Read Books Online and Download eBooks, EPub, PDF, Mobi, Kindle, Text Full Free.
Control Of The Interaction Between An Oblique Shock Wave And A Supersonic Turbulent Boundary Layer By Localized Arc Filament Plasma Actuators
Download Control Of The Interaction Between An Oblique Shock Wave And A Supersonic Turbulent Boundary Layer By Localized Arc Filament Plasma Actuators full books in PDF, epub, and Kindle. Read online Control Of The Interaction Between An Oblique Shock Wave And A Supersonic Turbulent Boundary Layer By Localized Arc Filament Plasma Actuators ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!
Book Synopsis Control of the Interaction Between an Oblique Shock Wave and a Supersonic Turbulent Boundary Layer by Localized Arc Filament Plasma Actuators by : Nathan J. Webb
Download or read book 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 published by . This book was released on 2009 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Control of a Shock Wave-boundary Layer Interaction Using Localized Arc Filament Plasma Actuators by : Nathan Joseph Webb
Download or read book Control of a Shock Wave-boundary Layer Interaction Using Localized Arc Filament Plasma Actuators written by Nathan Joseph Webb and published by . This book was released on 2013 with total page 111 pages. Available in PDF, EPUB and Kindle. Book excerpt: The potentially severe consequences associated with SWBLIs require flow control to ensure proper operation. Traditionally, boundary layer bleed has been used to control the interaction. Although this method is effective, it has inherent efficiency penalties. Localized Arc Filament Plasma Actuators (LAFPAs) are designed to generate perturbations for flow control. Natural flow instabilities act to amplify certain perturbations, allowing the LAFPAs to control the flow with minimal power input. LAFPAs also have the flexibility to maintain control over a variety of operating conditions.
Book Synopsis Theoretical and Experimental Aerodynamics by : Mrinal Kaushik
Download or read book Theoretical and Experimental Aerodynamics written by Mrinal Kaushik and published by Springer. This book was released on 2018-12-15 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is intended as a text for undergraduate and graduate courses in aerodynamics, typically offered to students of aerospace and mechanical engineering programs. It covers all aspects of aerodynamics. The book begins with a description of the standard atmosphere and basic concepts, then moves on to cover the equations and mathematical models used to describe and characterize flow fields, as well as their thermodynamic aspects and applications. Specific emphasis is placed on the relation between concepts and their use in aircraft design. Additional topics of interest to the reader are presented in the Appendix, which draws on the teachings provided in the text. The book is written in an easy to understand manner, with pedagogical aids such as chapter overviews, summaries, and descriptive and objective questions to help students evaluate their progress. Atmospheric and gas tables are provided to facilitate problem solving. Lastly, a detailed bibliography is included at the end of each chapter to provide students with further resources. The book can also be used as a text for professional development courses in aerodynamics.
Book Synopsis Shock Wave-Boundary-Layer Interactions by : Holger Babinsky
Download or read book Shock Wave-Boundary-Layer Interactions written by Holger Babinsky and published by Cambridge University Press. This book was released on 2011-09-12 with total page 481 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Study of Arc-discharge Plasma Actuators for the Control of Shock-wave Boundary-layer Interaction by : X. Chen
Download or read book Study of Arc-discharge Plasma Actuators for the Control of Shock-wave Boundary-layer Interaction written by X. Chen and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Active Control of High Reynolds Number Supersonic Jets Using Plasma Actuators by :
Download or read book Active Control of High Reynolds Number Supersonic Jets Using Plasma Actuators written by and published by . This book was released on 2010 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Noise Mitigation of a Jet Using Localized Arc Filament Plasma Actuators by : Casey B. Hahn
Download or read book Noise Mitigation of a Jet Using Localized Arc Filament Plasma Actuators written by Casey B. Hahn and published by . This book was released on 2010 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Localized arc filament plasma actuators (LAFPAs) are used at The Gas Dynamics and Turbulence Laboratory (GDTL) for the purpose of controlling the downstream development of a 1-inch exit diameter jet. The lab has the capability to study both subsonic and supersonic jets with a primary goal being the mitigation of noise emitted by a jet. However, the mechanism by which the actuators are capable of perturbing the instabilities of the jet is unclear. It has been proposed that the ring groove, initially added to shield the plasma arcs from the high-speed jet flow, of the nozzle extension that houses the actuators is crucial for effective actuation. To study this possibility a new nozzle extension, which relocates the electrodes to the nozzle extension face and deletes the ring groove, is used. A comparison of the acoustic results of a traditional extension with a ring groove and the new nozzle extension without the ring groove is used to determine the effect of the ring groove. The results show that the same general trends and levels of noise attenuation and amplification are achieved with either extension. Thus, it is concluded that the ring groove is not essential for effective actuation.
Book Synopsis Scalability of Localized Arc Filament Plasma Actuators by : Clifford A. Brown
Download or read book Scalability of Localized Arc Filament Plasma Actuators written by Clifford A. Brown and published by BiblioGov. This book was released on 2013-07 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Temporal flow control of a jet has been widely studied in the past to enhance jet mixing or reduce jet noise. Most of this research, however, has been done using small diameter low Reynolds number jets that often have little resemblance to the much larger jets common in real world applications because the flow actuators available lacked either the power or bandwidth to sufficiently impact these larger higher energy jets. The Localized Arc Filament Plasma Actuators (LAFPA), developed at the Ohio State University (OSU), have demonstrated the ability to impact a small high speed jet in experiments conducted at OSU and the power to perturb a larger high Reynolds number jet in experiments conducted at the NASA Glenn Research Center. However, the response measured in the large-scale experiments was significantly reduced for the same number of actuators compared to the jet response found in the small-scale experiments. A computational study has been initiated to simulate the LAFPA system with additional actuators on a large-scale jet to determine the number of actuators required to achieve the same desired response for a given jet diameter. Central to this computational study is a model for the LAFPA that both accurately represents the physics of the actuator and can be implemented into a computational fluid dynamics solver. One possible model, based on pressure waves created by the rapid localized heating that occurs at the actuator, is investigated using simplified axisymmetric simulations. The results of these simulations will be used to determine the validity of the model before more realistic and time consuming three-dimensional simulations are conducted to ultimately determine the scalability of the LAFPA system.
Book Synopsis Simulation of the Localized Arc Filament Plasma Actuators for Jet Excitation by : Clifford A. Brown
Download or read book Simulation of the Localized Arc Filament Plasma Actuators for Jet Excitation written by Clifford A. Brown and published by . This book was released on 2010 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The concept of jet control by external forcing is not new. The first published demonstration of a jet responding to outside forces occurred in the mid-1800's. It was not, however, until the 1950's, with the advent of commercial jet aircraft, that scientific study of the subject greatly increased as researchers used external forcing to study the structure and noise sources present in a jet plume. Interest in active jet control continues today, particularly with the additional possibilities afforded by significant advances in measurement and simulation technology, even though it remains limited by the available jet actuators to relatively small, low Reynolds number jets that are of little similarity to the large, highly turbulent jets common in real world applications. However, the recently developed Localized Arc Filament Plasma Actuators (LAFPA) have the potential to expand active jet control research to include these larger, higher Reynolds number jets. The LAFPA have been used successfully to control a small-diameter, high-speed turbulent jet to achieve some plume mixing enhancement and limited noise mitigation. The system, however, must still be extended to a larger class of jets common in the real world and optimized for an application. This work addresses both of these issues. First, experiments are conducted to determine the impact of the LAFPA on a large-scale jet. A model of the LAFPA is then developed for use in the future CFD based studies of excited jets. The model performance is investigated using multiple CFD methodologies to determine the optimal combination of actuator model and CFD scheme for excited jet simulations. Ultimately, the model developed will be used by researchers in future simulations to optimize the actuator system for noise reduction, IR signature reduction, or to system scalability for deployment on larger jets in real-world applications."--Abstract.
Book Synopsis Mixing Control in Supersonic Rectangular Jets Using Plasma Actuators by : Robert M. Snyder
Download or read book Mixing Control in Supersonic Rectangular Jets Using Plasma Actuators written by Robert M. Snyder and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Understanding and Control of Coupling of Supersonic Twin Jets Using Localized Arc Filament Plasma Actuators by : Jordan D. Cluts
Download or read book Understanding and Control of Coupling of Supersonic Twin Jets Using Localized Arc Filament Plasma Actuators written by Jordan D. Cluts and published by . This book was released on 2018 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Control of Hypersonic High Angle-of-attack Re-entry Flow Using a Semi-empirical Plasma Actuator Model by : Michael D. Atkinson
Download or read book Control of Hypersonic High Angle-of-attack Re-entry Flow Using a Semi-empirical Plasma Actuator Model written by Michael D. Atkinson and published by . This book was released on 2012 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this dissertation was to explore the possibility of using flow control to stabilize re-entry flight at very high angle-of-attack. This was carried out in three steps: 1) study the structure of representative high angle-of-attack re-entry flows; 2) develop a semi-empirical plasma actuator model that can be applied to control high angle-of-attack re-entry flows; 3) application of the plasma actuator model to study the control of representative re-entry flows. The calculations include viscous and thermochemical non-equilibrium effects, and a high-fidelity physical model to resolve complex flow structure. The contribution of this dissertation was to provide a detailed description of hypersonic viscous flow around blunt-nosed elliptical cone at very high angle-of-attack. High-fidelity, thermochemical non-equilibrium numerical solutions of high angle-of-attack re-entry flows were not published prior to this research, and thus this research can provide a foundation to calculate, analyze, and describe very high angle-of-attack hypersonic re-entry flows. Paramount to this dissertation was the development of a new phenomenological MHD plasma actuator model. A semi-empirical actuator model was developed by adding source terms to the momentum equation, vibrational energy equation, and total energy equation, employing an exponential decay function based on the formulations of Kalra et al. and Poggie. This new plasma actuator model was extended from Poggie's model to include thermochemical non-equilibrium effects and expanded from Kalra's et al. two-dimensional model to include three-dimensional effects. Development, validation, and calibration of the plasma actuator model was based on a qualitative comparison to the experiment of Kalra et al. on manipulating turbulent shock-wave/bounday layer interaction using plasma actuators. The effect of the plasma actuators on turbulent shock-wave/boundary-layer interaction was simulated numerically and a detailed description of the complex flow structure with and without actuation was provided. Finally, application of the plasma actuators to control the complex flow structure of high angle-of-attack re-entry flight vehicles was investigated. To the best of the author's knowledge, no prior research on high angle-of-attack re-entry vehicle control using plasma actuators has been published. Lastly, this dissertation serves as a foundation to compute, analyze, and control complex flow generated around re-entry vehicles at high angle-of-attack.
Book Synopsis Fundamental Physics and Application of Plasma Actuators for High-speed Flows by : Eli S. Lazar
Download or read book Fundamental Physics and Application of Plasma Actuators for High-speed Flows written by Eli S. Lazar and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, a detailed investigation is given discussing three plasma-based flow control methods. These methods included plasma generated by laser energy, microwaves, and electric arc. The plasma generated by laser energy was also applied to a sonic transverse jet in a supersonic cross flow. Lastly, the particle image velocimetry diagnostic was considered and a technique developed to evaluate measurement uncertainty and using experimental velocity data to solve for density from the continuity equation. In the laser-spark system, the effect of ambient pressure in the range of 0.1 to 1.0 atm and wavelength (266 nm and 532 nm) on the size, temperature, electron number density, and fraction of laser energy absorbed in a laser-induced plasma in air has been conducted. The plasma was generated by using optics to focus the laser energy. The focused laser pulse resulted in the induced optical breakdown of air, creating a plasma to perturb the flow field. As pressure or wavelength are reduced, the size of the plasma, its electron number density, and the fraction of incident laser energy that is absorbed are all found to decrease significantly. For the plasma generated by microwaves, the feasibility of using the system for flow control was demonstrated at pressures ranging from 0.05 atm to 1 atm and for pulsing frequencies between 400 Hz to 10 kHz. The setup was based on a quarter-wave coaxial resonator being operated with a microwave frequency of 2.45 GHz. Analysis of reflected power measurements suggested that the microwave energy could be best coupled into the resonator by using a small inductive loop, where the geometry can be experimentally optimized. The plasma was first characterized by recording images of the emission and taking temporal emission waveform profiles. Tests were conducted in quiescent air and analyzed with schlieren photography to determine the effectiveness of a plasma pulse to produce an instantaneous flow perturbation. Examination of phase averaged schlieren images revealed that a blast was produced by the emission and could be used to alter a flow field. The emission was also thermally characterized through emission spectroscopy measurements where the vibrational and rotational temperatures of the plasma were determined. The last system considered was a localized arc filament plasma actuator, or LAFPA-type device. The system creates electric arcs by generating electric fields in the range of 20 kV/cm between two pin-type electrodes. The potential of the actuator to influence surrounding quiescent flow was investigated using emission imaging, schlieren imaging, current and voltage probes, particle image velocimetry (PIV), and emission spectroscopy. The schlieren imaging revealed a potential to cause blast 0́−Mach0́+ waves and a synthetic jet with controllable directionality dependent on cavity orientation. The electric measurements revealed that, in order to increase the power discharged by the plasma, the electrode separation will only aid mildly and that an optimum plasma current exists (between 300-400 mA for the tested parameter space). The PIV data were acquired for various actuation frequencies and showed a trend between discharge frequency and maximum induced jet velocity. Finally, the emission spectroscopy data were acquired for four different cases: two electrode separations and two plasma currents. For each of the four conditions tested, the spectrum fit very well to a thermal distribution for early times in the emission. However, at later times in the emission, the spectrum no longer matched that of the second positive system under optically thick conditions for any combination of rotational and vibrational temperatures. Using the plasma generated by laser energy, an experimental investigation of flow control on a sonic underexpanded jet injected normally into a Mach 2.45 crossflow is reported. The jet exit geometry was circular and was operated at a jet-to-crossflow momentum flux ratio of 1.7. The unperturbed flow field was analyzed with schlieren imaging, PIV velocity data, surface oil flow visualizations, and pressure sensitive paint measurements. As a means of excitation to the flow field, the plasma energy was focused in the center of the jet exit at three different vertical locations. The perturbed resulting flow field was analyzed with schlieren photography and particle image velocimetry. Analysis of phase averaged schlieren images suggested that the resulting blast wave from the laser pulse disrupted the structure of the barrel shock and Mach disk. The two-component velocity field data revealed that the excitation pulse also caused a perturbation to the jet shear layer and induced the formation of vortices that convect downstream. Finally, additional techniques were developed for the PIV diagnostics. First, while PIV is an established experimental technique for determining a velocity field, quantifying the uncertainty related with this method remains a challenging task. To this end, four sources of uncertainty are assessed: equipment, particle lag, sampling size, and processing algorithm. An example uncertainty analysis is conducted for a transverse sonic jet injected into a supersonic crossflow. However, the analysis is not specific to the example flow field and may be generally applied to any mean velocity field. Secondly, using the velocity data from PIV, a technique was developed to solve for density from the continuity equation over the entire flow field. The technique is validated using data from CFD simulations and demonstrated for experimental data for two flow fields.
Book Synopsis Development of Localized Arc Filament RF Plasma Actuators for High-Speed and High Reynolds Number Flow Control by :
Download or read book Development of Localized Arc Filament RF Plasma Actuators for High-Speed and High Reynolds Number Flow Control written by and published by . This book was released on 2010 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Turbulent Boundary-layer Control with DBD Plasma Actuators Using Spanwise Travelling-wave Technique by : Richard David Whalley
Download or read book Turbulent Boundary-layer Control with DBD Plasma Actuators Using Spanwise Travelling-wave Technique written by Richard David Whalley and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent boundary-layer control has been investigated experimentally using a low-speed wind tunnel at the University of Nottingham, with an overall aim of achieving skin-friction drag reduction. The important part of this investigation is to understand the mechanism of drag reduction and the associated changes in the structure of the turbulent boundary layer. It was demonstrated with Direct Numerical Simulations (DNSs) nearly a decade ago that by applying a spanwise travelling wave in the near-wall region of a turbulent wall flow can lead to a skin-friction drag reduction on the order of 30%. To date, spanwise travelling waves are predominantly created by a Lorentz force, limiting the study of this technique to water flows and numerical investigations. As an aeronautical application of this innovative flow control technique, an investigation into the use of Dielectric-Barrier-Discharge (DBD) plasma actuators to generate spanwise travelling waves in air has been conducted. DBD plasma actuators have received enormous interest over the past ten years within the flow control community due to their unique properties. DBD plasma actuators are completely electrical and ionize the nearby air to couple momentum to the surrounding flow. Hence, DBD plasma actuators require no moving parts, which makes their design simple and without the need for complicated ducting, holes or cavities. They are fast acting, of low power, low in weight, cheap to manufacture and can be fitted to existing airframes. As the body force that the DBD plasma actuator creates is at the wall, DBD plasma actuators are an ideal candidate for wall-based flow control techniques such as the spanwise travelling wave-technique. In this study, DBD plasma actuators have been found to have the ability to greatly modify the near-wall region of the turbulent boundary layer with a potential to reduce skin-friction drag. The near-wall structures modified by the spanwise travelling waves were studied using the PIV technique, while the associated turbulence statistics were carefully documented using hot-wire anemometry. On initiation of DBD plasma in the turbulent boundary layer, streamwise vortices were generated. Spreading of low-speed fluid by the streamwise vortices that were travelling in the spanwise direction was observed, which seems to have greatly attenuated the turbulence production process. This is very much in line with the finding of DNS studies, where wide low-speed ribbons replaced the low-speed streaks.
Book Synopsis Active Control of High Speed Subsonic Cavity Flow Using Plasma Actuators by : Douglas Alan Mitchell
Download or read book Active Control of High Speed Subsonic Cavity Flow Using Plasma Actuators written by Douglas Alan Mitchell and published by . This book was released on 2007 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis High-lift Airfoil Separation Control with Dielectric Barrier Discharge Plasma Actuators by : Jesse Little
Download or read book High-lift Airfoil Separation Control with Dielectric Barrier Discharge Plasma Actuators written by Jesse Little and published by . This book was released on 2010 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: This work examines the performance of dielectric barrier discharge (DBD) plasma actuators for controlling separation from the leading edge and trailing edge flap shoulder of a supercritical high-lift airfoil. DBD plasma actuators driven by both typical AC voltages (AC-DBD) and more developmental nanosecond duration pulses (NS-DBD) are investigated. Characterization of the two actuators shows that very different behavior is created when exciting the plasma discharge using these two waveforms. The AC-DBD plasma actuator functions through electrohydrodynamic effects that introduce zero net mass, but nonzero net momentum into the flow. Conversely, the electrohydrodynamic effects of the NS-DBD are quite weak suggesting thermal effects from rapid localized heating by the plasma are responsible for control authority. The performance of both devices as separation control actuators is tested on a high-lift airfoil system. The AC-DBD is effective for controlling turbulent boundary layer separation from a deflected trailing edge flap between Reynolds numbers of 240,000 and 750,000. Momentum coefficients for the AC-DBD plasma actuator are generally an order of magnitude lower than those usually employed for such studies yet control authority is still realized through amplification of natural vortex shedding from the flap shoulder. The corresponding lift enhancement is primarily due to upstream effects from increased circulation around the entire model rather than full separated flow reattachment to the deflected flap surface. Lift enhancement via instability amplification is found to be relatively insensitive to changes in angle of attack provided that the separation location and underlying dynamics do not change. Control authority decreases with increasing Reynolds number and flap deflection highlighting the necessity for further optimization of AC-DBD plasma actuators for use in realistic takeoff and landing transport aircraft applications. As a whole, these findings compare favorably to studies on a similar high-lift platform using piezoelectric driven zero net mass flux actuation. The NS-DBD plasma actuator is ineffective for controlling separation from the deflected trailing edge flap. However, the device is found to be superior to the tested AC-DBD plasma actuators for controlling leading edge separation and rivals the performance of a passive droop by extending the stall angle by six degrees in the Reynolds number range 750,000-1,000,000. Detailed flow diagnostics show the NS-DBD plasma actuator functions as an active trip for pre-stall incidence angles and generates coherent spanwise vortices that entrain freestream momentum into the separated region at post-stall angles. These structures are generated across all surveyed frequencies, but optimal dimensionless frequencies for controlling separation are in the range four to six depending on the incidence angle. The contrasting performance of the NS-DBD plasma actuator at the leading and trailing edge in comparison to the AC-DBD is discussed and recommendations for future work are provided.
