Understanding And Control Of Coupling Of Supersonic Twin Jets Using Localized Arc Filament Plasma Actuators
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Understanding And Control Of Coupling Of Supersonic Twin Jets Using Localized Arc Filament Plasma Actuators
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Author : Jordan D. Cluts
language : en
Publisher:
Release Date : 2018
Understanding And Control Of Coupling Of Supersonic Twin Jets Using Localized Arc Filament Plasma Actuators written by Jordan D. Cluts and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with Aerospace engineering categories.
A twin-jet consists of two jet engines that are close enough to one another on an aircraft for the plumes to interact and merge downstream of the nozzle exit. This interaction can cause the noise generated by twin jets to be louder than an equivalent single jet under certain operating conditions. The noise of all jets is a health concern for communities near airports and personnel on aircraft carrier decks, but twin jets are of particular concern due to their increased noise levels. Additionally, the coupling of twin jets can cause strong near field pressure fluctuations that have the potential to damage airframes of military aircraft through sonic fatigue as occurred on both the F-15 and the B-1A during their development. Previous research into twin jets has studied a variety of twin-jet nozzle configurations. This study focuses on round converging-diverging nozzles with a center-to-center spacing of 2.0 nozzle diameters---close to that found in military aircraft. Localized arc filament plasma actuators (LAFPAs) are perturbation-based flow control devices that excite jet instabilities with small energy input and alter their characteristics. They have been used to control the noise generated by single jets. These actuators can alter the dominant mode (the shape of the large-scale turbulent structures) present in the jet plume by creating small thermal perturbations near the nozzle exit. LAFPAs were applied to test their efficacy at altering the dominant mode and as a diagnostic tool to study the behavior of the different modes in the twin-jet. Regardless of the naturally dominant mode in the twin-jet at a given operating condition, the LAFPAs can change the mode present to match the excited mode. This includes eliminating the strong coupling at modes and conditions where it normally occurs. Far field and near field acoustic measurements show that when the flapping mode is dominant in the twin-jet, the resulting coupling causes higher noise and near field pressure fluctuations than other modes. Axisymmetric and helical modes synchronize the large-scale turbulent structures so that they are generated simultaneously, but do not amplify one another to create the higher noise and pressure fluctuations of the flapping mode. The identities of these modes were confirmed using phase-averaged schlieren imaging which reveals the shape of the different modes in the twin-jet, both naturally occurring and excited using LAFPAs Both schlieren images and screech tone frequencies were captured for a twin-jet at elevated temperatures. These images revealed that the flapping mode disappears in the twin-jet as the temperature increases and is replaced by the helical mode. A theoretical model in the literature designed to predict the screech tone frequency in single jets was applied to the twin-jet. This model accurately predicted the tones present in the twin-jet and was able to predict a shift from one frequency to another when a mode shifts from the flapping mode to the helical mode due to increased jet temperature. The screech tones of the twin-jet closely match the feedback loop of the single jet.
Active Control Of High Reynolds Number Supersonic Jets Using Plasma Actuators
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Author :
language : en
Publisher:
Release Date : 2010
Active Control Of High Reynolds Number Supersonic Jets Using Plasma Actuators written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Active flow control of jets with Localized Arc Filament Plasma Actuators (LAFPAs) is conducted over a wide range of the fully expanded jet Mach numbers (M(J) or simply jet Mach number). The jet Mach numbers covered in the present research are 0.9 (with a converging nozzle), 1.2 (overexpanded), 1.3 (perfectly expanded), and 1.4 (underexpanded) with a design Mach number 1.3. Additionally, limited experiments are carried out for an M(J) = 1.65 perfectly-expanded jet. The exit diameter is 2.54 cm (1 inch) for all cases and eight LAFPAs are equally distributed on the perimeter of a boron nitride nozzle extension. The jet spreading is strongly dependent on duty cycle, forcing frequency, and azimuthal modes. The performance of LAFPAs for jet spreading is investigated using two-dimensional particle image velocimetry (PIV). There is an optimum duty cycle, producing maximum jet spreading, for each forcing frequency. A relationship between the optimum duty cycle and forcing frequency is determined from the extensive results in the MJ 0.9, and this relation is used for all experiments. The effect of forcing frequency is investigated for a wide range of forcing Strouhal numbers (StDF = f(F)D/U(e), where f(F), D, and U(e), are forcing frequency, nozzle exit diameter, and jet exit velocity respectively), ranging from 0.09 to 3.0. The azimuthal modes (m) investigated are m = 0 - 3, +/-1, +/-2, and +/-4 - this comprises all modes available with eight actuators. The performance of LAFPAs does also strongly depend on the stagnation temperature of the jet and M(J). The effects of stagnation temperature are investigated for 1.0, 1.4, and 2.0 times the ambient temperature in M(J) 0.9 jet for very limited azimuthal modes and St(DF). In an M(J) 1.65 perfectly-expanded jet, the control authority of LAFPAs is investigated for only m = +/-1 and St(DF) tilde 0.3.
Development Of Localized Arc Filament Rf Plasma Actuators For High Speed And High Reynolds Number Flow Control
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Author :
language : en
Publisher:
Release Date : 2010
Development Of Localized Arc Filament Rf Plasma Actuators For High Speed And High Reynolds Number Flow Control written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Recently developed Localized Arc Filament Plasma Actuators (LAFPAs) have shown tremendous control authority in high-speed and high Reynolds number flow for mixing enhancement and noise mitigation. Previously, these actuators were powered by a high voltage pulsed DC plasma generator with low energy coupling efficiency of 5-10%. In the present work, a new custom-designed 8-channel pulsed radio frequency (RF) plasma generator has been developed to power up to 8 plasma actuators operated over a wide range of forcing frequencies (up to 50 kHz) and duty cycles (1-50%), and at high energy coupling efficiency (up to 80-85%). This reduces input electrical power requirements by approximately an order of magnitude, down to 12 W per actuator operating at 10% duty cycle. The new pulsed RF plasma generator is scalable to a system with a large number of channels. Performance of pulsed RF plasma actuators used for flow control was studied in a Mach 0.9 circular jet with a Reynolds number of about 623,000 and compared with that of pulsed DC actuators. Eight actuators were distributed uniformly on the perimeter of a 2.54 cm diameter circular nozzle extension. Both types of actuators coupled approximately the same amount of power to the flow, but with drastically different electrical inputs to the power supplies. Particle image velocimetry measurements showed that jet centerline Mach number decay produced by DC and RF actuators operating at the same forcing frequencies and duty cycles is very similar. At a forcing Strouhal number near 0.3, close to the jet column instability frequency, well-organized periodic structures, with similar patterns and dimensions, were generated in the jets forced by both DC and RF actuators. Farfield acoustic measurements demonstrated similar trends in the Overall Sound Pressure Level (OASPL) change produced by both types of actuators, resulting in OASPL reduction up to 1.2- 1.5 dB in both cases.
Mixing Control In Supersonic Rectangular Jets Using Plasma Actuators
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Author : Robert M. Snyder
language : en
Publisher:
Release Date : 2007
Mixing Control In Supersonic Rectangular Jets Using Plasma Actuators written by Robert M. Snyder and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with categories.
Abstract: The flow through the exhaust nozzle of a jet engine has been of crucial importance in aerospace applications over the past several decades. A variety of modifications can be made to the nozzles of high-speed jet engines to increase or decrease mixing between the exiting flow and the ambient air; including adding tabs, chevrons, or actuators. Localized arc filament plasma actuators (LAFPA) developed in the Gas Dynamics and Turbulence Laboratory at The Ohio State University have both high amplitude and bandwidth and are suitable for active control of high-speed, high Reynolds number flows. These actuators were implemented on a rectangular nozzle in order to optimize the efficiency of mixing enhancement between the jet and the ambient air. Actuators were tested for a Mach 2.0 flow over a wide range of forcing frequencies and the effects were evaluated using flow visualization techniques. Results show the effects of forcing frequency and other parameters on the development of large-scale structures within the flow. Flow visualization testing over a broad range of forcing frequencies and duty cycles revealed the presence of large coherent structures and thus most favorable mixing enhancement in the 6-8 kHz (StF = 0.15-0.2) range. The m = " 1 (flapping) mode produced a clear pattern of alternating structures within the aforementioned frequency band. It was also observed that the effect of varying duty cycle within this frequency range has little effect on the control authority.
Active Control Of Supersonic Jets Operating In Various Flow Regimes
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Author : Robert Michael Snyder
language : en
Publisher:
Release Date : 2008
Active Control Of Supersonic Jets Operating In Various Flow Regimes written by Robert Michael Snyder and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with Jet engines categories.
Abstract: The flow through the exhaust nozzle of a jet engine has been of crucial importance in aerospace applications over the past several decades. A variety of modifications can be made to the nozzles of high-speed jet engines to increase or decrease mixing between the exiting flow and the ambient air; including adding tabs, chevrons, or actuators. Localized arc filament plasma actuators (LAFPAs) developed in the Gas Dynamics and Turbulence Laboratory at The Ohio State University have both high amplitude and bandwidth and are suitable for active control of high-speed, high Reynolds number flows. LAFPAs were used to control a supersonic jet from an axisymmetric nozzle of design Mach number of 1.3 operating from overexpanded to underexpanded flow regimes with the fully expanded jet Mach number (MJ) from 1.1 to 1.5 in order to explore their characteristics and their potential for mixing enhancement between the jet and the ambient air. The Reynolds number based on the 2.54 cm nozzle exit diameter was from 1.0x106 to 1.4x106. Laser based planar flow visualizations, schlieren imaging, and particle image velocimetry measurements were used to evaluate the effects of control. Results show the effects of forcing frequency and other parameters on the development of large-scale structures within the flow. Eight actuators, distributed azimuthally approximately 1 mm upstream of the nozzle exit, were used to force various azimuthal modes over a large Strouhal number range (StDF of 0.07 to 2.68). The preliminary results in underexpanded jets (MJ = 1.4 and 1.5) were quite similar to results in the ideally expanded jet (MJ = 1.3) previously obtained in similar studies at GDTL. The ideally expanded jet responded to the forcing over the entire range of frequencies, but the response was optimum (in terms of development of large coherent structures and mixing enhancement) around the jet preferred Strouhal number of 0.34 (fF = 5 kHz). Similarly, the optimum response was found at a jet preferred Strouhal number of 0.27 (fF = 4 kHz) for the slightly underexpanded jet (MJ = 1.4) and 0.34 (fF = 5 kHz) for the strongly underexpanded jet (MJ = 1.5). The jet also responded to forcing with various azimuthal modes (m=0 to 3 and m= ± 1, ±2, ±4). Forcing the jet with the azimuthal mode m= ±1 at the jet preferred mode frequency provided the maximum mixing enhancement in the visualized plane. Conversely, the preliminary results showed that the overexpanded jets (MJ = 1.1 and 1.2) did not respond at all or the response was relatively small. Subsequent surface pressure measurements with an extension without actuators revealed significant pressure increases near the nozzle exit for the strongly overexpanded MJ = 1.1 case, suggesting the existence of flow separation. Flow separation would cause the flow to pass over actuator location, thus nullifying the effect of control.
Control Of Supersonic Mixed Compression Inlets Using Localized Arc Filament Plasma Actuators
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Author : Nathan Joseph Webb
language : en
Publisher:
Release Date : 2010
Control Of Supersonic Mixed Compression Inlets Using Localized Arc Filament Plasma Actuators written by Nathan Joseph Webb and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Abstract: Shock wave/boundary layer interactions (SWBLIs) occur in many supersonic internal flow applications, specifically in mixed compression inlets, as well as in external flows. In this study a nominally Mach 2 mixed compression inlet is modeled by two experimental setups: 1) A compression ramp-generated impinging SWBLI, and 2) a variable angle wedge (VAW) generated impinging SWBLI. The compression ramp and the wedge both serve to generate an oblique shock wave that impinges on the boundary layer on the opposite surface of the wind tunnel. This produces an impinging SWBLI within the test section that replicates the flow found in a mixed compression inlet. A SWBLI can cause flow separation and it is desirable to efficiently prevent this to avoid the many adverse consequences that may result otherwise. The goal of this study is to investigate the ability of localized arc-filament plasma actuators (LAFPAs) to effectively control the interaction. The LAFPAs show significant ability to beneficially affect the SWBLI depending on various operating parameters such as geometry and forcing Strouhal number. This ability apparently stems from a manipulation of instabilities naturally present in the flow. For the compression ramp facility the LAFPAs were most effective when located upstream of the shock foot, forcing with a Strouhal number of 0.03, and operated in-phase. The VAW facility is currently being debugged and will be used for future detailed experiments investigating the control authority of the LAFPAs.
Control Of The Interaction Between An Oblique Shock Wave And A Supersonic Turbulent Boundary Layer By Localized Arc Filament Plasma Actuators
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Author : Nathan J. Webb
language : en
Publisher:
Release Date : 2009
Control Of The Interaction Between An Oblique Shock Wave And A Supersonic Turbulent Boundary Layer By Localized Arc Filament Plasma Actuators written by Nathan J. Webb and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
Abstract: The ability of localized arc filament plasma actuators to eliminate or reduce the extent of boundary layer separation in the interaction between an oblique shock wave and a turbulent boundary layer is examined. This is an important phenomenon occurring in many applications including supersonic aircraft engine inlets. The effects of the actuators on the flow were studied for varying frequency, location, and mode of actuation of the actuators. The effectiveness of the forcing was determined by using schlieren imaging techniques, particle image velocimetry, and unsteady pressure measurements. The data collected shows that the actuators do have significant effects on the flow and can effectively remove the separation caused by the shock wave/boundary layer interaction.
Active Control Of High Speed Subsonic Cavity Flow Using Plasma Actuators
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Author : Douglas Alan Mitchell
language : en
Publisher:
Release Date : 2007
Active Control Of High Speed Subsonic Cavity Flow Using Plasma Actuators written by Douglas Alan Mitchell and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with Aerodynamics categories.
Abstract: The study and control of cavity flow fields began in the 1950's and has remained an active area of research for the past fifty years. Grazing flow over an open cavity which leads to resonance is a common occurrence generated by the flow-acoustic coupling mechanism. When the natural instabilities in the shear layer phase match with the acoustic waves generated from the impingement of the structures in the shear layer at the trailing edge of the cavity, high amplitude background noise and discrete cavity tones are generated in the form of high amplitude pressure fluctuations. Common examples of this phenomenon are aircraft landing gear openings, aircraft weapons bays, and engine air intakes. Unchecked cavity flow resonance can lead to weapon stores damage and incorrect deployment, reduction in lift, increase in drag, and structural fatigue. Initial research concentrated on using a compression driver as a synthetic jet type actuator to reduce acoustic resonance peaks, to operate the actuator at optimal forcing frequencies using reduced order modeling in order to shrink the peaks without triggering adjacent tones, and to develop logic based controls to damp pressure fluctuations within the system. The compression driver was ultimately limited by its frequency bandwidth and power output. The limited capabilities of the compression driver led to the development of the localized arc filament plasma actuator which is capable of high bandwidth and high amplitude actuation. The focus of this research was on the development of a high speed subsonic cavity flow facility and its control using localized arc filament plasma actuators (LAFPA). A cavity flow facility was designed and fabricated which allowed for the study of both baseline and forced cavity flows. The baseline flow characteristics were studied using flow visualization techniques in the form of particle image velocimetry (PIV) and schlieren photography, dynamic surface pressure measurements, and instantaneous and time-averaged dynamic pressure correlations to gain further understanding in cavity flow physics. Once the flow was sufficiently understood, LAFPAs were then used to force the flow into different modes or non-preferred frequencies in order to reduce the cavity tones or reduce the overall sound pressure level. Resonant, non-resonant, and multi-mode resonance are studied and actuated at various forcing frequencies, duty cycles, and modes. Furthermore, several different plasma actuator platforms were developed and tested to determine an optimal electrode arrangement during actuation.
Active Control Of Subsonic Cavity Flow Using Plasma Actuators
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Author : Nathan George Kamps
language : en
Publisher:
Release Date : 2007
Active Control Of Subsonic Cavity Flow Using Plasma Actuators written by Nathan George Kamps and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with categories.
Abstract: Due to the prevalence of stealth technology on increasing numbers of new aircraft, weapons and electronics that had previously been stored under the aircraft wings are now being stored in weapons bays inside the fuselage. When these bays are opened however, a damaging flow situation can arise to create high amplitude pressure fluctuations capable of damaging structures and systems of the aircraft and the weapons stored in the bay. Thus a major area of research at the Gas Dynamics and Turbulence Laboratory (GDTL) has been focused on the suppression of these pressure fluctuations. Previous results using active flow control and a compression driver showed good flow authority up to Mach 0.40, when actuator effectiveness was lost. Other research at the GDTL has focused on the use of localized arc filament plasma actuators (LAFPA's) to control flow instabilities in a high Mach number free jet. The focus of this research was to incorporate the plasma actuators in a cavity flow facility and investigate their effectiveness at suppressing the tone generated by flows of higher Mach numbers. The results presented in this paper detail the results of testing several different actuator configurations on Mach 0.69 flow over a shallow cavity.
Shock Wave Boundary Layer Interactions
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Author : Holger Babinsky
language : en
Publisher: Cambridge University Press
Release Date : 2011-09-12
Shock Wave Boundary Layer Interactions written by Holger Babinsky and has been published by Cambridge University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011-09-12 with Technology & Engineering categories.
Shock wave-boundary-layer interaction (SBLI) is a fundamental phenomenon in gas dynamics that is observed in many practical situations, ranging from transonic aircraft wings to hypersonic vehicles and engines. SBLIs have the potential to pose serious problems in a flowfield; hence they often prove to be a critical - or even design limiting - issue for many aerospace applications. This is the first book devoted solely to a comprehensive, state-of-the-art explanation of this phenomenon. It includes a description of the basic fluid mechanics of SBLIs plus contributions from leading international experts who share their insight into their physics and the impact they have in practical flow situations. This book is for practitioners and graduate students in aerodynamics who wish to familiarize themselves with all aspects of SBLI flows. It is a valuable resource for specialists because it compiles experimental, computational and theoretical knowledge in one place.