Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 34
Book Description
Turbulent Structures in Wall-bounded Shear Flows Observed Via Three-dimensional Numerical Simulators
Author: Numerical Simulation of Unsteady Three-Dimensional Turbulent Structures in Boundary Layer Flows
Author: Nan S. LuiPublisher:
ISBN:
Category :
Languages : en
Pages : 45
Book Description
The capabilities for numerical simulations of the dynamical effects of the underlying structures occurring in turbulent boundary layers have been developed. A mathematically operational model of hairpin vortex, which closely resembles the experimentally observed underlying structure of wall turbulence, has been constructed and the evolution of this incipient hairpin vortex as well as the distortion of a background laminar boundary layer has been successfully simulated. The height of the incipient hairpin vortex is about 1/5 fo the local boundary layer thickness. The calculated results not only exhibit most of the prominent features associated with turbulent spots and turbulent boundary layer flows, but also reveal dynamic processes which have been very difficult to observe in experimental studies, notably, the formation and intensification of another counter rotating hairpin vortex immediately upstream of the incipient hairpin vortex. Keywords: Navier-Stokes equations; Coherent wall structure.
Structure and Proper Orthogonal Decomposition in Simulations of Wall-bounded Turbulent Shear Flows with Canonical Geometries
Author: Jon Ronald BaltzerPublisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 427
Book Description
Structural features of canonical wall-bounded turbulent flows are described using several techniques, including proper orthogonal decomposition (POD). The canonical wall-bounded turbulent flows of channels, pipes, and flat-plate boundary layers include physics important to a wide variety of practical fluid flows with a minimum of geometric complications. Yet, significant questions remain for their turbulent motions' form, organization to compose very long motions, and relationship to vortical structures. POD extracts highly energetic structures from flow fields and is one tool to further understand the turbulence physics. A variety of direct numerical simulations provide velocity fields suitable for detailed analysis. Since POD modes require significant interpretation, this study begins with wall-normal, one-dimensional POD for a set of turbulent channel flows. Important features of the modes and their scaling are interpreted in light of flow physics, also leading to a method of synthesizing one-dimensional POD modes. Properties of a pipe flow simulation are then studied via several methods. The presence of very long streamwise motions is assessed using a number of statistical quantities, including energy spectra, which are compared to experiments. Further properties of energy spectra, including their relation to fictitious forces associated with mean Reynolds stress, are considered in depth. After reviewing salient features of turbulent structures previously observed in relevant experiments, structures in the pipe flow are examined in greater detail. A variety of methods reveal organization patterns of structures in instantaneous fields and their associated vortical structures. Properties of POD modes for a boundary layer flow are considered. Finally, very wide modes that occur when computing POD modes in all three canonical flows are compared. The results demonstrate that POD extracts structures relevant to characterizing wall-bounded turbulent flows. However, significant care is necessary in interpreting POD results, for which modes can be categorized according to their self-similarity. Additional analysis techniques reveal the organization of smaller motions in characteristic patterns to compose very long motions in pipe flows. The very large scale motions are observed to contribute large fractions of turbulent kinetic energy and Reynolds stress. The associated vortical structures possess characteristics of hairpins, but are commonly distorted from pristine hairpin geometries.
Turbulent Flow Structure Near Walls
Author: J. D. A. WalkerPublisher:
ISBN:
Category : Boundary value problems
Languages : en
Pages : 184
Book Description
In the past decade, progress has been made in determining the nature of turbulent flow near walls. Many of these advances, which have occurred through new experimental methodologies, direct numerical simulations, and new theoretical developments, are described in this volume.
Direct Numerical Simulation of Turbulent Couette Flow. Part 2
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 40
Book Description
A direct simulation of fully developed turbulent channel flow has been performed, through a direct solution of the time-varying, incompressible, Navier-Stokes equations. Reynolds shear stress appears to mark structures that are similar to those marked by hydrogen bubbles in the near-wall region of wall bounded shear flows. This has been observed by others, but not from animated views that match closely the physical experiments. Three-dimensional views of the Reynolds shear stress reveal elongated structures in the near-wall region that do not appear to be connected at larger normal distances. Keywords: Projectiles, Base flow, Turbulence, Simulation. (jhd).
Numerical Simulation of Wall-bounded Turbulent Shear Flows
Author: Scientific and Technical Aerospace Reports
Author: High Performance Computing in Science and Engineering ́16
Author: Wolfgang E. NagelPublisher: Springer
ISBN: 3319470663
Category : Computers
Languages : en
Pages : 666
Book Description
This book presents the state-of-the-art in supercomputer simulation. It includes the latest findings from leading researchers using systems from the High Performance Computing Center Stuttgart (HLRS) in 2016. The reports cover all fields of computational science and engineering ranging from CFD to computational physics and from chemistry to computer science with a special emphasis on industrially relevant applications. Presenting findings of one of Europe’s leading systems, this volume covers a wide variety of applications that deliver a high level of sustained performance. The book covers the main methods in high-performance computing. Its outstanding results in achieving the best performance for production codes are of particular interest for both scientists and engineers. The book comes with a wealth of color illustrations and tables of results.
The Near Wall Mechanics of Three-dimensional Turbulent Boundary Layers
Author: Olav SendstadThree-dimensional Turbulent Boundary Layers
Author: O. SendstadPublisher:
ISBN:
Category : Simulation methods
Languages : en
Pages : 130
Book Description