Turbulence Control In Wall Jets
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Turbulence Control In Wall Jets
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Author : Jonathan Latim
language : en
Publisher:
Release Date : 2016
Turbulence Control In Wall Jets written by Jonathan Latim and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with Boundary layer categories.
The turbulent boundary layer has been the focus of many studies over the last century or so due to its engineering significance. Recent studies have shown that the turbulent boundary layer encapsulates extremely energetic large-scale structures which play a much more significant role in its dynamics than has been previously thought. Further, these large scales amplitude and frequency modulate the finer scales of turbulence. This offers a path to control wall turbulence by controlling the large-scales of the flow. The focus of this thesis is to establish ways to manipulate the energy of the large-scale structures in a model turbulent boundary layer and characterize its effect. The plane wall jet was chosen as the model flow field because it is possible to perturb/excite the large-scales at the onset of turbulence independent of the finer scales of turbulence. Hot-wire anemometry was used to carryout velocity measurements in at plane wall jet at streamwise locations up to three hundred times the jet exit slot height. Three different passive perturbation configurations were used to manipulate the energy of the large-scale structures of the plane wall jet. The different perturbation configurations used were a rod, sandpaper and sandpaper and a still wire. All the perturbations were carried out in the vicinity of the jet exit. The unforced wall jet was used as the baseline to compare the effect of these perturbations. All the perturbation cases were able to alter the energy of the large-scale structures in the flow. However, the large-scale structures were shown to be most energetic and reached closest to the wall in the flow that was perturbed using the rod than in all other flow cases at all streamwise positions considered. Last but not least, tic and reached closest to the wall in the flow that was perturbed using the sandpaper and the sandpaper and string configurations showed less energetic large-scale structures at all streamwise locations than in an unforced wall jet. However, the large-scale structures in the sandpaper and string configuration were more energetic than the large scale structures in the sandpaper configuration at all streamwise locations.
Turbulent Boundary Layer Control By A Wall Jet
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Author : James E. Hubbartt
language : en
Publisher:
Release Date : 1970
Turbulent Boundary Layer Control By A Wall Jet written by James E. Hubbartt and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1970 with Turbulence categories.
Transition And Turbulence Control
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Author : Mohamed Gad-el-Hak
language : en
Publisher: World Scientific
Release Date : 2006
Transition And Turbulence Control written by Mohamed Gad-el-Hak and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Technology & Engineering categories.
This volume contains articles based on lectures given at the Workshop on Transition and Turbulence Control, hosted by the Institute for Mathematical Sciences, National University of Singapore, 8-10 December 2004. The lecturers included 13 of the world's foremost experts in the control of transitioning and turbulent flows. The chapters cover a wide range of subjects in the broad area of flow control, and will be useful to researchers working in this area in academia, government laboratories and industry. The coverage includes control theory, passive, active and reactive methods for controlling transitional and turbulent wall-bounded flows, noise suppression and mixing enhancement of supersonic turbulent jets, compliant coatings, modern flow diagnostic systems, and swept wing instabilities.
The Turbulent Wall Jet
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Author :
language : en
Publisher:
Release Date : 1993
The Turbulent Wall Jet written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1993 with categories.
The flow of a wall jet embedded in an external stream or in a quiescent surrounding fluid was investigated experimentally. It was determined that the flow scales with the excess momentum injected into the stream and the viscosity of the fluid rather than the jet efflux velocity and the dimension of the nozzle. In the presence of an external stream, a velocity ratio parameter R = (U i - U.)/(Uj + U) had to be added in order to obtain a universal scaling of this flow. Low-amplitude external excitation, of the wall jet resulted in a reduction of skin friction and therefore a reduction of drag. The only possible cause for this behavior observed is the enhancement of the two-dimensionality of the large eddies as expressed by spanwise coherence and correlation measurements ... Turbulence, Control of Shear Flows, Wall Jet, Boundary Layer Control.
Wall Jet Turbulence And Mixing Control By Way Of A Pulsed Inlet Velocity
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Author : Cristale D. Garnica Vallejo
language : en
Publisher:
Release Date : 2019
Wall Jet Turbulence And Mixing Control By Way Of A Pulsed Inlet Velocity written by Cristale D. Garnica Vallejo and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with Aerospace engineering categories.
"Understanding wall-jet-induced turbulence and mixing is an important challenge in modern engineering, as drag reduction and mixing enhancement are attainable by modifying the flow development. Simulations are performed to investigate the effect on skin friction and flow mixing due to introducing controlled perturbations, at the initial shear layer of a planar wall-jet using jet inlet cyclic pulsing. The billow production by the Kelvin-Helmholtz instability, the instability that drives turbulence in a wall-jet, is modified by the excitation of the inlet velocity profile by a sine wave perturbation. Two types of wall-jet simulations are carried out, a two-dimensional compressible case at Rein = 5000 using the PyFR solver and a three-dimensional incompressible case at Rein = 6000 using the Nek5000 solver. The compressible wall-jet simulation indicates that the addition of a sine wave perturbation of 1% on the inlet velocity, at the initial shear layer, increases the wall-normal turbulence intensity at a Strouhal number (Sr) of 0.05 and reduces the turbulence intensity in all directions at a Sr of 0.25. The incompressible wall-jet simulations show that a perturbation of magnitude 40% of the inlet velocity at a low Sr number of 0.0048 damps turbulence and leads to skin friction reduction. The forced wall-jet experiences a repetitive re-laminarization process that delays transition as well as separation from the wall. A qualitative parametric analysis of the perturbation of the global behavior of the flow development on a plane wall-jet under forced velocity profiles is also presented. Cases at Sr = 0.0048 experience a reduction in the number of turbulent structures while becoming more stable, indicating potential drag reduction. Cases at Sr = 0.02 experience a frequent energy re-supply from the inlet that helps maintain large turbulent structures at further downstream locations, useful for mixing related applications."--Abstract.
Acoustic Control Of Turbulent Jets
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Author : A.S. Ginevsky
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-11-02
Acoustic Control Of Turbulent Jets written by A.S. Ginevsky and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-11-02 with Technology & Engineering categories.
Results of experimental research on aerodynamic and acoustic control of subsonic turbulent jets by acoustic excitation are presented. It was demonstrated that these control methods, originated by authors, not only can intensify mixing (by acoustic irradiation at low frequency), but also notably ease it (at high-frequency irradiation). This research monograph presents the updated results of the authors supplemented by other investigations conducted in USA, Germany and Great Britain. The methods for the numerical simulation of subsonic turbulent jets under acoustic excitation are described in detail, and examples are reviewed of practical applications, including reduction of turbojet engine noise and acoustic control of self-sustained oscillations in wind tunnels.
Turbulent Flow Control
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Author : William C. Reynolds
language : en
Publisher:
Release Date : 1995
Turbulent Flow Control written by William C. Reynolds and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1995 with Actuators categories.
The primary purpose of this project was to explore actuators, sensors, and control strategies for active control of turbulent jets and boundary layers. Potential applications of this work are to boundary layer control in aircraft and propulsion systems, which should be enabled by concurrent developments in MEMS fabrication technology. The present experiments were performed in a low-speed water flow, where the turbulence is large scale and slow, allowing easy measurement of flow properties and use of actuators and sensors that could be fabricated individually. A zero net mass flow actuator was developed and used in conjunction with wall stress sensors to demonstrate control of laminar flows containing steady and unsteady streamwise vorticies similar to those found in the near-wall region of turbulent boundary layers. Various closed loop control schemes, including an adaptive inverse neural net control, were explored. An early phase of the project was devoted to extension of work on control of round jets by acoustic excitation. It was shown that the jet direction and mixing can be strongly influenced by acoustic and fluidic actuation.
Turbulent Wall Jet In A Coflowing Stream
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Author : James Franklin Campbell
language : en
Publisher:
Release Date : 1975
Turbulent Wall Jet In A Coflowing Stream written by James Franklin Campbell and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1975 with Jets categories.
The Deflection Of Plane Turbulent Jets By Convex Walls
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Author : Turgut Sarpkaya
language : en
Publisher:
Release Date : 1968
The Deflection Of Plane Turbulent Jets By Convex Walls written by Turgut Sarpkaya and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1968 with Fluid amplifiers categories.
The effects of geometry and Reynolds number on the attachment of a jet to a convex wall and the mechanism of high pressure recovery in convex-walled amplifiers are investigated. The results are presented in terms of normalized parameters in a form suitable for comparison with theoretical results. Reasonably good agreement is obtained between the experimental results and those predicted theoretically by Gortler and Glauert, particularly for regions of flow away from the control port. The effects of the wall setback and control port are most pronounced in a region near the power nozzle where u sub m/u sub o attains values as high as 1.25. (Author).
Wall Turbulence Control
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Author : Sedat Tardu
language : en
Publisher: John Wiley & Sons
Release Date : 2017-02-07
Wall Turbulence Control written by Sedat Tardu and has been published by John Wiley & Sons this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017-02-07 with Science categories.
Wall turbulence control is a major subject, the investigation of which involves significant industrial, environmental and fundamental consequences. Wall Turbulence Control addresses recent advances achieved in active and passive wall turbulence control over the past two decades. This valuable reference for scientists, researchers and engineers provides an updated view of the research into this topic, including passive control, optimal and suboptimal control methodology, linear control and control using adaptive methods (neural networks), polymer and bubble injection, electromagnetic control and recent advances in control by plasma.