Author: 吳冠廷Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Characterization of Turbulent Flow Statistics Under the Spatial-temporal Influence of Ejection and Sweep Events in Wall-bounded Turbulent Flows
Author: 吳冠廷Statistical Approach to Wall Turbulence
Author: Sedat TarduPublisher: John Wiley & Sons
ISBN: 1118601580
Category : Science
Languages : en
Pages : 234
Book Description
Wall turbulence is encountered in many technological applications as well as in the atmosphere, and a detailed understanding leading to its management would have considerable beneficial consequences in many areas. A lot of inspired work by experimenters, theoreticians, engineers and mathematicians has been accomplished over recent decades on this important topic and Statistical Approach to Wall Turbulence provides an updated and integrated view on the progress made in this area. Wall turbulence is a complex phenomenon that has several industrial applications, such as in aerodynamics, turbomachinery, geophysical flows, internal engines, etc. Several books exist on fluid turbulence, but Statistical Approach to Wall Turbulence is original in the sense that it focuses solely on the turbulent flows bounded by solid boundaries. The book covers the different physical aspects of wall turbulence, beginning with classical phenomenological aspects before advancing to recent research in the effects of the Reynolds numbers, near wall coherent structures, and wall turbulent transport process. This book would be of interest to postgraduate and undergraduate students in mechanical, chemical, and aerospace engineering, as well as researchers in aerodynamics, combustion, and all applications of wall turbulence.
Turbulence Structures Associated with the Bursting Event
Author: Near-wall Turbulence and Utilisation of the Nonlinear Dynamics Towards Control of Turbulent Flows
Author: Anubhav KushwahaPublisher:
ISBN:
Category :
Languages : en
Pages : 390
Book Description
Direct numerical simulations of plane Poiseuille flow are performed in an extended domain at transitional Reynolds numbers. In minimal domains, turbulence in this Reynolds number range displays substantial intermittency that is associated with chaotic movement of turbulent trajectories between lower (LB) and upper branch (UB) invariant solutions known as exact coherent states (ECS). We address the relationship between temporal dynamics in minimal channels and spatiotemporal dynamics in extended domains. Both temporal and spatial analyses of the turbulent velocity fields are performed. These analyses partition the flow characteristics into low-, intermediate- and high-drag classes. The temporal and spatial analysis methods, although completely independent of one another, yield very similar results for both low- and high-drag regions. The conditional mean profiles in regions of low-drag closely resemble those found in low-drag temporal intervals in the minimal channel. Finally, we compare turbulence and LB-ECS and show that both the local near-wall structure in the low-drag patches of the large domain and the conditional mean profiles in the near-wall region resemble those of an LB minimal domain ECS. Lower and upper branch ECS from one particular family of solutions are imprinted separately on a turbulent flow in the minimal channel at transitional Reynolds numbers. Specifically, the spatial patterns of their wall shear stress are imprinted on the channel-wall that moves in the wall-normal direction only. The motion of the wall results in a travelling wave of wall deformation in streamwise or spanwise direction. When an LB-ECS is imprinted, drag-reduction is observed for most of the cases, and a maximum drag reduction of just over 15% is achieved. The resultant flow field shows characteristics of a flow with lesser drag and the flow trajectories pass through the vicinity of the imprinted LB-ECS in the state space. When a UB is imprinted on the flow, the drag increases. In such cases, the trajectories remain in the high-drag region of the state space. These results indicate that flow can be driven toward a desired state by manipulating the near-wall dynamics using information from that state. This opens many avenues for the development of new flow control strategies.
Turbulence in Open Channel Flows
Author: Hiroji NakagawaPublisher: Routledge
ISBN: 1351406604
Category : Technology & Engineering
Languages : en
Pages : 246
Book Description
A review of open channel turbulence, focusing especially on certain features stemming from the presence of the free surface and the bed of a river. Part one presents the statistical theory of turbulence; Part two addresses the coherent structures in open-channel flows and boundary layers.
Scientific and Technical Aerospace Reports
Author: Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 744
Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Turbulent Flow Analysis and Coherent Structure Identification in Experimental Models with Complex Geometries
Author: Noushin AminiPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Turbulent flows and coherent structures emerging within turbulent flow fields have been extensively studied for the past few decades and a wide variety of experimental and numerical techniques have been developed for measurement and analysis of turbulent flows. The complex nature of turbulence requires methods that can accurately estimate its highly chaotic spatial and temporal behavior. Some of the classical cases of turbulent flows with simpler geometries have been well characterized by means of the existing experimental techniques and numerical models. Nevertheless, since most turbulent fields are of complex geometries; there is an increasing interest in the study of turbulent flows through models with more complicated geometries. In this dissertation, characteristics of turbulent flows through two different facilities with complex geometries are studied applying two different experimental methods. The first study involves the investigation of turbulent impinging jets through a staggered array of rods with or without crossflow. Such flows are crucial in various engineering disciplines. This experiment aimed at modeling the coolant flow behavior and mixing phenomena within the lower plenum of a Very High Temperature Reactor (VHTR). Dynamic Particle Image Velocimetry (PIV) and Matched Index of Refraction (MIR) techniques were applied to acquire the turbulent velocity fields within the model. Some key flow features that may significantly enhance the flow mixing within the test section or actively affect some of the structural components were identified in the velocity fields. The evolution of coherent structures within the flow field is further investigated using a Snapshot Proper Orthogonal Decomposition (POD) technique. Furthermore, a comparative POD method is proposed and successfully implemented for identification of the smaller but highly influential coherent structures which may not be captured in the full-field POD analysis. The second experimental study portrays the coolant flow through the core of an annular pebble bed VHTR. The complex geometry of the core and the highly turbulent nature of the coolant flow passing through the gaps of fuel pebbles make this case quite challenging. In this experiment, a high frequency Hot Wire Anemometry (HWA) system is applied for velocity measurements and investigation of the bypass flow phenomena within the near wall gaps of the core. The velocity profiles within the gaps verify the presence of an area of increased velocity close to the outer reflector wall; however, the characteristics of the coolant flow profile is highly dependent on the gap geometry and to a less extent on the Reynolds number of the flow. The time histories of the velocity are further analyzed using a Power Spectra Density (PSD) technique to acquire information about the energy content and energy transfer between eddies of different sizes at each point within the gaps.
Flow Noise Modeling, Measurement, and Control
Author: Fundamental Problematic Issues in Turbulence
Author: Albert GyrPublisher: Birkhäuser
ISBN: 3034886896
Category : Science
Languages : en
Pages : 464
Book Description
A collection of contributions on a variety of mathematical, physical and engineering subjects related to turbulence. Topics include mathematical issues, control and related problems, observational aspects, two- and quasi-two-dimensional flows, basic aspects of turbulence modeling, statistical issues and passive scalars.
Prediction Methods for Turbulent Flows
Author: Wolfgang Kollmann (mechanika)Publisher: Hemisphere Pub
ISBN:
Category : Science
Languages : en
Pages : 482
Book Description