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Plasma Actuator with Arc Breakdown in a Magnetic Field for Active Flow Control Applications
... This paper summarizes the most recent experimental investigations performed for the development of the cyclotronic plasma actuator, and is a continuation of the recently reported work [32][33][34][35]; the technology was recently patented [36]. Early work evaluated the actuator configuration in low-speed wind tunnel tests using PIV in a zeropressure gradient boundary layer, as well as pressure recovery measurements with the actuator placed upstream of an expansion ramp [32]. ...
... This paper summarizes the most recent experimental investigations performed for the development of the cyclotronic plasma actuator, and is a continuation of the recently reported work [32][33][34][35]; the technology was recently patented [36]. Early work evaluated the actuator configuration in low-speed wind tunnel tests using PIV in a zeropressure gradient boundary layer, as well as pressure recovery measurements with the actuator placed upstream of an expansion ramp [32]. It was observed that the actuator acts to introduce a local velocity defect immediately downstream of the actuator location. ...
... Initial work applied a GBS Minpuls 2.2 system and also a 60 Hz neon sign transformer as high-voltage driver circuits for the actuators [32]. The recent work has focused on more compact circuits that can readily be configured to power arrays of actuators. ...
... This paper summarizes the most recent experimental investigations performed for the development of the cyclotronic plasma actuator. The experiments discussed here are a continuation of the recently reported work [32][33][34] which evaluated the actuator configuration in low-speed wind tunnel tests using PIV in a zero-pressure gradient boundary layer, as well as pressure recovery measurements with the actuator placed upstream of an expansion ramp. It was observed that the actuator acts to introduce a local velocity defect immediately downstream of the actuator location. ...
... By placing this detector above the coaxial actuator, collimated to view one segment of the arc path, and passing the output to an oscilloscope through an amplifier stage, a frequency signal corresponding to the rotation rate of the arc was measured, as the detector responded to the emission from the arc as it passed through the collimated region. This same sensor was used to measure low frequency pulsing of the discharge in preliminary work by viewing the entire actuator [32]. An alternative method applied a ferrite-core (215 H) inductor to sense the disturbance of the magnetic field near the actuator as the arc rotated [33]. ...
... Initial work applied a GBS Minpuls 2.2 system and also a neon sign transformer as a means to power the actuators [32]. Recent work has focused on more compact circuits that can readily be configured to power arrays of actuators. ...
... This paper summarizes the most recent experimental bench tests performed for study of the cyclotronic plasma actuator. The experiments discussed here are a continuation of the recently reported work [32,33]. Earlier studies evaluated the actuator configuration in low-speed wind tunnel tests using PIV in a zero-pressure gradient boundary layer, as well as pressure recovery measurements with the actuator placed upstream of an expansion ramp [32]. ...
... The experiments discussed here are a continuation of the recently reported work [32,33]. Earlier studies evaluated the actuator configuration in low-speed wind tunnel tests using PIV in a zero-pressure gradient boundary layer, as well as pressure recovery measurements with the actuator placed upstream of an expansion ramp [32]. It was observed that the actuator acts to introduce a local velocity defect immediately downstream of the actuator location. ...
... It was observed that the actuator acts to introduce a local velocity defect immediately downstream of the actuator location. Subsequent recovery in near-wall streamwise velocity was then observed, where actuation produces a higher streamwise velocity in the region immediately adjacent to the wind tunnel wall [32]. This velocity defect and recovery is believed to be linked to the formation of streamwise vortex structures induced by the actuation, with similarities to velocity profile development downstream of passive vortex generators [34]. ...
... This paper summarizes the most recent experimental investigations performed for the development of the cyclotronic plasma actuator. The experiments discussed here are a continuation of the recently reported work [32] which evaluated the actuator configuration in low-speed wind tunnel tests using PIV in a zero-pressure gradient boundary layer, as well as pressure recovery measurements with the actuator placed upstream of an expansion ramp. It was observed that the actuator acts to introduce a local velocity defect immediately downstream of the actuator location. ...
... By placing this detector above the coaxial actuator, collimated to view one segment of the arc path, and passing the output to an oscilloscope through an amplifier stage, a frequency signal corresponding to the rotation rate of the arc was measured, as the detector responded to the emission from the arc as it passed through the collimated region. This same sensor was used to measure low frequency pulsing of the discharge in prior work by viewing the entire actuator [32]. An alternative method applied a ferrite-core (215 H) inductor to sense the disturbance of the magnetic field near the actuator as the arc rotated. ...
... Previous work applied a GBS Minpuls 2.2 system and also a neon sign transformer as a means to power the actuators [32]. Recent work has focused on more compact circuits that can readily be configured to power arrays of actuators. ...
... Non-thermal plasma devices can offer strategies for flow control [1][2][3][4][5][6][7]. Amongst active flow control devices, plasma actuators have the potential to control a fluid system while staying silent, instantaneous, and compact [8][9][10]. ...
Dielectric barrier discharge (DBD) plasma actuators can generate a wall jet without moving parts through interaction between ionized and neutral molecules in an electric field. The coupling between electro-hydrodynamic, turbulence, and viscous effects in the flow boundary layer remains unclear and deserves careful investigation. We present an experimental investigation of momentum injection by DBD actuators in a U_external = 5 m/s and U_external = 11 m/s co-flow and counter-flow configuration over a range of VAC = 12 kV - 19.5 kV peak-to-peak at a frequency of 2 kHz. In the co-flow configuration, the DBD actuator adds momentum to the boundary layer, similar to an electrohydrodynamic (EHD) jet in quiescent conditions. In the counter-flow configuration, flow separation is observed at free stream velocity U_external = 5 m/s. The momentum displacement in the counter-flow configuration is ~ 6x greater than EHD jet momentum in a quiescent environment. Both co-flow and counter-flow momentum injections show diminishing effects with increased external flow speed. This work highlights that the resulting flow pattern is not a simple superposition of the EHD jet and the free stream but is determined by a balance between the inertial, viscous and Coulombic forces of the EHD and the external flow. The velocity profiles and momentum characteristics can be used to validate numerical models and inform the design of DBD actuators for active flow control.
... Over the past decade, there has been a great interest in using non-thermal plasma actuators for active flow control of aerodynamic surfaces [1][2][3][4][5][6][7]. Plasma actuators have the potential to control a fluid system while staying silent, instantaneous, and compact [8][9][10]. ...
Dielectric barrier discharge (DBD) plasma actuators with an asymmetric, straight edge electrode configuration generate a wall-bounded jet without moving parts. Mechanistic description of the interaction between the Coulombic forces and fluid motion as a function of DBD parameters remains unclear. This paper presents an experimental investigation of DBD actuator, including electrical current associated with microdischarges, plasma volume, and the wall jet momentum over a range of alternating current (AC) frequencies (0.5 – 2 kHz) and peak-to-peak voltages up to 19.5 kV. Discharge current is measured with a high temporal resolution, and plasma volume is characterized optically, and the momentum induced by the DBD wall jet is computed based on the axial velocities measured downstream of the actuator using a custom-built pitot tube. Discharge current analysis demonstrated asymmetry between the positive and negative semi-cycle; both currents yielded a power-law relationship with empirical fitting coefficients. Plasma length varies linearly and volume quadratically with voltage. Although plasma length reached an asymptotic value at a higher frequency, the plasma volume grows due to the increasing height of the ionization region. In a simple 2D configuration, the DBD wall jet momentum shows near-linear dependency with discharge current in the range of voltages and frequencies considered in this work. The presented empirical model characterizes the DBD wall jet momentum and the discharge current based only on the AC inputs. With the estimation of plasma volume, the model can be applied for determining more realistic boundary conditions in numerical simulations.
View Video Presentation: https://doi.org/10.2514/6.2022-2257.vid Magnetically-guided atmospheric arc devices were applied to provide plasma-excitation to premixed methane-air flames. Researchers have recently applied similar technology to study vortex generation for aerodynamic flow control, and the scaling and driver circuits used for those devices has been leveraged in the presented work. To provide a plasma-exited volume, an arc is produced in the gap of coaxial electrodes placed within the field of a strong rare-earth magnet. Due to drift motion in the magnetic field, the charged particles experience Lorentz force which causes the arc filament to sweep about the center of the coaxial electrodes. To observers, this takes on the apparent form of a plasma “disc” at the tip of the coax. The technique is applied to flame holding by integrating flow channels in the dielectric spacers of the coax, through which fuel and oxidizer are injected and mixed in the rotating plasma filament. The use of zero-voltage-switching circuits operating in the 70-80 kHz range to introduce plasma power in the flame zone is reported, with these circuit modules being powered by low voltage DC supplies (e.g., 24 V). The enhanced mixing effect of the plasma-excitation technique was demonstrated through high-speed imaging and schlieren. Gas analyzers were used to measure the reduction in the unburnt CO level above the lean flame zone when the plasma system was engaged. The methodology for sizing the coaxial plasma burners for natural gas combustion is presented. An array of plasma-assisted burners is demonstrated using this technique, with lean methane flow rates (fi = 0.76) corresponding to available heat release between 46 and 138 kW.
The atmospheric coaxial direct-coupled microwave torch configuration offers a convenient experimental format for validating multiphysics simulations of plasma-assisted combustion (PAC). The optical accessibility of this configuration allows for the application of various diagnostics to the PAC flame such as planar laser-induced fluorescence (PLIF) to determine quantitative two-dimensional density distributions of radicals (e.g. OH, CH, NO), Rayleigh scattering thermometry (RST) for temperature profiles, and particle image velocimetry (PIV) to characterize the flame flow-field, as well as assessment of plasma nonequilibrium effects via probe measurements and spectroscopic emission measurements. Furthermore, the flexible system enables premixed and non-premixed configurations to be addressed, and the most recent modifications have added tangential swirling flows. Here, recent changes to the experimental apparatus to combine PAC with swirl-stabilization are overviewed, and initial PLIF measurements of OH radicals are presented, as well as measurements of flame stability limits and acoustics. Cold flow simulations of the swirl-stabilized chamber using BLAZE Multiphysics simulation suite are presented. Nomenclature EEDF = electron energy distribution function E/N = electric field to gas density ratio (reduced electric field) fn = acoustic mode frequency Le = effective acoustic length n = mode number ne = electron density SLPM = standard liters per minute Te = electron temperature Tg = gas temperature U = flow velocity Vs = sound speed t = turbulent kinematic viscosity p = primary fuel-to-oxidizer equivalence ratio
Several variants of an ejector mixing nozzle concept for a high-pressure chemical oxygen-iodine laser (COIL) have been experimentally tested. To obtain a better understanding of how much performance enhancement could be expected with increased mixing and to facilitate a larger parametric study we utilized the quasi-1D BLAZE-IV model to simulate these experiments. While computational fluid dynamic (CFD) computations provide critical detailed information about individual flow fields that cannot be obtained with a model such as BLAZE-IV, the computing time required for these CFD calculations inherently limits the number of such computations that can be performed in a reasonable amount of time. Simulation of COIL ejector mixing nozzle experiments required the development of a BLAZE-IV model component capable of treating the simultaneous expansion of multiple mixing streams into a flow region with an initial base area, which is equivalent to the instantaneous introduction of a disparity between the sum of all stream areas and the total internal geometric cross–sectional area. In addition, the model now treats the supersonic expansion of the initially subsonic mixed stream [the O 2 (a 1 ∆) stream in the COIL case] which is known to occur downstream of an aerodynamic throat created by the expansion of the higher pressure unmixed streams. A method consistent with all applicable physical laws by which the desired flow conditions are achieved via asymptotic apportionment of the base area was required. A Russian design served as our baseline for the BLAZE-IV modeling calculations performed herein. Comparisons with experimental data and estimations of performance enhancement with faster mixing are presented.
Stereoscopic PIV measurements investigating the effect of Vortex Generators on the lift force near stall and on glide ratio at best aerodynamic performance have been carried out in the LM Glasfiber wind tunnel on a DU 91-W2-250 profile. Measurements at two Reynolds numbers were analyzed; Re=0.9·10^6 and 2.4·10^6 . The results show that one can resolve the longitudinal vortex structures generated by the devices and that mixing is created close to the wall, transferring high momentum fluid into the near wall region. It is also seen that the vortex generators successfully can obstruct separation near stall.
A new system for active how control using smart vortex generators (SVG) is presented. Increments in C-l max from modern vortex generators (VGs) are determined through wind-tunnel testing on a two-dimensional wing section. Using an optimized VG configuration, a system was built with 1) a shear-flow sensor that detected the onset and depth of stall, 2) a series of shape-memory-alloy VGs, and 3) a lift-to-drag (L/D) maximizing controller. The system demonstrated a 14% increase in C-l max, a 2.7-deg rise in alpha(stall) a 42% jump in L/D through the stall, and a low alpha C-d0 penalty of less than 0.1%. Further testing demonstrated that the system consumed only 9.2 W of power, responded in less than 0.8 s, and was capable of unstalling an airfoil that had exceeded alpha(stall) by up to 3 deg.
Experiments were performed on a flat-plate airfoil and an Eppler E338 airfoil at very low flight Reynolds numbers (3000 ≤ Re ≤ 50,000), in which dielectric barrier discharge plasma actuators were employed at the airfoil leading edges to effect flow control. The actuators were driven in a high-frequency (kilohertz) steady mode and a pulsed mode in which pulse frequency and duty cycle were varied in a systematic fashion. Optimum reduced frequencies for generating poststall lift were approximately between 0.4 and 1, and this was broadly consistent with zero-mass-flux slot-blowing data acquired at Reynolds numbers that were approximately 200 times higher. Nevertheless, profound differences in the response to reduced frequency and duty cycle were observed between the flat-plate and E338 airfoils. In general, actuation produced considerable performance improvements, including an increase in maximum lift coefficient of 0.4 to 0.8 and maintained elevated endurance at significantly higher lift coefficients. Actuation in the steady mode resulted in circulation control at Re = 3000. Pulsed actuation also exerted a significant effect on the wake at prestall angles of attack, in which control of the upper-surface flat-plate bubble shedding produced significant differences in wake spreading and vortex shedding. The flat plate was also tested in a semispan-wing configuration (AR = 6), and the effect of control was comparable with that observed on the airfoil. Copyright © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
chemical O 2 (a 1 Δ) generation system. In this paper we present post-discharge modeling results obtained using a modified version of the Blaze-II chemical laser code. The effects of proposed chemical kinetic reactions on post discharge kinetics were studied and simulations were compared with experimental data. The modified Blaze-II code was used to study gain and power as a function of reactant mass flow rates. While agreement with experimental data was improved with the addition of new kinetics, there still appear to be significant kinetic and mixing mechanisms that are absent from the present model.
Several studies have shown that a surface dielectric barrier discharge (DBD) may be used as an electrohydrodynamic (EHD) actuator
in order to control airflows. In this paper, a parametric study has been performed in order to increase the velocity of the
ionic wind induced by such actuators. The results show that an optimization of geometrical and electrical parameters allows
us to obtain a time-averaged ionic wind velocity up to 8m/s at 0.5mm from the wall. Moreover, non-stationary measurements
of the induced wind have been performed with synchronized records of current and voltage signals. These experiments show that
the DBD actuator seems to generate a pulsed velocity at the same frequency than the applied high voltage.
This article summarizes the results of an optimization study of a micro-vortex generator flow control in an inlet. Five parametric optimization was carried out using the classical Design of Experiment DOE method. Two main objectives were in focus. First, to develop the methodology and skills necessary to conduct a DOE optimization study in relatively new area of the flow control. Second, to develop the procedures which would be used as a lead during design of flow control in inlets. New information about the behavior of the channel with flow control were obtained during tests and analyzed. Several interesting configurations were located. The parameters of optimal settings were then used to set up the vortex generator installation in a generic inlet.
Photoionization of Cs (6p 2P3/2) atoms during the operation of a Cs D2 line (852.1 nm: 6p 2P3/2→6s 2S1/2) laser, pumped by free→free transitions of thermal Cs-Ar ground state pairs, has been investigated experimentally and computationally. Photoexcitation of Cs vapor/Ar mixtures through the blue satellite of the D2 transition (peaking at 836.7 nm) selectively populates the 2P3/2 upper laser level by the dissociation of the CsAr excited complex. Comparison of laser output energy data, for instantaneous pump powers up to 3 MW, with the predictions of a numerical model sets an upper bound of 8 × 10-26 cm4 W-1 on the Cs (6p 2P3/2) two photon ionization cross-section at 836.7 nm which corresponds to a single photon cross-section of 2.4 × 10-19 cm2 for a peak pump intensity of 3 MW cm-2.
Practical application of active flow control is dependent upon the development of robust actuators that are reliable, low cost, and responsive, and that consume little power. Development continues on a system for high-speed flow control called the SparkJet. The SparkJet, which produces a synthetic jet with high exhaust velocities, holds the promise of manipulating high-speed flows without moving structures. JHU/APL is investigating the operational aspects of the SparkJet with the envisioned long-term payoff of a micro- actuated flow control system for enhanced aerodynamic performance of small, highly maneuverable, high-speed vehicles. Combined computational and experimental techniques are being applied to investigate the effects of device geometry and power deposition levels on the operation of a cavity SparkJet device. This paper focuses on experimental and computational parametric studies of a second-generation SparkJet device. A sparse matrix of experiments was completed and the results were compared with an analytical model. Computations were conducted to quantify the sensitivities of single-pulse device performance on orifice diameter, chamber volume, and energy deposited. Investigation of axisymmetric and 2- dimensional operation suggests that more than one operating domain is possible. OBJECTIVE Effective manipulation of a flow field can lead to a number of significant benefits to aerospace vehicle systems, including enhanced performance, maneuverability, payload, and range, as well as lowered overall cost. These macro benefits are directly achievable through the application of flow-control technology to impact fluid phenomena such as transition, turbulence, and flow separation on the
The efficacy of dielectric barrier discharge (DBD) plasmas driven by high voltage (~15 kV) repetitive nanosecond pulses (~100 ns FWHM) for flow separation control is investigated experimentally on an airfoil leading edge up to Re=1x10 6 (62 m/s). Unlike AC-DBDs, the nanosecond pulse driven DBD plasma actuator transfers very little momentum to the neutral air, but generates compression waves similar to localized arc filament plasma actuators. A complex pattern of quasi-planar and spherical compression waves is observed in still air. Measurements suggest that some of these compression waves are generated by discharge filaments that remain fairly reproducible pulse-to-pulse. The device performs as an active trip at high Re pre-stall angles of attack and provides perturbations that generate coherent spanwise vortices at post-stall. These coherent structures entrain freestream momentum thereby reattaching the normally separated flow to the suction surface of the airfoil. Coherent structures are identified at all tested frequencies, but values of F c + =4-6 are most effective for control. Such devices which are believed to function through thermal effects could be an alternative to AC-DBD plasmas that rely on momentum addition.
Multiple flow diagnostics have been applied to planar panels revered by strips of glow-discharge surface plasma in atmospheric pressure air generated by the one atmosphere uniform glow discharge plasma. Direct drag measurements, smoke wire and titanium tetrachloride Row visualization, and boundary-layer velocity profiles were obtained. The plasma generated along streamwise-oriented, symmetric strip electrodes is shown to cause a large increase in drag, whereas the plasma along spanwise-oriented, asymmetric strip electrodes can generate a significant thrust. Flow visualization and mean velocity measurements show the primary cause of the phenomena to be a combination of mass transport and vortical structures induced by strong electrohydrodynamic body forces on the Row, known as paraelectric forcing.
An experimental investigation has been conducted to evaluate boundary-layer separation control on a two-dimensional single-flap, three-clement, high-lift system at near-flight Reynolds numbers with small surface-mounted vortex generators. The wind-tunnel testing was carried out in the NASA Langley Low-Turbulence Pressure Tunnel as part of a cooperative program between McDonnell Douglas Aerospace and NASA Langley Research Center to develop code validation data bases and to improve physical understanding of multielement airfoil flows. This article describes results obtained for small (subboundary-layer) vane-type vortex generators mounted on a multielement airfoil in a landing configuration. Measurements include lift, drag, surface pressure, wake profile, and fluctuating surface heat fluxes. The results reveal that vortex generators as small as 0.18% of reference (slat and flap stowed) wing chord (''micro-vortex generators'') can effectively reduce boundary-layer separation on the flap for landing configurations. Reduction of nap separation can significantly improve performance of the high-lift system by reducing drag and increasing lift for a given approach angle of attack. At their optimum chordwise placement on the flap, the micro-vortex generators are hidden inside the wing when the nap is retracted, thus extracting no cruise drag penalty.
Boundary layer separation control by plasma actuator with high-voltage
pulsed periodic nanosecond excitation is presented. Actuator-induced gas
velocities show near-zero values for nanosecond pulses. The measurements
performed have shown overheating of discharge region at fast (τ 1
μs) thermalization of the plasma imputed energy. The mean values of
such heating for the plasma layer can reach 70, 200 and even 400 K for
7, 12 and 50 ns pulse duration, respectively. The emerging shock wave
together with the secondary vortex flows disturbs the main flow. The
resulting pulsed-periodic disturbance causes an efficient transversal
momentum transfer into the boundary layer and further flow attachment to
the airfoil surface. Thus for pulsed nanosecond periodic DBD the main
mechanism of impact is the energy transfer and heating the near-surface
gas layer. The following pulse-periodic vortex movement stimulates
redistribution of the main flow momentum. The experiments have shown
high efficiency of the given mechanism to control boundary layer
separation, lift and drag force coefficients, and acoustic noise
reduction in the Mach number range of 0.05 to 0.85.
This paper presents the results of a parametric experimental investigation aimed at optimizing the body force produced by single dielectric barrier discharge plasma actuators used for aerodynamic flow control. A primary goal of the study is the improvement of actuator authority for flow control applications at higher Reynolds number than previously possible. The study examines the effects of dielectric material and thickness, applied voltage amplitude and frequency, voltage waveform, exposed electrode geometry, covered electrode width, and multiple actuator arrays. The metric used to evaluate the performance of the actuator in each case is the measured actuator-induced thrust which is proportional to the total body force. It is demonstrated that actuators constructed with thick dielectric material of low dielectric constant produce a body force that is an order of magnitude larger than that obtained by the Kapton-based actuators used in many previous plasma flow control studies. These actuators allow operation at much higher applied voltages without the formation of discrete streamers which lead to body force saturation. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.
Bow shock perturbations in a Mach 5 air flow, produced by low-temperature, nanosecond pulse, and surface dielectric barrier discharge (DBD), are detected by phase-locked schlieren imaging. A diffuse nanosecond pulse discharge is generated in a DBD plasma actuator on a surface of a cylinder model placed in air flow in a small scale blow-down supersonic wind tunnel. Discharge energy coupled to the actuator is 7.3-7.8 mJ/pulse. Plasma temperature inferred from nitrogen emission spectra is a few tens of degrees higher than flow stagnation temperature, T = 340 +/- 30 K. Phase-locked Schlieren images are used to detect compression waves generated by individual nanosecond discharge pulses near the actuator surface. The compression wave propagates upstream toward the baseline bow shock standing in front of the cylinder model. Interaction of the compression wave and the bow shock causes its displacement in the upstream direction, increasing shock stand-off distance by up to 25%. The compression wave speed behind the bow shock and the perturbed bow shock velocity are inferred from the Schlieren images. The effect of compression waves generated by nanosecond discharge pulses on shock stand-off distance is demonstrated in a single-pulse regime (at pulse repetition rates of a few hundred Hz) and in a quasi-continuous mode (using a two-pulse sequence at a pulse repetition rate of 100 kHz). The results demonstrate feasibility of hypersonic flow control by low-temperature, repetitive nanosecond pulse discharges.
The canard airfoil from the Voyager aircraft was tested in Ohio State University's subsonic wind tunnel. This highly optimized laminar flow section had good clean airfoil performance, but suffered severe lift and drag penalties with early boundary-layer transition. These performance penalties resulted from a midchord boundary-layer separation. An experimental program was conducted to document this problem and then to design and test vortex generators in order to improve the tripped airfoil performance while having the least effect on the clean airfoil. A set of properly designed vortex generators were found to increase the lift and reduce the drag of the contaminated airfoil. A brief study documented a significant drag rise due to rough surface in the turbulent boundary-layer region.
The term plasma actuator has now been a part of the fluid dynamics flow-control vernacular for more than a decade. A particular type of plasma actuator that has gained wide use is based on a single–dielectric barrier discharge (SDBD) mechanism that has desirable features for use in air at atmospheric pressures. For these actuators, the mechanism of flow control is through a generated body-force vector field that couples with the momentum in the external flow. The body force can be derived from first principles, and the effect of plasma actuators can be easily incorporated into flow solvers so that their placement and operation can be optimized. They have been used in a wide range of internal and external flow applications. Although initially considered useful only at low speeds, plasma actuators are effective in a number of applications at high subsonic, transonic, and supersonic Mach numbers, owing largely to more optimized actuator designs that were developed through better understanding and modeling of...
The control of boundary layer separation on the suction side of an airfoil at high angle of attack has been renewed by the possibilities of active control. Nevertheless, such an active control needs a deep understanding of the flow to manipulate and of the actuating flow, both being 3D and unsteady. For that purpose, a model experiment has been designed in the frame of a coordinated European project called AEROMEMS, with a simpler (2D) geometry and with a dilatation of the scales in order to be able to characterize the actuation flow. This model is a bump in a boundary layer wind tunnel, which mimics the adverse pressure gradient on the suction side of an airfoil at the verge of separation. The present contribution describes preliminary tests done to optimize standard passive devices before testing active systems. The optimization was done with hot film shear stress probes, the characterization with hot wire anemometry and PIV. The results show quantitatively the improvement brought by the passive devices in terms of skin friction. They also show the mechanism which is at the origin of this improvement. The next step of the project is to replace passive devices by synthetic jets.
An in-depth review of boundary-layer flow-separation control by a passive method using low-profile vortex generators is presented. The generators are defined as those with a device height between 10% and 50% of the boundary-layer thickness. Key results are presented for several research efforts, all of which were performed within the past decade and a half where the majority of these works emphasize experimentation with some recent efforts on numerical simulations. Topics of discussion consist of both basic fluid dynamics and applied aerodynamics research. The fluid dynamics research includes comparative studies on separation control effectiveness as well as device-induced vortex characterization and correlation. The comparative studies cover the controlling of low-speed separated flows in adverse pressure gradient and supersonic shock-induced separation. The aerodynamics research includes several applications for aircraft performance enhancement and covers a wide range of speeds. Significant performance improvements are achieved through increased lift and/or reduced drag for various airfoils—low-Reynolds number, high-lift, and transonic—as well as highly swept wings. Performance enhancements for non-airfoil applications include aircraft interior noise reduction, inlet flow distortion alleviation inside compact ducts, and a more efficient overwing fairing. The low-profile vortex generators are best for being applied to applications where flow-separation locations are relatively fixed and the generators can be placed reasonably close upstream of the separation. Using the approach of minimal near-wall protuberances through substantially reduced device height, these devices can produce streamwise vortices just strong enough to overcome the separation without unnecessarily persisting within the boundary layer once the flow-control objective is achieved. Practical advantages of low-profile vortex generators, such as their inherent simplicity and low device drag, are demonstrated to be critically important for many applications as well.
The paper demonstrates several ways of use of the UV–vis optical emission spectroscopy of medium resolution for the diagnostics of atmospheric pressure air and nitrogen plasmas relevant to bio-medical and environmental applications. Plasmas generated by DC discharges (streamer corona, transient spark, and glow discharge), AC microdischarges in porous ceramics, and microwave plasma were investigated. Molecular (OH, NO, CN) and atomic (H, O, N) radicals, and other active species, e.g. N2 (C, B, A), (B), were identified. The composition of the emission spectra gives insight in the ongoing plasma chemistry. Rotational, i.e. gas, and vibrational temperatures were evaluated by fitting experimental with simulated spectra. Streamer corona, transient spark and microdischarges generate cold, strongly non-equilibrium plasmas (300–550 K), glow discharge plasma is hotter, yet non-equilibrium (1900 K), and microwave plasma is very hot and thermal (∼3000–4000 K). Electronic excitation temperature and OH radical concentration were estimated in the glow discharge assuming the chemical equilibrium and Boltzmann distribution (9800 K, 3 × 1016 cm−3). Optical emission also provided the measurement of the active plasma size of the glow discharge, and enabled calculating its electron number density (1012 cm−3).
Pulsed-DC Plasma Actuator Characteristics and Application in Compressor Stall Control
- R Mcgowan
- T C Corke
- E Matlis
- R Kaszeta
- C Gold
McGowan, R., Corke, T.C., Matlis, E., Kaszeta, R., and Gold, C., "Pulsed-DC Plasma Actuator Characteristics and
Application in Compressor Stall Control," AIAA Paper 2016-0394, 2016.
Simulations of Plasma-Assisted Combustion Flames in Coaxial Microwave Reactors
- J Zimmerman
- A Palla
- D King
- D Carroll
- C Mitsingas
- S Hammack
Zimmerman, J., Palla, A., King, D., Carroll, D., Mitsingas, C., Hammack, S., and Lee T., "Simulations of Plasma-Assisted
Combustion Flames in Coaxial Microwave Reactors," 54 th AIAA Aerospace Sciences Meeting, 4-8 January 2016, San
Diego, CA (AIAA 2016-0190).
automatic three-dimensional finite element mesh generator, Software Package, Ver. 2.8.5, copyright C
- Gmsh
Gmsh, automatic three-dimensional finite element mesh generator, Software Package, Ver. 2.8.5, copyright C. Geuzaine
and J.-F. Remacle, 2014