Author: Wolfgang Balzer
Publisher:
ISBN:
Category :
Languages : en
Pages : 586
Book Description
The aerodynamic performance of lifting surfaces operating at low Reynolds number conditions is impaired by laminar separation. Understanding of the physical mechanisms and hydrodynamic instabilities that are associated with laminar separation and the formation of laminar separation bubbles (LSBs) is key for the design and development of effective and efficient active flow control (AFC) devices. For the present work, laminar separation and its control were investigated numerically by employing highly-accurate direct numerical simulations (DNS). For a LSB on a curved plate, the primary and secondary instability of the uncontrolled flow were investigated. An inviscid Kelvin-Helmholtz (KH) instability was found to be responsible for the shedding of predominantly two-dimensional (2D) vortices. The onset of transition was caused by temporally-growing three-dimensional (3D) disturbances inside the separated region, which were supported by elliptical and hyperbolic secondary instabilities. The hyperbolic instability was demonstrated to be of absolute/global nature. High-amplitude forcing using pulsed vortex generator jets and 2D time-periodic blowing was found to exploit the KH instability and lead to a significant reduction in bubble size. In addition, the 2D forcing was found to suppress the secondary instabilities such that transition to turbulence was delayed. The role of free-stream turbulence (FST) in the transition process was investigated for a LSB on a flat plate. FST was shown to cause the formation of streamwise-elongated streaks inside the boundary layer. For the uncontrolled LSB, increasing the FST levels led to accelerated transition and a reduction in bubble size. The stage of linear disturbance growth due to the inviscid KH instability was not b̀̀ypassed''. Flow control by means of 2D periodic excitation was found to remain effective, since it could exploit the KH instability and suppress secondary absolute instabilities. Transition was initiated by an interaction of the 2D wave introduced by the forcing and the streamwise boundary-layer streaks. The interaction led to a spanwise modulation of the 2D wave, which was amplified due to a convective elliptical instability.
Numerical Investigation of the Role of Free-Stream Turbulence on Boundary-Layer Separation and Separation Control
Author: Wolfgang Balzer
Publisher:
ISBN:
Category :
Languages : en
Pages : 586
Book Description
The aerodynamic performance of lifting surfaces operating at low Reynolds number conditions is impaired by laminar separation. Understanding of the physical mechanisms and hydrodynamic instabilities that are associated with laminar separation and the formation of laminar separation bubbles (LSBs) is key for the design and development of effective and efficient active flow control (AFC) devices. For the present work, laminar separation and its control were investigated numerically by employing highly-accurate direct numerical simulations (DNS). For a LSB on a curved plate, the primary and secondary instability of the uncontrolled flow were investigated. An inviscid Kelvin-Helmholtz (KH) instability was found to be responsible for the shedding of predominantly two-dimensional (2D) vortices. The onset of transition was caused by temporally-growing three-dimensional (3D) disturbances inside the separated region, which were supported by elliptical and hyperbolic secondary instabilities. The hyperbolic instability was demonstrated to be of absolute/global nature. High-amplitude forcing using pulsed vortex generator jets and 2D time-periodic blowing was found to exploit the KH instability and lead to a significant reduction in bubble size. In addition, the 2D forcing was found to suppress the secondary instabilities such that transition to turbulence was delayed. The role of free-stream turbulence (FST) in the transition process was investigated for a LSB on a flat plate. FST was shown to cause the formation of streamwise-elongated streaks inside the boundary layer. For the uncontrolled LSB, increasing the FST levels led to accelerated transition and a reduction in bubble size. The stage of linear disturbance growth due to the inviscid KH instability was not b̀̀ypassed''. Flow control by means of 2D periodic excitation was found to remain effective, since it could exploit the KH instability and suppress secondary absolute instabilities. Transition was initiated by an interaction of the 2D wave introduced by the forcing and the streamwise boundary-layer streaks. The interaction led to a spanwise modulation of the 2D wave, which was amplified due to a convective elliptical instability.
Publisher:
ISBN:
Category :
Languages : en
Pages : 586
Book Description
The aerodynamic performance of lifting surfaces operating at low Reynolds number conditions is impaired by laminar separation. Understanding of the physical mechanisms and hydrodynamic instabilities that are associated with laminar separation and the formation of laminar separation bubbles (LSBs) is key for the design and development of effective and efficient active flow control (AFC) devices. For the present work, laminar separation and its control were investigated numerically by employing highly-accurate direct numerical simulations (DNS). For a LSB on a curved plate, the primary and secondary instability of the uncontrolled flow were investigated. An inviscid Kelvin-Helmholtz (KH) instability was found to be responsible for the shedding of predominantly two-dimensional (2D) vortices. The onset of transition was caused by temporally-growing three-dimensional (3D) disturbances inside the separated region, which were supported by elliptical and hyperbolic secondary instabilities. The hyperbolic instability was demonstrated to be of absolute/global nature. High-amplitude forcing using pulsed vortex generator jets and 2D time-periodic blowing was found to exploit the KH instability and lead to a significant reduction in bubble size. In addition, the 2D forcing was found to suppress the secondary instabilities such that transition to turbulence was delayed. The role of free-stream turbulence (FST) in the transition process was investigated for a LSB on a flat plate. FST was shown to cause the formation of streamwise-elongated streaks inside the boundary layer. For the uncontrolled LSB, increasing the FST levels led to accelerated transition and a reduction in bubble size. The stage of linear disturbance growth due to the inviscid KH instability was not b̀̀ypassed''. Flow control by means of 2D periodic excitation was found to remain effective, since it could exploit the KH instability and suppress secondary absolute instabilities. Transition was initiated by an interaction of the 2D wave introduced by the forcing and the streamwise boundary-layer streaks. The interaction led to a spanwise modulation of the 2D wave, which was amplified due to a convective elliptical instability.
The Numerical Investigation of a Turbulent Boundary Layer with an Elevated Freestream Turbulence Intensity
Author: Michael Joseph Barrett
Publisher:
ISBN:
Category : Turbulent boundary layer
Languages : en
Pages : 176
Book Description
Publisher:
ISBN:
Category : Turbulent boundary layer
Languages : en
Pages : 176
Book Description
Applied Mathematics, Modeling and Computer Simulation
Author: C.-H. Chen
Publisher: IOS Press
ISBN: 1643682555
Category : Computers
Languages : en
Pages : 1154
Book Description
The pervasiveness of computers in every field of science, industry and everyday life has meant that applied mathematics, particularly in relation to modeling and simulation, has become ever more important in recent years. This book presents the proceedings of the 2021 International Conference on Applied Mathematics, Modeling and Computer Simulation (AMMCS 2021), hosted in Wuhan, China, and held as a virtual event from 13 to 14 November 2021. The aim of the conference is to foster the knowledge and understanding of recent advances across the broad fields of applied mathematics, modeling and computer simulation, and it provides an annual platform for scholars and researchers to communicate important recent developments in their areas of specialization to colleagues and other scientists in related disciplines. This year more than 150 participants were able to exchange knowledge and discuss recent developments via the conference. The book contains 115 peer-reviewed papers, selected from more than 250 submissions and ranging from the theoretical and conceptual to the strongly pragmatic and all addressing industrial best practice. Topics covered include mathematical modeling and applications, engineering applications and scientific computations, and the simulation of intelligent systems. Providing an overview of recent development and with a mix of practical experiences and enlightening ideas, the book will be of interest to researchers and practitioners everywhere.
Publisher: IOS Press
ISBN: 1643682555
Category : Computers
Languages : en
Pages : 1154
Book Description
The pervasiveness of computers in every field of science, industry and everyday life has meant that applied mathematics, particularly in relation to modeling and simulation, has become ever more important in recent years. This book presents the proceedings of the 2021 International Conference on Applied Mathematics, Modeling and Computer Simulation (AMMCS 2021), hosted in Wuhan, China, and held as a virtual event from 13 to 14 November 2021. The aim of the conference is to foster the knowledge and understanding of recent advances across the broad fields of applied mathematics, modeling and computer simulation, and it provides an annual platform for scholars and researchers to communicate important recent developments in their areas of specialization to colleagues and other scientists in related disciplines. This year more than 150 participants were able to exchange knowledge and discuss recent developments via the conference. The book contains 115 peer-reviewed papers, selected from more than 250 submissions and ranging from the theoretical and conceptual to the strongly pragmatic and all addressing industrial best practice. Topics covered include mathematical modeling and applications, engineering applications and scientific computations, and the simulation of intelligent systems. Providing an overview of recent development and with a mix of practical experiences and enlightening ideas, the book will be of interest to researchers and practitioners everywhere.
Control of Separation for Turbulent Boundary Layers Subjected to Wall Curvature and Streamwise Pressure Gradients
Author: Hermann F. Fasel
Publisher:
ISBN:
Category : Jet engines
Languages : en
Pages : 90
Book Description
Publisher:
ISBN:
Category : Jet engines
Languages : en
Pages : 90
Book Description
Scientific and Technical Aerospace Reports
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 456
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.
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 456
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.
Advances In Computation, Modeling And Control Of Transitional And Turbulent Flows
Author: Tapan K Sengupta
Publisher: World Scientific
ISBN: 9814635170
Category : Science
Languages : en
Pages : 551
Book Description
The role of high performance computing in current research on transitional and turbulent flows is undoubtedly very important. This review volume provides a good platform for leading experts and researchers in various fields of fluid mechanics dealing with transitional and turbulent flows to synergistically exchange ideas and present the state of the art in the fields.Contributed by eminent researchers, the book chapters feature keynote lectures, panel discussions and the best invited contributed papers.
Publisher: World Scientific
ISBN: 9814635170
Category : Science
Languages : en
Pages : 551
Book Description
The role of high performance computing in current research on transitional and turbulent flows is undoubtedly very important. This review volume provides a good platform for leading experts and researchers in various fields of fluid mechanics dealing with transitional and turbulent flows to synergistically exchange ideas and present the state of the art in the fields.Contributed by eminent researchers, the book chapters feature keynote lectures, panel discussions and the best invited contributed papers.
Hydraulic Research in the United States 1970
Author: United States. National Bureau of Standards
Publisher:
ISBN:
Category : Hydraulic engineering
Languages : en
Pages : 360
Book Description
Publisher:
ISBN:
Category : Hydraulic engineering
Languages : en
Pages : 360
Book Description
Numerical Study of Separated Turbulent Flows
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Turbulent boundary layer separation was studied numerically using a special code to integrate the model equations for transient two-dimensional turbulent flow. For three calculations, separation was induced by interaction of a boundary layer with oblique shock waves; for three others, separation was caused by flow into the compression corner formed by an adiabatic flat-plate and ramp. In every case the free-stream Mach number was 2.96, the Reynolds number based on boundary layer thickness just upstream of the interaction region ranged from 1/4 to 1 million, and the static pressure rose by a factor of either 3.7 or 5.1.
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Turbulent boundary layer separation was studied numerically using a special code to integrate the model equations for transient two-dimensional turbulent flow. For three calculations, separation was induced by interaction of a boundary layer with oblique shock waves; for three others, separation was caused by flow into the compression corner formed by an adiabatic flat-plate and ramp. In every case the free-stream Mach number was 2.96, the Reynolds number based on boundary layer thickness just upstream of the interaction region ranged from 1/4 to 1 million, and the static pressure rose by a factor of either 3.7 or 5.1.
NASA Technical Memorandum
Report
Author: United States. National Bureau of Standards
Publisher:
ISBN:
Category : Hydraulic engineering
Languages : en
Pages : 696
Book Description
Publisher:
ISBN:
Category : Hydraulic engineering
Languages : en
Pages : 696
Book Description