Behaviour of Energetic Coherent Structures in Turbulent Pipe Flow at High Reynolds Numbers
Behaviour of Energetic Coherent Structures in Turbulent Pipe Flow at High Reynolds Numbers

Author: Zeinab Hallol

Publisher: Cuvillier Verlag

Published: 2021-10-26

Total Pages: 146

ISBN-13: 373696501X

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In this thesis, coherent turbulent structures in turbulent pipe flow are investigated at relatively high Reynolds numbers and study their association in both total kinetic energy and Reynolds shear stress. Experimental investigations have been performed in Cottbus Large Pipe test facility (CoLaPipe) for pipe flow over a wide range of Reynolds number 8 × 104 ≤ ReD ≤ 1 × 106, located at the Aerodynamics and Fluid Mechanics Department, Brandenburg University of Technology Cottbus- Senftenberg (BTU). The first part of the thesis focuses on determining the contribution of the coherent structures using one-dimensional spectral analysis and assessing the structures behaviour in the outer region of pipe flow using high spatial resolution Hot-wire measurement up to 30kHz. The results of the power and pre-multiplied spectrum of stream-wise velocity indicate that the wavelength value of very large scale motions (VLSMs) acquires 19R at a maximum Reynolds number range ReD=1 × 106 (Reτ =19000). On the other hand, large-scale motions have a wavelength value of 3R over different Reynolds number range. Regarding the identified wavelength values, it is observed that contribution to energy for structures greater than 3R carries 55% of total kinetic energy. In addition, temporal-spatial resolution using the High-speed PIV measurements has been performed in CoLaPipe to estimate the contribution magnitude of stream-wise/wall-normal velocity fluctuations to total kinetic energy and Reynolds shear stress in the logarithmic and outer layer.

On the Large Scale Structure of Turbulence in Boundary Layer and Shear Flows
On the Large Scale Structure of Turbulence in Boundary Layer and Shear Flows

Author: M. A. Badri Narayanan

Publisher:

Published: 1982

Total Pages: 21

ISBN-13:

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The basic understanding of the physics of turbulence has undergone many radical changes in the last few years. Turbulent fluctuations which were considered to be purely random in nature is no more accepted to behave in that fashion but made up of somewhat coherent and orderly structures mixed with noise like random disturbances. The major difficulty experienced in the experimental investigations is the identification of these coherent structures from the overall signal. New methods are being developed to identify them. These orderly motions are large in scale and seem to play an important role in the dynamics of the mixing and the transport processes which are the essential features of turbulence. In this paper the properties of the large scale fluctuations in boundary layers as well as in shear flows are discussed. (Author).

Advances in Critical Flow Dynamics Involving Moving/Deformable Structures with Design Applications
Advances in Critical Flow Dynamics Involving Moving/Deformable Structures with Design Applications

Author: Marianna Braza

Publisher: Springer Nature

Published: 2021-02-10

Total Pages: 599

ISBN-13: 3030555941

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This book reports on the latest knowledge concerning critical phenomena arising in fluid-structure interaction due to movement and/or deformation of bodies. The focus of the book is on reporting progress in understanding turbulence and flow control to improve aerodynamic / hydrodynamic performance by reducing drag, increasing lift or thrust and reducing noise under critical conditions that may result in massive separation, strong vortex dynamics, amplification of harmful instabilities (flutter, buffet), and flow -induced vibrations. Theory together with large-scale simulations and experiments have revealed new features of turbulent flow in the boundary layer over bodies and in thin shear layers immediately downstream of separation. New insights into turbulent flow interacting with actively deformable structures, leading to new ways of adapting and controlling the body shape and vibrations to respond to these critical conditions, are investigated. The book covers new features of turbulent flows in boundary layers over wings and in shear layers immediately downstream: studies of natural and artificially generated fluctuations; reduction of noise and drag; and electromechanical conversion topics. Smart actuators as well as how smart designs lead to considerable benefits compared with conventional methods are also extensively discussed. Based on contributions presented at the IUTAM Symposium “Critical Flow Dynamics involving Moving/Deformable Structures with Design applications”, held in June 18-22, 2018, in Santorini, Greece, the book provides readers with extensive information about current theories, methods and challenges in flow and turbulence control, and practical knowledge about how to use this information together with smart and bio-inspired design tools to improve aerodynamic and hydrodynamic design and safety.

Recent Results in Laminar-Turbulent Transition
Recent Results in Laminar-Turbulent Transition

Author: Siegfried Wagner

Publisher: Springer Science & Business Media

Published: 2004

Total Pages: 350

ISBN-13: 9783540404903

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Methodic investigations of laminar-turbulent transition in wall-bounded she ar flows under controlled conditions are essential for untangling the various complex phenomena of the transition process occurring in flows at practical conditions. They allow understanding of the instability processes of the la minar flow, and thus enable the development of tools for flow control. On the one hand the laminar flow regime can be extended by delaying transition to reduce viscous drag, and on the other hand large-scale flow disturbances or transition can be forced in order to enhance momentum and mass ex change. Thus flow separation can be prevented, or mixing of fuel and air in combustion engines enhanced, for instance. The "DFG Verbund-Schwerpunktprogramm Transition" - a cooperative priority research program of universities, research establishments and indu stry in Germany - has been launched in April 1996 with the aim to explore transition by a coordinated use, development and validation of advanced experimental techniques and theoretical/numerical simulation methods, bin ding together all the appropriate resources available in Germany. At the very beginning of the six-year research period specifically selected test problems were to be investigated by various theoretical and experimental methods to identify and possibly rule out inadequate numerical or experimental methods. With respect to experiments it was planned to use multi-sensor-surface measuring techniques, the infrared measuring technique, and particle image velocimetry (PlV) in addition to hot-wire techniques to get instantaneous images of flows in sections, on surfaces, or within the complete flow field.