model form is shown to considerably improve the Reynolds stress evolution and, consequently, the mean defect velocity decay rate.
Author: Ibrahim Hadžić
Publisher:
ISBN: 9789064644221
Category :
Languages : en
Pages : 187
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Book Description
