Investigation of Turbulent Flow Over Irregular Rough Surfaces Using Direct Numerical Simulations PDF Download
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Author: Manan Thakkar
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Manan Thakkar
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: G. Biswas
Publisher: CRC Press
ISBN: 9780849310140
Category : Technology & Engineering
Languages : en
Pages : 478
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Book Description
This book allows readers to tackle the challenges of turbulent flow problems with confidence. It covers the fundamentals of turbulence, various modeling approaches, and experimental studies. The fundamentals section includes isotropic turbulence and anistropic turbulence, turbulent flow dynamics, free shear layers, turbulent boundary layers and plumes. The modeling section focuses on topics such as eddy viscosity models, standard K-E Models, Direct Numerical Stimulation, Large Eddy Simulation, and their applications. The measurement of turbulent fluctuations experiments in isothermal and stratified turbulent flows are explored in the experimental methods section. Special topics include modeling of near wall turbulent flows, compressible turbulent flows, and more.
Author: K. Tsujimoto
Publisher:
ISBN:
Category :
Languages : en
Pages : 8
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Book Description
Rough-wall turbulent flows are more common in engineering application than smooth-wall turbulent flows. Modification of mean flow and turbulence property have been established by enormous experiments. However, details of mechanism of rough-wall turbulence has been understood little because spatial resolution is limited in experiments. Meanwhile, Direct Numerical Simulation (DNS) of a rough-wall turbulent flows which is capable of giving high resolution data requires prohibitively heavy computer power and accordingly, no other DNS data are available than those published by the present authors (Miyake et al., 1999). Our first DNS considered sandgrain roughness whose effect was implemented by profile drag based on Stokes drag and could successfully reproduce experimentally established rough-wall turbulent flow such as downward shift of straight line of logarithmic mean velocity distribution and vanishing of viscous sublayer. It was confirmed that the layer adjacent to the wall up to several tens in wall unit where smooth-wall turbulence exhibits autonomous property independent on the layer above it, is taken over by the layer having property of logarithmic layer, in rough-wall turbulence. While quasi-streamwise vortices play major role to generate high turbulent shear stress in this near-wall layer in smooth-wall turbulent flow, roughness destroy this vortical system and consequently, different mixing system which replaces the role of quasi-streamwise vortices should be found in rough-wall layer. Present work intends to investigate the turbulent mixing in the layer close to the wall of rough-wall turbulence by a DNS of more sound numerical conditions, i.e., without using any model for roughness element.
Author: Jeremiah J. Gutierrez-Jensen
Publisher:
ISBN:
Category : Computational fluid dynamics
Languages : en
Pages : 106
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Book Description
Many methods of passive flow control rely on changes to surface morphology. Roughening surfaces to induce boundary layer transition to turbulence and in turn delay separation is a powerful approach to lowering drag on bluff bodies. While the influence in broad terms of how roughness and other means of passive flow control to delay separation on bluff bodies is known, basic mechanisms are not well understood. Of particular interest for the current work is understanding the role of surface dimpling on boundary layers. A computational approach is employed and the study has two main goals. The first is to understand and advance the numerical methodology utilized for the computations. The second is to shed some light on the details of how surface dimples distort boundary layers and cause transition to turbulence. Simulations are performed of the flow over a simplified configuration: the flow of a boundary layer over a dimpled flat plate. The flow is modeled using an immersed boundary as a representation of the dimpled surface along with direct numerical simulation of the Navier-Stokes equations. The dimple geometry used is fixed and is that of a spherical depression in the flat plate with a depth-to-diameter ratio of 0.1. The dimples are arranged in staggered rows separated by spacing of the center of the bottom of the dimples by one diameter in both the spanwise and streamwise dimensions. The simulations are conducted for both two and three staggered rows of dimples. Flow variables are normalized at the inlet by the dimple depth and the Reynolds number is specified as 4000 (based on freestream velocity and inlet boundary layer thickness). First and second order statistics show the turbulent boundary layers correlate well to channel flow and flow of a zero pressure gradient flat plate boundary layers in the viscous sublayer and the buffer layer, but deviates further away from the wall. The forcing of transition to turbulence by the dimples is unlike the transition caused by a naturally transitioning flow, a small perturbation such as trip tape in experimental flows, or noise in the inlet condition for computational flows.
Author: Center for Turbulence Research (U.S.)
Publisher:
ISBN:
Category : Mathematical models
Languages : en
Pages : 368
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Author: H. Schlichting
Publisher:
ISBN:
Category : Mathematics
Languages : en
Pages : 604
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Book Description
Based on the universal laws of turbulent velocity distribution at rough and smooth walls, there is in the present work presented a method that allows surface roughness tests and in particular, measurements on the roughness of ship surfaces to be carried out in a much simpler manner. The types of roughness investigated were in the form of flat, rough plates installed in a square-section rectangular channel, the other three walls always being smooth. Twenty-one plates of various roughness were investigated, the roughness elements being the following: spheres of diameter 0.41 and 0.21, respectively, spherical segments, cones, and "short" and "long" angles.
Author: Jean Piquet
Publisher: Springer Science & Business Media
ISBN: 9783540654117
Category : Technology & Engineering
Languages : en
Pages : 778
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Book Description
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: Luigi Carlo Berselli
Publisher: Springer Science & Business Media
ISBN: 9783540263166
Category : Computers
Languages : en
Pages : 378
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Book Description
The LES-method is rapidly developing in many practical applications in engineering The mathematical background is presented here for the first time in book form by one of the leaders in the field
Author: Sheng Xu
Publisher:
ISBN:
Category :
Languages : en
Pages : 324
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Author: Prakash Mohan (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Turbulence is a complex fluid phenomenon that is present in high Reynolds number flows. It has a profound effect on the flows in which it occurs, and it is therefore important to understand and model its effects. It occurs in multiple domains from flows inside our bodies to ocean currents and atmospheric winds. The difficulty in modeling and simulating turbulence arises from the fact that it is comprised of a wide range of scales that interact with each other non-linearly. The field of turbulence still has many open problems — from fundamental questions about the underlying physics to enabling tractable engineering models. The Navier-Stokes equations are a reliable representation of turbulent flows and solving them with sufficient accuracy gives us the detailed turbulent flow field. These are called Direct Numerical Simulations (DNS) and are an invaluable tool to study the turbulence phenomenon. In this work, we first consider how DNS of forced isotropic turbulence can be used to study time predictability of turbulence using Lyapunov exponents. Further analysis of the DNS field shows that flow instabilities act on the smallest eddies, and that at any time, there are many sites of local instabilities. DNS, however, is generally too expensive for simulating practical flows. Alternatively, Large Eddy Simulations (LES), in which only the largest scales of turbulent motion are simulated, is more promising as an engineering tool. However, in the near-wall region the large, dynamically important eddies are on the order of viscous scales, which makes resolving them very expensive. It is therefore desirable to formulate an approach in which the near-wall region is modeled, leading to the so-called wall-modeled LES. Spectral analysis of DNS data indicates that thin-film type asymptotics is a promising approach to model the interactions between the near-wall layer and the outer flow. For this approach an asymptotic analysis of the filtered Navier-Stokes equations is pursued in the limit in which the horizontal filter scale is large compared to the thickness of the wall layer. In the second part of this work, we present a new wall model formulated using the asymptotic analysis and insights from DNS data
