Note: This page contains sample records for the topic barrier plasma actuators from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Experimental Demonstration of Multi Barrier Plasma Actuators (MBPA).  

National Technical Information Service (NTIS)

This report is a summary of a one-year effort on demonstration experiments of a novel set of multi-barrier plasma actuators (MBPA) by the PI s research team. The typical dielectric barrier discharge (DBD) plasma actuator consists of two electrodes separat...

R. Durscher S. Roy

2011-01-01

2

Jet noise control using the dielectric barrier discharge plasma actuators  

NASA Astrophysics Data System (ADS)

We study experimentally how plasma actuators operating on the basis of surface barrier high-frequency discharge affect jet noise characteristics. The results of investigations of air jets (100-200 m/s) have demonstrated that the studied plasma actuators have control authority over the noise characteristics of these jets. An actuator's effect on the jet in the applied configuration is related to acoustic discharge excitation and to a large extent is similar to the well-known Vlasov-Ginevsky effect. It has been shown that jet excitation in the case of St ˜ 0.5 using the barrier-discharge plasma actuator leads to broadband amplification of jet sound radiation. The jet excitation in the case of St > 2 leads to broadband noise reduction if the action is sufficiently intensive.

Kopiev, V. F.; Bityurin, V. A.; Belyaev, I. V.; Godin, S. M.; Zaitsev, M. Yu.; Klimov, A. I.; Kopiev, V. A.; Moralev, I. A.; Ostrikov, N. N.

2012-07-01

3

Parametric Optimization of Single Dielectric Barrier Discharge (SDBD) Plasma Actuators.  

NASA Astrophysics Data System (ADS)

There has been growing interest in flow control using dielectric barrier discharge plasma actuators in recent years. However, studies regarding optimization of plasma actuators are relatively scarce. Current study is intended to optimize the body force produced by plasma discharge (steady and unsteady) which is a function of various parameters such as dielectric material, size of electrodes, their overlap, frequency, voltage, etc. Detailed experiments are performed in a controlled environment with no-external-flow condition with several different dielectric materials of various thicknesses. Plasma induced velocity (using glass pitot probe), body force (using high precision weighing scale), and power dissipation are measured at various voltages and frequencies. Optimal voltage waveform and frequency has been found which resulted in time averaged maximum induced velocity and body force. This has resulted in an order of magnitude improvement of the actuator effect. The results obtained follow a relatively simple mathematical model that allows one to derive analytical expressions for electrical characteristics of plasma actuators.

Iqbal, Muhammad O.; Kozlov, Alexey; Schatzman, David; Othman, Hesham; Thomas, Flint; Corke, Thomas

2006-11-01

4

Surface charge in dielectric barrier discharge plasma actuators  

SciTech Connect

Direct measurements of the dielectric surface potential and its dynamics in asymmetric dielectric barrier discharge (DBD) plasma actuators show that the charge builds up at the dielectric surface and extends far downstream of the plasma. The surface charge persists for a long time (tens of minutes) after the driving voltage has been turned off. For a sinusoidal voltage waveform, the dielectric surface charges positively. With the voltage waveform consisting of nanosecond pulses superimposed on a dc bias, the sign of the dielectric surface charge is the same as the sign (polarity) of the bias voltage. The surface charging significantly affects DBD plasma actuator performance.

Opaits, D. F.; Shneider, M. N.; Miles, Richard B. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Likhanskii, A. V. [Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Macheret, S. O. [Lockheed Martin Aeronautics Company, Palmdale, California 93599 (United States)

2008-07-15

5

Electrohydrodynamic force in dielectric barrier discharge plasma actuators  

Microsoft Academic Search

Surface dielectric barrier discharges (DBDs) have been proposed as actuators for flow control. In this paper we discuss the basic mechanisms responsible for the electrohydrodynamic (EHD) force exerted by the discharge on the gas molecules. A two-dimensional fluid model of the DBD is used to describe the plasma dynamics, to understand the basic physics associated with the EHD force and

J. P. Boeuf; Y. Lagmich; Th Unfer; Th Callegari; L. C. Pitchford

2007-01-01

6

Dielectric barrier discharge plasma actuator for flow control  

NASA Astrophysics Data System (ADS)

Electrohydrodynamic (EHD) and magnetohydrodynamic phenomena are being widely studied for aerodynamic applications. The major effects of these phenomena are heating of the gas, body force generation, and enthalpy addition or extraction, [1, 2, 3]. In particular, asymmetric dielectric barrier discharge (DBD) plasma actuators are known to be effective EHD device in aerodynamic control, [4, 5]. Experiments have demonstrated their effectiveness in separation control, acoustic noise reduction, and other aeronautic applications. In contrast to conventional DBD actuators driven by sinusoidal voltages, we proposed and used a voltage profile consisting of nanosecond pulses superimposed on dc bias voltage. This produces what is essentially a non-self-sustained discharge: the plasma is generated by repetitive short pulses, and the pushing of the gas occurs primarily due to the bias voltage. The advantage of this non-self-sustained discharge is that the parameters of ionizing pulses and the driving bias voltage can be varied independently, which adds flexibility to control and optimization of the actuators performance. Experimental studies were conducted of a flow induced in a quiescent room air by a single DBD actuator. A new approach for non-intrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the Schlieren technique, burst mode of plasma actuator operation, and 2-D numerical fluid modeling. During the experiments, it was found that DBD performance is severely limited by surface charge accumulation on the dielectric. Several ways to mitigate the surface charge were found: using a reversing DC bias potential, three-electrode configuration, slightly conductive dielectrics, and semi conductive coatings. Force balance measurements proved the effectiveness of the suggested configurations and advantages of the new voltage profile (pulses+bias) over the traditional sinusoidal one at relatively low voltages. In view of practical applications certain questions have been also addressed, such as electrodynamic effects which accompany scaling of the actuators to real size models, and environmental effects of ozone production by the plasma actuators.

Opaits, Dmitry Florievich

7

Dielectric Barrier Discharge Plasma Actuator for Flow Control  

NASA Technical Reports Server (NTRS)

This report is Part II of the final report of NASA Cooperative Agreement contract no. NNX07AC02A. It includes a Ph.D. dissertation. The period of performance was January 1, 2007 to December 31, 2010. Part I of the final report is the overview published as NASA/CR-2012- 217654. Asymmetric dielectric barrier discharge (DBD) plasma actuators driven by nanosecond pulses superimposed on dc bias voltage are studied experimentally. This produces non-self-sustained discharge: the plasma is generated by repetitive short pulses, and the pushing of the gas occurs primarily due to the bias voltage. The parameters of ionizing pulses and the driving bias voltage can be varied independently, which adds flexibility to control and optimization of the actuators performance. The approach consisted of three elements coupled together: the Schlieren technique, burst mode of plasma actuator operation, and 2-D numerical fluid modeling. During the experiments, it was found that DBD performance is severely limited by surface charge accumulation on the dielectric. Several ways to mitigate the surface charge were found: using a reversing DC bias potential, three-electrode configuration, slightly conductive dielectrics, and semi conductive coatings. Force balance measurements proved the effectiveness of the suggested configurations and advantages of the new voltage profile (pulses+bias) over the traditional sinusoidal one at relatively low voltages. In view of practical applications certain questions have been also addressed, such as electrodynamic effects which accompany scaling of the actuators to real size models, and environmental effects of ozone production by the plasma actuators.

Opaits, Dmitry, F.

2012-01-01

8

Force measurements of single and double barrier DBD plasma actuators in quiescent air  

Microsoft Academic Search

We present the results of our experimental measurements of how variations in the discharge geometry of surface-mounted dielectric barrier discharges (DBDs) affect the force transferred to atmospheric pressure air. Our studies include both single barrier plasma actuators (one electrode insulated) and double barrier plasma actuators (both electrodes insulated) operated in quiescent air. Stagnation probe measurements of the induced air flow

A R Hoskinson; N Hershkowitz; D E Ashpis

2008-01-01

9

Control of endwall secondary flow in a compressor cascade with dielectric barrier discharge plasma actuation  

Microsoft Academic Search

Three dielectric barrier discharge plasma actuators were mounted at the positions of 20%, 40% and 60% of chord length on the\\u000a endwall in a compressor cascade. The downstream flow field of the cascade has been measured with a mini five-hole pressure\\u000a probe with and without the plasma actuation. The measured results show that the plasma actuation most effectively reduces\\u000a total

Gang Li; YanJi Xu; Bin Lin; JunQiang Zhu; ChaoQun Nie; HongWei Ma; ZhaoFeng Wang

2009-01-01

10

Measurements and Simulations of Surface Dielectric Barrier Discharges Used as Plasma Actuators  

NASA Technical Reports Server (NTRS)

This report is a Ph.D. dissertation performed under NRA cooperative agreement and submitted as part of the final report. Asymmetric surface dielectric barrier discharges (DBDs) have shown promise for use as aerodynamic actuators for active flow control. In this project we studied DBD actuators experimentally and numerically. Our DBDs used a symmetric triangular high voltage waveform to generate plasma in atmospheric pressure air. Time-averaged measurements indicated that the induced force of a single barrier actuator design (one electrode insulated from the plasma) can be increased exponentially above the results of previous studies by decreasing both the length and thickness of the electrode exposed to the plasma. This increased force may allow these devices to control flow separation in a wider range of flow environments. Experiments using an intensified digital camera to examine the plasma on time scales of a few nanoseconds showed that, in addition to the previously-observed filamentary and jet-like plasma structures, discharges with very thin exposed electrodes exhibited a weak but constant plasma immediately adjacent to those electrodes. In double-barrier actuators (both electrodes insulated), decreasing the diameter of the narrower electrode lead to increasing forces, and recorded images showed the simultaneous existence of both filamentary and jet-like plasma structures. The development and application of a time-dependent, two-dimensional computational fluid plasma model has aided in understanding the detailed physics of surface DBDs at all-time scales. For simulated single-barrier discharges, the model qualitatively reproduced the filamentary and jet-like micro-discharge structures. The model was somewhat successful in reproducing the observed characteristics of double-barrier actuators. For both actuator geometries, the model indicated that the majority of the forces induced on the neutral gas occur in between micro-discharges as the plasmas decay.

Hoskinson, Alan R.

2012-01-01

11

Study of Control Parameters for Separation Mitigation Using an Asymmetric Single Dielectric Barrier Plasma Actuator.  

National Technical Information Service (NTIS)

Separation mitigation using asymmetric dielectric barrier discharges is studied by considering the neutral gas flow past a flat plate at an angle of attack. A self-consistent plasma actuator model is employed to couple the electric force field to the mome...

D. V. Gaitonde K. P. Singh S. Roy

2006-01-01

12

Influence of shock wave propagation on dielectric barrier discharge plasma actuator performance  

NASA Astrophysics Data System (ADS)

Interest in plasma actuators as active flow control devices is growing rapidly due to their lack of mechanical parts, light weight and high response frequency. Although the flow induced by these actuators has received much attention, the effect that the external flow has on the performance of the actuator itself must also be considered, especially the influence of unsteady high-speed flows which are fast becoming a norm in the operating flight envelopes. The primary objective of this study is to examine the characteristics of a dielectric barrier discharge (DBD) plasma actuator when exposed to an unsteady flow generated by a shock tube. This type of flow, which is often used in different studies, contains a range of flow regimes from sudden pressure and density changes to relatively uniform high-speed flow regions. A small circular shock tube is employed along with the schlieren photography technique to visualize the flow. The voltage and current traces of the plasma actuator are monitored throughout, and using the well-established shock tube theory the change in the actuator characteristics are related to the physical processes which occur inside the shock tube. The results show that not only is the shear layer outside of the shock tube affected by the plasma but the passage of the shock front and high-speed flow behind it also greatly influences the properties of the plasma.

Erfani, Rasool; Zare-Behtash, Hossein; Kontis, Konstantinos

2012-06-01

13

Force Measurements of Single and Double Barrier DBD Plasma Actuators in Quiescent Air  

NASA Technical Reports Server (NTRS)

We have performed measurements of the force induced by both single (one electrode insulated) and double (both electrodes insulated) dielectric barrier discharge plasma actuators in quiescent air. We have shown that, for single barrier actuators, as the electrode diameter decreased below those values previously studied the induced Force increases exponentially rather than linearly. This behavior has been experimentally verified using two different measurement techniques: stagnation probe measurements of the induced flow velocity and direct measurement of the force using an electronic balance. In addition, we have shown the the induced force is independent of the material used for the exposed electrode. The same techniques have shown that the induced force of a double barrier actuator increases with decreasing narrow electrode diameter.

Hoskinson, Alan R.; Hershkowitz, Noah; Ashpis, David E.

2008-01-01

14

Optical and electrical characterization of a surface dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

An experimental characterization of the properties of asymmetric surface dielectric barrier discharges used as plasma actuators was performed. Optical emission spectroscopy was used to measure the radiated power and some plasma parameters such as the electron and vibrational temperature. Electrical characterization of the discharge was executed by recording individual current pulses with high temporal resolution, and collecting a large dataset of these events. Statistical analysis performed on them allowed one to correlate microdischarge (MD) properties with the voltage phase and to spot differences arising from the actual breakdown mechanism in such asymmetric configurations. In particular, the asymmetry between the two different half-cycles of the discharges was characterized, and it was found that it directly influences plasma actuator efficiency. Differences arising in the multiplicity, amplitude and temporal duration of the MDs were investigated. Some effects connected with the dielectric material and high voltage supply properties were evaluated and correlated with the induced velocity provided by the plasma actuators.

Biganzoli, I.; Barni, R.; Riccardi, C.; Gurioli, A.; Pertile, R.

2013-04-01

15

Three-dimensional simulations of discharge plasma evolution on a dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

To develop simulation techniques for reconstructing microdischarges in a dielectric barrier discharge (DBD) plasma actuator and analyze spanwise non-uniformity in a body force field, three-dimensional discharge plasma simulations of a DBD plasma actuator were conducted assuming step-like positive and negative applied voltages. Our study showed that to break the spanwise uniformity, some disturbances were required in the computational conditions to reconstruct the three-dimensional microdischarges, and the attachment of some minute bumps (several tens of micrometers in size) on the electrode edge allowed for the successful reconstruction of glow-type microdischarges and streamer-type filamentary discharges in the negative and positive applied voltage cases, respectively. The tentative body force field has strong spanwise non-uniformity corresponding to the plasma structure, and in addition, a spanwise directional body force also exists, especially in the streamer discharge. However, the spanwise averaged body force has the same spatial-distribution and time-evolution characteristics obtained with the two-dimensional simulation.

Nishida, Hiroyuki; Nonomura, Taku; Abe, Takashi

2014-04-01

16

Phase effect on flow control for dielectric barrier plasma actuators  

SciTech Connect

Active control of flow has a wide range of applications. Specifically, mitigation of detachment due to the weakly ionized gas flow past a flat plate at an angle of attack is studied using two asymmetric sets of electrode pairs kept at a phase lag. The equations governing the dynamics of electrons, helium ions, and neutrals are solved self-consistently with charge-Poisson equation. The electrodynamic forces produced by two actuators largely depend on the relative phase between the potentials applied to rf electrodes and distance between them. A suitable phase and an optimum distance exist between two actuators for effective separation control.

Singh, K. P.; Roy, Subrata [Computational Plasma Dynamics Laboratory, Mechanical Engineering, Kettering University, Flint, Michigan 48504 (United States)

2006-07-03

17

Spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

The spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator is investigated using a photomultiplier tube, a high-sensitivity camera, particle image velocimetry, and electrohydrodynamics simulations. Plasma actuators have typically demonstrated their utility in flow separation control, but on a millimetric scale they have also shown to be promising in the control of crossflow instabilities in crossflow-dominated laminar-turbulent boundary-layer transition. In view of the subtleties associated with creating an initial disturbance to excite subcritical wavelengths, it is desirable to characterize the local plasma discharge structure, body force organization, and induced velocity field in detail. The results show that, similar to their linear centimetric counterpart, the plasma discharge has a highly dynamic and somewhat organized spatiotemporal structure. Under quiescent flow conditions, the actuator induces a velocity field that consists of two counter-rotating vortices, accompanied by a wall-normal synthetic jet region, which in three-dimensions describes a toroidal vortex around the aperture's periphery. The surprising result, however, is that these vortices rotate in the opposite direction to vortices generated by similar centimetric annular designs. Three-dimensional electrohydrodynamics simulations correctly reproduce this behavior. Because the body force organization may be qualitatively perceived as being the axisymmetric counterpart of the more classical linear actuator, this flow reversal is thought to be due to the actuator scale. When an array of millimetric actuators is considered in close proximity, an interaction takes place between the vortices created from each actuator and those of neighboring actuators, resulting in a significant reduction in vortex size compared with the single aperture case, accompanied by an increase in the maximum induced flow velocity magnitude.

Humble, R. A.; Craig, S. A.; Vadyak, J.; McClure, P. D.; Hofferth, J. W.; Saric, W. S.

2013-01-01

18

Surface dielectric barrier discharge: Effect of encapsulation of the grounded electrode on the electromechanical characteristics of the plasma actuator  

Microsoft Academic Search

Active flow control is a rapidly developing topic because the associated industrial applications are of immense importance, particularly for aeronautics. Among all the flow control actuators, plasma-based devices are very promising. In most cases, the plasma actuator is based on a surface dielectric barrier discharge (DBD) established between two electrodes flush mounted on both sides of a dielectric layer. In

Jean-Charles Laurentie; Jérôme Jolibois; Eric Moreau

2009-01-01

19

Determination of the phase-resolved body force produced by a dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge (DBD) plasma actuators are a promissing tool for active flow control applications. In order to determine the time-resolved body force induced by a DBD plasma actuator, which was driven by a 9.5 kHz sinusoidal signal, the flow has to be captured with a high spatial and temporal resolution. For this purpose we applied a laser Doppler velocity profile sensor for the measurements of the two-component velocity field and Lagrangian acceleration. A temporal and spatial resolution of 7.3 µs and 40 µm was achieved. We present the time-resolved local flow behaviours induced by the DBD actuator. Based on these measurement data the time-resolved body force generated by the plasma actuator was derived. Experiments revealed a defined dependence of the force direction on the phase angle of the ac operating voltage. This result is a contribution to the controversy on the temporal behaviour of the body force of plasma actuators.

Neumann, Mathias; Friedrich, Christian; Czarske, Jürgen; Kriegseis, Jochen; Grundmann, Sven

2013-01-01

20

Velocity-information-based force-term estimation of dielectric-barrier discharge plasma actuators  

NASA Astrophysics Data System (ADS)

Particle image velocimetry measurements in close proximity to dielectric-barrier discharge plasma actuators are conducted to quantify the momentum transfer of the plasma to the surrounding air flow. Based on these data a comparative analysis of six existing approaches to estimate the induced body force is presented. Integral methods calculate an integral value for the actuator force based on the momentum-balance equation. Insight into the spatial distribution of the body force is provided by differential methods, which are based either on the Navier-Stokes equations or on the vorticity equation. It is demonstrated that the intensity as well as the domain of the force increase with increasing operating power levels. Emphasis is also placed on the issue of self-induced drag. It is shown that 30% of the induced momentum is consumed by wall friction. All results are validated with previously obtained balance force data and luminosity analysis of identical actuators.

Kriegseis, J.; Schwarz, C.; Tropea, C.; Grundmann, S.

2013-02-01

21

Characterization of nanosecond pulse driven dielectric barrier discharge plasma actuators for aerodynamic flow control  

NASA Astrophysics Data System (ADS)

Positive polarity nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuators are studied experimentally in quiescent atmosphere. Pulse energy and instantaneous pulse power (hereafter referred to as energy and power) are calculated using simultaneous voltage and current measurements. Electrical characteristics are evaluated as a function of peak voltage, pulse frequency, discharge length, and dielectric thickness. Schlieren imaging is used to provide a relative estimate of discharge energy that is coupled to the near surface gas as heat for the same parameters. Characteristics of the DBD load have a substantial effect on the individual voltage and current traces which are reflected in the energy and power values. Power is mainly dependent on actuator length which is inconsistent with schlieren data as expected. Higher per unit length energy indicates a stronger compression wave for a given actuator geometry, but this is not universally true across different actuators suggesting some constructions more efficiently couple energy to the gas. Energy and compression wave strength are linearly related. Higher pulse frequency produces higher energy but is primarily attributed to heating of the actuator and power supply components and not to an optimal discharge frequency. Both energy and wave strength increase as peak voltage to the power of approximately 3.5 over a substantial range similar to ac-DBD plasma actuators.

Dawson, Robert; Little, Jesse

2013-03-01

22

Spatio-temporal filament behaviour in a dielectric barrier discharge plasma actuator  

Microsoft Academic Search

The behaviour of filaments in a dielectric barrier discharge plasma actuator in atmospheric air has been visualized through high-speed framing photography. A filament is recognized by its radiation emission in the positive, ascending phase of an applied ac voltage (1-5 kV, 1-5 kHz). A current pulse appears with a random time-interval typically of the order of 10 µs. A filament

A. Sasoh; K. Kikuchi; T. Sakai

2007-01-01

23

Role of the electric waveform supplying a dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

The paper compares the influence of different waveforms as input for a dielectric barrier discharge plasma actuator investigated in context of plasma-assisted flow control. The electrical aspects, the plasma morphology, the body force production, and the two-component time-resolved electric wind produced over a single ac period of signal are investigated. Results shown that square waveform is optimal in terms of body force and mean electric wind production, but the velocity fluctuations are enhanced by using a sinusoidal waveform. The time-resolved measurements of the produced velocity demonstrate that the electromechanical conversion mechanism is quasi-linear in the vicinity of the discharge.

Benard, N.; Moreau, E.

2012-05-01

24

Capacitances and energy deposition curve of nanosecond pulse surface dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

Nanosecond pulse surface dielectric barrier discharge (NPSDBD) plasma actuator is preferred to generate aerodynamic actuation which relies on the deposited energy during nanosecond time scale, named as the mechanism of fast thermalization. It is very important to understand the energy deposition process of NPSDBD plasma actuator. In this paper, an equivalent circuit model is presented to describe a typical asymmetric NPSDBD plasma actuator first. Of the three key capacitances in the equivalent circuit, the values of Capacitance Cm and Cg can be gotten by the calculation of the electric field, with the method of undetermined coefficients, while the value of Capacitance Cd is determined from the charge-voltage (Q-V) plot, also called Lissajous figure. It is found that the value of Capacitance Cd varies with the amplitude of applied pulse voltage, due to the change of the dimension of plasma sheet. Based on the circuit parameters and the measured waveforms of discharge voltage and current, the time varying characteristics of deposited energy can be obtained finally. It is indicated that the calculated results of deposited energy show a good agreement with conventional method.

Pang, Lei; He, Kun; Di, Dongxu; Zhang, Qiaogen; Liu, Chunliang

2014-05-01

25

Capacitances and energy deposition curve of nanosecond pulse surface dielectric barrier discharge plasma actuator.  

PubMed

Nanosecond pulse surface dielectric barrier discharge (NPSDBD) plasma actuator is preferred to generate aerodynamic actuation which relies on the deposited energy during nanosecond time scale, named as the mechanism of fast thermalization. It is very important to understand the energy deposition process of NPSDBD plasma actuator. In this paper, an equivalent circuit model is presented to describe a typical asymmetric NPSDBD plasma actuator first. Of the three key capacitances in the equivalent circuit, the values of Capacitance Cm and Cg can be gotten by the calculation of the electric field, with the method of undetermined coefficients, while the value of Capacitance Cd is determined from the charge-voltage (Q-V) plot, also called Lissajous figure. It is found that the value of Capacitance Cd varies with the amplitude of applied pulse voltage, due to the change of the dimension of plasma sheet. Based on the circuit parameters and the measured waveforms of discharge voltage and current, the time varying characteristics of deposited energy can be obtained finally. It is indicated that the calculated results of deposited energy show a good agreement with conventional method. PMID:24880363

Pang, Lei; He, Kun; Di, Dongxu; Zhang, Qiaogen; Liu, Chunliang

2014-05-01

26

Experimental investigation on a vectorized aerodynamic dielectric barrier discharge plasma actuator array  

NASA Astrophysics Data System (ADS)

The Electro-Hydro-Dynamics (EHD) interaction, induced in atmospheric pressure still air by a surface dielectric barrier discharge (DBD) actuator, had been experimentally studied. A plasma aerodynamic actuator array, able to produce a vectorized jet, with the induced airflow oriented toward the desired direction, had been developed. The array was constituted by a sequence of single surface DBD actuators with kapton as dielectric material. An ac voltage in the range of 0-6 kV peak at 15 kHz had been used. The vectorization had been obtained by feeding the upper electrodes with different voltages and by varying the electrical connections. The lower electrodes had been connected either to ground or to the high voltage source, to produce the desired jet orientation and to avoid plasma formation acting in an undesired direction. Voltage and current measurements had been carried out to evaluate waveforms and to estimate the active power delivered to the discharge. Schlieren imaging allowed to visualize the induced jet and to estimate its orientation. Pitot measurements had been performed to obtain velocity profiles for all jet configurations. A proportional relation between the jet deflection angle and the applied voltage had been found. Moreover, a linear relation had been obtained between the maximum speed in the jet direction and the applied voltage. The active power of the discharge is approximated by both a power law function and an exponential function of the applied voltage.

Neretti, Gabriele; Cristofolini, Andrea; Borghi, Carlo A.

2014-04-01

27

Airflow influence on the discharge performance of dielectric barrier discharge plasma actuators  

NASA Astrophysics Data System (ADS)

In the present work, the effect of the airflow on the performance of dielectric barrier discharge plasma-actuators is investigated experimentally. In order to analyze the actuator's performance, luminosity measurements have been carried out simultaneously with the recording of the relevant electrical parameters. A performance drop of about 10% is observed for the entire measured parameter range at a flow speed of M = 0.145 (U?=50 m/s). This insight is of particular importance, since the plasma-actuator control authority is already significantly reduced at this modest speed level. The results at higher Mach numbers (0.4

Kriegseis, J.; Grundmann, S.; Tropea, C.

2012-07-01

28

Microscale plasma actuators for improved thrust density  

Microsoft Academic Search

We present a study of the dielectric barrier discharge (DBD) plasma actuators for microscale applications. Traditional macroscale DBD actuators suffer from relatively small actuation effect as characterized by small induced force density and resulting flow velocity. As a remedy we propose microscale plasma actuators that may induce orders of magnitude higher force density. We study the physics of such actuation

Chin-Cheng Wang; Subrata Roy

2009-01-01

29

Preliminary Experiments of Barrier Discharge Plasma Actuators using Dry and Humid Air  

Microsoft Academic Search

Experiments are performed using dry and humid air to ascertain the effect of humidity on the performance of a plasma actuator in flight conditions. These actuators are becoming popular in controlling flow about low to moderate speed aerospace vehicles. These experiments are performed at a new Test Facility of the Computational Plasma Dynamics Laboratory (CPDL) in Kettering University. A blow-down

Richard Anderson; Subrata Roy

2006-01-01

30

On the classification of dielectric barrier discharge plasma actuators: A comprehensive performance evaluation study  

NASA Astrophysics Data System (ADS)

The increasing popularity and maturity of plasma actuators for many flow control applications requires a common standard for plasma actuator performance evaluation. In the present work, a comprehensive comparative study of existing and new evaluation measures is presented, based on results from identical plasma-actuator configurations. A power-flow diagram is introduced that covers the entire range of power stages from the energy source to the flow-control success. All individual power stages are explained, existing controversial definitions are clarified, and an evaluation guideline is applied to previously obtained data. Finally, the defined systematic analysis is applied to the results of a recently conducted plasma-actuator in-flight experiment.

Kriegseis, J.; Duchmann, A.; Tropea, C.; Grundmann, S.

2013-08-01

31

Novel applications of plasma actuators  

Microsoft Academic Search

The current study investigates the effectiveness of two different dielectric barrier discharge plasma actuator configurations, a 3-D annular geometry for use in micro thrusters and internal duct aerodynamics and a jet vectoring actuator that acts as a vortex generator and flow control device. The first configuration consists of a closed circumferential arrangement which yields a body force when a voltage

Arzu Ceren Ozturk

2009-01-01

32

Dielectric Barrier Discharge Plasma Actuators with Novel Geometries for Flow Modification: Experimental Measurements and Validation with a 2-D Fluid Model.  

National Technical Information Service (NTIS)

Optical characteristics of surface dielectric barrier discharge (DBD) plasma actuators with wire/planar electrodes were studied using an intensified charge-coupled device camera and a monochromator in atmospheric pressure air. Spatial and temporal images ...

N. Hershkowitz R. Bonazza

2013-01-01

33

Flow control over a NACA 0012 airfoil using dielectric-barrier-discharge plasma actuator with a Gurney flap  

NASA Astrophysics Data System (ADS)

Flow control study of a NACA 0012 airfoil with a Gurney flap was carried out in a wind tunnel, where it was demonstrated that a dielectric-barrier-discharge (DBD) plasma actuator attached to the flap could increase the lift further, but with a small drag penalty. Time-resolved PIV measurements of the near-wake region indicated that the plasma forcing shifted the wake downwards, reducing its recirculation length. Analysis of wake vortex dynamics suggested that the plasma actuator initially amplified the lower wake shear layer by adding momentum along the downstream surface of the Gurney flap. This enhanced mutual entrainment between the upper and lower wake vortices, leading to an increase in lift on the airfoil.

Feng, Li-Hao; Jukes, Timothy N.; Choi, Kwing-So; Wang, Jin-Jun

2012-06-01

34

Simulation Tool for Dielectric Barrier Discharge Plasma Actuators at Atmospheric and Sub-Atmospheric Pressures: SBIR Phase I Final Report  

NASA Technical Reports Server (NTRS)

This report is the final report of a SBIR Phase I project. It is identical to the final report submitted, after some proprietary information of administrative nature has been removed. The development of a numerical simulation tool for dielectric barrier discharge (DBD) plasma actuator is reported. The objectives of the project were to analyze and predict DBD operation at wide range of ambient gas pressures. It overcomes the limitations of traditional DBD codes which are limited to low-speed applications and have weak prediction capabilities. The software tool allows DBD actuator analysis and prediction for subsonic to hypersonic flow regime. The simulation tool is based on the VORPAL code developed by Tech-X Corporation. VORPAL's capability of modeling DBD plasma actuator at low pressures (0.1 to 10 torr) using kinetic plasma modeling approach, and at moderate to atmospheric pressures (1 to 10 atm) using hydrodynamic plasma modeling approach, were demonstrated. In addition, results of experiments with pulsed+bias DBD configuration that were performed for validation purposes are reported.

Likhanskii, Alexandre

2012-01-01

35

Serpentine Geometry Plasma Actuators for Flow Control.  

National Technical Information Service (NTIS)

In this paper, a curved class of plasma actuator geometries is presented. The intension of this paper is to extend the versatility of a dielectric barrier discharge plasma actuator by modifying the geometry of its electrodes, so that the plasma generated ...

M. Riherd S. Roy

2013-01-01

36

Two-Dimensional Plasma Actuator Analysis Code.  

National Technical Information Service (NTIS)

A two-dimensional plasma actuator analysis code has been developed. A time-accurate Navier-Stokes CFD code was coupled with a time-dependent, phenomenological model of an alternating current, single dielectric barrier discharge plasma actuator. The accura...

S. Ellison

2006-01-01

37

Effective Discharge Dynamics for Plasma Actuators.  

National Technical Information Service (NTIS)

Some effective control parameters for active separation mitigation using asymmetric dielectric barrier discharges is studied by considering the weakly ionized gas flow past a flat plate at angle of attack. A self-consistent plasma actuator model is employ...

D. V. Gaitonde H. Kumar K. P. Singh M. Visbal S. Roy

2006-01-01

38

Contribution of positive and negative ions to the electrohydrodynamic force in a dielectric barrier discharge plasma actuator operating in air  

SciTech Connect

We present a parametric study of the electrohydrodynamic force generated by surface dielectric barrier discharge plasma actuators in air for sinusoidal voltage waveforms. The simulation results confirm that momentum is transferred from the charged particles to the neutral species in the same direction during both positive and negative parts of the cycle. The momentum transfer is due to positive ions during the positive part of the cycle (electrode above the dielectric layer is the anode), and to negative ions during the negative part of the cycle. The relative contribution of the positive and negative parts of the cycle depends on the voltage amplitude and frequency. The model predicts that the contribution of negative ions tends to be dominant at low voltage frequencies and high voltage amplitudes.

Boeuf, J. P.; Lagmich, Y.; Pitchford, L. C. [UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d'Energie), Universite de Toulouse, 118 route de Narbonne, F-31062 Toulouse Cedex 9 (France); LAPLACE, CNRS, F-31062 Toulouse (France)

2009-07-15

39

Modeling of dielectric barrier discharge plasma actuators driven by repetitive nanosecond pulses  

SciTech Connect

A detailed physical model for an asymmetric dielectric barrier discharge (DBD) in air driven by repetitive nanosecond voltage pulses is developed. In particular, modeling of DBD with high voltage repetitive negative and positive nanosecond pulses combined with positive dc bias is carried out. Operation at high voltage is compared with operation at low voltage, highlighting the advantage of high voltages, however the effect of backward-directed breakdown in the case of negative pulses results in a decrease of the integral momentum transferred to the gas. The use of positive repetitive pulses with dc bias is demonstrated to be promising for DBD performance improvement. The effects of the voltage waveform not only on force magnitude, but also on the spatial profile of the force, are shown. The crucial role of background photoionization in numerical modeling of ionization waves (streamers) in DBD plasmas is demonstrated.

Likhanskii, Alexandre V.; Shneider, Mikhail N.; Macheret, Sergey O.; Miles, Richard B. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Lockheed Martin Skunk Works, 1011 Lockheed Way, Palmdale, California 93599 (United States); Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

2007-07-15

40

Bluff Body Flow Control Using Plasma Actuators  

NASA Astrophysics Data System (ADS)

In this study, the use of single dielectric barrier discharge plasma actuators for the control of bluff body flow separation is investigated. In particular, surface mounted plasma actuators are used to reduce both drag and unsteady vortex shedding from circular cylinders in cross-flow. It is demonstrated that the plasma-induced surface blowing gives rise to a local Coanda effect that promotes the maintenance of flow attachment. Large reductions in vortex shedding and drag are demonstrated for Reynolds numbers ˜ 10^410^5. Both steady and unsteady plasma-induced surface blowing is explored. Results are presented from experiments involving both two and four surface mounted actuators.

Thomas, Flint

2005-11-01

41

Scaling of maximum velocity, body force, and power consumption of dielectric barrier discharge plasma actuators via particle image velocimetry  

NASA Astrophysics Data System (ADS)

This study presents Particle Image Velocimetry (PIV) measurements of the induced flow characteristics generated by single dielectric barrier discharge (DBD) actuators in quiescent conditions. The primary aim is to establish accurate empirical trends for model development on both the maximum induced velocity and body force with voltage and consumed power. The results reveal a power law variation for the maximum velocity at low voltages which is followed by an asymptotic behavior. In contrast, the body force is characterized by two power law regions. The power law exponent is shown to be a function of the dielectric thickness, frequency and dielectric constant. Reducing the former or increasing the latter two result in a higher coefficient and lower voltage at which the trend changes. The onset of the second region occurs at a Re ~ 100 (based on the maximum velocity, um, and corresponding half height, y1/2) and is characterized by a velocity profile which no longer agrees with the laminar profile of Glauert whilst moving increasingly towards the turbulent case. Phase locked PIV measurements show that as the voltage increases the peak momentum transfer shifts from the middle of the AC cycle to the latter end of the forward stroke. Lissajous plots of um? against the corresponding x location and plasma length ?x demonstrate that the peak momentum transfer remains relatively fixed in space as the voltage and plasma length increase.

Murphy, J. P.; Kriegseis, J.; Lavoie, P.

2013-06-01

42

On Plasma Synthetic Jet Actuators  

Microsoft Academic Search

The term plasma actuator refers to an asymmetric arrangement of two electrodes (typ- ically rectangular strips) separated by dielectric material that can be used as active flow control devices. A plasma actuator design consisting of an annular electrode array, the plasma synthetic jet actuator (PSJA), is experimentally investigated in this paper. This particular geometry creates a zero-net mass flux (or

Arvind Santhanakrishnan; Jamey D. Jacob

2006-01-01

43

Plasma actuated heat transfer  

NASA Astrophysics Data System (ADS)

We introduce plasmas for film cooling enhancement in gas turbines and other engineering applications. We identify mechanisms to actuate essentially stagnant fluid just downstream of the cooling hole by employing three-dimensional body force for different hole geometries. Such methods actively alter flow structures in the vicinity of an actuator using an electrodynamic mechanism that induces attachment of cold jet to the work surface. Numerical results are compared with published experimental data and other numerical predictions for the latest film cooling technology. An effectiveness improvement of above 100% over the standard baseline design is predicted.

Roy, Subrata; Wang, Chin-Cheng

2008-06-01

44

Experimental investigation of dielectric barrier discharge plasma actuators driven by repetitive high-voltage nanosecond pulses with dc or low frequency sinusoidal bias  

SciTech Connect

Experimental studies were conducted of a flow induced in an initially quiescent room air by a single asymmetric dielectric barrier discharge driven by voltage waveforms consisting of repetitive nanosecond high-voltage pulses superimposed on dc or alternating sinusoidal or square-wave bias voltage. To characterize the pulses and to optimize their matching to the plasma, a numerical code for short pulse calculations with an arbitrary impedance load was developed. A new approach for nonintrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the schlieren technique, burst mode of plasma actuator operation, and two-dimensional numerical fluid modeling. The force and heating rate calculated by a plasma model was used as an input to two-dimensional viscous flow solver to predict the time-dependent dielectric barrier discharge induced flow field. This approach allowed us to restore the entire two-dimensional unsteady plasma induced flow pattern as well as characteristics of the plasma induced force. Both the experiments and computations showed the same vortex flow structures induced by the actuator. Parametric studies of the vortices at different bias voltages, pulse polarities, peak pulse voltages, and pulse repetition rates were conducted experimentally. The significance of charge buildup on the dielectric surface was demonstrated. The charge buildup decreases the effective electric field in the plasma and reduces the plasma actuator performance. The accumulated surface charge can be removed by switching the bias polarity, which leads to a newly proposed voltage waveform consisting of high-voltage nanosecond repetitive pulses superimposed on a high-voltage low frequency sinusoidal voltage. Advantages of the new voltage waveform were demonstrated experimentally.

Opaits, Dmitry F.; Likhanskii, Alexandre V.; Neretti, Gabriele; Zaidi, Sohail; Shneider, Mikhail N.; Miles, Richard B. [Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Macheret, Sergey O. [Lockheed Martin Aeronautics Company, Palmdale, California 93599 (United States)

2008-08-15

45

Serpentine geometry plasma actuators for flow control  

NASA Astrophysics Data System (ADS)

In this paper, a curved class of plasma actuator geometries is presented. The intension of this paper is to extend the versatility of a dielectric barrier discharge plasma actuator by modifying the geometry of its electrodes, so that the plasma generated body force is able to excite a broader spectrum of flow physics than plasma actuators with a more standard geometry. Two examples of flow control are demonstrated numerically. An example of this class of actuators is shown to generate boundary layer streaks, which can be used to accelerate or delay the laminar to turbulent transition process, depending on how they are applied. Simulations of a low Reynolds number airfoil are also performed using additional examples of this class of actuators, where it is shown that this plasma actuator geometry is able to introduce energy into and excite a secondary instability mode and increase unsteady kinetic energy in the boundary layer. These two cases show that this general class of curved actuators possesses an increased versatility with respect to the standard geometry actuators.

Riherd, Mark; Roy, Subrata

2013-08-01

46

Optimization of Dielectric Barrier Discharge Plasma Actuators Driven By Repetitive Nanosecond Pulses  

Microsoft Academic Search

A detailed physical model for an asymmetric dielectric barrier discharge (DBD) in air driven by repetitive nanosecond voltage pulses is developed. In particular, modeling of DBD with high voltage repetitive negative and positive nanosecond pulses combined with positive dc bias is carried out. Operation at high voltage is compared with operation at low voltage, highlighting the advantage of high voltages,

A. V. Likhanskii; M. N. Shneider; S. O. Macheret; R. B. Miles

2007-01-01

47

Plasma actuators for bluff body flow control  

NASA Astrophysics Data System (ADS)

The aerodynamic plasma actuators have shown to be efficient flow control devices in various applications. In this study the results of flow control experiments utilizing single dielectric barrier discharge plasma actuators to control flow separation and unsteady vortex shedding from a circular cylinder in cross-flow are reported. This work is motivated by the need to reduce landing gear noise for commercial transport aircraft via an effective streamlining created by the actuators. The experiments are performed at Re D = 20,000...164,000. Circular cylinders in cross-flow are chosen for study since they represent a generic flow geometry that is similar in all essential aspects to a landing gear oleo or strut. The minimization of the unsteady flow separation from the models and associated large-scale wake vorticity by using actuators reduces the radiated aerodynamic noise. Using either steady or unsteady actuation at ReD = 25,000, Karman shedding is totally eliminated, turbulence levels in the wake decrease significantly and near-field sound pressure levels are reduced by 13.3 dB. Unsteady actuation at an excitation frequency of St D = 1 is found to be most effective. The unsteady actuation also has the advantage that total suppression of shedding is achieved for a duty cycle of only 25%. However, since unsteady actuation is associated with an unsteady body force and produces a tone at the actuation frequency, steady actuation is more suitable for noise control applications. Two actuation strategies are used at ReD = 82,000: spanwise and streamwise oriented actuators. Near field microphone measurements in an anechoic wind tunnel and detailed study of the near wake using LDA are presented in the study. Both spanwise and streamwise actuators give nearly the same noise reduction level of 11.2 dB and 14.2 dB, respectively, and similar changes in the wake velocity profiles. The contribution of the actuator induced noise is found to be small compared to the natural shedding noise. A tandem cylinder configuration with the plasma actuation on the upstream cylinder is investigated using surface dynamic pressure sensors. As a result of the plasma actuation, the surface pressure fluctuations on the downstream cylinder are reduced by about two times at the free-stream velocity of 40 m/s (ReD = 164,000). In addition, this study presents the results of a parametric experimental investigation aimed at optimizing the body force produced by single dielectric barrier discharge (SDBD) 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 and operated at low frequency AC voltage 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.

Kozlov, Alexey V.

48

Effect of the voltage waveform on induced flow of a dielectric barrier discharge plasma actuator  

NASA Astrophysics Data System (ADS)

Flow control technique using surface plasma is attracting a lot of attention because of its ability to be the innovative technology for the wide range application. In this paper, we have conducted experiments to inspect relationship of velocity of the induced flow, frequency and voltage of power source. First, when sinusoidal voltage was applied between the electrodes, the result showed the induced flow was the faster, the greater the power was, regardless of the frequency and voltage. Then, the waveform was changed to bipolar pulse with shorter ON period than that of sine wave with a frequency of 3 kHz, almost the same induced velocity was observed at the same power, regardless of the voltage waveform. By the same experiment with a frequency of 10 kHz, the relationship of induced velocity and the power was affected by the waveform unlike the case of frequency at 3 kHz. The highest induced velocity was observed in case of sine wave. Induced velocity was able to be expressed as a function of the full width half maximum of voltage waveform, under constant power. From these facts, it is believed that it is required for external electric field to be applied for more than certain period of time in order for ions to be accelerated by electric field even in a case that almost same amount of ions were generated under an almost same condition of discharge power.

Shimura, Naohiko; Tanaka, Motofumi; Yasui, Hiroyuki

2012-10-01

49

Effective Discharge Dynamics for Plasma Actuators  

Microsoft Academic Search

Some effective control parameters for active separation mitigation using asymmetric dielectric barrier discharges is studied by considering the weakly ionized gas flow past a flat plate at angle of attack. A self- consistent plasma actuator model is employed to couple the electric force field to the momentum of the neutral gas. The equations governing the motion of electrons, ions and

Subrata Roy; K. P. Singh; Haribalan Kumar; Datta V. Gaitonde; Miguel Visbal

50

Micro Jet Generation with Annular Plasma Actuators  

Microsoft Academic Search

The effectiveness of dielectric barrier discharge plasma actuators for use in micro thrusters and internal duct aerodynamics are investigated. The primary flow is driven by tha zero-net mass flux jet at the wall in a closed circumferential arrangemen that then entrains fluid in the core of the duct. This results in a unique configuration for studying impulsively started jet phenomena.

Ceren Ozturk; Jamey Jacob

2008-01-01

51

Microscale plasma actuators for improved thrust density  

SciTech Connect

We present a study of the dielectric barrier discharge (DBD) plasma actuators for microscale applications. Traditional macroscale DBD actuators suffer from relatively small actuation effect as characterized by small induced force density and resulting flow velocity. As a remedy we propose microscale plasma actuators that may induce orders of magnitude higher force density. We study the physics of such actuation using a multiscale ionized gas flow code based on the high-fidelity finite-element procedure. First, a two-dimensional volume discharge with nitrogen as a working gas is investigated using a first-principles approach solving coupled system of hydrodynamic plasma equations and Poisson equation for ion density, electron density, and electric field distribution. The quasi-neutral plasma and the sheath regions are identified. As the gap between electrodes is reduced, the sheath structure dominates the plasma region. Second, we simulate a first generation plasma micropump. We solve multiscale plasma-gas interaction inside a two-dimensional cross section of the microscale pump geometry. The result shows that a reasonable mass flow rate can be pumped using a set of small active electrodes.

Wang, C.-C.; Roy, Subrata [Department of Mechanical and Aerospace Engineering, Computational Plasma Dynamics Laboratory and Test Facility, Applied Physics Research Group, University of Florida, Gainesville, Florida 32611 (United States)

2009-07-01

52

Novel applications of plasma actuators  

NASA Astrophysics Data System (ADS)

The current study investigates the effectiveness of two different dielectric barrier discharge plasma actuator configurations, a 3-D annular geometry for use in micro thrusters and internal duct aerodynamics and a jet vectoring actuator that acts as a vortex generator and flow control device. The first configuration consists of a closed circumferential arrangement which yields a body force when a voltage difference is applied across the inner and outer electrodes separated by a dielectric. The primary flow is driven by this zero-net mass flux jet at the wall that then entrains fluid in the core of the duct. PIV experiments in both quiescent flow and freestream are conducted on tubes of different diameters while varying parameters such as the modulation frequency, duty cycle and tunnel speed. The values of the induced velocities increase with the forcing frequency and duty cycle although there is a peak value for the forcing frequency after which the velocity and thrust decrease for each thruster. The velocities and thrust increase as the inner diameter of the tubes are increased while the velocity profiles show a great difference with the (l/di) ratio; recirculation occurs after going below a critical value. Experiments in the wind tunnel illustrate that the jet exit characteristics significantly change upon actuation in freestream flow but the effect tends to diminish with increasing inner diameters and tunnel speeds. Using staged arrays of these thrusters result in higher velocities while operating at both in phase and out of phase. The jet vectoring configuration consists of a single embedded electrode separated from two exposed electrodes on either side by the dielectric. The embedded electrode is grounded while the exposed electrodes are driven with a high frequency high voltage input signal. PIV measurements of the actuator in a freestream show that vectoring the jet yields stronger vortices than a linear configuration and increasing the difference between the duty cycles of the channels increases the vortex strength. It is seen that while the vortex is barely visible at the leading edge with little strength, it grows significantly large in the streamwise direction and reaches its maximum strength around mid-chord locations while the circulation distribution shows that the bulk of the circulation is added here. The motion of the vortex along this direction illustrates a braiding phenomena that can be observed via flow visualizations. Streamwise PIV data for this configuration on a wing with a NACA 0012 airfoil is used to plot the reverse flow probability, which in turn reveals that the use of the jet vectoring actuator as a vortex generator jet does suppress separation, but the actuator tends to lose its efficacy with increasing tunnel speeds.

Ozturk, Arzu Ceren

53

Cylinder Flow Control Using Plasma Actuators  

NASA Astrophysics Data System (ADS)

In this study the results of flow control experiments utilizing single dielectric barrier discharge plasma actuators to control flow separation and unsteady vortex shedding from a circular cylinder in cross-flow are reported. Two optimized quartz dielectric plasma actuators mounted on the cylinder surface utilizing an improved saw-tooth waveform high-voltage generator allowed flow control at Reynolds number approaching supercritical. Using either steady or unsteady actuation, it is demonstrated that the plasma-induced surface blowing gives rise to a local Coanda effect that promotes the maintenance of flow attachment. PIV based flow fields and wake velocity profiles obtained with hot-wire anemometry show large reductions in vortex shedding, wake width and turbulence intensity.

Kozlov, Alexey; Thomas, Flint

2007-11-01

54

Pressure Dependence of Plasma Actuated Flow Control  

NASA Astrophysics Data System (ADS)

An experimental investigation was conducted to determine how Single Dielectric-Barrier Discharge (SDBD) plasma actuators performed under variable ambient pressure. The static pressure was varied from 0.17 to 9.0 bar. The plasma initiation voltage and static thrust were measured and compared to similar data in literature. The results showed that at a given pressure, the plasma initiation voltage scaled with the actuator capacitor per unit area. The measured thrust showed the previously observed power-law relation with voltage, but the exponent varied with pressure. These trends were evaluated against simulations from the SDBD Space-Time Lumped Element Model. Parameters in the model affected by ambient pressure (capacitance, resistance, and Debye length of the air) were then systematically investigated to determine their effects on the plasma-produced body force. The overall trends were best modeled through a pressure dependence of the Debye length.

Valerioti, Joseph; Corke, Thomas

2010-11-01

55

Characterization of novel and conventional dielectric barrier discharge actuators  

NASA Astrophysics Data System (ADS)

This document outlines efforts to improve upon the dielectric barrier discharge plasma actuator. These devices have been studied for use in various aerodynamic applications and have been particularly effective for freestream velocities up to ˜50 m s-1. In order to be truly applicable for a wide range of applications, however, a demonstration of sufficient control authority at higher speeds is necessary. To accomplish this, the plasma actuator requires a significant improvement in output performance, whether the metric be momentum transfer or peak induced velocity. The following work presents efforts to improve these metrics, in part through the development of new actuator configurations. Actuators consisting of multiple powered electrodes are demonstrated to show a substantial reduction in the device's power consumption, while a novel electrode layout is experimentally shown to induce a three-dimensional flow field. To date most actuator configurations used result in two-dimensional vector fields. Furthermore, two materials with extreme dielectric constants, relative to those typically investigated, are characterized. The net thrust of the actuator is shown to improve drastically while simultaneously reducing the actuator's weight by using silica aerogel, a previously unexplored dielectric material. The problem of thrust saturation is also investigated and characterized. The physical mechanisms involved in this limiting factor are identified and a manipulation of the effect is demonstrated.

Durscher, Ryan J.

56

Numerical Investigation of Serpentine Plasma Actuators for Separation Control at Low Reynolds Number.  

National Technical Information Service (NTIS)

Dielectric Barrier Discharge (DBD) plasma actuators with serpentine shaped electrodes cause a change in the operational behavior of the flow control mechanism relative to the standard linear actuator due to the introduction of fully three dimensional vort...

M. Riherd M. Visbal S. Roy

2011-01-01

57

Application of an AC barrier discharge actuator to control airflow separation above a NACA 0015 airfoil: Optimization of the actuation location along the chord  

Microsoft Academic Search

This paper deals with the control of airflow separation above a NACA 0015 airfoil with the help of a surface plasma actuator. A dielectric barrier discharge plasma is used to modify velocity in the boundary layer, tangentially to the wall. The goal of the actuation is to displace (upstream or downstream) the separation location, in either reattaching a naturally detached

Jérôme Jolibois; Maxime Forte; Éric Moreau

2008-01-01

58

Control of an axisymmetric subsonic air jet by plasma actuator  

Microsoft Academic Search

It is known that surface non-thermal plasma actuators have proved their efficiency for aerodynamics flow control. In this\\u000a study, a dielectric barrier discharge (DBD) is mounted on the diffuser of an axisymmetric turbulent air jet in order to control\\u000a the flow separation along a 12-degree diffuser bevel. The momentum created by the actuator is applied to separate an air flow

N. Benard; J. Jolibois; M. Forte; G. Touchard; E. Moreau

2007-01-01

59

Simulation Tool for Dielectric Barrier Discharge Plasma Actuators at Atmospheric and Sub-Atmospheric Pressures: SBIR Phase I Final Report.  

National Technical Information Service (NTIS)

This report is the final report of a SBIR Phase I project. It is identical to the final report submitted, after some proprietary information of administrative nature has been removed. The development of a numerical simulation tool for dielectric barrier d...

A. Likhanskii

2012-01-01

60

Separation Control on Generic ROBIN Rotorcraft Fuselage Using Plasma Actuators  

NASA Astrophysics Data System (ADS)

Active flow control, in the form of dielectric barrier discharge (DBD) plasma actuators, is applied to a NASA ROBIN mod7 generic rotorcraft fuselage model. The control objective is reduce the massive 3-D flow separation occurring over the aft ramp section of the fuselage, thereby improving the vehicle flight characteristics. The plasma actuation methods investigated include: plasma streamwise vortex generators (PSVGs), as well as steady and unsteady spanwise actuation, combined with passive geometric modifications to the ramp section. Experiments were conducted at freestream Mach and Reynolds numbers of M?= 0.12 and ReL= 2.65 x10^6, respectively. Aerodynamic loads from each technique were quantified by means of 3-component force balance measurements (drag, lift, and pitching moment), a 128 count static pressure array, and time-resolved PIV wake surveys. Results are compared with previous studies that utilized active flow control in the form of pulsed jets and combustion actuators.

Coleman, Dustin

2011-11-01

61

Electric wind produced by surface plasma actuators: a new dielectric barrier discharge based on a three-electrode geometry  

Microsoft Academic Search

Active flow control is a rapidly developing topic because the associated industrial applications are of immense importance, particularly for aeronautics. Among all the flow control methods, such as the use of mechanical flaps or wall jets, plasma-based devices are very promising devices. The main advantages of such systems are their robustness, their simplicity, their low-power consumption and that they allow

Eric Moreau; Roberto Sosa; Guillermo Artana

2008-01-01

62

Separation Control along a NACA 0015 Airfoil Using a Dielectric Barrier Discharge Actuator  

Microsoft Academic Search

\\u000a This paper deals with the control of airflow separation above a NACA 0015 airfoil using a surface plasma actuator. A dieletric\\u000a barrier discharge plasma is used to bring velocity in the boundary layer, tangentially to the wall. The goal of the actuation\\u000a is to displace (upstream or downstream) the separation point, in either reattaching a naturally detached airflow or in

Jérôme Jolibois; Maxime Forte; Eric Moreau

63

Combustion stabilization using serpentine plasma actuators  

NASA Astrophysics Data System (ADS)

This letter presents a numerical model for combustion stabilization with plasma actuators. Recently, we demonstrated that serpentine actuators induce complex neighboring flow structures due to pinching and spreading effects suitable for rapid flow mixing. Here, the influence of serpentine plasma actuator is numerically investigated on inner and outer recirculation zones of a gas turbine combustor. Beyond benchmarking with reported experimental data, we show that the swirl generated by the serpentine plasma actuators creates local low velocity regions stabilizing the flame. Such simple flow-mixing device does not need any moving parts, hence may be useful in the any combustors.

Wang, Chin-Cheng; Roy, Subrata

2011-07-01

64

Measurement of the body force field of plasma actuators  

Microsoft Academic Search

A novel technique is proposed and investigated for the estimation of the body force field resulting from the operation of a dielectric barrier discharge plasma actuator. The technique relies on the measurement of the spatio-temporal evolution of the induced velocity field using high-speed particle image velocimetry (PIV). The technique has the advantage of providing spatial distribution of the body force

M. Kotsonis; S. Ghaemi; L. Veldhuis; F. Scarano

2011-01-01

65

SDBD plasma actuator with nanosecond pulse-periodic discharge  

Microsoft Academic Search

This paper presents a detailed explanation of the physical mechanism of the nanosecond pulsed surface dielectric barrier discharge (SDBD) effect on the flow. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region on fast (tau sime 1 µs) thermalization of the plasma input energy. The mean values of such heating of

A. Yu Starikovskii; A. A. Nikipelov; M. M. Nudnova; D. V. Roupassov

2009-01-01

66

Plasma actuators for airflow control: measurement of the non-stationary induced flow velocity  

Microsoft Academic Search

This paper deals with the measurement of the instantaneous flow velocity induced by surface plasma actuators in air at atmospheric pressure. More accurately, experiments with Laser Doppler Velocimetry (LDV) are conducted with two different types of plasma actuators in order to determine the establishment time of the induced airflow. DC corona discharges and AC dielectric barrier discharges are investigated in

Maxime Forte; Luc Leger; Jérôme Pons; Eric Moreau; Gérard Touchard

2005-01-01

67

Airfoil Leading Edge Flow Separation Control using DBD Plasma Actuators driven by Nanosecond Pulses  

Microsoft Academic Search

This work continues an ongoing exploration of the use of dielectric barrier discharge plasma actuators driven by repetitive nanosecond pulses (NS-DBD hereafter) for aerodynamic flow control. The NS-DBD transfers very little momentum to the neutral air, but generates compression waves that manipulate flow instabilities similar to localized arc filament plasma actuators. Such devices which are believed to function through thermal

Jesse Little; Chris Rethmel; Keisuke Takashima; Chris Wiet; Igor Adamovich; Mo Samimy

2010-01-01

68

Modeling of Fluid Dynamics and Heat Transfer Induced by Dielectric Barrier Plasma Actuator Glow discharge at atmospheric pressure using a dielectric barrier discharge can induce  

Microsoft Academic Search

fluid flow, and can be used for active control of aerodynamics and heat transfer. In the present work, a modeling framework is presented to study the evolution and interaction of such athermal nonequilibrium plasma discharges in conjunction with low Mach number fluid dynamics and heat transfer. The model is self-consistent, coupling the first- principles-based discharge dynamics with the fluid dynamics

Balaji Jayaraman; Siddharth Thakur; Wei Shyy

69

Dielectric barrier plasma dynamics for active aerodynamic flow control  

NASA Astrophysics Data System (ADS)

The paper investigates the dynamics of a new multiple bipolar multiple Dielectric Barrier Discharges (DBD) actuator using in large-scale flow control. Particle image velocimetry experiments are performed to characteristic the effectiveness of the multiple bipolar DBD plasma actuator. The results show that the mutual interaction between the electrodes, one major disadvantage of traditional DBD characterized by reverse discharge can be entirely avoided, and a constantly accelerating electric wind velocity can be obtained by using the new multiple bipolar DBD plasma actuator.

Hao, JiangNan; Tian, BaLin; Wang, YuLin; Song, YaHui; Pan, ShuCheng; Li, WenFeng

2014-01-01

70

Tip Clearance Control Using Plasma Actuators.  

National Technical Information Service (NTIS)

This report documents experimental results from a series of experiments using active flow control to improve the performance and efficiency of turbine tip clearance flows. The flow control was based on plasma actuators. Two experimental facilities were us...

S. C. Morris T. C. Corke

2007-01-01

71

On the role of oxygen in dielectric barrier discharge actuation of aerodynamic flows  

SciTech Connect

Phase-locked particle image velocimetry is used to study the mechanism of induced flow in the near field of a rf dielectric barrier discharge actuator mounted in the separated flow region of a bluff body. Flow actuation is found to be asymmetric, with suction toward the buried downstream electrode when it is biased positively relative to the upstream exposed electrode. Lesser flow is seen on the reverse voltage swing, where the buried electrode should attract positive ions. This phenomenon is enhanced when oxygen is added to the flow, suggesting that oxygen negative ions, possibly O{sub 2}{sup -}, play a dominant role in plasma actuation.

Kim, W.; Do, H.; Mungal, M. G.; Cappelli, M. A. [Mechanical Engineering Department, Stanford University, Stanford, California 94305-3032 (United States)

2007-10-29

72

Surface plasma actuators modeling for flow control  

NASA Astrophysics Data System (ADS)

The surface plasma actuators over the entire speed region have been intensely investigated for flow control. Most of the fundamental phenomena have been firmly identified by experimental observations but ambiguities still remained. The direct computational simulation for multiple microdischarges is presently beyond our reach, thus the essential physics may be better understood on the framework of physics-based modeling. To achieve this objective, the drift-diffusion approximation is adopted as a transport property approximation to the nonequilibrium air plasma. The most challenging issue of electron impact ionization process at the low-temperature environment is addressed by the Townsend mechanism together with electron attachment, detachment, bulk, and ion-ion recombination. The effects and quantifications of Joule heating, periodic electrostatic force, as well as, the Lorentz acceleration for flow control are examined. The clarification to the hot spot of heat transfer in direct current discharge and the orientations of the periodic force associated with AC cycle of dielectric barrier discharge are also included.

Shang, J. S.; Huang, P. G.

2014-05-01

73

Hybrid transition control approach for plasma actuators  

NASA Astrophysics Data System (ADS)

This work reports on the development of a novel hybrid transition control method for single DBD plasma actuators. The experiments have been carried out on a natural laminar flow airfoil in a wind tunnel and combine two methods previously used for transition control purposes with DBD plasma actuators: boundary-layer stabilization by quasi-steady wall-parallel momentum addition, and active wave cancelation by linear superposition utilizing modulated momentum injection. For this purpose, the modulated body force is controlled using an improved extremum seeking controller based on an extended Kalman filter. Combining the two methods in a single actuator has advantages. Applied to 2-D Tollmien-Schlichting waves, the achievable transition delay in hybrid mode is significantly larger than the isolated effects, while the energy consumption remains almost unchanged compared to the case of continuous actuation. For a Reynolds number of , a transition delay of could be observed.

Kurz, A.; Goldin, N.; King, R.; Tropea, C.; Grundmann, S.

2013-11-01

74

Separation control using plasma actuators: application to a free turbulent jet  

Microsoft Academic Search

This experimental work deals with active airflow control using non-thermal surface plasma actuators in the case of a rectangular cross section turbulent jet. A wide-angle diffuser composed of two adjustable hinged baseplates is linked at the jet exit. Two types of actuators are considered: the DC corona discharge and the dielectric barrier discharge (DBD). In both cases, an ionic wind

A. Labergue; E. Moreau; N. Zouzou; G. Touchard

2007-01-01

75

Atmospheric Plasma Actuators for Aeroacoustic Applications  

Microsoft Academic Search

A plasma actuator operating in atmospheric air was applied to attenuate low-speed cavity flow-induced tones. It demonstrated the working effect of glow discharges for aeroacoustic applications. The details of the overall system were summarized. To improve the power efficiency, several plasma driving signals were tested on a real-time system. The corresponding results were discussed in this paper.

Xun Huang; Sammie Chan; Xin Zhang

2007-01-01

76

Sensing and control of flow separation using plasma actuators.  

PubMed

Single dielectric barrier discharge plasma actuators have been used to control flow separation in a large number of applications. An often used configuration involves spanwise-oriented asymmetric electrodes that are arranged to induce a tangential wall jet in the mean flow direction. For the best effect, the plasma actuator is placed just upstream of where the flow separation will occur. This approach is generally more effective when the plasma actuator is periodically pulsed at a frequency that scales with the streamwise length of the separation zone and the free-stream velocity. The optimum frequency produces two coherent spanwise vortices within the separation zone. It has been recently shown that this periodic pulsing of the plasma actuator could be sensed by a surface pressure sensor only when the boundary layer was about to separate, and therefore could provide a flow separation indicator that could be used for feedback control. The paper demonstrates this approach on an aerofoil that is slowly increasing its angle of attack, and on a sinusoidally pitching aerofoil undergoing dynamic stall. Short-time spectral analysis of time series from a static pressure sensor on the aerofoil is used to determine the separation state that ranges from attached, to imminent separation, to fully separated. A feedback control approach is then proposed, and demonstrated on the aerofoil with the slow angle of attack motion. PMID:21382825

Corke, Thomas C; Bowles, Patrick O; He, Chuan; Matlis, Eric H

2011-04-13

77

Use of Plasma Actuators as a Moving-Wake Generator  

NASA Technical Reports Server (NTRS)

The work documented in this report tests the concept of using plasma actuators as a simple and easy way to generate a simulated moving-wake and the disturbances associated with it in turbines. This wake is caused by the blades of the upstream stages of the turbine. Two types of devices, one constructed of arrays of NACA 0018 airfoils, and the one constructed of flat plates were studied. The airfoils or plates were equipped with surface mounted dielectric barrier discharge (DBD) plasma actuators, which were used to generate flow disturbances resembling moving-wakes. CTA hot-wire anemometry and flow visualization using a smoke-wire were used to investigate the wake independence at various spacings and downstream locations. The flat plates were found to produce better results than the airfoils in creating large velocity fluctuations in the free-stream flow. Different dielectric materials, plasma actuator locations, leading edge contours, angles of attack and plate spacings were investigated, some with positive results. The magnitudes of the velocity fluctuations were found to be comparable to existing mechanical moving-wake generators, thus proving the feasibility of using plasma actuators as a moving-wake generator.

Corke, Thomas C.; Thomas, Flint O.; Klapetzky Michael J.

2007-01-01

78

Three-dimensional effects of curved plasma actuators in quiescent air  

NASA Astrophysics Data System (ADS)

This paper presents results on a new class of curved plasma actuators for the inducement of three-dimensional vortical structures. The nature of the fluid flow inducement on a flat plate, in quiescent conditions, due to four different shapes of dielectric barrier discharge (DBD) plasma actuators is numerically investigated. The three-dimensional plasma kinetic equations are solved using our in-house, finite element based, multiscale ionized gas (MIG) flow code. Numerical results show electron temperature and three dimensional plasma force vectors for four shapes, which include linear, triangular, serpentine, and square actuators. Three-dimensional effects such as pinching and spreading the neighboring fluid are observed for serpentine and square actuators. The mechanisms of vorticity generation for DBD actuators are discussed. Also the influence of geometric wavelength (?) and amplitude (?) of the serpentine and square actuators on vectored thrust inducement is predicted. This results in these actuators producing significantly better flow mixing downstream as compared to the standard linear actuator. Increasing the wavelengths of serpentine and square actuators in the spanwise direction is shown to enhance the pinching effect giving a much higher vertical velocity. On the contrary, changing the amplitude of the curved actuator varies the streamwise velocity significantly influencing the near wall jet. Experimental data for a serpentine actuator are also reported for validation purpose.

Wang, Chin-Cheng; Durscher, Ryan; Roy, Subrata

2011-04-01

79

Three-dimensional effects of curved plasma actuators in quiescent air  

SciTech Connect

This paper presents results on a new class of curved plasma actuators for the inducement of three-dimensional vortical structures. The nature of the fluid flow inducement on a flat plate, in quiescent conditions, due to four different shapes of dielectric barrier discharge (DBD) plasma actuators is numerically investigated. The three-dimensional plasma kinetic equations are solved using our in-house, finite element based, multiscale ionized gas (MIG) flow code. Numerical results show electron temperature and three dimensional plasma force vectors for four shapes, which include linear, triangular, serpentine, and square actuators. Three-dimensional effects such as pinching and spreading the neighboring fluid are observed for serpentine and square actuators. The mechanisms of vorticity generation for DBD actuators are discussed. Also the influence of geometric wavelength ({lambda}) and amplitude ({Lambda}) of the serpentine and square actuators on vectored thrust inducement is predicted. This results in these actuators producing significantly better flow mixing downstream as compared to the standard linear actuator. Increasing the wavelengths of serpentine and square actuators in the spanwise direction is shown to enhance the pinching effect giving a much higher vertical velocity. On the contrary, changing the amplitude of the curved actuator varies the streamwise velocity significantly influencing the near wall jet. Experimental data for a serpentine actuator are also reported for validation purpose.

Wang Chincheng; Durscher, Ryan; Roy, Subrata

2011-04-15

80

Reattachment of a Separated Boundary Layer on a Flat Plate in a Highly Adverse Pressure Gradient Using a Plasma Actuator(POSTPRINT).  

National Technical Information Service (NTIS)

An experimental study was performed to examine the phase-dependent response characteristics of a dielectric barrier discharge plasma flow control actuator. The actuator was investigated on a fully separated flat plate boundary layer with an adverse freest...

I. G. Boxx R. B. Rivir J. M. Newcamp N. M. Woods

2006-01-01

81

Reattachment of a Separated Boundary Layer on a Flat Plate in a Highly Adverse Pressure Gradient Using a Plasma Actuator (Postprint).  

National Technical Information Service (NTIS)

An experimental study was performed to examine the phase-dependent response characteristics of a dielectric barrier discharge plasma flow control actuator. The actuator was investigated on a fully separated flat plate boundary layer with an adverse freest...

I. G. Boxx J. M. Newcamp N. M. Woods R. B. Rivir

2006-01-01

82

Receptivity of Laminar Boundary Layers to Spanwise-Periodic Forcing by an Array of Plasma Actuators  

NASA Astrophysics Data System (ADS)

This work is concerned with the response of a Blasius boundary layer to dielectric-barrier- discharge (DBD) plasma actuators for the purpose of using these devices in bypass transition control. The plasma actuators consist of a spanwise-periodic array of high voltage electrodes, which are oriented to produce streamwise vortex pairs. The structure of actuator-induced streaks is measured using hot-wire anemometry over a streamwise distance of approximately 100 boundary layer thicknesses, and is decomposed into 4 span-wise Fourier modes. The modal content and corresponding streamwise growth characteristics are discussed for ten plasma actuator geometries over multiple excitation voltages and freestream velocities. Actuator power consumption was found to control the streak amplitude, whereas freestream velocity affected both amplitude and streamwise extent of the streaks. A common relationship between disturbance energy and power consumption was found among actuators of different dielectric thickness and similar electrode geometry.

Osmokrovic, Luke

83

The manipulation of an unstarting supersonic flow by plasma actuator  

NASA Astrophysics Data System (ADS)

The manipulation of an unstarting supersonic flow is demonstrated using a dielectric barrier discharge (DBD). Experiments are carried out in a Mach 4.7 model inlet flow. Flow features, such as boundary layers and shockwaves at low freestream static pressure (1 kPa) and temperature (60 K) are visualized with Rayleigh scattering from condensed CO2 particles. Flow unstart, initiated by mass injection, is studied for three model inlet flow configurations, distinguished by the initial conditions (untripped or tripped, plasma actuated or not) of the boundary layers. Unstart in the presence of thick, tripped boundary layers is characterized by the formation of an oblique unstart shock just upstream of a separating and propagating boundary layer. The presence of plasma actuation of this tripped boundary layer seems to arrest the boundary layer separation and leads to the formation of a quasi-stationary pseudo-shock, delaying unstart. The flow generated with DBD actuation is more characteristic of what is seen when unstart is generated in a model flow in which thin boundary layers grow naturally. Planar laser Rayleigh scattering visualizations suggest that the DBD actuation thins the tripped boundary layer over the exposed electrode region.

Im, S.; Do, H.; Cappelli, M. A.

2012-12-01

84

Temperature characterization of dielectric barrier discharge actuators: influence of electrical and geometric parameters  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge (DBD) based surface plasma actuators have been well studied as flow manipulation devices. However, there is a dearth of research on their application for convective heat transfer enhancement. The adoption of DBD actuators to such areas requires a detailed study on the thermal characteristics of the plasma discharge. The present study conducts infrared thermography measurements on the surface of a thick dielectric (2–4 mm) based DBD actuator and characterizes it against various electrical and geometrical parameters. The temperature distribution is also studied in relation to the regimes of the discharge cycle through comparison with intensified charge-coupled device (iCCD) imaging. Measurements are also conducted with thin cylindrical electrode (wire) based configurations to study the influence of streamer inhibition. Based on the observed experimental results, a hypothesis is proposed on the mechanism of dielectric heating and the relationship between dielectric surface temperature and gas temperature.

Tirumala, Rakshit; Benard, Nicolas; Moreau, Eric; Fenot, Matthieu; Lalizel, Gildas; Dorignac, Eva

2014-06-01

85

Scalability of Localized Arc Filament Plasma Actuators  

NASA Technical Reports Server (NTRS)

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.

Brown, Clifford A.

2008-01-01

86

Air Plasma Actuators for Effective Flow Control.  

National Technical Information Service (NTIS)

An asymmetric dielectric barrier discharge model is presented for real gas eight species air chemistry using a self-consistent multi-body system of plasma, dielectric and neutral gas modeled together to predict the electrodynamic momentum imparted to the ...

D. V. Gaitonde K. P. Singh S. Roy

2007-01-01

87

Modeling and Experiment of Leading Edge Separation Control Using SDBD Plasma Actuators  

Microsoft Academic Search

This work presents the study of the single-dielectric barrier discharge aerodynamic plasma actuator. To model the physics of the plasma discharge, a space-time lumped- element circuit model was developed. The model solution compared well to some of the characteristic features of the discharge such as the dependence of the sweep velocity and maximum extent of the ionized air as functions

Dmitriy M. Orlov; Thomas Apker; Chuan He; Hesham Othman; Thomas C. Corke

2007-01-01

88

Turbulent boundary-layer control with plasma actuators.  

PubMed

This paper reviews turbulent boundary-layer control strategies for skin-friction reduction of aerodynamic bodies. The focus is placed on the drag-reduction mechanisms by two flow control techniques-spanwise oscillation and spanwise travelling wave, which were demonstrated to give up to 45 per cent skin-friction reductions. We show that these techniques can be implemented by dielectric-barrier discharge plasma actuators, which are electric devices that do not require any moving parts or complicated ducting. The experimental results show different modifications to the near-wall structures depending on the control technique. PMID:21382824

Choi, Kwing-So; Jukes, Timothy; Whalley, Richard

2011-04-13

89

Mechanisms of plasma actuators for hypersonic flow control  

Microsoft Academic Search

A summary of recent research progress in hypersonic plasma actuators for flow control is attempted. It is found that the most effective plasma actuator is derived from an electromagnetic perturbation and amplifies by a subsequent viscous–inviscid interaction. Computational efforts using drift-diffusion theory and a simple phenomenological plasma model, as well as experiments in a hypersonic plasma channel, have shown the

J. S. Shang; S. T. Surzhikov; R. Kimmel; D. Gaitonde; J. Menart; J. Hayes

2005-01-01

90

Evaluation of thrust measurement techniques for dielectric barrier discharge actuators  

NASA Astrophysics Data System (ADS)

Despite its popularity in the recent literature, plasma actuators lack a consistent study to identify limitations, and remedy thereof, of various thrust measurement techniques. This paper focuses on comparing two different experimental techniques commonly used to measure the global, plasma-induced thrust. A force balance is used to make a direct measurement of the thrust produced, which is then compared with a control volume analysis on data obtained through particle image velocimetry. The local velocity measured by particle image velocimetry is also validated with a fine-tip pressure probe. For the direct thrust measurements, the effect of varying the actuator plate length upon which the induced flow acts is investigated. The results from these tests show that the length of the actuator plate is most influential at higher voltages with the measured thrust increasing as much as 20 % for a six times reduction in the length of the plate. For the indirect thrust measurement, the influence of the control volume size is analyzed. When the two methods are compared against each other, good agreement is found when the control volume size has a sufficient downstream extent. Also, the discharge length is optically measured using visible light emission. A linear correlation is found between the discharge length and the thrust measurements for the actuator configurations studied. Finally, the energy conversion efficiency curve for a representative actuator is also presented.

Durscher, Ryan; Roy, Subrata

2012-10-01

91

Comparisons of Force Measurement Methods for DBD Plasma Actuators in Quiescent Air  

NASA Technical Reports Server (NTRS)

We have performed measurements of the force induced by both single (one electrode insulated) and double (both electrodes insulated) dielectric barrier discharge plasma actuators in quiescent air. We have shown that, for single barrier actuators with cylindrical exposed electrodes, as the electrode diameter decrease the force efficiencies increase much faster than a previously reported linear trend. This behavior has been experimentally verified using two different measurement techniques: stagnation probe measurements of the induced flow velocity and direct measurement of the force using an electronic balance. Actuators with rectangular cross-section exposed electrodes do not show the same rapid increase at small thicknesses. We have also shown that the induced force is independent of the material used for the exposed electrode. The same techniques have shown that the induced force of a double barrier actuator increases with decreasing narrow electrode diameter.

Hoskinson, Alan R.; Hershkowitz, Noah; Ashpis, David E.

2009-01-01

92

Separation Control from the Flap of a High-Lift Airfoil using DBD Plasma Actuators  

Microsoft Academic Search

Control of separation from the deflected flap of a high-lift airfoil is explored using two asymmetric dielectric barrier discharge (DBD) plasma actuators straddling the flap shoulder for Reynolds numbers of 240,000 and 410,000. Actuators are found to be most effective when operated in an unsteady fashion at the natural oscillation frequency of the trailing edge flow field. The use of

Jesse Little; Munetake Nishihara; Igor Adamovich; Mo Samimy

2009-01-01

93

Control of Transitional and Turbulent Flows Using Plasma-Based Actuators  

Microsoft Academic Search

An exploratory numerical study of the control of transitional and turbulent separated flows by means of asymmetric dielectric-barrier-discharge (DBD) actuators is presented. The flow fields are simulated employ- ing an extensively validated high-fidelity Navier-Stokes s olver which is augmented with both phenomenological and first-principles models representing the plasma-induc ed body forces imparted by the actuator on the fluid. Several applications

Miguel R. Visbal; Datta V. Gaitonde; Subrata Roy

94

Active Flow Control by Surface Smooth Plasma Actuators  

Microsoft Academic Search

\\u000a Surface smooth plasma actuators were used to control leading-edge flow separation on the flying wing airfoil Eppler E338 for\\u000a angles of attack of up to 12° past stall at low Reynolds numbers. The plasma actuators were operated over a range of free-stream\\u000a speeds from 2.2 to 6.6 m\\/s giving chord Reynolds numbers from 26K to 79K. The plasma actuators produced

B. Göksel; I. Rechenberg

95

CONTROL OF LAMINAR AND TURBULENT SHEAR FLOWS USING PLASMA ACTUATORS  

Microsoft Academic Search

The use of AC discharge plasma actuators in flow control applications is experimentally investigated using PIV. Exper- imental observations include actuators in quiescent flow, a flat plate boundary layer, and a low pressure turbine blade cascade. The actuators are shown to generate a high ve- locity region near the wall downstream of the interface with large fluctuating components. Even in

Jamey D. Jacob; Karthik Ramakumar; Rich Anthony; Richard B. Rivir

96

Modeling plasma actuators with air chemistry for effective flow control  

SciTech Connect

An asymmetric dielectric barrier discharge model is presented for real gas air chemistry using a self-consistent multibody system of plasma, dielectric, and neutral gas modeled together to predict the electrodynamic force imparted to the working gas. The equations governing the motion of charged and neutral species are solved with Poisson equation using finite element method using a Galerkin weak formulation. Electric field profile changes with the increase in grounded electrode and the density increases downstream. The electrodynamic force development mechanism is studied over a flat plate due to charge and neutral species production from adjacent air in a radio frequency driven barrier discharge. The time average of the force shows mostly acceleration above the actuator. Numerical simulation confirms that the magnitude of force increases very slightly with the increase in the length of grounded electrode.

Singh, Kunwar Pal; Roy, Subrata [Computational Plasma Dynamics Laboratory and Test Facility, Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611-6300 (United States)

2007-06-15

97

Shock Generation and Control Using DBD Plasma Actuators  

NASA Technical Reports Server (NTRS)

This report is the final report of a NASA Phase I SBIR contract, with some revisions to remove company proprietary data. The Shock Boundary Layer Interaction (SBLI) phenomena in a supersonic inlet involve mutual interaction of oblique shocks with boundary layers, forcing the boundary layer to separate from the inlet wall. To improve the inlet efficiency, it is desired to prevent or delay shock-induced boundary layer separation. In this effort, Innovative Technology Applications Company (ITAC), LLC and the University of Notre Dame (UND) jointly investigated the use of dielectric-barrier-discharge (DBD) plasma actuators for control of SBLI in a supersonic inlet. The research investigated the potential for DBD plasma actuators to suppress flow separation caused by a shock in a turbulent boundary layer. The research involved both numerical and experimental investigations of plasma flow control for a few different SBLI configurations: (a) a 12 wedge flow test case at Mach 1.5 (numerical and experimental), (b) an impinging shock test case at Mach 1.5 using an airfoil as a shock generator (numerical and experimental), and (c) a Mach 2.0 nozzle flow case in a simulated 15 X 15 cm wind tunnel with a shock generator (numerical). Numerical studies were performed for all three test cases to examine the feasibility of plasma flow control concepts. These results were used to guide the wind tunnel experiments conducted on the Mach 1.5 12 degree wedge flow (case a) and the Mach 1.5 impinging shock test case (case b) which were at similar flow conditions as the corresponding numerical studies to obtain experimental evidence of plasma control effects for SBLI control. The experiments also generated data that were used in validating the numerical studies for the baseline cases (without plasma actuators). The experiments were conducted in a Mach 1.5 test section in the University of Notre Dame Hessert Laboratory. The simulation results from cases a and b indicated that multiple spanwise actuators in series and at a voltage of 75 kVp-p could fully suppress the flow separation downstream of the shock. The simulation results from case c showed that the streamwise plasma actuators are highly effective in creating pairs of counter-rotating vortices, much like the mechanical vortex generators, and could also potentially have beneficial effects for SBLI control. However, to achieve these effects, the positioning and the quantity of the DBD actuators used must be optimized. The wind tunnel experiments mapped the baseline flow with good agreement to the numerical simulations. The experimental results were conducted with spanwise actuators for cases a and b, but were limited by the inability to generate a sufficiently high voltage due to arcing in the wind-tunnel test-section. The static pressure in the tunnel was lower than the static pressure in an inlet at flight conditions, promoting arching and degrading the actuator performance.

Patel, Mehul P.; Cain, Alan B.; Nelson, Christopher C.; Corke, Thomas C.; Matlis, Eric H.

2012-01-01

98

Numerical investigation of pulsed-driven DBD plasma actuator  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge (DBD) plasma actuators are promising devices for flow separation control. The operation of conventional DBDs, driven by AC or pulses+bias voltage, is based on direct induction of momentum into boundary layer by transferring momenta from charged particles to neutrals. However, the maximum DBD induced flow velocity for the conventional DBD is limited to ˜10-20 m/s, since conventional DBD operates in corona regime. The way to overcome this limitation is to use ns pulses, which transfer much more momentum to the flow during discharge propagation (forward breakdown), as driving voltage. However, on the back slope of the ns pulse, the backward breakdown induces strong negative force on the gas, significantly decreasing to effect of forward pushing. The second problem is the surface charge accumulation, which is reported to be one of the major limiting factors for pulsed DBDs. In this talk, we will present numerical simulations of both forward and backward breakdowns for DBD plasma actuators using 2D/3D hybrid plasma simulation tool VORPAL. We will also discuss potential solutions for the backward breakdown elimination.

Likhanskii, Alexandre; Shneider, Mikhail; Miles, Richard; Macheret, Sergey

2011-11-01

99

Experimental Investigation on the Characteristics of Sliding Discharge Plasma Aerodynamic Actuation  

NASA Astrophysics Data System (ADS)

A new electrical discharge called sliding discharge was developed to generate plasma aerodynamic actuation for flow control. A microsecond-pulse high voltage with a DC component was used to energize a three-electrode actuator to generate sliding discharge. The characteristics of plasma aerodynamic actuation by sliding discharge were experimentally investigated. Discharge morphology shows that sliding discharge is formed when energized by properly adjusting microsecond-pulse and DC voltage. Compared to dielectric barrier discharge (DBD), the plasma extension of sliding discharge is quasi-diffusive and stable but longer and more intensive. Results from particle image velocimetry (PIV) test indicate that plasma aerodynamic actuation by sliding discharge can induce a ‘starting vortex’ and a quasi-steady ‘near-wall jet’. Body force induced by plasma aerodynamic actuation is about the order of mN, which is stronger than that induced by single DBD. It is inferred that microsecond-pulse sliding discharge may be more effective to generate large-scale plasma aerodynamic actuation, which is very promising for improving aircraft aerodynamic characteristics and propulsion efficiency.

Song, Huimin; Li, Yinghong; Zhang, Qiaogen; Jia, Min; Wu, Yun

2011-10-01

100

Single dielectric barrier discharge plasma enhanced aerodynamics: physics, modeling and applications  

Microsoft Academic Search

The term “plasma actuator” has been a part of the fluid dynamics flow control vernacular for more than a decade. A particular\\u000a type of plasma actuator that has gained wide use is based on a single dielectric barrier discharge (SDBD) mechanism that has\\u000a desirable features for use in air at atmospheric pressures. For these actuators, the mechanism of flow control

Thomas C. Corke; Martiqua L. Post; Dmitriy M. Orlov

2009-01-01

101

Low pressure characterization of dielectric barrier discharge actuators  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge actuators tested for thrust inducement between 13 and 101 kPa ambient air pressure show that as the pressure decreases, the thrust increases to a maximum, then drops steadily approaching zero while the power consumption monotonically increases. The amplification in induced thrust at the peak ranges from a few percent to several folds of the thrust measured at atmospheric condition. The effect is more pronounced for thinner dielectrics at lower operating voltages than thicker dielectrics at higher operating voltages and is fairly independent of the ground electrode width. Results identify several optimal control parameters for high-altitude operations.

Soni, Jignesh; Roy, Subrata

2013-03-01

102

Experimental Investigation on Airfoil Shock Control by Plasma Aerodynamic Actuation  

NASA Astrophysics Data System (ADS)

An experimental investigation on airfoil (NACA64—215) shock control is performed by plasma aerodynamic actuation in a supersonic tunnel (Ma = 2). The results of schlieren and pressure measurement show that when plasma aerodynamic actuation is applied, the position moves forward and the intensity of shock at the head of the airfoil weakens. With the increase in actuating voltage, the total pressure measured at the head of the airfoil increases, which means that the shock intensity decreases and the control effect increases. The best actuation effect is caused by upwind-direction actuation with a magnetic field, and then downwind-direction actuation with a magnetic field, while the control effect of aerodynamic actuation without a magnetic field is the most inconspicuous. The mean intensity of the normal shock at the head of the airfoil is relatively decreased by 16.33%, and the normal shock intensity is relatively reduced by 27.5% when 1000 V actuating voltage and upwind-direction actuation are applied with a magnetic field. This paper theoretically analyzes the Joule heating effect generated by DC discharge and the Lorentz force effect caused by the magnetic field. The discharge characteristics are compared for all kinds of actuation conditions to reveal the mechanism of shock control by plasma aerodynamic actuation.

Sun, Quan; Cheng, Bangqin; Li, Yinghong; Cui, Wei; Jin, Di; Li, Jun

2013-11-01

103

Schlieren imaging in a dielectric barrier discharge actuator for airflow control  

NASA Astrophysics Data System (ADS)

The operation of a surface dielectric barrier discharge actuator for airflow control has been experimentally investigated. The actuator is constituted by an electrode pair separated by a dielectric Teflon sheet. Several ac supply conditions have been utilized. An electrohydrodynamics interaction was induced in still air, and several fluid-dynamic regimes were obtained. Visualization of the plasma boundary layer during the discharge ignition phase and during the steady state regime was obtained by utilizing a Schlieren diagnostic technique. The vortex morphology and propagation velocities at all supply conditions utilized have been evaluated. Velocity profiles perpendicular to the actuator surface, obtained from Pitot tube measurements, and line intensity profiles, determined by means of Schlieren imaging, have been determined for the steady regime operation. The integral along a line perpendicular to the actuator surface of the light intensity of the Schlieren image has been calculated. The profile obtained is in good agreement with the Pitot velocity profile in all the supply conditions investigated. Numerical simulations were also performed. The calculations confirm the relation between the flow velocity distribution in the boundary layer and the gas density distribution, which is the cause of the Schlieren image.

Cristofolini, A.; Neretti, G.; Roveda, F.; Borghi, C. A.

2012-02-01

104

Experimental transition delay using glow-discharge plasma actuators  

Microsoft Academic Search

In the present work plasma actuators were applied in a flat-plate boundary layer with an adverse pressure gradient to influence\\u000a the transition of the boundary layer. The first actuator downstream of the leading edge is operated in pulsed mode to introduce\\u000a perturbations into the boundary layer to promote transition. Two steady operating actuators further downstream damp the perturbations\\u000a significantly, which

Sven Grundmann; Cameron Tropea

2007-01-01

105

SDBD plasma actuator with nanosecond pulse-periodic discharge  

NASA Astrophysics Data System (ADS)

This paper presents a detailed explanation of the physical mechanism of the nanosecond pulsed surface dielectric barrier discharge (SDBD) effect on the flow. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region on fast (? sime 1 µs) thermalization of the plasma input energy. The mean values of such heating of the plasma layer can reach 70 K, 200 K and even 400 K for 7 ns, 12 ns and 50 ns pulse durations, 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 periodic pulsed nanosecond dielectric barrier discharge, the main mechanism of impact is the energy transfer and heating of the near-surface gas layer. The following pulse-periodic vortex movement stimulates redistribution of the main flow momentum.

Starikovskii, A. Yu; Nikipelov, A. A.; Nudnova, M. M.; Roupassov, D. V.

2009-08-01

106

Plasma Actuators for Separation Control on Stationary and Oscillating Airfoils.  

National Technical Information Service (NTIS)

Given the importance of separation control associated with retreating blade stall on helicopters, the primary objective of this work was to develop a plasma actuator flow control device for its use in controlling leading-edge separation on stationary and ...

M. L. Post T. Corke

2004-01-01

107

Mechanism of flow separation control using plasma actuation  

NASA Astrophysics Data System (ADS)

The mechanism of flow separation control was investigated experimentally and computationally using pulse-modulated dielectric barrier discharge (DBD) plasma actuation on a stalled flat plate airfoil at a Reynolds number of 3000. Load measurements were complimented with two-dimensional phase-averaged particle image velocimetry performed in the flowfield above the airfoil. A parametric study was carried out where the pulse-modulation frequency, duty cycle, and peak plasma body-force were varied. The two-dimensional Navier-Stokes equations, with no turbulence modeling, were solved directly using a commercial flow solver and a simple but satisfactory heuristic DBD plasma body-force model was incorporated. The overall experimental trends were well predicted by the computations, where the frequencies that produced the largest increases in lift coefficient excited bluff-body shedding at a frequency corresponding approximately to its unforced sub-harmonic. At non-dimensional frequencies most effective for increasing lift (~0.2 to 0.5), the leading-edge shear layer was severed by the perturbations and then merged with a downstream vortex. In a time-mean sense this mechanism forced relatively high momentum fluid towards the surface with typically two re-circulating structures present on the airfoil. Although the essential flow control mechanism was captured by the computation, the idealized 2D approach was identified as a weakness due to the shedding instability not being present in the baseline experiments and the inability to account for three-dimensional structures in the shear layer.

Greenblatt, David; Schneider, Torsten; Schüle, Chan Yong

2012-07-01

108

Detachment and attachment of an axisymmetric non-reactive jet with turbulent shear layer: Control by plasma actuator  

Microsoft Academic Search

The control of an axisymmetric air jet equipped with a small-angle diffuser exhaust using a single non-thermal plasma actuator is studied with a stereoscopic PIV system. A single Dielectric Barrier Discharge (DBD) actuator is used to separate a naturally attached flow (12° angle diffuser) or to reattach a naturally separated one (22° angle diffuser). The experimental set-up allows us to

N. Benard; P. Braud; G. Touchard; E. Moreau

2008-01-01

109

Sensitivity of an asymmetric 3D diffuser to plasma-actuator induced inlet condition perturbations  

Microsoft Academic Search

Experiments were conducted for the flow in a straight-walled 3D diffuser fed by a fully developed turbulent duct flow. Previous\\u000a work found that this diffuser has a stable 3D separation bubble whose configuration is affected by the secondary flows in\\u000a the upstream duct. Dielectric barrier discharge plasma actuators were used to produce low-momentum wall jets to determine\\u000a if the separation

S. Grundmann; E. L. Sayles; J. K. Eaton

2011-01-01

110

Charge distribution on the surface of a dielectric barrier discharge actuator for the fluid-dynamic control  

NASA Astrophysics Data System (ADS)

The electric potential distribution induced on the surface of an aerodynamic plasma actuator, operating by means of a surface dielectric barrier discharge (DBD), has been studied both numerically and experimentally. Three actuators made with three different dielectric materials (Teflon, Plexiglas, and glass) have been used. The geometric configuration of the three actuators is the same one. An electrode pair separated by a 2 mm thick dielectric sheet constitutes the DBD actuator. The exposed high voltage electrode has been fed by a 5 kHz a.c. electrical signal. Voltage values between 7.5 and 15 kVp have been used. Measurements of the distribution of the electrical potential in the dielectric surface, generated by the charge deposited on it, have been done. Numerical simulations allowed to evaluating the charge distribution on the dielectric surface. The discharge has been switched off after positive and negative plasma currents. The measurements have been carried out after both phases. The potential distribution is always positive. The charge build up takes place several centimeters downstream of the upper electrode for an extension broader than that of the plasma on the dielectric surface. The charge distribution strongly depends on the switching off phase and is heavily affected by the dielectric material. In order to evaluate the discharge structure and the extension of the plasma, images have been taken also.

Cristofolini, Andrea; Borghi, Carlo A.; Neretti, Gabriele

2013-04-01

111

Boundary Layer Control by Means of Plasma Actuators  

SciTech Connect

The development of controlled transition in a flat-plate boundary layer is investigated using Large Eddy Simulations (LES) with the dynamic Smagorinsky model. The analysis of flow control with the objective to optimize the effects of Tollmien-Schlichting waves on a flat plate by means of plasma actuators was studied. The plasma effect is modeled as a body force in the momentum equations. These equations are solved in a uniform grid using a 2nd-order finite difference scheme in time and space. The response of plasma actuators operating in different time-dependent conditions, produced by transient or periodic inputs at different frequencies, is also analyzed.

Quadros, R. [UFRGS/PPGMAp-TUD-Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt, Petersenstr. 30, 64287 Darmstadt (Germany); Bortoli, A. L. de [UFRGS/DMPA-Departamento de Matematica Pura e Aplicada, Bento Goncalves 9500, Agronomia-P.O. Box 15080, Porto Alegre-RS (Brazil); Tropea, C. [TUD/SLA-Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt, Petersenstr. 30, 64287 Darmstadt (Germany)

2007-09-06

112

Effects of Boundary Layer Flow Control Using Plasma Actuator Discharges.  

National Technical Information Service (NTIS)

This study addresses the usage and effects of atmospheric plasma discharges on the near wall flow conditions for a Pak-B low-pressure turbine blade. A plasma actuator was built normal to the freestream flow in a low-speed wind tunnel. The test section of ...

J. M. Newcamp

2005-01-01

113

Experimental Investigation of Hypersonic Flow and Plasma Aerodynamic Actuation Interaction  

NASA Astrophysics Data System (ADS)

For hypersonic flow, it was found that the most effective plasma actuator is derived from an electromagnetic perturbation. An experimental study was performed between hypersonic flow and plasma aerodynamic actuation interaction in a hypersonic shock tunnel, in which a Mach number of 7 was reached. The plasma discharging characteristic was acquired in static flows. In a hypersonic flow, the flow field can affect the plasma discharging characteristics. DC discharging without magnetic force is unstable, and the discharge channel cannot be maintained. When there is a magnetic field, the energy consumption of the plasma source is approximately three to four times larger than that without a magnetic field, and at the same time plasma discharge can also affect the hypersonic flow field. Through schlieren pictures and pressure measurement, it was found that plasma discharging could induce shockwaves and change the total pressure and wall pressure of the flow field.

Sun, Quan; Cheng, Bangqin; Li, Yinghong; Cui, Wei; Yu, Yonggui; Jie, Junhun

2013-09-01

114

Suppression of Trailing-Edge Noise Using a Plasma Actuator  

NASA Astrophysics Data System (ADS)

Suppression control of noise generation from an airfoil trailing edge is examined experimentally by using a plasma actuator for a NACA0012 airfoil at an angle of attack of -2°, at a chord Reynolds number Re = 1.54 × 105. The boundary layer on the suction surface undergoes transition to turbulence at a location upstream of the trailing edge at the present flow condition and the generation of tonal trailing-edge noise is governed by vortex roll-up of boundary layer on the pressure surface in the vicinity of the trailing-edge which produces a strong acoustic (dipole) source by diffraction of vortex-induced fluctuations at the trailing-edge. When the plasma actuator is operated at an appropriate location on the pressure-side boundary layer, the trailing-edge noise is completely suppressed through delaying the development of the boundary-layer instability wave by the blowing effect of plasma actuator.

Inasawa, A.; Asai, M.; Itoh, K.; Kamijo, T.

2011-09-01

115

Numerical simulation of a plasma actuator based on ion transport  

NASA Astrophysics Data System (ADS)

Two-dimensional numerical simulation of ion transport and flow around a single dielectric barrier discharge plasma actuator (PA) is performed. Spatial distributions of ions and electrons as well as their time evolution are obtained by solving the transport equations of monovalent positive ions, monovalent negative ions, and electrons. Voltage and frequency of the driving alternating-current signal are assumed to be 8 kV and 5 kHz, respectively. Special focus is laid upon the effect of voltage gradient dV/dt on the magnitude of the body force. The validity of steady force models often used in flow simulation is also examined. The simulation results show that the magnitude of the body force induced by the PA increases as the voltage gradient dV/dt increases and its increase rate becomes milder at higher voltage. The mechanism of body force generation is explained from the time evolution of number density fields of ions and electrons. A comparison between flow simulations using a time-resolved body force and its time-averaged counterpart demonstrates that the time-averaged model gives sufficiently accurate results when the time scale of the flow is more than 30 times greater than that of the PA.

Yamamoto, Seiya; Fukagata, Koji

2013-06-01

116

Numerical simulation of a plasma actuator based on ion transport  

SciTech Connect

Two-dimensional numerical simulation of ion transport and flow around a single dielectric barrier discharge plasma actuator (PA) is performed. Spatial distributions of ions and electrons as well as their time evolution are obtained by solving the transport equations of monovalent positive ions, monovalent negative ions, and electrons. Voltage and frequency of the driving alternating-current signal are assumed to be 8 kV and 5 kHz, respectively. Special focus is laid upon the effect of voltage gradient dV/dt on the magnitude of the body force. The validity of steady force models often used in flow simulation is also examined. The simulation results show that the magnitude of the body force induced by the PA increases as the voltage gradient dV/dt increases and its increase rate becomes milder at higher voltage. The mechanism of body force generation is explained from the time evolution of number density fields of ions and electrons. A comparison between flow simulations using a time-resolved body force and its time-averaged counterpart demonstrates that the time-averaged model gives sufficiently accurate results when the time scale of the flow is more than 30 times greater than that of the PA.

Yamamoto, Seiya; Fukagata, Koji [Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522 (Japan)] [Department of Mechanical Engineering, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522 (Japan)

2013-06-28

117

Aerogel and ferroelectric dielectric materials for plasma actuators  

NASA Astrophysics Data System (ADS)

This paper presents performance evaluation of two thick materials with extreme permittivity as dielectric barrier discharge actuators. Specifically, the use of silica aerogels and ferroelectrics is investigated. Due to high polarizability of the ferroelectric material the supplied power manifests itself primarily as heat generation with no measurable thrust. The silica aerogel, however, has a significant impact on thrust saturation as compared with other dielectrics reported to date. Specifically, the silica aerogel is found to have an order of magnitude better thrust to actuator weight ratio than acrylic and twice than that of Kapton with no power penalty, making it potentially useful for small vehicle applications.

Durscher, Ryan; Roy, Subrata

2012-01-01

118

Numerical simulation of the effect of plasma aerodynamic actuation on improving film hole cooling performance  

NASA Astrophysics Data System (ADS)

The primary goal of this paper is to study film cooling performance for a cylindrical hole with plasma aerodynamic actuation. The simulation model of plasma aerodynamic actuation on improving film hole cooling effectiveness was established. The heat effect of plasma aerodynamic actuation model was taken into consideration. It was firstly found that the velocity and blowing ratio greatly affect the film cooling effectiveness. Then, position, power input, and the number of plasma actuators were particularly investigated.

Yu, Jin-Lu; He, Li-ming; Zhu, Yi-fei; Ding, Wei; Wang, Yu-qian

2013-06-01

119

Streamwise and spanwise plasma actuators for flow-induced cavity noise control  

Microsoft Academic Search

Plasma actuators operating in atmospheric air can induce a body force through collisions between electrically charged particles and neutral air molecules by an externally applied electric field. The fast response and the simple structure make the plasma actuator a promising option in aerospace applications. In this work, experiments were performed with several alternative current excited plasma (streamwise and spanwise) actuators

Xun Huang; Xin Zhang

2008-01-01

120

Use of Plasma Actuators as a Moving-Wake Generator.  

National Technical Information Service (NTIS)

The work documented in this report tests the concept of using plasma actuators as a simple and easy way to generate a simulated moving-wake and the disturbances associated with it in turbines. This wake is caused by the blades of the upstream stages of th...

F. O. Thomas T. C. Corke

2007-01-01

121

Separation control in low pressure turbines using plasma actuators with passing wakes  

NASA Astrophysics Data System (ADS)

A Dielectric Barrier Discharge (DBD) plasma actuator is operated in flow over the suction surface of a Pack-B Low Pressure Turbine (LPT) airfoil at a Reynolds number of 50,000 (based on exit velocity and suction surface length) and inlet free-stream turbulence intensity of 2.5%. Preliminary characterization studies were made of the effect of varying actuator pulsing frequency and duty cycle, actuator edge effects, and orientation of the actuator with the flow. Flow control was demonstrated with the actuator imparting momentum opposite to the stream-wise flow direction, showing that it is possible to use disturbances alone to destabilize the flow and effect transition. No frequencies of strong influence were found over the range tested, indicating that a broad band of effective frequencies exists. Edge effects were found to considerably enhance separation control. Total pressure measurements of the flow without passing wakes were taken using a glass total-pressure tube. Corrections for streamline displacement due to shear and wall effects were made, and comparisons with previous hot-wire measurements were used to validate data. Performance features of conventional two-electrode and a novel three-electrode actuator configuration were compared. Hot-wire anemometry was used to take time-varying ensemble-averaged near-wall velocity measurements of the flow with periodic passing wakes. Corrections were made for near-wall effects, temperature effects, and interference of the electric field. The wakes were generated by a wake generator mechanism located upstream of the airfoil passage. The near-suction-surface total pressure field (flow without wakes) and velocity field (flow with wakes) in the trailing part of the airfoil passage, and the wall-normal gradient of these quantities, were used to demonstrate effective prevention of flow separation using the plasma actuator. Both flows (with and without passing wakes) showed fully attached flow (or very thin separation zones) when the actuator was activated. The flow with passing wakes and the actuator on showed relatively little time variation in the boundary layer, and qualitative similarities to the corresponding flow without passing wakes and with the actuator on were noted.

Burman, Debashish

122

Mechanisms of plasma actuators for hypersonic flow control  

NASA Astrophysics Data System (ADS)

A summary of recent research progress in hypersonic plasma actuators for flow control is attempted. It is found that the most effective plasma actuator is derived from an electromagnetic perturbation and amplifies by a subsequent viscous-inviscid interaction. Computational efforts using drift-diffusion theory and a simple phenomenological plasma model, as well as experiments in a hypersonic plasma channel, have shown the effectiveness of using electro-aerodynamic interaction as a hypersonic flow control mechanism. In principle, the plasma actuator based on magneto-aerodynamic interaction should have an added mechanism in the Lorentz force, making it even more effective as a flow control mechanism. However, this approach also incurs additional challenges and complications due to the Hall effect. Magneto-aerodynamic interactions have also been demonstrated for separated flow control, albeit in a very limited scope. Numerical simulations based on a simple phenomenological plasma model have shown the feasibility of separated flow suppression in shock-boundary-layer interaction over a compression ramp at a hypersonic flow of Mach 14.1. The control mechanism relies on the Lorentz force to energize the retarded shear layer in the viscous interacting region, but the effectiveness of momentum transfer via inelastic collision requires further validation.

Shang, J. S.; Surzhikov, S. T.; Kimmel, R.; Gaitonde, D.; Menart, J.; Hayes, J.

2005-11-01

123

Experimental Characterization of the Plasma Synthetic Jet Actuator  

NASA Astrophysics Data System (ADS)

The plasma synthetic jet is a novel active flow control method because of advantages such as fast response, high frequency and non-moving parts, and it has received more attention recently, especially regarding its application to high-speed flow control. In this paper, the experimental characterization of the plasma synthetic jet actuator is investigated. The actuator consists of a copper anode, a tungsten cathode and a ceramic shell, and with these three parts a cavity can be formed inside the actuator. A pulsed-DC power supply was adopted to generate the arc plasma between the electrodes, through which the gas inside was heated and expanded from the orifice. Discharge parameters such as voltage and current were recorded, respectively, by voltage and current probes. The schlieren system was used for flow visualization, and jet velocities with different discharge parameters were measured. The schlieren images showed that the strength of plasma jets in a series of pulses varies from each other. Through velocity measurement, it is found that at a fixed frequency, the jet velocity hardly increases when the discharge voltage ranges from 16 kV to 20 kV. However, with the discharge voltage fixed, the jet velocity suddenly decreases when the pulse frequency rises above 500 Hz, whereas at other testing frequencies no such decrease was observed. The maximum jet velocity measured in the experiment was up to 110 m/s, which is believed to be effective for high-speed flow control.

Jin, Di; Li, Yinghong; Jia, Min; Song, Huimin; Cui, Wei; Sun, Quan; Li, Fanyu

2013-10-01

124

Turbine Tip Clearance Flow Control using Plasma Actuators  

Microsoft Academic Search

The tip clearance gap leakage ?ow is of continuing concern in reducing e-ciency losses that occur within turbines. Active ?ow control using a blade-tip-mounted unsteady plasma actuator was implemented in a low pressure linear turbine cascade. Downstream ?ow velocity and pressure were acquired using a flve-hole probe to document changes in leakage vortex size and strength. Reynolds numbers of 5£104

Daniel K. Van Ness II; Thomas C. Corke; Scott C. Morris; Axial Blade Chord; Fifl Pitch; Yaw Angles; Debye Length; Plasma Net Charge Density

125

Discharge characteristics of plasma sheet actuators  

Microsoft Academic Search

The electrical characteristics of a plasma sheet device used for subsonic airflow control are studied in this paper. Experiments are undertaken with a two-wire asymmetrical (different diameters, opposite polarity) electrode configuration connected to dc high voltage sources in the presence of a dielectric plate and under different gases (dry air, nitrogen and oxygen). For large distances electrode-plates it has been

R. Sosa; G. Artana; D. Grondona; H. Kelly; A. Márquez; F. Minotti

2007-01-01

126

Tethered cube stabilization by means of leading-edge DBD plasma actuation  

NASA Astrophysics Data System (ADS)

An experimental investigation was carried out to assess the effectiveness of active flow control as a means for suppressing oscillations of a tethered cube. Two experimental configurations were considered: a static configuration involving surface pressure and particle image velocimetry (PIV) flow field measurements and a dynamic, tethered, configuration. Corner-mounted, dielectric barrier discharge plasma actuators were employed at the leading-edges and were pulsed at reduced frequencies of order one and at varying duty cycles. On the static configuration, actuation changed the direction of the side-forces and virtually eliminated yawing-moment excursions. Surface pressure and flow field measurements showed that control of separation bubbles on the surfaces, as well as control of the separated shear layer, were responsible for these effects. Phase-averaged PIV measurements elucidated the mechanism whereby actuation severs the leading-edge vortex that subsequently sheds downstream. For the tethered cube, actuation dramatically reduced the yawing motions, particularly when the momentum coefficient exceeded 0.3 %. Drag reduction, based on the deflection of the cube, was estimated to be approximately 12 %, consistent with the static data. Reduced frequency and duty cycle had a marked effect on control effectiveness.

Goyta, Snir; Mueller-Vahl, Hanns; Greenblatt, David

2013-01-01

127

Progress Toward Accurate Measurements of Power Consumptions of DBD Plasma Actuators  

NASA Technical Reports Server (NTRS)

The accurate measurement of power consumption by Dielectric Barrier Discharge (DBD) plasma actuators is a challenge due to the characteristics of the actuator current signal. Micro-discharges generate high-amplitude, high-frequency current spike transients superimposed on a low-amplitude, low-frequency current. We have used a high-speed digital oscilloscope to measure the actuator power consumption using the Shunt Resistor method and the Monitor Capacitor method. The measurements were performed simultaneously and compared to each other in a time-accurate manner. It was found that low signal-to-noise ratios of the oscilloscopes used, in combination with the high dynamic range of the current spikes, make the Shunt Resistor method inaccurate. An innovative, nonlinear signal compression circuit was applied to the actuator current signal and yielded excellent agreement between the two methods. The paper describes the issues and challenges associated with performing accurate power measurements. It provides insights into the two methods including new insight into the Lissajous curve of the Monitor Capacitor method. Extension to a broad range of parameters and further development of the compression hardware will be performed in future work.

Ashpis, David E.; Laun, Matthew C.; Griebeler, Elmer L.

2012-01-01

128

Experimental Investigation of the Plasma Aerodynamic Actuation Generated by Nanosecond-pulse Sliding Discharge  

Microsoft Academic Search

Plasma flow control, based on plasma aerodynamic actuation, has become a newly-rising research focus in international aerodynamic field. Sliding discharge is a novel approach to generate plasma aerodynamic actuation. In this paper, a three-electrode plasma sheet actuator driven by repetitive nanosecond pulses with negative DC component is used to generate sliding discharge, which can be called nanosecond-pulse sliding discharge. The

Song Huimin; Jia Min; Liang Hua; Wu Yun

2011-01-01

129

Development and use of localized arc filament plasma actuators for high-speed flow control  

Microsoft Academic Search

The paper discusses recent results on the development of localized arc filament plasma actuators and their use in controlling high-speed and high Reynolds number jet flows. Multiple plasma actuators (up to 8) are controlled using a custom-built 8-channel high-voltage pulsed plasma generator. The plasma generator independently controls pulse repetition rate (0-200 kHz), duty cycle and phase for each individual actuator.

Yurii G. Utkin; Saurabh Keshav; Jin-Hwa Kim; Jeff Kastner; Igor V. Adamovich; Mo Samimy

2007-01-01

130

Demonstration of Separation Control Using Glow-Discharge Plasma Actuators  

NASA Technical Reports Server (NTRS)

Active flow control of boundary-layer separation using glow-discharge plasma actuators is studied experimentally. Separation is induced on a flat plate installed in a closed-circuit wind tunnel by a shaped insert on the opposite wall. The flow conditions represent flow over the suction surface of a modem low-pressure-turbine airfoil. The Reynolds number, based on wetted plate length and nominal exit velocity, is varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low (0.2%) and high (2.5%) free-stream turbulence intensities are set using passive grids. A spanwise-oriented phased-plasma-array actuator, fabricated on a printed circuit board, is surface-flush-mounted upstream of the separation point and can provide forcing in a wide frequency range. Static surface pressure measurements and hot-wire anemometry of the base and controlled flows are performed and indicate that the glow-discharge plasma actuator is an effective device for separation control.

Hultgren, Lennart S.; Ashpis, David E.

2003-01-01

131

Demonstration of Separation Delay With Glow-Discharge Plasma Actuators  

NASA Technical Reports Server (NTRS)

Active flow control of boundary-layer separation using glow-discharge plasma actuators is studied experimentally. Separation is induced on a flat plate installed in a closed-circuit wind tunnel by a shaped insert on the opposite wall. The flow conditions represent flow over the suction surface of a modern low-pressure-turbine airfoil. The Reynolds number, based on wetted plate length and nominal exit velocity, is varied from 50; 000 to 300,000, covering cruise to takeoff conditions. Low (0.2%) and high (2.5%) free-stream turbulence intensities are set using passive grids. A spanwise-oriented phased-plasma-array actuator, fabricated on a printed circuit board, is surface-flush-mounted upstream of the separation point and can provide forcing in a wide frequency range. Static surface pressure measurements and hot-wire anemometry of the base and controlled flows are performed and indicate that the glow-discharge plasma actuator is an effective device for separation control.

Hultgren, Lennart S.; Ashpis, David E.

2003-01-01

132

Demonstration of Separation Delay with Glow-Discharge Plasma Actuators  

NASA Technical Reports Server (NTRS)

Active flow control of boundary-layer separation using glow-discharge plasma actuators is studied experimentally. Separation is induced on a flat plate installed in a closed-circuit wind tunnel by a shaped insert on the opposite wall. The flow conditions represent flow over the suction surface of a modern low-pressure-turbine airfoil. The Reynolds number, based on wetted plate length and nominal exit velocity, is varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low (0.2 percent) and high (2.5 percent) free-stream turbulence intensities are set using passive grids. A spanwise-oriented phased-plasma-array actuator, fabricated on a printed circuit board, is surface-flush-mounted upstream of the separation point and can provide forcing in a wide frequency range. Static surface pressure measurements and hot-wire anemometry of the base and controlled flows are performed and indicate that the glow-discharge plasma actuator is an effective device for separation control.

Hultgren, Lennart S.; Ashpis, David E.

2004-01-01

133

Performance improvement of plasma actuators using asymmetric high voltage waveforms  

NASA Astrophysics Data System (ADS)

An experimental study is conducted on high voltage waveforms used to power plasma actuators. Shapes that present an asymmetry between the two half cycles are investigated by means of induced thrust and velocity measurements. A parametric study is performed based on thrust measurements in order to find the optimum shape within the tested range. An asymmetric waveform which is made as a combination of sinusoidal and square shapes is found to increase produced thrust by almost 30% compared with the conventional sinusoidal waveform. The asymmetric waveform is further analysed using time-resolved particle image velocimetry in order to reveal the forcing mechanism governed by the shape differences. It is shown that the shape of the waveform has a significant effect on the performance of the actuator. Push and pull events occur within the actuation period and their respective strength and duration closely correlates with the shape of the waveform. It is found that the pull event is significantly weakened for the case of the optimized asymmetric waveform in comparison with the sinusoidal shape. This effectively increases the net momentum transfer and an improvement of approximately 40% in maximum induced velocity is achieved compared with sine waveform. Power consumption due to the asymmetric waveform is marginally increased which provides a significant increase in the actuator's relative efficiency.

Kotsonis, M.; Ghaemi, S.

2012-02-01

134

Measurements and simulations of a channel flow powered by plasma actuators  

NASA Astrophysics Data System (ADS)

Experimental measurements and numerical simulations of a dielectric barrier discharge driven flow inside a finite length channel have been performed. Plasma actuators have been used to impart momentum to the flow in the near wall region, which diffuses throughout the height of the channel as it convects downstream. This momentum addition is found to be of sufficient magnitude to create an unsteady channel flow with exit velocities on the order of 1-3 m/s. Pressure and velocity measurements have been taken in order to quantify the effects of varying the number of symmetrically placed pairs of plasma actuators in the channel and the operating voltage applied to the actuators, showing a monotonic increase with respect to both parameters. Power law relationships have been determined for these measurements with respect to the operating voltage, with exponents of 2.0 for the exit velocity and of 5.6 for the maximum pressure differential. The pressure measurements also suggest that the pressure increase due to each actuator is independent of the bulk flow inside the channel. Numerical predictions also agree with the measured pressure and velocity distributions across the channel. The bulk velocity and pressure measurements allow for efficiency calculations of the plasma channel, which are shown to also fit into a power law relationship with respect to the operating voltage. The data collected show that the efficiency of these devices is low, less than 0.1%, but that it increases with a power law exponent of 4.09 to 4.35 indicating the possibility of using such channel for pumping small flows.

Riherd, Mark; Roy, Subrata

2012-09-01

135

Plasma Actuators for Turbomachinery Flow Control  

NASA Technical Reports Server (NTRS)

This report is Part I of the final report of NASA Cooperative Agreement contract no. NNX07AC02A. The period of performance was January 1, 2007 to December 31, 2010. This report includes the project summary, a list of publications and reprints of the publications that appeared in archival journals. Part II of the final report includes a Ph.D. dissertation and is published separately as NASA/CR-2012-2172655. The research performed under this project was focused on the operation of surface dielectric barrier discharge (DBD) devices driven by high voltage, nanosecond scale pulses plus constant or time varying bias voltages. The main interest was in momentum production and the range of voltages applied eliminated significant heating effects. The approach was experimental supplemented by computational modeling. All the experiments were conducted at Princeton University. The project provided comprehensive understanding of the associated physical phenomena. Limitations on the performance of the devices for the generation of high velocity surface jets were established and various means for overcoming those limitations were proposed and tested. The major limitations included the maximum velocity limit of the jet due to electrical breakdown in air and across the dielectric, the occurrence of backward breakdown during the short pulse causing reverse thrust, the buildup of surface charge in the dielectric offsetting the forward driving potential of the bias voltage, and the interaction of the surface jet with the surface through viscous losses. It was also noted that the best performance occurred when the nanosecond pulse and the bias voltage were of opposite sign. Solutions include the development of partially conducting surface coatings, the development of a semiconductor diode inlaid surface material to suppress the backward breakdown. Extension to long discharge channels was studied and a new ozone imaging method developed for more quantitative determination of surface jet properties.

Miles, Richard, B; Shneider, Mikhail, N.

2012-01-01

136

Competition between pressure effects and airflow influence for the performance of plasma actuators  

NASA Astrophysics Data System (ADS)

The present work addresses the combined influence of pressure variations and different airflow velocities on the discharge intensity of plasma actuators. Power consumption, plasma length, and discharge capacitance were investigated systematically for varying pressure levels (p = 0.1-1 bar) and airflow velocities (U?=0-100 m/s) to characterize and quantify the favorable and adverse effects on the discharge intensity. In accordance with previous reports, an increasing plasma actuator discharge intensity is observed for decreasing pressure levels. At constant pressure levels, an adverse airflow influence on the electric actuator performance is demonstrated. Despite the improved discharge intensity at lower pressure levels, the seemingly improved performance of the plasma actuators is accompanied with a more pronounced drop of the relative performance. These findings demonstrate the dependency of the (kinematic and thermodynamic) environmental conditions on the electric performance of plasma actuators, which in turn affects the control authority of plasma actuators for flow control applications.

Kriegseis, J.; Barckmann, K.; Frey, J.; Tropea, C.; Grundmann, S.

2014-05-01

137

Streamwise and spanwise plasma actuators for flow-induced cavity noise control  

SciTech Connect

Plasma actuators operating in atmospheric air can induce a body force through collisions between electrically charged particles and neutral air molecules by an externally applied electric field. The fast response and the simple structure make the plasma actuator a promising option in aerospace applications. In this work, experiments were performed with several alternative current excited plasma (streamwise and spanwise) actuators to control flow-induced noise from a cavity. It was found that the streamwise actuator induced three-dimensional variations in the shear layer. The spanwise actuator, however, has little influence on the global flow field. As a result, the streamwise actuator is more effective than the spanwise actuator in cavity noise attenuation.

Huang Xun; Zhang Xin [Aeronautics and Astronautics, School of Engineering Sciences, University of Southampton, Southampton SO17 1BJ (United Kingdom)

2008-03-15

138

Flow separation control by plasma actuator with nanosecond pulse discharge  

NASA Astrophysics Data System (ADS)

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 (? 1 ?s) 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.

Starikovskii, Andrei; Roupassov, Dmirty; Nikipelov, Andrei; Nudnova, Maryia

2008-10-01

139

On the benefits of hysteresis effects for closed-loop separation control using plasma actuation  

NASA Astrophysics Data System (ADS)

Flow separation control by a non-thermal plasma actuator is considered for a NACA 0015 airfoil at a chord Reynolds number of 1.9 × 105. Static hysteresis in the lift coefficient is demonstrated for increasing and then decreasing sinusoidal voltage amplitude supplying a typical single dielectric barrier discharge actuator at the leading edge of the model. In addition to these open-loop experiments, unsteady surface pressure signals are examined for transient processes involving forced reattachment and natural separation. The results show that strong pressure oscillations in the relatively slow separation process, compared to reattachment, precede the ultimate massive flow separation. To enhance the contrast between the parts of the signal related to the attached flow and those related to the incipient separation, RMS estimate of filtered values of Cp is used to define a flow separation predictor that is implemented in feedback control. Two simple controllers are proposed, one based on a predefined threshold of the unsteady Cp and another that utilizes the flow separation predictor to identify incipient separation. The latter effectively leverages the hysteresis in the post-stall regime to reduce the electrical power consumed by the actuator while maintaining continuously attached flow.

Benard, N.; Cattafesta, L. N.; Moreau, E.; Griffin, J.; Bonnet, J. P.

2011-08-01

140

Plasma morphology and induced airflow characterization of a DBD actuator with serrated electrode  

NASA Astrophysics Data System (ADS)

Plasma morphology and airflow induced by a dielectric barrier discharge (DBD) actuator, whose exposed electrode geometry is designed with a serrated configuration, are investigated in quiescent air and compared with a DBD actuator consisting of electrodes designed with a standard linear strip configuration. ICCD imaging, electrical measurements and three-component laser Doppler velocimetry were carried out to compare various features of these two actuators. With the serrated configuration, ICCD images of the discharge show that streamers are bent, whereas with the linear configuration they are straight. These curved streamers induce a three-dimensional flow topology, which is confirmed by friction line visualization and velocity measurements. Whereas a two-dimensional wall-jet is induced with the linear configuration, a transverse velocity component is measured with the serrated configuration, implying the creation of spanwise-periodic vorticity. Phase-averaged velocity measurements allow the temporal variation of this transverse velocity to be highlighted. On both sides of a tooth, it has qualitatively the same variation as the longitudinal velocity with respect to the negative or positive half-cycles of the high voltage signal. Moreover, with the same electrical operating parameters, the measured longitudinal velocity was higher, particularly at the tips.

Joussot, R.; Leroy, A.; Weber, R.; Rabat, H.; Loyer, S.; Hong, D.

2013-03-01

141

Unmanned air vehicle flow separation control using dielectric barrier discharge plasma at high wind speed  

NASA Astrophysics Data System (ADS)

The present paper described an experimental investigation of separation control of an Unmanned Aerial Vehicle (UAV) at high wind speeds. The plasma actuator was based on Dielectric Barrier Discharge (DBD) and operated in a steady manner. The flow over a wing of UAV was performed with smoke flow visualization in the ?0.75 m low speed wind tunnel to reveal the flow structure over the wing so that the locations of plasma actuators could be optimized. A full model of the UAV was experimentally investigated in the ?3.2 m low speed wind tunnel using a six-component internal strain gauge balance. The effects of the key parameters, including the locations of the plasma actuators, the applied voltage amplitude and the operating frequency, were obtained. The whole test model was made of aluminium and acted as a cathode of the actuator. The results showed that the plasma acting on the surface of UAV could obviously suppress the boundary layer separation and reduce the model vibration at the high wind speeds. It was found that the maximum lift coefficient of the UAV was increased by 2.5% and the lift/drag ratio was increased by about 80% at the wind speed of 100 m/s. The control mechanism of the plasma actuator at the test configuration was also analyzed.

Zhang, Xin; Huang, Yong; Wang, WanBo; Wang, XunNian; Li, HuaXing

2014-06-01

142

Unmanned air vehicle flow separation control using dielectric barrier discharge plasma at high wind speed  

NASA Astrophysics Data System (ADS)

The present paper described an experimental investigation of separation control of an Unmanned Aerial Vehicle (UAV) at high wind speeds. The plasma actuator was based on Dielectric Barrier Discharge (DBD) and operated in a steady manner. The flow over a wing of UAV was performed with smoke flow visualization in the ?0.75 m low speed wind tunnel to reveal the flow structure over the wing so that the locations of plasma actuators could be optimized. A full model of the UAV was experimentally investigated in the ?3.2 m low speed wind tunnel using a six-component internal strain gauge balance. The effects of the key parameters, including the locations of the plasma actuators, the applied voltage amplitude and the operating frequency, were obtained. The whole test model was made of aluminium and acted as a cathode of the actuator. The results showed that the plasma acting on the surface of UAV could obviously suppress the boundary layer separation and reduce the model vibration at the high wind speeds. It was found that the maximum lift coefficient of the UAV was increased by 2.5% and the lift/drag ratio was increased by about 80% at the wind speed of 100 m/s. The control mechanism of the plasma actuator at the test configuration was also analyzed.

Zhang, Xin; Huang, Yong; Wang, WanBo; Wang, XunNian; Li, HuaXing

2014-03-01

143

Toward hybrid simulation of flow generation in DBD plasma actuator  

NASA Astrophysics Data System (ADS)

We developed a particle code based on the PIC-MCC method and a plasma fluid code solving drift-diffusion equations. Fluid simulation produces a streamer-type discharge for a positively biased input applied to the exposed electrode against to the buried electrode as obtained in particle simulation. However, we found differences in micro-discharge formation around the exposed electrode between the results of the two codes, suggesting that a hybrid approach based on particle and fluid models may be needed for a long-term precise simulation. Our hybrid code and perspective models are presented for reliably predicting the entire dynamics from micro-discharge to flow generation in a DBD plasma actuator.

Sugimoto, Kazuya; Ohnishi, Naofumi

2012-11-01

144

Effects of plasma aerodynamic actuation on oblique shock wave in a cold supersonic flow  

Microsoft Academic Search

Wedge oblique shock wave control using an arc discharge plasma aerodynamic actuator was investigated both experimentally and theoretically. Schlieren photography measurements in a small-scale short-duration supersonic wind tunnel indicated that the shock wave angle decreased and its start point shifted upstream with the plasma aerodynamic actuation. Also the shock wave intensity weakened, as shown by the decrease in the gas

Jian Wang; Yinghong Li; Bangqin Cheng; Changbing Su; Huimin Song; Yun Wu

2009-01-01

145

Response of a circular cylinder wake to a symmetric actuation by non-thermal plasma discharges  

NASA Astrophysics Data System (ADS)

In this study, the flow past a circular cylinder is manipulated by two plasma discharges placed on both sides of the model (at ±50°). A parametric investigation by force balance is conducted to define the sensitivity of the flow field to unsteady perturbations imparted by plasma actuators (dielectric barrier discharge) at 15.6 m/s ( Re D = 40,000). Effects of simple sinusoidal waveform, burst modulation and amplitude modulation are compared for low-frequency excitations. Regardless of the excitation mode, the cylinder experiences a large increase in the drag coefficient. The larger drag increase is observed for excitation related to the lock-on regime. Fast PIV measurements and triple decomposition by proper orthogonal decomposition are performed to extract the dynamical changes in the cylinder wake and to discriminate the control effects on the coherent and fluctuating turbulence. As expected, the control principally acts on the coherent flow structures. When forced, the vortices form closer to the base of the cylinder regardless of the actuation mode. This results in the drag increase observed by force measurements. The effectiveness of burst modulation is also due to the suppression of irregular shedding that is observed in the natural flow sequence and to a high level of correlation between the upper and lower vortex shedding. Finally, flow visualizations indicate that similar results can be obtained at higher Reynolds number ( Re D = 128,000, 50 m/s).

Benard, N.; Moreau, E.

2013-02-01

146

Study of flow induced by sine wave and saw tooth plasma actuators  

NASA Astrophysics Data System (ADS)

The effect of plasma actuator that uses saw-tooth or sine-wave shape electrodes on boundary layer flows is experimentally investigated. The measurement results are compared with a corresponding standard configuration (conventional design using two rectangular strip electrodes)—the actuator that produces a nearly two-dimensional horizontal wall jet upon actuation. PIV measurements are used to characterize the actuators in a quiescent chamber. Operating in a steady manner, the new actuators result in the formation of streamwise and spanwise vortices. That is to say, the new actuators render the plasma actuators inducing three-dimensional variations in the shear layer, offering significant flexibility in flow control. The affected flowfield with the new actuators is significantly larger than that with the conventional linear actuators. While the conventional linear actuators affect primarily the boundary layer flow on a scale of about 1 cm above the wall, the new actuators affect the near wall region at a significantly larger scale. This new design broadens the applicability and enhances the flow control effects and it is potentially a more efficient flow control device.

Liu, Zhifeng; Wang, Lianze; Fu, Song

2011-11-01

147

Optimization of Airfoil Design for Flow Control with Plasma Actuators  

NASA Astrophysics Data System (ADS)

Using computer simulations and design optimization methods, this research examines the implementation of active flow control devices on wind turbine blades. Through modifications to blade geometry in order to maximize the effectiveness of flow control devices, increases in aerodynamic performance and control of aerodynamic performance are expected. Due to this compliant flow, an increase in the power output of wind turbines is able to be realized with minimal modification and investment to existing turbine blades. This is achieved through dynamic lift control via virtual camber control. Methods using strategic flow separation near the trailing edge are analyzed to obtain desired aerodynamic performance. FLUENT is used to determine the aerodynamic performance of potential turbine blade design, and the post-processing uses optimization techniques to determine an optimal blade geometry and plasma actuator operating parameters. This work motivates the research and development of novel blade designs with flow control devices that will be tested at Notre Dame's Laboratory for Enhanced Wind Energy Design.

Williams, Theodore; Corke, Thomas; Cooney, John

2011-11-01

148

Physics of plasma actuator operating in atmospheric air  

SciTech Connect

The physics of plasma actuator operating in the atmospheric air has been numerically investigated. The O{sup -}, O{sub 2}{sup -}, O{sub 2}{sup +}, and N{sub 2}{sup +} ions have been included in the air chemistry to identify their role. For the specific case study, we find the density of positive ions is an order of magnitude higher at the positive peak of the cycle than that at the negative peak of the cycle. This difference in density levels of the species causes the development of the directional bias of the electrodynamic force. Numerical simulations indicate that positive ions play major role in the development of the positive force.

Singh, Kunwar Pal; Roy, Subrata [Computational Plasma Dynamics Laboratory and Test Facility, Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611-6300 (United States)

2008-03-17

149

Plasma Measurements with Surface Barrier Detectors.  

National Technical Information Service (NTIS)

A surface barrier detector system for measuring the loss rate of protons from a hydrogen plasma and their energy spectrum is described. A full width at half maximum (FWHM) resolution of 1.4 keV for 15-keV hydrogen atoms was obtained using a selected detec...

A. H. Futch A. E. Bradley

1969-01-01

150

Documentation and Control of Flow Separation on a Low Pressure Turbine Linear Cascade of Pak-B Blades Using Plasma Actuators  

NASA Technical Reports Server (NTRS)

This work involved the documentation and control of flow separation that occurs over low pressure turbine (LPT) blades at low Reynolds numbers. A specially constructed linear cascade was utilized to study the flow field over a generic LPT cascade consisting of Pratt & Whitney "Pak-B" shaped blades. Flow visualization, surface pressure measurements, LDV measurements, and hot-wire anemometry were conducted to examine the flow fields with and without separation control. Experimental conditions were chosen to give a range of chord Reynolds numbers (based on axial chord and inlet velocity) from 10,000 to 100,000, and a range of freestream turbulence intensities from u'/U(infinity) = 0.08 to 2.85 percent. The blade pressure distributions were measured and used to identify the region of separation that depends on Reynolds number and the turbulence intensity. Separation control was performed using dielectric barrier discharge (DBD) plasma actuators. Both steady and unsteady actuation were implemented and found to work well. The comparison between the steady and unsteady actuators showed that the unsteady actuators worked better than the steady ones. For the steady actuators, it was found that the separated region is significantly reduced. For the unsteady actuators, where the signal was pulsed, the separation was eliminated. The total pressure losses (a low Reynolds number) was reduced by approximately a factor of two. It was also found that lowest plasma duty cycle (10 percent in this work) was as effective as the highest plasma duty cycle (50 percent in this work). The mechanisms of the steady and unsteady plasma actuators were studied. It was suggested by the experimental results that the mechanism for the steady actuators is turbulence tripping, while the mechanism for the unsteady actuators is to generate a train of spanwise structures that promote mixing.

Corke, Thomas c.; Thomas, FLint, O.; Huang, Junhui

2007-01-01

151

Plasma sprayed functionally graded thermal barrier coatings  

Microsoft Academic Search

Functionally graded thermal barrier coatings of the system yttria stabilised zirconia\\/NiCoCrAlY were fabricated through plasma spraying using pre-alloyed composite powders as feedstock. Composite powders with different compositions (75% NiCoCrAlY:25% YSZ; 50% NiCoCrAly:50% YSZ and 25% NiCoCrAlY:75% YSZ) were prepared by mechanical alloying and plasma powder spheroidisation, and are subsequently sprayed successively in a single plasma torch to form the functionally

K. A. Khor; Z. L. Dong; Y. W. Gu

1999-01-01

152

Effect of the charge surface distribution on the flow field induced by a dielectric barrier discharge actuator  

NASA Astrophysics Data System (ADS)

The Electro-Hydro-Dynamics (EHD) interaction induced by a surface dielectric barrier discharge in the aerodynamic boundary layer at one atmosphere still air has been investigated. Three different geometrical configurations of the actuator have been utilized. In the first configuration, an electrode pair separated by a 2 mm dielectric sheet has been used. The second and the third configurations have been obtained by adding a third electrode on the upper side of the dielectric surface. This electrode has been placed downstream of the upper electrode and has been connected to ground or has been left floating. Three different dielectric materials have been utilized. The high voltage upper electrode was fed by an a.c. electric tension. Measurements of the dielectric surface potential generated by the charge deposition have been done. The discharge has been switched off after positive and negative phases of the plasma current (the current phase was characterized by a positive or a negative value, respectively). The measurements have been carried out after both phases. The charge distribution strongly depended on the switching off phase and was heavily affected by the geometrical configuration. A remarkable decrease of the charge deposited on the dielectric surface has been detected when the third electrode was connected to ground. Velocity profiles were obtained by using a Pitot probe. They showed that the presence of the third electrode limits the fluid dynamics performance of the actuator. A relation between the charge surface distribution and the EHD interaction phenomenon has been found. Imaging of the plasma has been done to evaluate the discharge structure and the extension of the plasma in the configurations investigated.

Cristofolini, Andrea; Neretti, Gabriele; Borghi, Carlo A.

2013-08-01

153

Active Control of Flow around NACA 0015 Airfoil by Using DBD Plasma Actuator  

NASA Astrophysics Data System (ADS)

In this study, effect of plasma actuator on a flat plate and manipulation of flow separation on NACA0015 airfoil with plasma actuator at low Reynolds numbers were experimentally investigated. In the first section of the study, plasma actuator which consists of positive and grounded electrode couple and dielectric layer, located on a flat plate was actuated at different frequencies and peak to peak voltages in range of 3-5 kHz and 6-12 kV respectively. Theinduced air flow velocity on the surface of flat plate was measured by pitot tube at different locations behind the actuator. The influence of dielectricthickness and unsteady actuation with duty cycle was also examined. In the second section, the effect of plasma actuator on NACA0015 airfoil was studied atReynolds number 15000 and 30000. Four plasma actuators were placed at x/C = 0.1, 0.3, 0.5 and 0.9, and different electrode combinations were activated by sinusoidal signal. Flow visualizations were done when the attack angles were 0°, 5°, 10°, 15° and 20°. The results indicate that up to the 15° attack angle, the separated flow was reattached by plasma actuator at 12kV peak to peak voltage and 4 kHz frequency. However, 12 kVpp voltage was insufficient to reattach the flow at 20° angle of attack. The separated flow could be reattached by increasing the voltage up to 13 kV. Lift coefficient was also increased by the manipulated flow over the airfoil. Results showed that even high attack angles, the actuators can control the flow separation and prevent the airfoil from stall at low Reynolds numbers.

Akansu, Y. E.; Karakaya, F.; ?anl?soy, A.

2013-04-01

154

Control of a high Reynolds number Mach 0.9 heated jet using plasma actuators  

Microsoft Academic Search

The results of particle image velocimetry (PIV) measurements in a high subsonic, heated, jet forced using localized arc filament plasma actuators (LAFPAs) show that LAFPAs can consistently produce significant mixing enhancement over a wide range of temperatures. These actuators have been used successfully in high Reynolds number, high-speed unheated jets. The facility consists of an axisymmetric jet with different nozzle

M. Kearney-Fischer; J.-H. Kim; M. Samimy

2009-01-01

155

DBD Plasma Actuators for Flow Control in Air Vehicles and Jet Engines - Simulation of Flight Conditions in Test Chambers by Density Matching  

NASA Technical Reports Server (NTRS)

Dielectric Barrier Discharge (DBD) Plasma actuators for active flow control in aircraft and jet engines need to be tested in the laboratory to characterize their performance at flight operating conditions. DBD plasma actuators generate a wall-jet electronically by creating weakly ionized plasma, therefore their performance is affected by gas discharge properties, which, in turn, depend on the pressure and temperature at the actuator placement location. Characterization of actuators is initially performed in a laboratory chamber without external flow. The pressure and temperature at the actuator flight operation conditions need to be simultaneously set in the chamber. A simplified approach is desired. It is assumed that the plasma discharge depends only on the gas density, while other temperature effects are assumed to be negligible. Therefore, tests can be performed at room temperature with chamber pressure set to yield the same density as in operating flight conditions. The needed chamber pressures are shown for altitude flight of an air vehicle and for jet engines at sea-level takeoff and altitude cruise conditions. Atmospheric flight conditions are calculated from standard atmosphere with and without shock waves. The engine data was obtained from four generic engine models; 300-, 150-, and 50-passenger (PAX) aircraft engines, and a military jet-fighter engine. The static and total pressure, temperature, and density distributions along the engine were calculated for sea-level takeoff and for altitude cruise conditions. The corresponding chamber pressures needed to test the actuators were calculated. The results show that, to simulate engine component flows at in-flight conditions, plasma actuator should be tested over a wide range of pressures. For the four model engines the range is from 12.4 to 0.03 atm, depending on the placement of the actuator in the engine. For example, if a DBD plasma actuator is to be placed at the compressor exit of a 300 PAX engine, it has to be tested at 12.4 atm for takeoff, and 6 atm for cruise conditions. If it is to be placed at the low-pressure turbine, it has to be tested at 0.5 and 0.2 atm, respectively. These results have implications for the feasibility and design of DBD plasma actuators for jet engine flow control applications. In addition, the distributions of unit Reynolds number, Mach number, and velocity along the engine are provided. The engine models are non-proprietary and this information can be used for evaluation of other types of actuators and for other purposes.

Ashpis, David E.; Thurman, Douglas R.

2011-01-01

156

Development of Localized Arc Filament RF Plasma Actuators for High- Speed and High Reynolds Number Flow Control.  

National Technical Information Service (NTIS)

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...

I. V. Adamovich J. H. Kim M. Nishihara M. Samimy S. V. Gorbatov

2010-01-01

157

Pulsed Plasma Actuators for Active Flow Control at MAV Reynolds Numbers  

Microsoft Academic Search

An experimental investigation of separation control using steady and pulsed plasma actuators was carried out on an Eppler\\u000a E338 airfoil at typical micro air vehicle Reynolds numbers (20,000?Re?140,000). Pulsing was achieved by modulating the high frequency plasma excitation voltage. The actuators were calibrated\\u000a directly using a laser doppler anemometer, with and without free-stream velocity, and this allowed the quantification of

B. Göksel; D. Greenblatt; I. Rechenberg; Y. Kastantin; C. N. NAYERI; C. O. PASCHEREIT

158

Flow separation control by plasma actuator with nanosecond pulse periodic discharge  

Microsoft Academic Search

Currently, the problem of flow active control by low-temperature plasma is considered to be one of the most booming realms of aerodynamics . The paper presents a results on controlling boundary layer attachment by plasma actuator withhighvoltage pulsed periodic nanosecond excitation. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region at

D. V. Roupassov; A. A. Nikipelov; M. M. Nudnova; A. Yu. Starikovskii

2008-01-01

159

Experimental and Numerical Investigations of Boundary-Layer Influence Using Plasma-Actuators  

Microsoft Academic Search

This is a fundamental study about the influence of plasma-actuators on boundary-layer flows, including both experimental and\\u000a numerical investigations. The first set of experiments is conducted in quiescent air and these results are used to calibrate\\u000a a numerical model which simulates the plasma-actuator in an existing RANS (Reynolds Averaged Navier-Stokes) code. The second\\u000a set of experiments involves a flat-plate boundary

S. Grundmann; S. Klumpp; C. Tropea

160

Positive and negative sawtooth signals applied to a DBD plasma actuator – influence on the electric wind  

Microsoft Academic Search

The influence of the electric signal shape applied to a surface dielectric barrier discharge (DBD) actuator is investigated in order to optimise the produced electric wind. This report also gives insights on the mechanisms involved in the electro-fluido-dynamic (EFD) operated by actuators based on atmospheric non-thermal discharges in air. The parameters of the electric signal that maximises the produced electric

N. Balcon; N. Benard; Y. Lagmich; J.-P. Boeuf; G. Touchard; E. Moreau

2009-01-01

161

Vacuum application of thermal barrier plasma coatings  

NASA Technical Reports Server (NTRS)

Coatings are presently applied to Space Shuttle Main Engine (SSME) turbine blades for protection against the harsh environment realized in the engine during lift off-to-orbit. High performance nickel, chromium, aluminum, and yttrium (NiCrAlY) alloy coatings, which are applied by atmospheric plasma spraying, crack and spall off because of the severe thermal shock experienced during start-up and shut-down of the engine. Ceramic coatings of yttria stabilized zirconia (ZrO2-Y2O3) were applied initially as a thermal barrier over coating to the NiCrAlY but were removed because of even greater spalling. Utilizing a vacuum plasma spraying process, bond coatings of NiCrAlY were applied in a low pressure atmosphere of argon/helium, producing significantly improved coating-to-blade bonding. The improved coatings showed no spalling after 40 MSFC burner rig thermal shock cycles, cycling between 1700 and -423 F. The current atmospheric plasma NiCrAlY coatings spalled during 25 test cycles. Subsequently, a process was developed for applying a durable thermal barrier coating of ZrO2-Y2O3 to the turbine blades of first stage high-pressure fuel turbopumps utilizing the vacuum plasma process. The improved thermal barrier coating has successfully passed 40 burner rig thermal shock cycles without spalling. Hot firing in an SSME turbine engine is scheduled for the blades. Tooling was installed in preparation for vacuum plasma spray coating other SSME hardware, e.g., the titanium main fuel valve housing (MFVH) and the fuel turbopump nozzle/stator.

Holmes, R. R.; Mckechnie, T. N.

1988-01-01

162

Low-Reynolds Number Flow Control Using Dielectric Barrier Discharge Actuators  

Microsoft Academic Search

Dielectric Barrier Discharges (DBD), operated at KHz and KV range, can create athermal plasma via collision processes and induce near wall jet. In this paper, we investigate the potential of using DBD to conduct flow control at low Reynolds numbers, motivated by micro air vehicle (MAV) applications. A previously developed computational methodology, based on the eN transition model and the

Balaji Jayaraman; Yongsheng Lian; Wei Shyy

2007-01-01

163

Temporal evolution of a surface dielectric barrier discharge for different groups of plasma microdischarges  

NASA Astrophysics Data System (ADS)

We have experimentally investigated the properties of microdischarges originating in asymmetric surface dielectric barrier discharges fed by a high-voltage sinusoidal low-frequency drive. Devices exploiting such a configuration are currently proposed as plasma actuators, because they induce a directed airflow in the gas surrounding the surface. Light emission and electric current associated with individual microdischarges have been recorded with high temporal resolution. A statistical analysis of the dataset was performed to correlate microdischarge properties with the voltage phase and to spot peculiarities arising from the actual breakdown mechanism in such a configuration. In particular, we demonstrated the asymmetry between the two different semi-cycles of the discharge, which could affect plasma actuator efficiency. Differences arising in the multiplicity, amplitude, temporal duration as well as in the spatial pattern of the discharge emitting region also permitted identifying several different groups of microdischarges, presumably playing different roles in both the discharge dynamics and airflow induction.

Biganzoli, I.; Barni, R.; Riccardi, C.

2013-01-01

164

Flow Control over a Conical Forebody by Periodic Pulsed Plasma Actuation  

NASA Astrophysics Data System (ADS)

The flow control mechanism of plasma actuators with periodic pulsed discharge to control the bi-stable vortices over a cone-cylinder is investigated. The actuators are installed on the leeward surface near the apex of a cone which has a semi-apex angle of 10°. The effectiveness of the plasma actuation under different free-stream velocities and angles of attack is analyzed. The pressure distributions over the conical forebody are measured by both steady and dynamic pressure transducers. The transient dynamic pressure distribution tends to gradually become steady as the free-stream velocity increases, that is, the pulsed actuation approximates a continuous one. Furthermore, the flow control effectiveness becomes less noticeable as the free-stream velocity or the angle of attack increases under certain controlling electrical parameters.

Zheng, Borui; Gao, Chao; Li, Yibin; Liu, Feng; Luo, Shijun

2013-04-01

165

Dielectric Barrier Discharge Plasma Actuator for Flow Control.  

National Technical Information Service (NTIS)

This report is Part II of the final report of NASA Cooperative Agreement contract no. NNX07AC02A. It includes a Ph.D. dissertation. The period of performance was January 1, 2007 to December 31, 2010. Part I of the final report is the overview published as...

D. F. Opaits

2012-01-01

166

Lift and drag performances of an axisymmetric airfoil controlled by plasma actuator  

Microsoft Academic Search

A Dielectric Barrier Discharge (DBD) is mounted at the leading edge of a NACA 0015 airfoil model. The effects of steady and unsteady actuations on the lift and drag coefficients are investigated by time-averaged force measurements. Results demonstrate that the stall regime can be delayed of one or two degrees while the drag coefficient is reduced. The aerodynamic performances are

N. Benard; J. Jolibois; E. Moreau

2009-01-01

167

Characterization of linear plasma synthetic jet actuators in an initially quiescent medium  

SciTech Connect

The plasma synthetic jet actuator (PSJA) is a geometrical variant of the aerodynamic plasma actuator that can be used to produce zero-mass flux jets similar to those created by mechanical devices. This jet can be either three-dimensional using annular electrode arrays (annular PSJA) or nearly two dimensional using two rectangular-strip exposed electrodes and one embedded electrode (linear PSJA). Unsteady pulsing of the PSJA at time scales decoupled to the ac input frequency results in a flow field dominated by counter-rotating vortical structures similar to conventional synthetic jets, and the peak velocity and momentum of the jet is found to be affected by a combination of the pulsing frequency and input power. This paper investigates the fluid dynamic characteristics of linear plasma synthetic jet actuators in an initially quiescent medium. Two-dimensional particle image velocimetry measurements on the actuator are used to validate a previously developed numerical model wherein the plasma behavior is introduced into the Navier-Stokes equations as an electrohydrodynamic force term calculated from Maxwell's equations and solved for the fluid momentum. The numerical model was implemented in an incompressible, unstructured grid code. The results of the simulations are observed to reproduce some aspects of the qualitative and quantitative experimental behavior of the jet for steady and pulsed modes of actuator operation. The self-similarity behavior of plasma synthetic jets are examined and compared to mechanically driven continuous and synthetic jets.

Santhanakrishnan, Arvind [Department of Mathematics, Phillips Hall, CB 3250, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3250 (United States); Reasor, Daniel A. Jr. [School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); LeBeau, Raymond P. Jr. [Department of Mechanical Engineering, University of Kentucky, Lexington, Kentucky 40506 (United States)

2009-04-15

168

Study of flow fields induced by surface dielectric barrier discharge actuator in low-pressure air  

NASA Astrophysics Data System (ADS)

Surface dielectric barrier discharge (SDBD) is a promising method for a flow control. Flow fields induced by a SDBD actuator driven by the ac voltage in static air at low pressures varying from 1.0 to 27.7 kPa are measured by the particle image velocimetry method. The influence of the applied ac voltage frequency and magnitude on the induced flow fields is studied. The results show that three different classes of flow fields (wall jet flow field, complex flow field, and vortex-shape flow field) can be induced by the SDBD actuator in the low-pressure air. Among them, the wall jet flow field is the same as the tangential jet at atmospheric pressure, which is, together with the vertical jet, the complex flow field. The vortex-shape flow field is composed of one vertical jet which points towards the wall and two opposite tangential jets. The complex and the vortex-shape flow fields can be transformed to the wall jet flow field when the applied ac voltage frequency and magnitude are changed. It is found that the discharge power consumption increases initially, decreases, and then increases again at the same applied ac voltage magnitude when the air pressure decreases. The tangential velocity of the wall jet flow field increases when the air pressure decreases. It is however opposite for the complex flow field. The variation of the applied ac voltage frequency influences differently three different flow fields. When the applied ac voltage magnitude increases at the same applied ac voltage frequency, the maximal jet velocity increases, while the power efficiency increases only initially and then decreases again. The discharge power shows either linear or exponential dependences on the applied ac voltage magnitude.

Che, Xueke; Nie, Wansheng; Shao, Tao; Tian, Xihui; Hou, Zhiyong; He, Haobo; Zhou, Penghui; Zhou, Siyin; Yang, Chao

2014-04-01

169

Active Separation Control over a NACA0024 by DBD Plasma Actuator and FBG Sensor  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge plasma actuators (DBD-PA) and fiber Bragg grating (FBG) sensors have been investigated for active control of flow separation around a NACA0024 airfoil. Tangential jets were produced in the vicinity of the DBD-PA slightly aft of the leading edge of the airfoil. The flow separation control ability was evaluated at low Reynolds number in an open-circuit wind tunnel. Phase- and time-averaged velocity distributions around the airfoil were measured using Particle Image Velocimetry, and the flow separation control ability of the DBD-PA was assessed at 8°, 12° and 16° angle of attack. An FBG sensor was attached to a chord-wise cantilever near the trailing edge of the airfoil on the pressure surface. This was used to measure strain fluctuations in the cantilever root due to flow-induced oscillations. The feasibility of this system to detect flow separation was studied, where the standard deviations of strain fluctuations significantly increased when the flow was separated. This was utilized in an open-loop control system to detect flow separation by FBG then apply active control with the DBD-PA to reattach the flow.

Jukes, Timothy; Segawa, Takehiko; Walker, Seth; Furutani, Hirohide; Iki, Norihiko; Takekawa, Shinya

170

Design and characterization of a plasma actuator for controlling dynamic stall  

NASA Astrophysics Data System (ADS)

A repetitive pulsed spark discharge inside of a ˜1 mm cavity generates a high velocity (100-600 m/s) gas jets potentially capable of controlling dynamic stall on an airfoil at Re ˜1e6. High temperature compressible 2D CFD was used to determine the design and geometry of the actuator slot and plasma cavity. Experimental results measuring the time dependent plasma discharge emission and density variations (using gated ICCD and Schlieren) indicate that the plasma can be modeled as constant volume heating over 100 ns. The energy input to the actuator is controlled by the high voltage and capacitance initiating the discharge. During the discharge air in the cavity is rapidly heated. Temperature and pressure increase 5-10x, causing strong gradients and shocks. The flow is directed using an angled slot. In CFD designed geometries shock fronts and high temperature gas velocities are experimentally determined. The force generated by the actuator is also experimentally determined. Experimental results from the actuator show that velocities of 500 m/s can be achieved through 1mm2 orifices with energy inputs of 50 mJ. The CFD model predicts time scales and velocities similar to those observed, and it also indicates cavity cooling as important in optimizing the actuator pulse repetition rate.

Pollard, William; Staack, David

2012-10-01

171

Damping Tollmien-Schlichting waves in a boundary layer using plasma actuators  

NASA Astrophysics Data System (ADS)

The response of a zero pressure gradient boundary layer modified by flow-wise oriented momentum injection similar to that of a plasma actuator is calculated using a two-dimensional (bi-global) stability analysis. It is found that the addition of momentum into the boundary layer has a significant impact on Tollmien-Schlichting waves, which may be damped by up to two orders of magnitude. Changes to the exponential growth rate of the perturbations are also measured. These stabilizing effects are largely due to the momentum addition modifying the downstream boundary layer profiles, but localized stabilization effects are also noted. The relative stabilization of the TS wave appears to be a linear function with respect to the ratio of the plasma-induced wall jet velocity under quiescent conditions and the free-stream velocity for lower levels of plasma actuation (i.e. velocity ratios less than 0.1). For higher levels of plasma actuation, the relative stabilization of the TS wave appears to be exponential with respect to the total momentum addition to the boundary layer by the plasma actuator.

Riherd, Mark; Roy, Subrata

2013-12-01

172

On factors influencing arc filament plasma actuator performance in control of high speed jets  

NASA Astrophysics Data System (ADS)

Localized arc filament plasma actuators (LAFPAs) have been developed and used at The Gas Dynamics and Turbulence Laboratory for the purpose of controlling high-speed and high Reynolds number jets. The ability of LAFPAs for use in both subsonic and supersonic jets has been explored, and experiments to date have shown that these actuators have significant potential for mixing enhancement and noise control applications. While it has been established that the actuators manipulate instabilities of the jet, the exact nature of how the actuation couples to the flow is still unclear. All of the results previously reported have been based on a nozzle extension that has an azimuthal groove of 1 mm width and 0.5 mm depth along the inner surface approximately 1 mm upstream of nozzle extension exit. The ring groove was initially added to shield the plasma arcs from the high-momentum flow. However, the effect of the ring groove on the actuation mechanism is not known. To explore this effect, a new nozzle extension is designed, which relocates the actuators to the nozzle extension face and eliminates the ring groove. Schlieren images, particle image velocimetry and acoustic results of a Mach 0.9 jet of Reynolds number ~6.1 × 105 show similar trends and magnitudes with and without a ring groove. Thus, it is concluded that the ring groove does not play a primary role in the LAFPAs' control mechanism. Furthermore, the effect of the duty cycle of the actuator input pulse on the LAFPAs' control authority is investigated. The results show that the minimum duty cycle that provides complete plasma formation has the largest control over the jet.

Hahn, Casey; Kearney-Fischer, Martin; Samimy, Mo

2011-12-01

173

DCT-TCI: Real Gas Characterization of Plasma Flow Control - An Integrated Approach.  

National Technical Information Service (NTIS)

This report presents results culminated partially from the AFOSR grant FA9550-09-1-0372 on experimental and numerical characterization of novel plasma actuators. Specifically the serpentine and multi-barrier plasma actuators are considered. The serpentine...

C. Wang R. Durscher S. Roy

2011-01-01

174

Computational Modeling of the Dielectric Barrier Discharge (DBD) Device for Aeronautical Applications.  

National Technical Information Service (NTIS)

Dielectric Barrier Discharge (DBD) type devices, when used as plasma actuators, have shown significant promise for use in many aeronautical applications. Experimentally, DBD actuator devices have been shown to induce motion in initially still air, and to ...

C. S. Charles

2006-01-01

175

Flow and Noise Control in High Speed and High Reynolds Number Jets Using Plasma Actuators  

NASA Technical Reports Server (NTRS)

The idea of manipulating flow to change its characteristics is over a century old. Manipulating instabilities of a jet to increase its mixing and to reduce its radiated noise started in the 1970s. While the effort has been successful in low-speed and low Reynolds number jets, available actuators capabilities in terms of their amplitude, bandwidth, and phasing have fallen short in control of high-speed and high Reynolds number jets of practical interest. Localized arc filament plasma actuators have recently been developed and extensively used at Gas Dynamics and Turbulence Laboratory (GDTL) for control of highspeed and high Reynolds number jets. While the technique has been quite successful and is very promising, all the work up to this point had been carried out using small high subsonic and low supersonic jets from a 2.54 cm diameter nozzle exit with a Reynolds number of about a million. The preliminary work reported in this paper is a first attempt to evaluate the scalability of the technique. The power supply/plasma generator was designed and built in-house at GDTL to operate 8 actuators simultaneously over a large frequency range (0 to 200 kHz) with independent control over phase and duty cycle of each actuator. This allowed forcing the small jet at GDTL with azimuthal modes m = 0, 1, 2, 3, plus or minus 1, plus or minus 2, and plus or minus 4 over a large range of frequencies. This power supply was taken to and used, with minor modifications, at the NASA Nozzle Acoustic Test Rig (NATR). At NATR, 32 actuators were distributed around the 7.5 in. nozzle (a linear increase with nozzle exit diameter would require 60 actuators). With this arrangement only 8 actuators could operate simultaneously, thus limiting the forcing of the jet at NATR to only three azimuthal modes m = plus or minus 1, 4, and 8. Very preliminary results at NATR indicate that the trends observed in the larger NASA facility in terms of the effects of actuation frequency and azimuthal modes are similar in both small GDTL and larger NASA jets. However, the actuation authority seems to fall short in the larger jet at higher Mach numbers, resulting in decreased amplitude response compared to the small jet, which is attributed at this point to the lack of sufficient number of actuators. The preliminary results seem also to suggest that amplitude of actuation tones is similar in both the small and larger jets.

Samimy, M.; Kastner, J.; Kim, J.-H.; Utkin, Y.; Adamovich, I.; Brown, C. A.

2006-01-01

176

Aerodynamic plasma actuators: A directional micro-jet device  

Microsoft Academic Search

In recent years electroaerodynamic actuators have been rather intensively studied in order to control airflow [H. Velkoff, R. Godfrey, J. of Heat Transfer 101 (1979) 157; S. El-Khabiry, G.M. Colver, Phys. Fluids 9 3 (1997) 587; A. Soldati, S. Banerjee, Phys. Fluids 10 (1998) 1742; R. Vilela Mendes, J.A. Dente, J. Fluids Eng. 120 (1998) 626; A. Schütze, et al.,

Nicolas Bénard; Jérôme Jolibois; Eric Moreau; Roberto Sosa; Guillermo Artana; Gérard Touchard

2008-01-01

177

Propagating-arc magnetohydrodynamic plasma actuator for directional high-authority flow control in atmospheric air  

NASA Astrophysics Data System (ADS)

A propagating-arc magnetohydrodynamic plasma actuator for aerodynamic flow control is reported. The actuator comprises two rail electrodes flush mounted on an aerodynamic surface. A pulsed arc is propelled down the length of the rails by Lorentz forces supported by a self-induced magnetic field. The arc induces a high velocity pulsed air wall jet due to the pushing and entrainment actions. Experiments in quiescent air demonstrate that the plasma arc achieves a peak velocity of around 100 m s-1 and requires a discharge energy on the order of 300 J per pulse. Wind tunnel tests on a 14.5 inch chord airfoil section, at a Reynolds number of 0.45 million show induced flow velocities on the order of 10's m s-1 with significant penetration of the flow actuation effect perpendicular to the wall surface.

Pafford, Brent; Sirohi, Jayant; Raja, Laxminarayan L.

2013-12-01

178

Optical emission spectroscopy measurements within a single microdischarge of a dielectric barrier discharge actuator  

NASA Astrophysics Data System (ADS)

This paper reports optical emission spectroscopy measurements resolved laterally within a single microdischarge during the negative half-cycle of a sinusoidally driven dielectric barrier discharge. The maximum values of the reduced electric field, vibrational temperature of N2(C3?u), and rotational temperature of N2+(B2?u+) were approximately 300 Td, 3500 K, and 1200 K, respectively. These values were correlated to the outer-edges of the microdischarge near the plasma-dielectric surface interface. These maximum values were significantly greater than measurements made elsewhere within the microdischarge and suggest a strong sheath at the outer-edges of the microdischarge.

Stanfield, S. A.; Menart, J.

2013-07-01

179

LES of a Jet Excited by the Localized Arc Filament Plasma Actuators  

NASA Technical Reports Server (NTRS)

The fluid dynamics of a high-speed jet are governed by the instability waves that form in the free-shear boundary layer of the jet. Jet excitation manipulates the growth and saturation of particular instability waves to control the unsteady flow structures that characterize the energy cascade in the jet.The results may include jet noise mitigation or a reduction in the infrared signature of the jet. The Localized Arc Filament Plasma Actuators (LAFPA) have demonstrated the ability to excite a high-speed jets in laboratory experiments. Extending and optimizing this excitation technology, however, is a complex process that will require many tests and trials. Computational simulations can play an important role in understanding and optimizing this actuator technology for real-world applications. Previous research has focused on developing a suitable actuator model and coupling it with the appropriate computational fluid dynamics (CFD) methods using two-dimensional spatial flow approximations. This work is now extended to three-dimensions (3-D) in space. The actuator model is adapted to a series of discrete actuators and a 3-D LES simulation of an excited jet is run. The results are used to study the fluid dynamics near the actuator and in the jet plume.

Brown, Clifford A.

2011-01-01

180

Experimental damping of boundary-layer oscillations using DBD plasma actuators  

Microsoft Academic Search

In the present work artificially excited Tollmien–Schlichting waves were cancelled using plasma actuators operated both in continuous and pulsed modes. To achieve this a vibrating surface, driven by an electromagnetic turbulator, was flush-mounted in a flat plate to excite the TS waves. These were amplified by an adverse pressure gradient induced by an insert on the upper wall of the

Sven Grundmann; Cameron Tropea

2009-01-01

181

Plasma bolometry using a multislit shutter with piezoelectric actuator  

SciTech Connect

We offer to apply a shutter with a piezoelectric bimorph actuator as a modulator of radiation and particle fluxes. Such shutters may be useful to provide measurements in steady state regimes of tokamaks and stellarators because they allow one to avoid amplifier drifts and to simplify diagnostics calibration. Signal modulation makes it possible to apply the lock-in amplification technique, increasing the sensitivity and reducing the neutron doze collected by sensors. Experiments with pyroelectric sensors (LiTaO{sub 3}) at 350 Hz modulation frequency have demonstrated the detection limit at 30 Hz equal to 15 {mu}W/cm{sup 2}, which is comparable to metallic bolometers.

Kuteev, Boris V.; Outkine, Andrew A.; Gabdullin, Pavel G.; Kostrioukov, Artem Yu.; Kapralov, Vladimir G. [Nuclear Fusion Institute, RRC Kurchatov Institute, Moscow 123182 (Russian Federation); Technical University Applied Physics Ltd., St. Petersburg 195251 (Russian Federation)

2004-10-01

182

Parametric study of vortex train generated by plasma actuator in dependency on input voltage waveform  

NASA Astrophysics Data System (ADS)

This article is based on previous work of authors. The vortex train is created by a plasma DBD actuator after application of low-frequency amplitude modulation on high-frequency high-voltage carrier waveform. Data acquisition of flow field around actuators will be performed using time-resolved PIV measurement technique in plane parallel to flow and in cross-section. Phase-averaging will be used due to pseudo-periodical character of this process. The vortex behaviour dependency on modulation frequency, duty cycle, voltage value, electrode gap and other parameters will be shown. The generated flow patterns are to be applied for control of a boundary layer.

Procházka, P.; Uruba, V.

2013-04-01

183

[Experimental investigation on plasma assistant combustion actuator in argon/air].  

PubMed

In order to obtain the characteristics of argon/air plasma assistant combustion actuators, experiments of three different actuators with normal, paratactic and meshy electrode configurations were respectively performed in argon/air mixture firstly, the results showed that the shape of electrode has little influence on the discharge characteristics. Then normal electrode was applied to study spectrum and discharge characteristics under the condition of 100% air and 10% argon/90% air. The comparison showed that, though in mixture the law of discharge characteristic was the same as that of pure air, discharge current and emission spectrum were strengthened, and initial discharge voltage reduced from 27 to 24 kV. PMID:22512154

Du, Hong-liang; He, Li-ming; Ding, Wei; Zhao, Bing-bing; Wang, Feng

2012-02-01

184

Development of localized arc filament RF plasma actuators for high-speed and high Reynolds number flow control  

Microsoft Academic Search

Recently developed localized arc filament plasma actuators (LAFPAs) have shown tremendous control authority in high-speed\\u000a and high Reynolds number flow for mixing enhancement and noise mitigation. Previously, these actuators were powered by a high-voltage\\u000a pulsed DC plasma generator with low energy coupling efficiency of 5–10%. In the present work, a new custom-designed 8-channel\\u000a pulsed radio frequency (RF) plasma generator has

J.-H. Kim; M. Nishihara; I. V. Adamovich; M. Samimy; S. V. Gorbatov; F. V. Pliavaka

2010-01-01

185

Control of oblique shock wave/boundary layer interactions using plasma actuators  

NASA Astrophysics Data System (ADS)

Localized arc filament plasma actuators (LAFPAs) are used for shock wave/boundary layer interaction induced separation control in a Mach 2.3 flow. The boundary layer is fully turbulent with a Reynolds number based on the incompressible momentum thickness of 22,000 and shape factor of 1.37, and the impinging shock wave is generated by a 10° compression ramp. The LAFPAs are observed to have significant control authority over the interaction. The main effect is the displacement of the reflected shock and most of the interaction region upstream by approximately one boundary layer thickness (~5 mm). The initial goal of the control was to manipulate the low-frequency ( St~0.03) unsteadiness associated with the interaction region. A detailed investigation of the effect of actuator placement, frequency, and duty cycle on the control authority indicates the actuators' primary control mechanism is not the manipulation of low-frequency unsteadiness. Detailed measurements and analysis indicate that a modification to the boundary layer through heat addition by the actuators is the control mechanism, despite the extremely small power input of the actuators.

Webb, N.; Clifford, C.; Samimy, M.

2013-06-01

186

Aerodynamic modification of flow over bluff objects by plasma actuation  

Microsoft Academic Search

Particle image velocimetry and smoke visualization are used to study the alteration of the flow field in the wake of a bluff body by use of an alternating current (AC) surface dielectric barrier discharge. Staggered, surface, and buried electrodes were positioned on the downstream side of circular cylinders at conditions of Re\\u000a \\u000a D \\u000a = 1 × 104?4 × 104 configured to impose a force due

Y. Sung; W. Kim; M. G. Mungal; M. A. Cappelli

2006-01-01

187

Simulations of the linear plasma synthetic jet actuator utilizing a modified Suzen-Huang model  

NASA Astrophysics Data System (ADS)

The linear plasma synthetic jet actuator (L-PSJA) is a unique form of flow control device which harnesses the interaction of induced flows from two linear plasma actuators to form an upward jet. Since each injection can be manipulated in intensity, the synthetic jet has thrust vectoring properties. Our study simulates the L-PSJA by utilizing a modified Suzen-Huang (S-H) model that accounts for drift and diffusive properties in the surface charge. The results of the present model show that the centreline velocity is closer to the experimental values found in literature as compared to the default form of S-H modelling. Thrust vectoring simulations were also performed to demonstrate the feasibility of flow directional variation in the L-PSJA.

Ibrahim, I. H.; Skote, M.

2012-11-01

188

Numerical study of boundary layer separation control using magnetogasdynamic plasma actuators  

SciTech Connect

In this study, an efficient, time dependent, two-dimensional Navier-Stokes numerical code for shockwave boundary layer interaction in air is developed. Nonthermal surface plasma actuation is evaluated for effective shockwave induced boundary layer separation control within supersonic inlets. Specifically, high speed magnetogasdynamic plasma actuators are of interest. In these, localized ionization is produced close to the wall surface and then the flow is accelerated using strong magnetic fields. To replicate the experiments done at large boundary layer thickness, the code is divided into time independent and time dependent regimes to significantly reduce computation time. Computational results are in good agreement with experiments in terms of the flow structure as shown by Schlieren imaging, acetone planar laser scattering, and the static pressure profile on the test section wall.

Kalra, Chiranjeev S.; Shneider, Mikhail N.; Miles, Richard B. [Department of Mechanical and Aerospace Engineering, Applied Physics Group, Princeton University, Princeton, New Jersey 08544 (United States)

2009-10-15

189

Active Noise Control in a Mach 1.3 Ideally-Expanded Jet with Plasma Actuators  

Microsoft Academic Search

Our earlier work in noise mitigation using localized arc filament plasma actuators in a Mach 0.9 axisymmetric jet was extended in this paper to an ideally expanded Mach 1.3 axisymmetric jet. Far-field noise was measured at 30? and 90? locations relative to the jet axis to investigate the effects of azimuthal mode and forcing Strouhal number on the far-field noise.

J. H. Kim; I. Adamovich; M. Samimy

2008-01-01

190

Active cancellation of artificially introduced Tollmien–Schlichting waves using plasma actuators  

Microsoft Academic Search

In the present work artificially excited Tollmien–Schlichting (TS) waves were cancelled using plasma actuators operated in\\u000a pulsed mode. In order to achieve this a vibrating surface driven by an electromagnetic turbulator was flush mounted in a flat\\u000a plate to excite the TS waves. These were amplified by an adverse pressure gradient induced by an insert on the upper wall\\u000a of

Sven Grundmann; Cameron Tropea

2008-01-01

191

Control of the corner separation in a compressor cascade by steady and unsteady plasma aerodynamic actuation  

Microsoft Academic Search

This paper reports experimental results on using steady and unsteady plasma aerodynamic actuation to control the corner separation,\\u000a which forms over the suction surface and end wall corner of a compressor cascade blade passage. Total pressure recovery coefficient\\u000a distribution was adopted to evaluate the corner separation. Corner separation causes significant total pressure loss even\\u000a when the angle of attack is

Ying-hong LiYun; Yun Wu; Min Zhou; Chang-Bing Su; Xiong-Wei Zhang; Jun-Qiang Zhu

2010-01-01

192

Airflow control by non-thermal plasma actuators  

Microsoft Academic Search

Active flow control is a topic in full expansion due to associated industrial applications of huge importance, particularly for aeronautics. Among all flow control methods, such as the use of mechanical flaps, wall synthetic jets or MEMS, plasma-based devices are very promising. The main advantages of such systems are their robustness, simplicity, low power consumption and ability for real-time control

Eric Moreau

2007-01-01

193

Numerical Simulations of Flow Separation Control in Low-Pressure Turbines using Plasma Actuators  

NASA Technical Reports Server (NTRS)

A recently introduced phenomenological model to simulate flow control applications using plasma actuators has been further developed and improved in order to expand its use to complicated actuator geometries. The new modeling approach eliminates the requirement of an empirical charge density distribution shape by using the embedded electrode as a source for the charge density. The resulting model is validated against a flat plate experiment with quiescent environment. The modeling approach incorporates the effect of the plasma actuators on the external flow into Navier Stokes computations as a body force vector which is obtained as a product of the net charge density and the electric field. The model solves the Maxwell equation to obtain the electric field due to the applied AC voltage at the electrodes and an additional equation for the charge density distribution representing the plasma density. The new modeling approach solves the charge density equation in the computational domain assuming the embedded electrode as a source therefore automatically generating a charge density distribution on the surface exposed to the flow similar to that observed in the experiments without explicitly specifying an empirical distribution. The model is validated against a flat plate experiment with quiescent environment.

Suzen, Y. B.; Huang, P. G.; Ashpis, D. E.

2007-01-01

194

An experimental study of a plasma actuator in absence of free airflow: Ionic wind velocity profile  

SciTech Connect

In this study, we are interested in the direct current electrical corona discharge created between two wire electrodes. The experimental results are related to some electroaerodynamic actuators based on the direct current corona discharge at the surface of a dielectric material. Several geometrical forms are selected for the dielectric surface, such as a plate, a cylinder, and a NACA 0015 aircraft wing. The current density-electric field characteristics are presented for different cases in order to determine the discharge regimes. The corona discharge produces nonthermal plasma, so it is called plasma discharge. Plasma discharge creates a tangential ionic wind above the surface at the vicinity of the wall. The ionic wind induced by the corona discharge is measured in absence of free external airflow. The ionic wind velocity profiles and the maximum induced tangential force are given for different surface forms, so it is possible to compare the actuators effect based on the span of the ionic wind velocity and thrust values. The higher ionic wind velocity is obtained with the NACA profile, which shows the effectiveness of this actuator for the airflow control.

Mestiri, R.; Hadaji, R.; Ben Nasrallah, S. [Ecole Nationale d'Ingenieurs de Monastir, Monastir 5019 (Tunisia)

2010-08-15

195

Flow control around a circular cylinder using pulsed dielectric barrier discharge surface plasma  

SciTech Connect

Dielectric barrier discharge (DBD) plasma actuators have been used to control the flow around a circular cylinder at Re=15 000, where the near-wake structure was studied using time-resolved particle image velocimetry with simultaneous measurements of the dynamic lift and drag forces. It was shown that the vortex shedding was suppressed when the surface plasma placed near the natural separation point was activated in a pulsed mode at nondimensional frequency, f{sub p}{sup +}, above 0.6 with a force coefficient, C{sub p}, greater than 0.05%. Plasma actuator performance on flow control was summarized by mapping the changes in drag and lift fluctuations as a function of the forcing frequency and the force coefficient. They showed that more than 70% reduction in lift fluctuations was obtained with up to 32% drag reduction at f{sub p}{sup +}=2.0 and C{sub p}=0.32%. Here, narrowing of the wake was observed as the plasma promoted shear-layer roll-ups at the forcing frequency. This, however, did not affect the shear layer on the opposite side of the wake. At nondimensional forcing frequencies less than 0.6, the vortex shedding locked onto a multiple of the plasma frequency to amplify the wake oscillations. This caused more than 85% increase in lift fluctuations with 8% drag increase at f{sub p}{sup +}=0.2 and C{sub p}=0.01%. The efficiency of flow control using DBD plasma was found to be 1%-2% for drag reduction while around 6% for drag increase.

Jukes, Timothy N.; Choi, Kwing-So [Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2009-08-15

196

Plasma surface modification and hydrophobic barrier coating of paper  

NASA Astrophysics Data System (ADS)

Development of new technologies for production of alternative paper properties with minimal environmental hazards was the goal of this project. In this study, the utilization of various chemicals under radio frequency (RF) plasma environments was investigated for creation of hydrophobic barrier properties and deposition of electrically conductive conjugated thin layers on the surface of paper. Four basic approaches have been utilized to impart hydrophobic barriers to the paper without affecting bulk properties; argon plasma treatment after Teflon-like chemical; 1,1,1,2 tetrafluoroethane (TFE) predeposition, carbon tetrafluoride (CF4) plasma treatment after TFE pre-deposition, carbon tetrafluoride plasma treatment alone and octamethylcyclotetrasiloxane (OMCTSO) plasma treatment of paper under an RF-glow discharge. The chosen chemicals were found to enhance the properties of the paper substrates and surface analysis aided explanation of the mechanism of hydrophobic barrier improvements on paper. An attempt was also made to prepare oriented thin films of pi-conjugated polymers on paper surfaces with a pulsed plasma technique for incorporation of electrically conductive layers. Progressive changes in composition, with varying plasma duty cycles during the plasma polymerization, were observed with thiophene. The results of this study provide additional support for the unusually good control of film chemistry available via the pulsed plasma technique. Electrical conductivity measurements indicated that fragmented thiophene films were obtained under mild plasma conditions, but the discontinuous thiophene film was found to be oriented. The electrical behavior of the thiophene derived deposited layer was dramatically improved with chemical doping. Correlation of the changes of paper surface properties with changes in plasma parameters are partially explained by based on surface chemistry, although other structural features of the paper morphology were also affected to some extent by the treatments. It may be that some of the methods evaluated in this study could be applied by industry, particularly gas-vapor plasma treatments alone; however the approaches were designed to provide fundamental understanding of the mechanisms of plasma modification of the properties of paper.

Sahin, Halil Turgut

2001-07-01

197

Three-dimensional flow measurements induced from serpentine plasma actuators in quiescent air  

NASA Astrophysics Data System (ADS)

This paper presents three-dimensional flow measurements performed on a dielectric barrier discharge (DBD) actuator with the electrodes in a serpentine design. Such a configuration induces a local pinching and a local spreading of the fluid as one follows along the span of the actuator. In this work two different variations on the serpentine configuration are evaluated: one constructed from patterned circular arcs and one from patterned rectangles. The influence of applied voltage is studied for the former case. To quantify these effects stereo particle image velocimetry (PIV) is used to generate time averaged, spatially resolved measurements of the detailed flow structure. The three components of the velocity vector are measured along spanwise and streamwise cuts. These slices are then reconstructed to provide a three-dimensional view of the induced flow field. The results for the induced flow fields are also compared with stereo-PIV measurements made on a standard linear DBD actuator. A truly three-dimensional induced flow field was observed as a result of the serpentine configuration. These designs could be beneficial for rapid mixing of the local fluid.

Durscher, R. J.; Roy, S.

2012-01-01

198

Superior thermal barrier coatings using solution precursor plasma spray  

Microsoft Academic Search

A novel process, solution precursor plasma spray (SPPS), is presented for depositing thermal barrier coatings (TBCs), in which\\u000a aqueous chemical precursors are injected into a standard direct current plasma spray system. The resulting coatings microstructure\\u000a has three unique features: (1) ultra fine splats (1 µm), (2) nanometer and micron-sized interconnected porosity, and (3) closely\\u000a spaced, through-thickness cracks. Coatings over 3

E. H. Jordan; L. Xie; M. Gell; N. P. Padture; B. Cetegen; A. Ozturk; X. Ma; J. Roth; T. D. Xiao; P. E. C. Bryant

2004-01-01

199

[Investigation of the characteristics of the stagger electrodes dielectric barrier discharge plasmas in chord-wise direction].  

PubMed

The aerodynamic plasma actuator distinguishes itself from others by a set of highly asymmetric electrodes arranged on dielectric. So the plasma produced by the aerodynamic plasma actuator has special characteristics along chord-wise direction. In the present paper the characteristic of the stagger electrodes dielectric barrier discharge plasmas in chord-wise direction was investigated experimentally through spectrometer, infrared imager and laser induced fluorescence system. The mechanisms behind plasma flow control were discussed briefly based on these experimental results. It was found in the experiments that the distributions of light intensity and temperature in chord-wise direction accord with Gaussian distribution. Light intensity and temperature were enhanced by increasing supplied voltage. NO produced by DBD discharge was detected directly by the LIF system. Through numerical simulations, the distributions of electric potential and electric field near the electrodes were determined and the phenomena observed in experiments were explained. Based on these experimental results, the mechanisms behind plasma flow control were ascertained to be the consequence of collisions, temperature increasing and chemical reactions. PMID:19123374

Li, Gang; Li, Hang-ming; Mu, Ke-jin; Zhang, Yi; Nie, Chao-qun; Zhu, Jun-qiang

2008-10-01

200

Two-dimensional plasma photonic crystals in dielectric barrier discharge  

SciTech Connect

A series of two-dimensional plasma photonic crystals have been obtained by filaments' self-organization in atmospheric dielectric barrier discharge with two water electrodes, which undergo the transition from square to square superlattice and finally to the hexagon. The spatio-temporal behaviors of the plasma photonic crystals in nanosecond scale have been studied by optical method, which show that the plasma photonic crystal is actually an integration of different transient sublattices. The photonic band diagrams of the transverse electric (TE) mode and transverse magnetic mode for each sublattice of these plasma photonic crystals have been investigated theoretically. A wide complete band gap is formed in the hexagonal plasma photonic crystal with the TE mode. The changes of the band edge frequencies and the band gap widths in the evolvement of different structures are studied. A kind of tunable plasma photonic crystal which can be controlled both in space and time is suggested.

Fan Weili; Dong Lifang [College of Physics Science and Technology, Hebei University, Baoding 071002 (China); Zhang Xinchun [School of Energy and Power Engineering, North China Electric Power University, Baoding 071003 (China)

2010-11-15

201

Sterilization of Turmeric by Atmospheric Pressure Dielectric Barrier Discharge Plasma  

NASA Astrophysics Data System (ADS)

In this study atmospheric pressure dielectric barrier discharge (DBD) plasma has been employed for sterilizing dry turmeric powders. A 6 kV, 6 kHz frequency generator was used to generate plasma with Ar, Ar/O2, He, and He/O2 gases between the 5 mm gap of two quartz covered electrodes. The complete sterilization time of samples due to plasma treatment was measured. The most important contaminant of turmeric is bacillus subtilis. The results show that the shortest sterilization time of 15 min is achieved by exposing the samples to Ar/O2 plasma. Survival curves of samples are exponential functions of time and the addition of oxygen to plasma leads to a significant increase of the absolute value of time constant of the curves. Magnitudes of protein and DNA in treated samples were increased to a similar value for all samples. Taste, color, and solubility of samples were not changed after the plasma treatment.

Setareh, Salarieh; Davoud, Dorranian

2013-11-01

202

Atmospheric pressure resistive barrier cold plasma for biological decontamination  

Microsoft Academic Search

Steady-state atmospheric pressure nonthermal plasmas can splendidly debilitate bacteria in liquids, gases, and on surfaces, as well as can disintegrate hazardous chemicals. The nonthermal resistive barrier gas discharge at atmospheric pressure is currently investigated for low-temperature sterilization purposes. We have carried out electrical, chemical, optical, and biological studies of the discharge, with the intent of identifying the chemically and biologically

Magesh Thiyagarajan; Igor Alexeff; Sriram Parameswaran; Stephen Beebe

2005-01-01

203

Pulsed laser processing of plasma sprayed thermal barrier coatings  

Microsoft Academic Search

The requirements for thermal barrier coatings on turbine blades in jet engines and gas turbines are stringent due to the extreme temperatures and constant thermal cycling that demand a material with excellent thermal shock resistant and thermal insulation properties. Plasma sprayed zirconia alloys have been found to fit this role with some degrees of success. However, the presence of surface

K. A. Khor; S. Jana

1997-01-01

204

Failure analysis of plasma-sprayed thermal barrier coatings  

Microsoft Academic Search

Plasma-sprayed thermal barrier coatings have been subjected to thermal cycling tests with simultaneous acoustic emission (AE) monitoring. Process variables and their effect on coating integrity were evaluated in terms of cracking behavior. Failure of the thermal protection is progressive since cracking and crack growth were observed prior to ultimate failure. Catastrophic failure occurs when microcracks are transformed to macrocracks.

C. C. Berndt; R. A. Miller

1984-01-01

205

Effects of plasma spray parameters on two layer thermal barrier  

NASA Technical Reports Server (NTRS)

The power level and the type of arc gas used during plasma spraying of a two layer thermal barrier system (TBS) were found to affect the life of the system. Life at 1095 C in a cyclic furnace test was improved by about 140 percent by increasing the power during plasma spray applications of the bond and thermal barrier coatings. This improvement is due to increases in the densities of the bond and thermal barrier coatings by 3 and 5 percent, respectively. These increases in densities are equivalent to about 45 and 30 percent reduction in mean porosities, respectively. The addition of hydrogen to the argon arc gas had the same effect as the reduction in power level and caused a reduction in TBS life.

Stecura, S.

1981-01-01

206

Force generation due to three-dimensional plasma discharge on a conical forebody using pulsed direct current actuators  

SciTech Connect

Understanding the behavior of three-dimensional plasmas around a pulsed dc actuator can be useful for its efficient operation in many applications. The effect of such actuators is studied using a self-consistent multibody system of neutral oxygen species and its plasma. The equations governing the motion of charged species are solved with the drift diffusion approximation. The electrostatic potential is computed from Poisson's equation. The electric field and ionization level are the highest close to the junction of electrodes and dielectric. The plasma body force thus generated also follows a similar characteristic. Results also show some dc corona instabilities. The temporal average of such force shows mostly acceleration from anode to cathode above the actuator.

Singh, Kunwar Pal; Roy, Subrata [Computational Plasma Dynamics Laboratory and Test Facility, Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611 (United States)

2008-05-15

207

Coal Liquefaction by Using Dielectric Barrier Discharge Plasma  

NASA Astrophysics Data System (ADS)

An innovative method for coal liquefaction by using dielectric barrier discharge (DBD) plasma in a short reaction time was developed. Using tetralin as the reaction medium, DBD plasma as the energy source, and a reaction time of 10 min at 140°C, up to 10% of coal was converted to liquid material. The results showed the feasibility of coal's liquefaction by DBD plasma under relatively moderate conditions. Simultaneously, it was clarified that the effect of DBD plasma treatment was opposed to the thermal effect of heating. An acid plasma sheath could be formed on the coal powder surface in DBD conditions, liquefied reactions could be carried out in the absence of inorganic acid, and the products were nearly neutral and with low causticity.

Wang, Qiuying; Wu, Peng; Gu, Fan

2013-07-01

208

Reduced-order modeling of high-speed jets controlled by arc filament plasma actuators  

NASA Astrophysics Data System (ADS)

Arc filament plasma actuators applied to high-speed and high Reynolds number jets have demonstrated significant mixing enhancement when operated near the jet column mode (JCM) frequency. A feedback-oriented reduced-order model is developed for this flow from experimental data. The existent toolkit of stochastic estimation, proper orthogonal decomposition, and Galerkin projection is adapted to yield a 35-dimensional model for the unforced jet. Explicit inclusion of a "shift mode" stabilizes the model. The short-term predictive capability of instantaneous flow fields is found to degrade beyond a single flow time step, but this horizon may be adequate for feedback control. Statistical results from long-term simulations agree well with experimental observations. The model of the unforced jet is augmented to incorporate the effects of plasma actuation. Periodic forcing is modeled as a deterministic pressure wave specified on the inflow boundary of the modeling domain. Simulations of the forced model capture the nonlinear response that leads to optimal mixing enhancement in a small range of frequencies near the JCM.

Sinha, Aniruddha; Serrani, Andrea; Samimy, Mo

2013-02-01

209

Odor control using the AC barrier-type plasma reactors  

Microsoft Academic Search

Odor control from living environment has become of increased concern. In a previous paper, we investigated the removal of acetaldehyde (CH3CHO), which is one of the main odor components in cigarette smoke using the barrier-type packed-bed plasma reactor. In the present paper, we reported on the new results of acetaldehyde and ammonia (NH3) which is another odor component of cigarette

Masaaki Okubo; Tomoyuki Kuroki; Hideya Kametaka; Toshiaki Yamamoto

2001-01-01

210

Air plasma sprayed thermal barrier coatings on titanium alloy substrates  

Microsoft Academic Search

Titanium alloys as lightweight structure materials have been shown more interest in the use at moderately elevated temperatures. However, their poor oxidation resistance at temperature above 600 °C limits a wide application. Consequently, thermal protection becomes a concern. 8 wt.% yttria partially stabilized zirconia thermal barrier coatings (TBCs) were air plasma sprayed on titanium alloy substrates (Ti–6.6Al–3.61Mo–1.69Zr–0.28Si in wt.%). The microstructures and

Hong Zhou; Fei Li; Bo He; Jun Wang; Bao-de Sun

2007-01-01

211

Failure modes in plasma-sprayed thermal barrier coatings  

Microsoft Academic Search

Commercial plasma-sprayed thermal barrier coatings (TBCs) were investigated in an effort to elucidate the failure modes during thermal-cycling. Residual stresses in the thermally grown oxide (TGO) was measured using the Cr3+ photoluminescence piezo-spectroscopy (PLPS) method and the microstructures of the TBCs were characterized as a function of thermal cycles. The average residual stress in the TGO was found to be

K. W Schlichting; N. P Padture; E. H Jordan; M Gell

2003-01-01

212

Coherent structures in plasma-actuator controlled supersonic jets: Axisymmetric and mixed azimuthal modes  

NASA Astrophysics Data System (ADS)

High-fidelity simulations are employed to study the effect of eight localized arc filament plasma actuators placed around the periphery of a Mach 1.3 converging-diverging nozzle exit. Emphasis is placed on understanding the coherent structures generated by axisymmetric (m = 0), flapping or first mixed (m = +/-1) and second mixed (m = +/-2) modes, which are excited at the jet column-mode frequency corresponding to a Strouhal number based on jet diameter of 0.3. Baseline (no control) and constant excitation (actuators on continuously) cases are also simulated. Comparisons with experimental results indicate that the computational model reproduces the main features induced by the actuators. Furthermore, the mean flow exhibits many similarities with the theoretical predictions of Cohen and Wygnanski [J. Fluid Mech. 176, 221 (1987)]. Overall, the results indicate a complex coherent structure generation, evolution, and disintegration process. For m = +/-1, the phase-averaged flow reveals successive distorted elliptic vortex rings with axes in the flapping plane but alternating on either side of the jet axis. This generates a chain of structures each of which interacts with its predecessor on one side of the major plane and its successor on the other. Through self and mutual induction, the leading segment of each loop is pinched and passes through the previous ring before rapidly breaking up. The m = +/-2 mode yields elliptic structures with major axes of successive rings being aligned with the two symmetry planes, which are orthogonal to each other. The minor axis side is pulled downstream faster than the rest of the structure because of the higher velocity near the jet centerline and self-induced effects, yielding a horse-shoe shape when viewed in profile. The m = 0 mode exhibits axisymmetric roll-up events, with vortex ribs in the braid regions connecting successive large coherent structures. The constant excitation (with largest energy input) and baseline cases are similar to each other, indicating that the direct effect of heating is negligible.

Gaitonde, D. V.; Samimy, M.

2011-09-01

213

Diffusion barrier layer fabrication by plasma immersion ion implantation  

NASA Astrophysics Data System (ADS)

Plasma immersion Ion Implantation technique has been used to modify the diffusion barrier properties of titanium (Ti) metal layer against copper diffusion. Ti coated silicon wafer were implanted with doses viz. 1015ions/cm2 and 1017ions/cm2 corresponding to low and high dose regime. High dose of implantation of nitrogen ions in the film render it to become Ti(N). Cu/Ti(N)/Si structures were formed by depositing copper over the implanted samples. Diffusion barrier properties of Ti(N) was evaluated after annealing the samples up to 700 degrees C for 30 minutes. Sheet resistance, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) measurements were carried out to investigate the effect of annealing. Low dose implanted Ti layer does not show any change in its diffusion barrier properties and fails at about 400 degrees C. The failure of diffusion barrier properties of low dose implanted samples is attributed to the chemical reaction between titanium and copper films. The high dose implanted layer stops the diffusion of Cu metal through it even at high annealing temperature. The enhancement in its diffusion barrier properties is supposed to be due to nitridation of titanium film which increases the activation energy involved for its chemical reaction with copper metal film.

Kumar, Mukesh; Rajkumar, -; Kumar, Dinesh; George, P. J.; Paul, A. K.

2003-04-01

214

The impulse response of a high-speed jet forced with localized arc filament plasma actuators  

NASA Astrophysics Data System (ADS)

We present experimental and theoretical analyses of the response of high-speed, high-Reynolds-number, round jets to impulsive forcing with arc-filament-plasma actuators. The impulse response is obtained with forcing Strouhal numbers, based on the nozzle exit diameter and exit center line velocity, less than 0.1. The resulting phase-averaged near-field pressure signature displays a compact wave with a positive peak preceding a negative one, indicative of a large scale structure in the shear layer of the jet. Scaling laws derived by operating the jet at four subsonic Mach numbers are used to distinguish this hydrodynamic component of the phase-averaged jet response from the direct actuator noise. As the forcing frequency increases, the compact waves in the near-field pressure signal overlap each other, indicating interaction of the growing seeded structures. For this regime, the phase-averaged response is approximately replicated by linear superposition of the impulse response, thereby demonstrating the quasi-linearity of structure interaction. A novel application of linear parabolized stability theory yields a successful model of the impulse response.

Sinha, Aniruddha; Alkandry, Hind; Kearney-Fischer, Martin; Samimy, Mo; Colonius, Tim

2012-12-01

215

Control of a high Reynolds number Mach 0.9 heated jet using plasma actuators  

SciTech Connect

The results of particle image velocimetry (PIV) measurements in a high subsonic, heated, jet forced using localized arc filament plasma actuators (LAFPAs) show that LAFPAs can consistently produce significant mixing enhancement over a wide range of temperatures. These actuators have been used successfully in high Reynolds number, high-speed unheated jets. The facility consists of an axisymmetric jet with different nozzle blocks of exit diameter of 2.54 cm and variable jet temperature in an anechoic chamber. The focus of this paper is on a high subsonic (M{sub j}=0.9) jet. Twelve experiments with various forcing azimuthal modes (m=0, 1, and {+-}1) and temperatures (T{sub o}/T{sub a}=1.0, 1.4, and 2.0) at a fixed forcing Strouhal number (St{sub DF}=0.3) have been conducted and PIV results compared with the baseline results to characterize the effectiveness of LAFPAs for mixing enhancement. Centerline velocity and turbulent kinetic energy as well as jet width are used for determining the LAFPAs' effectiveness. The characteristics of large-scale structures are analyzed through the use of Galilean streamlines and swirling strength. Across the range of temperatures collected, the effectiveness of LAFPAs improves as temperature increases. Possible reasons for the increase in effectiveness are discussed.

Kearney-Fischer, M.; Kim, J.-H.; Samimy, M. [Department of Mechanical Engineering, Gas Dynamics and Turbulence Laboratory, Ohio State University (GDTL/OSU), 2300 West Case Road, Columbus, Ohio 43235-7531 (United States)

2009-09-15

216

Local stability effects of plasma actuation on a zero pressure gradient boundary layer  

NASA Astrophysics Data System (ADS)

The effects of plasma actuation in a flat plate boundary layer with zero pressure gradient have been simulated. Based on these simulations, non-dimensional parameters and a combined wall jet/boundary layer model of the velocity profile have been developed. A parametric study using local linear stability analysis has been performed to examine the hydrodynamic stability of the velocity profiles created through this model. Convective and absolute instability mechanisms are found to be important, some of which have not been previously documented. Neutral stability curves have been computed for the different instabilities, and when put in terms of the shape factor, they still compare favorably with reported canonical results, indicating that the critical Reynolds number is primarily a function of the shape factor. These results are also discussed in relation to existing experimental results as well as with respect to their implementation.

Riherd, Mark; Roy, Subrata; Balachandar, S.

2013-04-01

217

Local stability effects of plasma actuation on a zero pressure gradient boundary layer  

NASA Astrophysics Data System (ADS)

The effects of plasma actuation in a flat plate boundary layer with zero pressure gradient have been simulated. Based on these simulations, non-dimensional parameters and a combined wall jet/boundary layer model of the velocity profile have been developed. A parametric study using local linear stability analysis has been performed to examine the hydrodynamic stability of the velocity profiles created through this model. Convective and absolute instability mechanisms are found to be important, some of which have not been previously documented. Neutral stability curves have been computed for the different instabilities, and when put in terms of the shape factor, they still compare favorably with reported canonical results, indicating that the critical Reynolds number is primarily a function of the shape factor. These results are also discussed in relation to existing experimental results as well as with respect to their implementation.

Riherd, Mark; Roy, Subrata; Balachandar, S.

2014-02-01

218

On the Vortex Dynamic of Airflow Reattachment Forced by a Single Non-thermal Plasma Discharge Actuator  

Microsoft Academic Search

Commercial and military aircrafts or miniature aerial vehicles can suffer from massive flow separation when high angles of\\u000a attack are required. Single dielectric barrier discharge (DBD) actuators have demonstrated their capability of controlling\\u000a such a separated flow at low external velocity. However, the processes resulting in the improvement of the flight performances\\u000a remain unclear. In the present study, the reattachment

Nicolas Benard; Eric Moreau

2011-01-01

219

Nonintrusive microwave diagnostics of collisional plasmas in Hall thrusters and dielectric barrier discharges  

NASA Astrophysics Data System (ADS)

This research presents a numerical framework for diagnosing electron properties in collisional plasmas. Microwave diagnostics achieved a significant level of development during the middle part of the last century due to work in nuclear weapons and fusion plasma research. With the growing use of plasma-based devices in fields as diverse as space propulsion, materials processing and fluid flow control, there is a need for improved, flexible diagnostic techniques suitable for use under the practical constraints imposed by plasma fields generated in a wide variety of aerospace devices. Much of the current diagnostic methodology in the engineering literature is based on analytical diagnostic, or forward, models. The Appleton-Hartree formula is an oft-used analytical relation for the refractive index of a cold, collisional plasma. Most of the assumptions underlying the model are applicable to diagnostics for plasma fields such as those found in Hall Thrusters and dielectric barrier discharge (DBD) plasma actuators. Among the assumptions is uniform material properties, this assumption is relaxed in the present research by introducing a flexible, numerical model of diagnostic wave propagation that can capture the effects of spatial gradients in the plasma state. The numerical approach is chosen for its flexibility in handling future extensions such as multiple spatial dimensions to account for scattering effects when the spatial extent of the plasma is small relative to the probing beam's width, and velocity dependent collision frequency for situations where the constant collision frequency assumption is not justified. The numerical wave propagation model (forward model) is incorporated into a general tomographic reconstruction framework that enables the combination of multiple interferometry measurements. The combined measurements provide a quantitative picture of the spatial variation in the plasma properties. The benefit of combining multiple measurements in a coherent way (solving the inverse problem for the material properties) is the reconstruction provides a stronger empirical constraint on the predictions of high-fidelity predictive simulations than multiple un-reconstructed measurements in isolation. Use of the model for reconstructions informs the choice of numerical discretization technique. The model must be fast, low-storage and accurate to be useful for computing reconstructions. An important part of experimental work is error analysis, or uncertainty quantification. This becomes more difficult as sophistication of the measurement models increase. This research presents an uncertainty quantification technique based on complex-step sensitivity derivatives that is particularly well-suited for error propagation in sophisticated partial differential equation (PDE)-based measurement models, because it requires only trivial changes to the PDE solver to implement.

Stults, Joshua

220

Preliminary Development of a Computational Model of a Dielectric Barrier Discharge.  

National Technical Information Service (NTIS)

A 1D model of a plasma actuator has been developed. The plasma actuator is modeled as a dielectric barrier discharge (DBD) and is based on the numerical solution of the electron and ion conservation of mass and momentum equations, in the drift-diffusion r...

W. M. Hilbun B. J. Case

2004-01-01

221

Effects of Plasma Aerodynamic Actuation on Corner Separation in a Highly Loaded Compressor Cascade  

NASA Astrophysics Data System (ADS)

This paper reports experimental results on the effects of plasma aerodynamic actuation (PAA) on corner separation control in a highly loaded, low speed, linear compressor cascade. Total pressure loss coefficient distribution was adopted to evaluate the corner separation control effect in wind tunnel experiments. Results of pressure measurements and particle image velocimetry (PIV) show that the control effect of pitch-wise PAA on the endwall is much better than that of stream-wise PAA on the suction surface. When both the pitch-wise PAA on the endwall and stream-wise PAA on the suction surface are turned on simultaneously, the control effect is the best among all three PAA types. The mechanisms of nanosecond discharge and microsecond discharge PAA are different in corner separation control. The control effect of microsecond discharge PAA turns out better with the increase of discharge voltage and duty cycle. Compared with microsecond discharge PAA, nanosecond discharge PAA is more effective in preventing corner separation when the freestream velocity increases. Frequency is one of the most important parameters in plasma flow control. The optimum excitation frequency of microsecond discharge PAA is 500 Hz, which is different from the frequency corresponding to the case with a Strouhal number of unity.

Wang, Xuede; Zhao, Xiaohu; Li, Yinghong; Wu, Yun; Zhao, Qin

2014-03-01

222

Characteristics of dielectric barrier discharge plasmas in atmospheric humid air  

NASA Astrophysics Data System (ADS)

Atmospheric pressure plasmas have a great advantage for industrial applications such as surface modifications, sterilization and film preparation. In particular, reactive plasmas including OH radicals can be generated in humid air. On the other hand, it is known that dielectric barrier discharge (DBD) plasmas in air are strongly affected by humidity. In this study, a twisted pair sample is used as a DBD electrode. The twisted pair consists of two enameled wires, and it is installed in a climate chamber to control ambient temperature and humidity. Repetitive impulse voltage pulses were applied to the twisted pair to produce DBD plasmas. Light emission, electromagnetic wave and current pulses were used to detect discharge activities. The discharge inception voltage (DIV) is basically determined by Paschen curve in air, however, the DIV was decreased by increasing the humidity. In addition, it was found that there were largely scattered data of DIV at the low humidity condition. After the pre-discharges, the DIV reached to the steady state value. On the other hand, there was no scattering of the observed DIV at the high humidity condition. Measurements of surface potential of the sample after the discharge show these behaviors could be explained by surface charge accumulation on the enameled wire. It is noted that there was no fluctuation in the DIV data in the case of unipolar voltage pulse.

Fukuda, Y.; Fukui, K.; Iwami, R.; Matsuoka, Y.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2012-10-01

223

Inter- and intracellular signaling induced by magnetomechanical actuation of plasma membrane channels  

NASA Astrophysics Data System (ADS)

Magnetic particles allow for non-invasive control over their spatial orientation and motion which makes them ideally suitable for studying real-time processes in living cells. Lithographically defined ferromagnetic disks with spin-vortex ground state have the advantage of zero net magnetization in remanence. This eliminates long-range magnetic forces which otherwise lead to the interaction between particles and their agglomeration. Moreover, magnetically soft permalloy particles have high magnetization of saturation thus requiring very low external field for inducing high magnetomotive force, compared to superparamagnetic particles. Our group has previously demonstrated that micron-sized permalloy disks can be used for destruction of cancer cells (D.-H. Kim, E. A. Rozhkova, I. V. Ulasov, S. D. Bader, T. Rajh, M. S. Lesniak, V. Novosad, Nat. Mater. 9, 165-171 (2010). In this work, we investigate the effects of magnetomechanical stimulation of human brain cancer cells with these particles. It will be shown that the actuation of ion channels in cell plasma membrane induces, on the one hand side, intracellular signaling triggering cell apoptosis and, on the other hand, it stimulates the energy transfer between the cells which carries the information about apoptotic signal.

Vitol, Elina A.; Rozhkova, Elena A.; Novosad, Valentyn; Bader, Samuel D.

2012-02-01

224

MERCURY OXIDIZATION IN NON-THERMAL PLASMA BARRIER DISCHARGE SYSTEM  

SciTech Connect

In the past decade, the emission of toxic elements from human activities has become a matter of great public concern. Hg, As, Se and Cd typically volatilize during a combustion process and are not easily caught with conventional air pollution control techniques. In addition, there is no pollution prevention technique available now or likely be available in the foreseeable future that can prevent the emission of these trace elements. These trace elements pose additional scientific challenge as they are present at only ppb levels in large gas streams. Mercury, in particular, has attracted significant attention due to its high volatility, toxicity and potential threat to human health. In the present research work, a non-thermal plasma dielectric barrier discharge technique has been used to oxidize Hg{sup 0}(g) to HgO. The basic premise of this approach is that Hg{sup 0} in vapor form cannot be easily removed in an absorption tower whereas HgO as a particulate is amiable to water scrubbing. The work presented in this report consists of three steps: (1) setting-up of an experimental apparatus to generate mercury vapors at a constant rate and modifying the existing non-thermal plasma reactor system, (2) solving the analytical challenge for measuring mercury vapor concentration at ppb level, and (3) conducting experiments on mercury oxidation under plasma conditions to establish proof of concept.

V.K. Mathur

2003-02-01

225

Steady control of laminar separation over airfoils with plasma sheet actuators  

Microsoft Academic Search

This work analyzes the effects produced by an EHD actuator on the flow around an airfoil at low Re numbers (Re?104). The analysis is undertaken from flow visualizations and measurements of the surface pressure distributions. The experiments indicate that, for low Re number, the effects of the actuation depend on the power added to the flow and on the relative

Roberto Sosa; Guillermo Artana

2006-01-01

226

Development and characterization of plasma actuators for high-speed jet control  

Microsoft Academic Search

Active control of high Reynolds number and high-speed jets has been hampered due to the lack of suitable actuators. Some of the attributes that would make an actuator suitable for such flows are: high amplitude and bandwidth; small size for distribution around the jet; phase-locking ability for jet azimuthal mode forcing; and sufficient ruggedness for hot jets. We have been

M. Samimy; I. Adamovich; B. Webb; J. Kastner; J. Hileman; S. Keshav; P. Palm

2004-01-01

227

Modification of Polyimide in Barrier Discharge Air-Plasmas: Chemical and Morphological Effects  

Microsoft Academic Search

Chemical and physical modifications of polyimide (PI) surfaces caused by an air plasma have been studied. The plasma-induced surface changes of PI were investigated by using a local dielectric barrier discharge (DBD) in air at atmospheric pressure and room temperature as a function of the plasma exposure time and plasma power, while the excitation frequency was kept constant at about

R. Seeböck; H. Esrom; M. Charbonnier; M. Romand

2000-01-01

228

Efficiency enhancement of a dielectric barrier plasma discharge by dielectric barrier optimization  

SciTech Connect

The characteristic feature of a dielectric barrier discharge (DBD) is the dielectric barrier placed between the electrodes. In the present work, the influence of the dielectric barrier to the properties of a DBD in air was investigated. Spectroscopic characterization of the DBD and electrical measurements were carried out. It was shown that the efficiency of a DBD can be considerably improved by optimizing the dielectric barrier. The dielectric material should possess an appropriate relative permittivity and thickness. For thin dielectric barriers, a high secondary emission coefficient becomes important. Additionally, the use of only one dielectric barrier is advantageous.

Meiners, Annette; Leck, Michael [Department of Science and Technology, University of Applied Science and Arts, Von-Ossietzky-Str. 99, 37085 Goettingen (Germany); Abel, Bernd [Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry, University Leipzig, Linnestr. 2, 04103 Leipzig (Germany)

2010-11-15

229

Packaging barrier films deposited on PET by PECVD using a new high density plasma source  

Microsoft Academic Search

Barrier films for packaging applications are deposited by plasma enhanced chemical vapor deposition (PECVD) on PET film using a new, high density plasma source. The new source, termed the Penning Discharge Plasma source, implements a novel magnetic field\\/electrode configuration that confines the electron Hall current in an endless loop adjacent to the substrate. By confining the Hall current, a dense,

John Madocks; Jennifer Rewhinkle; Loren Barton

2005-01-01

230

Surface discharge plasma actuator driven by a pulsed 13.56 MHz-5 kHz voltage waveform  

NASA Astrophysics Data System (ADS)

The effect of incorporating pulses of radio-frequency (rf: 13.56 MHz) voltage into the driving waveform of a surface discharge plasma actuator is investigated. Rf voltage is applied to the actuator to increase the production of ions and thereby increase the thrust that is generated by the discharge. This waveform is coupled to the powered electrode in 5 µs pulses and combined with a relatively low-frequency (LF) 5 kHz sinusoid to form a pulsed 13.56 MHz-5 kHz (rf-LF) driving voltage. Measurements of the applied voltage, rf and LF currents, effective power, and velocity field of the surrounding air are undertaken at atmospheric pressure. The thrust that is generated using the rf-LF waveform is estimated from the velocity fields using a momentum balance and is found to increase for increasing rf voltage when the LF voltage remains constant. Maximum thrust is achieved when the rf pulses are positioned at the LF voltage minima and this suggests the importance of negative ions. The efficacy of rf-LF actuation is investigated by comparing the thrust that is generated per unit increase in peak voltage with that obtained using an LF-driven discharge.

Dedrick, J.; Im, S.; Cappelli, M. A.; Boswell, R. W.; Charles, C.

2013-10-01

231

Inelastic Deformation of Freestanding Plasma-sprayed Thermal Barrier Coatings  

NASA Astrophysics Data System (ADS)

A fundamental study for an inelastic deformation of freestanding plasma-sprayed thermal barrier coatings (TBCs) has been conducted. Cantilever-type bending tests are carried out to obtain a stress-strain curve of the freestanding ceramic coating peeled from the TBC coated sample by an electrochemical treatment. In order to investigate about an inelastic deformation and its mechanism appeared in the sample, in-situ scanning electron microscope (SEM) observation is performed by means of a small tensile testing device that can be inserted into the SEM vacuum chamber. The bending test result indicated that the coating deforms with a nonlinear behavior under a monotonic loading and with a hysteresis loop under cyclic loading, in spite of that it is ceramic material. In-flight particle velocity in the spraying parameter affected the stress-strain curve significantly. In-situ SEM observation during the bending test revealed that sliding at boundary between splats plays an important role in an inelastic deformation.

Arai, Masayuki; Wu, Xiaohong; Fujimoto, Koji

232

Plasma Surface Modification of Polymer Backsheets: Origins of Future Interfacial Barrier/Backsheet Failure  

SciTech Connect

Flexible polymer substrates coated with inorganic oxide moisture barriers are a potential replacement for glass backsheets in thin film PV modules. Silicon oxynitride (SiOxNy) deposited by PECVD on polyethylene terephthalate (PET) represents one potential new backsheet candidate. Barrier deposition runs at NREL have typically included a nitrogen-rich plasma pretreatment prior to actual barrier deposition with the intention of cleaning the PET surface as well as enhancing adhesion of the SiOxNy barrier film to PET; however, test coupons of PET/barrier/EVA/TPE failed after damp heat exposure. PET substrates exposed to plasma conditions similar to those used in pre-treatment were examined by X-ray photoelectron spectroscopy (XPS) to reveal new low molecular weight PET fragments are created which are volatile upon heating and water soluble. Failure analysis of the coupons determined that the moisture barrier is, in fact, transferred to the encapsulant side.

Pankow, J. W.; Glick, S. H.

2005-11-01

233

In-situ formation of multiphase air plasma sprayed barrier coatings for turbine components  

SciTech Connect

A turbine component (10), such as a turbine blade, is provided which is made of a metal alloy (22) and a base, planar-grained thermal barrier layer (28) applied by air plasma spraying on the alloy surface, where a heat resistant ceramic oxide overlay material (32') covers the bottom thermal barrier coating (28), and the overlay material is the reaction product of the precursor ceramic oxide overlay material (32) and the base thermal barrier coating material (28).

Subramanian, Ramesh (Oviedo, FL)

2001-01-01

234

The various dielectric barrier discharges lamps and plasma panel prototype designs developed in VNIIEF  

Microsoft Academic Search

The various dielectric barrier discharges (DBD) lamps and plasma panel prototype designs developed in VNIIEF are presented. The lamps given, depending on a configuration of electrodes, it is possible to divide into three types: 1) a lamp with a plane-parallel configuration of the electrodes, intended for researching of barrier discharges parameters and UV-radiation of various mixes. The design of this

V. M. Tsvetkov; A. A. Pikulev

2008-01-01

235

Spatially resolved spectroscopic measurements of a dielectric barrier discharge plasma jet applicable for soft ionization  

Microsoft Academic Search

An atmospheric pressure microplasma ionization source based on a dielectric barrier discharge with a helium plasma cone outside the electrode region has been developed for liquid chromatography\\/mass spectrometry and as ionization source for ion mobility spectrometry. It turned out that dielectric barrier discharge ionization could be regarded as a soft ionization technique characterized by only minor fragmentation similar to atmospheric

S. B. Olenici-Craciunescu; S. Müller; A. Michels; V. Horvatic; C. Vadla; J. Franzke

2011-01-01

236

Fatigue testing of plasma-sprayed thermal barrier coatings, volume 2  

NASA Technical Reports Server (NTRS)

A plasma sprayed thermal barrier coating for diesel engines were fatigue tested. Candidate thermal barrier coating materials were fatigue screened and a data base was generated for the selected candidate material. Specimen configurations are given for the bend fatigue tests, along with test setup, specimen preparation, test matrix and procedure, and data analysis.

Cruse, T. A.; Nagy, A.; Popelar, C. F.

1990-01-01

237

Laser drilling of cooling holes through plasma sprayed thermal barrier coatings  

Microsoft Academic Search

Laser drilling is a non-contact process that can be used to form small holes in a wide variety of materials with a high degree of precision and reproducibility. The advantages of being able to drill difficult materials, specifically superalloys and ceramics, are exploited in the laser drilling of cooling holes in thermal barrier coated superalloys. Plasma sprayed thermal barrier coatings

K. T. Voisey; T. W. Clyne

2004-01-01

238

The dielectric barrier discharge — a powerful microchip plasma for diode laser spectrometry  

Microsoft Academic Search

The dielectric barrier discharge plasma is presented as a powerful microchip source for analytical spectrometry. The dielectric barrier discharge is characterized by small size, low electric power (<1 W), low gas temperature (approx. 600 K) and excellent dissociation capability for molecular species, such as CCl2F2, CClF3 and CHClF2. It has been used here in the plasma modulation diode laser absorption

M. Miclea; K. Kunze; G. Musa; J. Franzke; K. Niemax

2001-01-01

239

Influence of heat treatment on nanocrystalline zirconia powder and plasma-sprayed thermal barrier coatings  

Microsoft Academic Search

Nanostructured zirconia top coat was deposited by air plasma spray and NiCoCrAlTaY bond coat was deposited on Ni substrate by low pressure plasma spray. Nanostructured and conventional thermal barrier coatings were heat-treated at temperature varying from 1050 to 1 250 °C for 2-20 h. The results show that obvious grain growth was found in both nanostructured and conventional thermal barrier

Xian-liang JIANG; Chun-bo LIU; Min LIU; Hui-zhao ZHU

2010-01-01

240

Toward Noise Mitigation in High Speed and High Reynolds Number Jets Using Plasma Actuators  

Microsoft Academic Search

5 . Eight actuators, distributed azimuthally inside the nozzle, near the nozzle exit, were used to excite various azimuthal modes of the jet over a large frequency range (StDF of 0.1 to 5.0). Dynamic pressure measurements were used to investigate the growth and decay of perturbations and instability waves in the flow, PIV measurements were used to evaluate the effects

M. Samimy; I. Adamovich; Y. Utkin; J. Kastner

2006-01-01

241

Barrier and electrode properties of high Tc Josephson junctions formed by a plasma discharge process  

Microsoft Academic Search

The influence of rf discharge in CF4 and O2 gases on the properties of thin YBCO films and edge junctions was investigated by transport measurements and Auger spectroscopy. It was found that oxygen plasma of short duration can serve as a cleaning step before the formation of the barrier. In contrast, CF4 plasma tends to substitute oxygen in the superconducting

E. Aharoni; G. Koren; E. Polturak; D. Cohen

1993-01-01

242

Plasma cleaning of “endless” substrates by use of a tandem dielectric barrier discharge  

Microsoft Academic Search

In this work a tandem dielectric barrier discharge plasma source for cleaning of elongated (“endless”), electrically conducting substrates is presented. It is powered by novel resonant power supply allowing high power densities up to 50 W\\/cm3. In investigated configuration, the conducting material is part of the plasma source. Even though no electrical currents leave the system. The used gases are

M. Teschke; D. Korzec; E. G. Finantu-Dinu; J. Engemann

2005-01-01

243

Understanding crack formation in plasma sprayed thermal barrier coatings and their effects on coating properties  

Microsoft Academic Search

As a key microstructural feature of plasma sprayed thermal barrier coatings (TBCs), microcracks determine the performance and service lifetimes of the coatings by influencing their thermal conductivity and compliance. The goal of this research is to obtain a fundamental understanding of crack formation in plasma sprayed microstructures, and their effect on mechanical and thermal properties through a synergistic combination of

Guosheng Ye

2004-01-01

244

Odor Removal Characteristics of Barrier-Type Packed-Bed Nonthermal Plasma Reactor  

Microsoft Academic Search

Odor control has gained importance for ensuring a comfortable living environment. In this paper, the authors report the experimental results of a study of the detailed characteristics of a barrier-type packed-bed nonthermal plasma reactor used for odor control. This plasma reactor has been widely used for volatile organic compound (VOC) decomposition and NOx reduction. The reactor is energized by a

Masaaki Okubo; Hidetaka Kametaka; Keiichiro Yoshida; Toshiaki Yamamoto

2007-01-01

245

Plasma methane conversion using dielectric-barrier discharges with zeolite A  

Microsoft Academic Search

Experimental investigation on plasma methane conversion in the presence of carbon dioxide using dielectric-barrier discharges (DBDs) has been conducted. Zeolite A has been applied to inhibit the formation of carbon black and plasma-polymerized film during such plasma methane conversion. A co-generation of syngas, light hydrocarbons and liquid fuels has been achieved. The conversions and selectivities are determined by the CH4\\/CO2

Tao Jiang; Yang Li; Chang-jun Liu; Gen-hui Xu; Baldur Eliasson; Bingzhang Xue

2002-01-01

246

Recent Developments in the Field of Plasma-Sprayed Thermal Barrier Coatings  

Microsoft Academic Search

Thermal barrier coating (TBC) systems are widely used in gas turbines on thermally highly loaded parts as blades, vanes or combustion chamber to improve the performance of the engines. The standard plasma-sprayed systems consist of a vacuum plasma-sprayed (VPS) MCrAlY (M = Ni or Co) and an atmospherically plasma sprayed (APS) ceramic top layer made of yttria partially stabilised zirconia

R. Vaßen; J.-E. Döring; M. Dietrich; H. Lehmann; D. Stöver

247

Thermal behavior of bovine serum albumin after exposure to barrier discharge helium plasma jet  

NASA Astrophysics Data System (ADS)

Non-thermal plasma jets at atmospheric pressure are useful tools nowadays in plasma medicine. Various applications are tested such as cauterization, coagulation, wound healing, natural and artificial surfaces decontamination, and sterilization. In order to know more about the effects of gas plasma on biological supramolecules, we exposed protein powders to a barrier discharge helium plasma jet. Then, spectroscopic investigations were carried out in order to obtain information on protein secondary, tertiary, and quaternary structures. We obtained a reduction of the protein alpha-helix content after the plasma exposure and a different behavior, for both thermal denaturation/renaturation kinetics and thermal aggregation process.

Jijie, R.; Pohoata, V.; Topala, I.

2012-10-01

248

Starting, Travelling & Colliding Vortices: DBD Plasma in Quiescent Air  

Microsoft Academic Search

Development and interaction of starting vortices initiated by Dielectric Barrier Discharge (DBD) plasma actuators in quiescent air are illustrated in the attached fluid dynamics videos. These include a series of smoke flow visualisations, showing the starting vortices moving parallel or normal to the wall at several different actuator configurations.

Richard Whalley; Kwing-So Choi

2009-01-01

249

Plasma Surface Modification of Polymer Backsheets: Origins of Future Interfacial Barrier/Backsheet Failure (Poster)  

SciTech Connect

Flexible polymer substrates coated with inorganic oxide moisture barriers are a potential replacement for glass backsheets in thin-film PV (photovoltaic) modules. Silicon oxynitride (SiO{sub x}N{sub y}) deposited by plasma enhanced chemical vapor deposition (PECVD) on polyethylene terephthalate (PET) represents one potential new backsheet candidate. Barrier deposition runs at NREL have included a nitrogen-rich plasma pretreatment prior to barrier deposition with the intention of cleaning the PET surface and enhancing adhesion of the SiO{sub x}N{sub y} barrier film to PET; however, test coupons of PET/barrier/EVA/TPE failed after damp-heat exposure. (EVA is ethylene vinyl acetate and TPE is Tedlar{reg_sign}-PET-EVA). PET substrates exposed to plasma conditions similar to those used in pretreatment were examined by X-ray photoelectron spectroscopy (XPS) to reveal that new low molecular weight PET fragments were created at the PET surface. These fragments are responsible for barrier/PET interfacial failure and barrier transfer to the EVA encapsulant side following damp heat exposure.

Pankow, J. W.; Glick, S. H.

2006-05-01

250

High quality plasma enhanced chemical vapour deposited silicon oxide gas barrier coatings on polyester films  

Microsoft Academic Search

Silicon oxide barrier coatings fabricated by a plasma enhanced chemical vapour deposition roll-to-roll process on polyester film have demonstrated impressive properties as a barrier to water vapour permeation. This study highlights the influence of the substrate on these coatings as we find that heat stabilised poly(ethylene terephthalate) (PET), with or without an additional acrylate primer layer, and poly(ethylene naphthalate) (PEN)

D. G. Howells; B. M. Henry; J. Madocks; H. E. Assender

2008-01-01

251

Thermal properties of plasma-sprayed functionally graded thermal barrier coatings  

Microsoft Academic Search

Plasma-sprayed thermal barrier coatings often have the problems of spallation and cracking in service owing to their poor bond strength and high residual stresses. Functionally graded thermal barrier coatings with a gradual compositional variation from heat resistant ceramics to fracture-resistant metals are proposed to mitigate these problems. In this paper, functionally graded yttria stabilized ZrO2\\/NiCoCrAlY coatings were prepared using pre-alloyed

K. A Khor; Y. W Gu

2000-01-01

252

Atmospheric Pressure Resistive Barrier Cold Plasma for Biological Decontamination  

Microsoft Academic Search

Summary form only given. We have investigated the non thermal resistive barrier gas discharge at atmospheric pressure for low temperature sterilization purposes. We have carried out electrical, chemical, optical, and biological studies on the discharge, with the intent of identifying the chemically and biologically active species produced. We have also demonstrated that effective decontamination can be achieved without causing any

I. Alexeff; S. Beebe; S. Parameswaran; M. Thiyagarajan; E. P. Michael; J. Dhanraj

2005-01-01

253

The various dielectric barrier discharges lamps and plasma panel prototype designs developed in VNIIEF  

NASA Astrophysics Data System (ADS)

The various dielectric barrier discharges (DBD) lamps and plasma panel prototype designs developed in VNIIEF are presented. The lamps given, depending on a configuration of electrodes, it is possible to divide into three types: 1) a lamp with a plane-parallel configuration of the electrodes, intended for researching of barrier discharges parameters and UV-radiation of various mixes. The design of this lamp allows changing electrodes and varying distance between them; 2) lamps of cylindrical geometry. The external electrode is a spiral or a grid, and internal electrode is a metallic foil. Such design of lamps is the most widespread; 3) lamps with a planar configuration of electrodes. There are two types of lamps with a planar configuration of electrodes: 1) plasma panel prototypes and 2) lamps with ceramic barriers. Plasma panel prototypes are increased (in 50-100 times) copies of plasma display panels (PDP) and are intended for researching of the processes taking place in PDP. Using ceramic barriers of high capacity in DBD lamps allows receiving bigger power density of UV-radiation, than in case of glass (quartz) barriers.

Tsvetkov, V. M.; Pikulev, A. A.

2008-02-01

254

Tunable one-dimensional plasma photonic crystals in dielectric barrier discharge  

SciTech Connect

A tunable one-dimensional plasma photonic crystal is obtained by using a dielectric barrier discharge with two liquid electrodes. It is formed by the self-organization of the filaments, rather than that in an artificial array of electrodes. The dispersion relations of the plasma photonic crystals are calculated by solving the Helmholtz equation using a method analogous to Kronig-Penney's problem. The photonic band diagrams of the plasma photonic crystals are studied when changing the filling factor, the lattice constant, and the electron density, based on the experimental results. The critical electron density is given, beyond which the plasma photonic crystal will have a remarkable band structure.

Fan Weili; Dong Lifang [College of Physics Science and Technology, Hebei University, Baoding 071002 (China)

2010-07-15

255

Development of a stable dielectric-barrier discharge enhanced laminar plasma jet generated at atmospheric pressure  

NASA Astrophysics Data System (ADS)

A stable nonthermal laminar atmospheric-pressure plasma source equipped with dielectric-barrier discharge was developed to realize more efficient plasma generation, with the total energy consumption reduced to nearly 25% of the original. Temperature and emission spectra monitoring indicates that this plasma is uniform in the lateral direction of the jet core region. It is also found that this plasma contains not only abundant excited argon atoms but also sufficient excited N2 and OH. This is mainly resulted from the escape of abundant electrons from the exit, due to the sharp decrease of sustaining voltage and the coupling between ions and electrons.

Tang, Jie; Li, Shibo; Zhao, Wei; Wang, Yishan; Duan, Yixiang

2012-06-01

256

Development of a stable dielectric-barrier discharge enhanced laminar plasma jet generated at atmospheric pressure  

SciTech Connect

A stable nonthermal laminar atmospheric-pressure plasma source equipped with dielectric-barrier discharge was developed to realize more efficient plasma generation, with the total energy consumption reduced to nearly 25% of the original. Temperature and emission spectra monitoring indicates that this plasma is uniform in the lateral direction of the jet core region. It is also found that this plasma contains not only abundant excited argon atoms but also sufficient excited N{sub 2} and OH. This is mainly resulted from the escape of abundant electrons from the exit, due to the sharp decrease of sustaining voltage and the coupling between ions and electrons.

Tang Jie; Li Shibo; Zhao Wei; Wang Yishan [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an (China); Duan Yixiang [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an (China); Research Center of Analytical Instrumentation, Sichuan University, Chengdu (China)

2012-06-18

257

Inactivation of Microcystis aeruginosa using dielectric barrier discharge low-temperature plasma  

SciTech Connect

The efficiency of Microcystis aeruginosa plasma inactivation was investigated using dielectric barrier discharge low-temperature plasma. The inactivation efficiency was characterized in terms of optical density. The influence of electrical and physicochemical parameters on M. aeruginosa inactivation was studied to determine the optimal experimental conditions. The influence of active species was studied. The proliferation of the M. aeruginosa cells was significantly decreased under plasma exposure. The morphologic changes in M. aeruginosa were characterized under scanning electron microscopy. These results suggest that the low-temperature plasma technology is a promising method for water pollution control.

Pu, Sichuan [School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049 (China)] [School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049 (China); Chen, Jierong [Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049 (China)] [Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049 (China); Wang, Gang [BMEI CO., LTD, Beijing 100027 (China)] [BMEI CO., LTD, Beijing 100027 (China); Li, Xiaoyong [School of Science, Xi'an Jiaotong University, Xi'an 710049 (China)] [School of Science, Xi'an Jiaotong University, Xi'an 710049 (China); Ma, Yun [School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049 (China) [School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049 (China); College of Chemistry and Chemical Engineering, Xi'an Shiyou University, Xi'an 710065 (China)

2013-05-13

258

Inactivation of Microcystis aeruginosa using dielectric barrier discharge low-temperature plasma  

NASA Astrophysics Data System (ADS)

The efficiency of Microcystis aeruginosa plasma inactivation was investigated using dielectric barrier discharge low-temperature plasma. The inactivation efficiency was characterized in terms of optical density. The influence of electrical and physicochemical parameters on M. aeruginosa inactivation was studied to determine the optimal experimental conditions. The influence of active species was studied. The proliferation of the M. aeruginosa cells was significantly decreased under plasma exposure. The morphologic changes in M. aeruginosa were characterized under scanning electron microscopy. These results suggest that the low-temperature plasma technology is a promising method for water pollution control.

Pu, Sichuan; Chen, Jierong; Wang, Gang; Li, Xiaoyong; Ma, Yun

2013-05-01

259

Polishing of Optical Media by Dielectric Barrier Discharge Inert Gas Plasma at Atmospheric Pressure  

NASA Astrophysics Data System (ADS)

In this paper, surface smoothing of optical glasses, glass ceramic and sapphire using a low-power dielectric barrier discharge inert gas plasma at atmospheric pressure is presented. For this low temperature treatment method, no vacuum devices or chemicals are required. It is shown that by such plasma treatment the micro roughness and waviness of the investigated polished surfaces were significantly decreased, resulting in a decrease in surface scattering. Further, plasma polishing of lapped fused silica is introduced. Based on simulation results, a plasma physical process is suggested to be the underlying mechanism for initialising the observed smoothing effect.

Gerhard, C.; Weihs, T.; Luca, A.; Wieneke, S.; Viöl, W.

2013-12-01

260

Technical note - Plasma-sprayed ceramic thermal barrier coatings for smooth intermetallic alloys  

NASA Technical Reports Server (NTRS)

A new approach for plasma spray deposition of ceramic thermal barrier coatings directly to smooth substrates is described. Ceramic thermal barrier coatings were directly applied to substrates that had been coated with low-pressure plasma sprayed NiCrAlY bond coats and then centerless ground to simulate a smooth oxidation-resistant substrate. As the high-temperature oxidation behavior of NiAl+Zr is superior to that of MCrALY alloy, the bond coat is not required for oxidation resistance.

Miller, R. A.; Doychak, J.

1992-01-01

261

Technical note - Plasma-sprayed ceramic thermal barrier coatings for smooth intermetallic alloys  

NASA Astrophysics Data System (ADS)

A new approach for plasma spray deposition of ceramic thermal barrier coatings directly to smooth substrates is described. Ceramic thermal barrier coatings were directly applied to substrates that had been coated with low-pressure plasma sprayed NiCrAlY bond coats and then centerless ground to simulate a smooth oxidation-resistant substrate. As the high-temperature oxidation behavior of NiAl+Zr is superior to that of MCrALY alloy, the bond coat is not required for oxidation resistance.

Miller, R. A.; Doychak, J.

1992-09-01

262

Visualization by discharge illumination technique and modification by plasma actuator of rarefied Mach 2 airflow around a cylinder  

NASA Astrophysics Data System (ADS)

The use of plasma actuators for flow control has received considerable attention in recent years. This kind of device seems to be an appropriate means of raising abilities in flow control thanks to total electric control, no moving parts and a fast response time. The experimental work presented here shows, firstly, the non-intrusive character of the visualization of the density field of an airflow around a cylinder obtained using a plasma luminescence technique. Experiments are made in a continuous supersonic wind tunnel. The static pressure in the flow is 8 Pa, the mean free path is about 0.3 mm and the airflow velocity is 510 m s-1. Pressure measurements obtained by means of glass Pitot tube without the visualization discharge are proposed. Measured and simulated pressure profiles are in good agreement in the region near the cylinder. There is good correlation between numerical simulations of the supersonic flow field, analytical model predictions and experimental flow visualizations obtained by a plasma luminescence technique. Consequently, we show that the plasma luminescence technique is non-intrusive. Secondly, the effect of a dc discharge on a supersonic rarefied air flow around a cylinder is studied. An electrode is flush mounted on the cylinder. Stagnation pressure profiles are examined for different electrode positions on the cylinder. A shock wave modification depending on the electrode location is observed. The discharge placed at the upstream stagnation point induces an upstream shift of the bow shock, whereas a modification of the shock wave shape is observed when it is placed at 45° or 90°.

Leger, L.; Sellam, M.; Barbosa, E.; Depussay, E.

2013-06-01

263

Unraveling quasiperiodic relaxations of transport barriers with gyrokinetic simulations of tokamak plasmas.  

PubMed

The generation and dynamics of transport barriers governed by sheared poloidal flows are analyzed in flux-driven 5D gyrokinetic simulations of ion temperature gradient driven turbulence in tokamak plasmas. The transport barrier is triggered by a vorticity source that polarizes the system. The chosen source captures characteristic features of some experimental scenarios, namely, the generation of a sheared electric field coupled to anisotropic heating. For sufficiently large shearing rates, turbulent transport is suppressed and a transport barrier builds up, in agreement with the common understanding of transport barriers. The vorticity source also governs a secondary instability--driven by the temperature anisotropy (T(?)?T(?)). Turbulence and its associated zonal flows are generated in the vicinity of the barrier, destroying the latter due to the screening of the polarization source by the zonal flows. These barrier relaxations occur quasiperiodically, and generically result from the decoupling between the dynamics of the barrier generation, triggered by the source driven sheared flow, and that of the crash, triggered by the secondary instability. This result underlines that barriers triggered by sheared flows are prone to relaxations whenever secondary instabilities come into play. PMID:24138245

Strugarek, A; Sarazin, Y; Zarzoso, D; Abiteboul, J; Brun, A S; Cartier-Michaud, T; Dif-Pradalier, G; Garbet, X; Ghendrih, Ph; Grandgirard, V; Latu, G; Passeron, C; Thomine, O

2013-10-01

264

Plasma sprayed ceramic thermal barrier coating for NiAl-based intermetallic alloys  

NASA Technical Reports Server (NTRS)

A thermal barrier coating system consists of two layers of a zirconia-yttria ceramic. The first layer is applied by low pressure plasma spraying. The second layer is applied by conventional atmospheric pressure plasma spraying. This facilitates the attachment of a durable thermally insulating ceramic coating directly to the surface of a highly oxidation resistant NiAl-based intermetallic alloy after the alloy has been preoxidized to promote the formation of a desirable Al2O3 scale.

Miller, Robert A. (inventor); Doychak, Joseph (inventor)

1994-01-01

265

Thermal barrier coatings on turbine blades by plasma spraying with improved cooling  

Microsoft Academic Search

Turbine blades were coated with a thermal barrier coating system consisting of an MCrAlY bond coat about 100 micron thick deposited by Low Pressure Plasma Spraying (LPPS) and a 300 micron thick ZrO2-7 wt pct Y2O3 top coat. The latter was manufactured by both Atmosphere and Temperature Controlled Spraying (ATCS) and Air Plasma Spraying using internal air cooling through the

T. Cosack; L. Pawlowski; S. Schneiderbanger; S. Sturlese

1992-01-01

266

Development of a micromechanical life prediction model for plasma sprayed thermal barrier coatings  

Microsoft Academic Search

A widely used method to produce thermal barrier coating (TBC) systems is the vacuum plasma spraying of a highly dense bondcoat layer with a defined surface roughness and the atmospheric plasma spraying (APS) of a porous (10–15%) Y2O3-stabilized zirconia top coat. In thermal cycling operation these systems often fail by crack initiation and propagation close to the bondcoat–top coat interface.

R. Vaßen; G. Kerkhoff; D. Stöver

2001-01-01

267

Thermal barrier coatings on turbine blades by plasma spraying with improved cooling  

Microsoft Academic Search

Turbine blades were coated with a thermal barrier coating system consisting of an MCrAlY bond coat about 100 [mu]m thick deposited by Low-Pressure Plasma Spraying (LPPS) and a 300 [mu]m thick ZrO[sub 2]-7 wt.% Y[sub 2]O[sub 3] top coat. The latter was manufactured by both Atmosphere and Temperature Controlled Spraying (ATCS) and Air Plasma Spraying (APS) using internal air cooling

T. Cosack; S. Schneiderbanger; L. Pawlowski; S. Sturlese

1994-01-01

268

Origin of darkening in 8 wt% yttria-zirconia plasma-sprayed thermal barrier coatings  

Microsoft Academic Search

This paper reports on the origins of darkening of 8 wt% YâOâ-ZrOâ air plasma-sprayed (APS) and low-pressure plasma-sprayed (LPPS) thermal barrier coatings (TBC) studied using x-ray photoelectron spectroscopy. The change of valence states of zirconium, due to the reduction of ZrOâ to ZrâOâ, was responsible for darkening of TBC. Quantification of Zr{sup 3+} oxide was related both to the black

Gabriel Maria Ingo

1991-01-01

269

Towards durable thermal barrier coatings with novel microstructures deposited by solution-precursor plasma spray  

Microsoft Academic Search

The feasibility of a new processing method—solution precursor plasma spray (SPPS)—for the deposition of ZrO2-based thermal barrier coatings (TBCs) with novel structures has been demonstrated. These desirable structures in the new TBCs appear to be responsible for their improved thermal cycling life relative to conventional plasma-sprayed TBCs. Preliminary results from experiments aimed at understanding the SPPS deposition mechanisms suggest that

N. P. Padture; K. W. Schlichting; T. Bhatia; A. Ozturk; B. Cetegen; E. H. Jordan; M. Gell; S. Jiang; T. D. Xiao; P. R. Strutt; E Garc??a; P Miranzo; M. I Osendi

2001-01-01

270

Structure–property differences between supersonic and conventional atmospheric plasma sprayed zirconia thermal barrier coatings  

Microsoft Academic Search

Yttria-stabilized zirconia (YSZ) based thermal barrier coatings (TBCs) were deposited by high efficiency supersonic atmospheric plasma spraying (SAPS) system. The microstructure and thermal shock resistance of the SAPS-TBCs were investigated. As compared to conventional atmospheric plasma sprayed TBCs (APS-TBCs) with the same composition, the microstructure of SAPS-TBCs was much finer. It was found that the thickness of lamellar structure consisted

Y. Bai; Z. H. Han; H. Q. Li; C. Xu; Y. L. Xu; C. H. Ding; J. F. Yang

2011-01-01

271

VOCs Decomposition via Modified Ferroelectric Packed Bed Dielectric Barrier Discharge Plasma  

Microsoft Academic Search

A series of experiments are performed to remove toluene from a gaseous influent at room temperature and at- mospheric pressure by nonthermal plasma (NTP) generated di- electric barrier discharge. Four packed bed plasma reactors are compared in terms of energy density, toluene removal, energy efficiency, and other factors, with four conditions: no packing materials, ceramic materials, BaTiO3 rings, and Ba0.8Sr0.2Zr0.1Ti0.9O3

Tao Zhu; Yandong Wan; Hairong Li; Sha Chen; Yan Fang

2011-01-01

272

Life modeling of atmospheric and low pressure plasma-sprayed thermal-barrier coating  

Microsoft Academic Search

The cycles-to-failure vs cycle duration data for three different thermal barrier coating systems, which consist of atmospheric pressure plasma-sprayed ZrO2-8 percent Y2O3 over similarly deposited or low pressure plasma sprayed Ni-base alloys, are presently analyzed by means of the Miller (1980) oxidation-based life model. Specimens were tested at 1100 C for heating cycle lengths of 1, 6, and 20 h,

R. A. Miller; P. Argarwal; E. C. Duderstadt

1984-01-01

273

Life modeling of atmospheric and low pressure plasma-sprayed thermal-barrier coating  

NASA Technical Reports Server (NTRS)

The cycles-to-failure vs cycle duration data for three different thermal barrier coating systems, which consist of atmospheric pressure plasma-sprayed ZrO2-8 percent Y2O3 over similarly deposited or low pressure plasma sprayed Ni-base alloys, are presently analyzed by means of the Miller (1980) oxidation-based life model. Specimens were tested at 1100 C for heating cycle lengths of 1, 6, and 20 h, yielding results supporting the model's value.

Miller, R. A.; Argarwal, P.; Duderstadt, E. C.

1984-01-01

274

Electron dynamics and plasma jet formation in a helium atmospheric pressure dielectric barrier discharge jet  

SciTech Connect

The excitation dynamics within the main plasma production region and the plasma jets of a kHz atmospheric pressure dielectric barrier discharge (DBD) jet operated in helium was investigated. Within the dielectric tube, the plasma ignites as a streamer-type discharge. Plasma jets are emitted from both the powered and grounded electrode end; their dynamics are compared and contrasted. Ignition of these jets are quite different; the jet emitted from the powered electrode is ignited with a slight time delay to plasma ignition inside the dielectric tube, while breakdown of the jet at the grounded electrode end is from charging of the dielectric and is therefore dependent on plasma production and transport within the dielectric tube. Present streamer theories can explain these dynamics.

Algwari, Q. Th. [Centre for Plasma Physics, School of Maths and Physics, Queen's University Belfast, University Road, Belfast, Northern Ireland BT7 1NN (United Kingdom); Electronic Department, College of Electronics Engineering, Mosul University, Mosul 41002 (Iraq); O'Connell, D. [Centre for Plasma Physics, School of Maths and Physics, Queen's University Belfast, University Road, Belfast, Northern Ireland BT7 1NN (United Kingdom); York Plasma Institute, Department of Physics, University of York, York YO10 5DD (United Kingdom)

2011-09-19

275

Attenuation of single-tone ultrasound by an atmospheric glow discharge plasma barrier  

SciTech Connect

Propagation of 143 kHz ultrasound through an atmospheric pressure glow discharge in air was studied experimentally. The plasma was a continuous dc discharge formed by a multipin electrode system. Distributions of the gas temperature were also obtained in and around the plasma using laser-induced Rayleigh scattering technique. Results show significant attenuation of the ultrasound by the glow discharge plasma barrier (up to -24 dB). The results indicate that sound attenuation does not depend on the thickness of the plasma and attenuation is caused primarily by reflection of the sound waves from the plasma due to the sharp gas temperatures gradients that form at the plasma boundary. These gradients can be as high as 80 K/mm.

Stepaniuk, Vadim P. [Lenterra Inc., 7 Tenney Road, West Orange, New Jersey 07052 (United States); Ioppolo, Tindaro; Oetuegen, M. Volkan [Southern Methodist University, 3101 Dyer Street, Dallas, Texas 75205 (United States); Sheverev, Valery A. [Lenterra Inc., 7 Tenney Road, West Orange, New Jersey 07052 (United States); Polytechnic Institute of NYU, 6 Metrotech Center, Brooklyn, New York 11201 (United States)

2010-09-15

276

The Effect of Air Plasma on Sterilization of Escherichia coli in Dielectric Barrier Discharge  

NASA Astrophysics Data System (ADS)

In this work, a Dielectric Barrier Discharge (DBD) air plasma was used to sterilize Escherichia coli (E. coli) on the surface of medical Polyethylene Terephthalate (PET) film. The leakage of cellular DNA and protein by optical absorbance measurement at 260 nm and 280 nm, together with transmission electron microscopy (TEM) about cell morphology were performed after sterilization to analyse inactivation mechanisms. The results indicated that the DBD air plasma was very effective in E. coli sterilization. The plasma germicidal efficiency depended on the plasma treatment time, the air-gap distance, and the applied voltage. Within 5 min of plasma treatment, the germicidal efficiency against E. coli could reach 99.99%. An etching action on cell membranes by electrons, ions and radicals is the primary mechanism for DBD air plasma sterilization, which leads to the effusion of cellular contents (DNA and protein) and bacterial death.

Hu, Miao; Guo, Yun

2012-08-01

277

Fast Opening Microwave Barrier and Independency of Polarization in Plasma tubes  

NASA Astrophysics Data System (ADS)

Plasma barriers are used to protect sensitive microwave apparatus from potentially damaging electronic warfare signals. We have found both experimentally and theoretically that we can open such a barrier on a time scale of microseconds instead of typically many milliseconds. We do this by increasing the plasma density rather than waiting for it to decay. We produce a standing wave between the two layers that results in microwave transmission, analogous to the transmission found in an optical Fabry-Perot Resonator. The plasma tubes work extremely well in intercepting microwave radiation when the incident wave electric field is parallel to the tubes. However, if the electric field is perpendicular to the tubes, the normally induced plasma current cannot flow, and the plasma effects are not expected to appear. To our surprise, when the plasma tubes were experimentally tested with the electric field perpendicular to the tubes, the plasma tubes not only intercepted the microwave signal, but the observed cut-off with a pulsed plasma lasted about twice as long. The effect appears to be due to an electrostatic resonance, and preliminary calculations suggest that a normally ignored term in Maxwell's Equations is responsible.

Anderson, Ted; Alexeff, Igor; Farshi, Esmaeil; Dyer, Fred; Peck, Jeffry; Pradeep, Eric P.; Pulsani, Nanditha; Karnam, Naresh

2007-11-01

278

Effect of Sintering on Mechanical and Physical Properties of Plasma-Sprayed Thermal Barrier Coatings.  

National Technical Information Service (NTIS)

The effect of sintering on mechanical and physical properties of free-standing plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings (TBCs) was determined by annealing them at 1316 C in air. Mechanical and physical properties of the TBCs, including stre...

S. R. Choi D. M. Zhu R. A. Miller

2004-01-01

279

Formation of High Quality AlN Tunnel Barriers via an Inductively Couple Plasma  

NASA Astrophysics Data System (ADS)

Increasing operating frequencies of SIS receivers requires junctions that can operate at higher current densities. A major limiting factor of higher current density junctions is the increase in subgap leakage that occurs in AlOX barriers as current densities approach and exceed 10kA/cm2. AlN insulators are a promising alternative due to their lower leakage current at these high current densities. In this paper we present a more detailed analysis of the formation of AlN barriers using our previously reported inductively coupled plasma (ICP) source growth technique. The ICP allows for independent control of ion energy and current density in the plasma. Additionally, plasmas with very low ion energy (~20eV) and a high degree of dissociation (~80%) can be achieved. This improved control allows for the repeatable formation of high quality barriers. In particular, we report on the relationship between barrier thickness and plasma conditions as determined by in-situ discrete ellipsometry. Ellipsometry results were verified by fabricating Nb/Al-AlN/Nb junctions and measuring current-voltage, I(V), curves. dc I(V) curves for a range of current densities are presented.

Cecil, Thomas W.; Lichtenberger, Arthur W.; Kerr, Anthony R.

2008-04-01

280

Plasma methane conversion in the presence of carbon dioxide using dielectric-barrier discharges  

Microsoft Academic Search

Methane conversion in the presence of carbon dioxide was investigated under the conditions of dielectric-barrier discharge plasmas. Different from the previous investigations, the grounded electrode is covered by the dielectric material (quartz) in the present reactor design. The product contains gaseous hydrocarbons, syngas and oxygenates. No liquid hydrocarbons can be detected with the present reactor design. The oxygenates produced includes

Yue-ping Zhang; Yang Li; Yu Wang; Chang-jun Liu; Baldur Eliasson

2003-01-01

281

Atmospheric plasma sprayed thick thermal barrier coatings with high segmentation crack density  

Microsoft Academic Search

Atmospheric plasma sprayed thick thermal barrier coatings (TBCs), comprising of 1.5 mm thickness yttria stabilized zirconia (YSZ) coating, have been developed for increasing thermal protection of combustor applications. Different segmentation crack densities of the YSZ coating were created by controlling the deposition conditions. It was found that the substrate temperature played a dominant role in determining the segmentation crack density.

H. B. Guo; R. Vaßen; D. Stöver

2004-01-01

282

Stress and cracking behavior of plasma sprayed thermal barrier coatings using an advanced constitutive model  

Microsoft Academic Search

A finite element simulation of a plasma sprayed thermal barrier coating (TBC) system represented as a three-layer structure with an interface asperity is presented. Loading due to thermal expansion mismatch and geometry changes from oxide growth are included. A realistic viscoplastic model is used to represent the behavior of the ceramic layer, which includes both time dependent behavior and strong

Wangang Xie; Eric Jordan; Maurice Gell

2006-01-01

283

Dielectric-barrier-discharge vortex generators: characterisation and optimisation for flow separation control  

NASA Astrophysics Data System (ADS)

We investigated the use of dielectric-barrier-discharge plasma actuators as vortex generators for flow separation control applications. Plasma actuators were placed at a yaw angle to the oncoming flow, so that they produced a spanwise wall jet. Through interaction with the oncoming boundary layer, this created a streamwise longitudinal vortex. In this experimental investigation, the effect of yaw angle, actuator length and plasma-induced velocity ratio was studied. Particular attention was given to the vortex formation mechanism and its development downstream. The DBD plasma actuators were then applied in the form of co-rotating and counter-rotating vortex arrays to control flow separation over a trailing-edge ramp. It was found that the vortex generators were successful in reducing the separation region, even at plasma-to-free-stream velocity ratios of less than 10%.

Jukes, Timothy N.; Choi, Kwing-So

2012-02-01

284

Simulations of self-organized filaments in a dielectric barrier glow discharge plasma  

NASA Astrophysics Data System (ADS)

The spontaneous filamentation of a dielectric barrier glow discharge plasma (Townsend, not streamer breakdown), i.e., an instability of the homogeneous state has been simulated and understood with the help of a self-consistent two-dimensional fluid model of the discharge. The formation of self-organized or solitary filaments observed experimentally and described in previous papers can be explained in terms of electron and ion transport coefficients only, without including gas heating, plasma chemistry or surface effects. The conditions favoring the plasma filamentation are discussed.

Brauer, I.; Punset, C.; Purwins, H.-G.; Boeuf, J. P.

1999-06-01

285

Failure of physical vapor deposition\\/plasma-sprayed thermal barrier coatings during thermal cycling  

Microsoft Academic Search

ZrO2-7 wt.% Y2O3 plasma-sprayed (PS) coatings were applied on high-temperature Ni-based alloys precoated by physical vapor deposition with\\u000a a thin, dense, stabilized zirconia coating (PVD bond coat). The PS coatings were applied by atmospheric plasma spraying (APS)\\u000a and inert gas plasma spraying (IPS) at 2 bar for different substrate temperatures. The thermal barrier coatings (TBCs) were\\u000a tested by furnace isothermal

V. Teixeira; M. Andritschky; H. Gruhn; W. Malléner; H. P. Buchkremer; D. Stöver

2000-01-01

286

Integrated Plasma Simulation of Ion Cyclotron and Lower Hybrid Range of Frequencies Actuators in Tokamaks  

NASA Astrophysics Data System (ADS)

Recent upgrades to the ion cyclotron RF (ICRF) and lower hybrid RF (LHRF) components of the Integrated Plasma Simulator [1] have made it possible to simulate LH current drive in the presence of ICRF minority heating and mode conversion electron heating. The background plasma is evolved in these simulations using the TSC transport code [2]. The driven LH current density profiles are computed using advanced ray tracing (GENRAY) and Fokker Planck (CQL3D) [3] components and predictions from GENRAY/CQL3D are compared with a ``reduced'' model for LHCD (the LSC [4] code). The ICRF TORIC solver is used for minority heating with a simplified (bi-Maxwellian) model for the non-thermal ion tail. Simulation results will be presented for LHCD in the presence of ICRF heating in Alcator C-Mod. [4pt] [1] D. Batchelor et al, Journal of Physics: Conf. Series 125, 012039 (2008).[0pt] [2] S. C. Jardin et al, J. Comp. Phys. 66, 481 (1986).[0pt] [3] R. W. Harvey and M. G. McCoy, Proc. of the IAEA Tech. Comm. Meeting on Simulation and Modeling of Therm. Plasmas, Montreal, Canada (1992).[0pt] [4] D. Ignat et al, Nucl. Fus. 34, 837 (1994).[0pt] [5] M. Brambilla, Plasma Phys. and Cont. Fusion 41,1 (1999).

Bonoli, P. T.; Shiraiwa, S.; Wright, J. C.; Harvey, R. W.; Batchelor, D. B.; Berry, L. A.; Chen, Jin; Poli, F.; Kessel, C. E.; Jardin, S. C.

2012-10-01

287

On the energy transport in internal transport barriers of RFP plasmas  

NASA Astrophysics Data System (ADS)

Single helical axis (SHAx) states obtained in high current reversed field pinch (RFP) plasmas feature an internal transport barrier delimiting the hot helical core region. The electron temperature jump across this region, and the related temperature gradient, display a clear relationship with the normalized amplitude of the secondary MHD modes. A transport analysis performed with the ASTRA code, taking into account the helical geometry, yields values of the thermal conductivity in the barrier region as low as 5 m2 s-1. The thermal conductivity is also related to the secondary mode amplitude. Since such amplitude is reduced when plasma current is increased, it is expected that higher current plasmas will display even steeper thermal gradients and hotter helical cores.

Lorenzini, R.; Alfier, A.; Auriemma, F.; Fassina, A.; Franz, P.; Innocente, P.; López-Bruna, D.; Martines, E.; Momo, B.; Pereverzev, G.; Piovesan, P.; Spizzo, G.; Spolaore, M.; Terranova, D.

2012-06-01

288

Permeation barrier coating and plasma sterilization of PET bottles and foils  

NASA Astrophysics Data System (ADS)

Modern packaging materials such as polyethylene terephthalate (PET) offer various advantages over glass or metal containers. Beside this they only offer poor barrier properties against gas permeation. Therefore, the shelf-live of packaged food is reduced. Additionally, common sterilization methods like heat, hydrogen peroxide or peracetic acid may not be applicable due to reduced heat or chemical resistance of the plastic packaging material. For the plasma sterilization and permeation barrier coating of PET bottles and foils, a microwave driven low pressure plasma reactor is developed based on a modified Plasmaline antenna. The dependencies of important plasma parameters, such as gas mixture, process pressure, power and pulse conditions on oxygen permeation through packaging foil are investigated. A residual permeation as low as J = 1.0 ±0.3 cm^3m-2day-1bar-1 for 60 nm thick silicon oxide (SiOx) coated PET foils is achieved. To discuss this residual permeation, coating defects are visualized by capacitively coupled atomic oxygen plasma etching of coated substrate. A defect density of 3000 mm-2 is revealed responsible for permeation. For plasma sterilization, optimized plasma parameters based on fundamental research of plasma sterilization mechanisms permit short treatment times of a few seconds.

Steves, Simon; Deilmann, Michael; Bibinov, Nikita; Awakowicz, Peter

2009-10-01

289

Instrumented adhesion tests on plasma sprayed thermal barrier coatings  

NASA Technical Reports Server (NTRS)

The failure mechanisms of plasma-sprayed two-layer coatings consisting of an NiCrAlY or NiCrAlZr bond coat with an yttria-stabilized zirconia overlay are presently examined by tensile adhesion tests. It has been found that adhesive failure within the bond coat exhibits greater failure strain than the cohesive failure of the ceramic overlay, supporting the view of the intermediate coatings being highly compliant. The absolute extension exhibited by failures occurring only through the ceramic coating is greater than that of adhesive failure, since the ceramic coating is much thicker than the bond coat.

Berndt, Christopher C.

1989-01-01

290

Localized arc filament plasma actuators for noise mitigation and mixing enhancement  

NASA Technical Reports Server (NTRS)

A device for controlling fluid flow. The device includes an arc generator coupled to electrodes. The electrodes are placed adjacent a fluid flowpath such that upon being energized by the arc generator, an arc filament plasma adjacent the electrodes is formed. In turn, this plasma forms a localized high temperature, high pressure perturbation in the adjacent fluid flowpath. The perturbations can be arranged to produce vortices, such as streamwise vortices, in the flowing fluid to control mixing and noise in such flows. The electrodes can further be arranged within a conduit configured to contain the flowing fluid such that when energized in a particular frequency and sequence, can excite flow instabilities in the flowing fluid. The placement of the electrodes is such that they are unobtrusive relative to the fluid flowpath being controlled.

Samimy, Mohammad (Inventor); Adamovich, Igor (Inventor)

2008-01-01

291

Plasma surface treatments by using a dielectric barrier discharge for the deposition of diamond films  

NASA Astrophysics Data System (ADS)

For plasma surface treatments at atmospheric pressure, a 2 kW dielectric barrier discharge (DBD) source was developed. It was investigated via an optical emission spectroscopy (OES), an IR camera and volt-ampere meters with a computer. It was confirmed that the developed source stably generated plasmas. After the diamonds had been seeded, the plasma surface treatments were performed as pretreatment to improve the deposition of the diamond films by using the developed DBD source with argon gas. The substrate surfaces were analyzed using a contact angle analysis (CAA), an atomic force microscopy (AFM) and a 3D Nano Profiling System. The results of the plasma surface treatments showed an improvement in the surface free energies of the substrates. The plasma surface treatments for 5 minutes also resulted in a more uniform distribution of the seeding diamonds on the substrates, which improved the depositions of the diamond films.

Kang, I. J.; Ko, M. G.; Yang, J. K.; Lee, H. J.

2013-07-01

292

Diagnostic of plasma discharge parameters in helium filled dielectric barrier discharge  

NASA Astrophysics Data System (ADS)

This paper reports the plasma discharge analysis of a dielectric barrier discharge (DBD) source. Helium is used as a working gas. The analysis is performed at fixed working pressure and operating frequency. The investigations are carried out using sinusoidal supply for the generation of discharges where two current pulses have been observed with different polarities in one period. A homogeneous type of discharge has been observed for different operating conditions in this DBD source. Since in situ diagnostics are not possible due to the small geometries in the used DBD source, the electrical measurements and spectroscopic analysis of the discharge have been performed to analyse the plasma discharge. The electrical analysis has been carried out using equivalent electrical circuit model. The plasma density and temperature within the discharge have been estimated using line ratio technique of the observed visible neutral helium lines. The estimated electron plasma density is found to be in close proximity with the plasma simulation code `OOPIC Pro'.

Gulati, Pooja; Pal, Udit Narayan; Kumar, Mahesh; Prakash, Ram; Srivastava, Vishnu; Vyas, Vimal

2012-11-01

293

Growth Control of Dry Yeast Using Scalable Atmospheric-Pressure Dielectric Barrier Discharge Plasma Irradiation  

NASA Astrophysics Data System (ADS)

We have investigated the effects of plasma irradiation on the growth of dry yeast (Saccharomyces cerevisiae) using a scalable atmospheric-pressure dielectric barrier discharge (DBD) device. NO of 380 ppm, NO2 of 10 ppm and O3 of 560 ppm were detected 1 mm below the discharges, which were produced by the DBD plasmas. DBD plasma irradiation of 10 to 100 s enhances the growth of yeast in the lag phase, whereas that of 120 and 150 s suppresses the growth. O3, NO2, photons, and heat generated by the plasma irradiation are not responsible for the growth enhancement of the dry yeast. Plasma etching has little effect on the growth of dry yeast cells. NO plays a key role in the growth enhancement of dry yeast cells.

Kitazaki, Satoshi; Koga, Kazunori; Shiratani, Masaharu; Hayashi, Nobuya

2012-11-01

294

Characterization of a Direct-Current Glow Discharge Plasma Actuator in Low-Pressure Supersonic Flow  

Microsoft Academic Search

DOI: 10.2514\\/1.27197 An experimental study of a direct-current, nonequilibrium glow plasma discharge in the presence of a Mach 2.85 supersonic flow is presented. The discharge is generated with pinlike electrodes flush-mounted on a plane surface with sustaining currents between 25 to 300 mA. In the presence of a supersonic flow, two distinct discharge modes (diffuse and constricted) are observed depending

Jichul Shin; V. Narayanaswamy; Laxminarayan L. Raja; Noel T. Clemens

2007-01-01

295

Phase transformation and bond coat oxidation behavior of plasma-sprayed zirconia thermal barrier coating  

Microsoft Academic Search

ZrO2–CeO2–Y2O3 and ZrO2–Y2O3 thermal barrier coatings were prepared using the air plasma spray process. Phase transformation in the ceramic top coating, bond coat oxidation and thermal barrier properties were investigated to compare ZrO2–CeO2–Y2O3 with ZrO2–Y2O3 at 1300°C under high temperature thermal cycles. In the as-sprayed condition, both coatings showed a 7?11% porosity fraction and typical lamellar structures formed by continuous

C. H. Lee; H. K. Kim; H. S. Choi; H. S. Ahn

2000-01-01

296

Plasma expansion of ZnO-coated surface barrier discharge in open air and its optical analysis  

SciTech Connect

Characteristics of the ZnO-coated surface barrier discharge in open air were diagnosed optically. Highly conductive ZnO film was deposited on the dielectric surface. We found that the increase of the surface conductivity induces wider discharge area. Moreover we analyzed the optical behavior of plasma transition of two barrier discharges by optical emission spectroscopy. Discharge characteristic of the normal dielectric barrier discharge is divided into only two modes: streamer and glow discharge. But in the case of ZnO-coated dielectric barrier discharge, pd range of glowlike discharge exists widely and this can be also an evidence of the enhancement of plasma uniformity.

Choi, Jai Hyuk; Han, Man Hyeop; Baik, Hong Koo; Song, Kie Moon [Department of Metallurgical Engineering, Yonsei University, 134 Shinchon-Dong, Seodaemoon-Ku, Seoul 120-749 (Korea, Republic of); Department of Applied Physics, KonKuk University, Chungju 380-701 (Korea, Republic of)

2007-02-01

297

Inactivation of Campylobacter jejuni with Dielectric Barrier Discharge Plasma Using Air and Nitrogen Gases.  

PubMed

Abstract Air and nitrogen gas are commonly used feed gases for plasma generation and are economically useful in industrial applications. The two gases were compared in dielectric barrier discharge plasma for the inactivation of Campylobacter jejuni on an agar surface. Plasma treatment with nitrogen gas for 20?s did not yield any reduction (p>0.05) in viable cell count. However, a 0.8-log reduction (p<0.05) in colony-forming units (CFU) occurred when the nitrogen gas was supplemented with 2% (vol/vol) air. The use of air only, air supplemented with 2% (vol/vol) nitrogen, or oxygen only further decreased the viable cell counts by 0.7-1.7-log CFU (p<0.05). These results suggest that oxygen in plasma generation is critically important for the increased inactivation effect. Scanning electron microscopy analysis showed much cell debris including fragmented flagella in the sample exposed to air plasma, while no cell debris was found in the sample exposed to nitrogen plasma. In transmission electron microscopy analysis, many C. jejuni cells exposed to air plasma had truncated flagella with sharp bends, while the cells exposed to nitrogen plasma were normal, strongly suggesting that the air plasma can reduce the virulence of C. jejuni. A BacLight assay showed that air plasma damaged the cellular membrane (p<0.05), whereas nitrogen plasma did not after 5- or 20-s treatment. The damage to the membrane was consistent with the reduced viable cell count. Based on confocal microscopic analysis, the similar results were found by visualizing the fluorescent-dye-stained cells. In addition, the prolonged nitrogen plasma for 2?min also damaged many cellular membranes. This study shows that air, especially oxygen, is more effective and destructive than nitrogen and provides evidence that membrane damage may be a major mechanism for the inactivation of C. jejuni exposed to plasma. PMID:24971667

Kim, Joo-Sung; Lee, Eun-Jung; Kim, Yun-Ji

2014-08-01

298

Treatment of Candida albicans biofilms with low-temperature plasma induced by dielectric barrier discharge and atmospheric pressure plasma jet  

NASA Astrophysics Data System (ADS)

Because of some disadvantages of chemical disinfection in dental practice (especially denture cleaning), we investigated the effects of physical methods on Candida albicans biofilms. For this purpose, the antifungal efficacy of three different low-temperature plasma devices (an atmospheric pressure plasma jet and two different dielectric barrier discharges (DBDs)) on Candida albicans biofilms grown on titanium discs in vitro was investigated. As positive treatment controls, we used 0.1% chlorhexidine digluconate (CHX) and 0.6% sodium hypochlorite (NaOCl). The corresponding gas streams without plasma ignition served as negative treatment controls. The efficacy of the plasma treatment was determined evaluating the number of colony-forming units (CFU) recovered from titanium discs. The plasma treatment reduced the CFU significantly compared to chemical disinfectants. While 10 min CHX or NaOCl exposure led to a CFU log10 reduction factor of 1.5, the log10 reduction factor of DBD plasma was up to 5. In conclusion, the use of low-temperature plasma is a promising physical alternative to chemical antiseptics for dental practice.

Koban, Ina; Matthes, Rutger; Hübner, Nils-Olaf; Welk, Alexander; Meisel, Peter; Holtfreter, Birte; Sietmann, Rabea; Kindel, Eckhard; Weltmann, Klaus-Dieter; Kramer, Axel; Kocher, Thomas

2010-07-01

299

Study of non-thermal plasma jet with dielectric barrier configuration in nitrogen and argon  

NASA Astrophysics Data System (ADS)

Dielectric barrier discharge (DBD) is advantageous in generating non-thermal plasma at atmospheric pressure, as it avoids transition to thermal arc and dispenses with costly vacuum system. It has found useful applications in treating heat-sensitive materials such as plastics and living tissue. In this work, the discharge formed between the Pyrex glass layer and the ground electrode is extruded through a nozzle to form the non-thermal plasma jet. The DBD characteristics were investigated in terms of charge transferred and mean power dissipated per cycle when operated in nitrogen and argon at various flow rates and applied voltages. These characteristics were then correlated to the dimension of the plasma jet. The mean power dissipated in the DBD was below 7 W giving an efficiency of 17 %. The length of the plasma jet was greatly limited to below 1 cm due to the configuration of the DBD system and nozzle.

Choo, C. Y.; Chin, O. H.

2014-03-01

300

Detection of hydroxyl radicals during regeneration of granular activated carbon in dielectric barrier discharge plasma system  

NASA Astrophysics Data System (ADS)

To understand the reactions taking place in the dielectric barrier discharge (DBD) plasma system of activated carbon regeneration, the determination of active species is necessary. A method based on High Performance Liquid Chromatography with radical trapping by salicylic acid, has been developed to measure hydroxyl radical (•OH) in the DBD plasma reactor. The effects of applied voltage, treatment time, and gas flow rate and atmosphere were investigated. Experimental results indicated that increasing voltage, treatment time and air flow rate could enhance the formation of •OH. Oxygen atmosphere and a suitable GAC water content were contributed to •OH generation. The results give an insight into plasma chemical processes, and can be helpful to optimize the design and application for the plasma system.

Tang, Shoufeng; Lu, Na; Shang, Kefeng; Li, Jie; Wu, Yan

2013-03-01

301

Internal Transport Barrier in Edge Plasma of Small Size Divertor Tokamak Using Neutral Beam Injection  

NASA Astrophysics Data System (ADS)

We model the internal transport barrier "ITB" in edge plasma of small size divertor tokamak with B2SOLPS0.5.2D fluid transport code. The simulation results demonstrated the following: (1) we control the internal transport barrier by altering the edge particle transport through changes the edge toroidal rotation which agree with the result of Burrell et al. (Edge Pedestal control in quiescent H-mode discharges in DIII-D using co-plus counter-neutral beam injection, Nucl Fusion, 49, 085024 (9pp) in 2009). (2) The radial electric field has neoclassical nature near separatrix with discharge by co-injection NBI. (3) The toroidal plasma viscosity has strong influence on the toroidal velocity.

Bekheit, A. H.

2013-08-01

302

Thermal barrier coatings on turbine blades by plasma spraying with improved cooling  

NASA Astrophysics Data System (ADS)

Turbine blades were coated with a thermal barrier coating system consisting of an MCrAlY bond coat about 100 micron thick deposited by Low Pressure Plasma Spraying (LPPS) and a 300 micron thick ZrO2-7 wt pct Y2O3 top coat. The latter was manufactured by both Atmosphere and Temperature Controlled Spraying (ATCS) and Air Plasma Spraying using internal air cooling through the cooling holes of the turbine blades. Coated blades were submitted to thermal cycling tests in a burner rig with hot gas temperature of 1485 C. In the case of ATCS coated blades the number of cycles until the first spallation at the leading edge of the blade was between 350 and 2400. The number of cycles of the thermal barrier coatings sprayed with internal cooling was between 1200 and 1800.

Cosack, T.; Pawlowski, L.; Schneiderbanger, S.; Sturlese, S.

1992-06-01

303

Mechanical property measurements of plasma-sprayed thermal-barrier coatings subjected to oxidation  

NASA Technical Reports Server (NTRS)

Techniques have been developed for measuring the tensile properties of plasma-sprayed coatings which are used in thermal barrier applications. The measurements have included the average Young's modulus, bond strength and elongation at failure. The oxidation behavior of the bond coat plays an important role in the integrity and adhesion of plasma-sprayed thermal barrier coatings. This work studies the nature of the high temperature degradation on the mechanical properties of the coating. Furnace tests have been carried out on U-700 alloy with bond coats of NiCrAlY or NiCrAlZr and an overlay of ZrO2-8 percent Y2O3. Weight gain measurements on the coatings have been examined with relation to the adhesion strength and failure observations. The results from an initial study are reported in this work.

Berndt, C. C.; Miller, R. A.

1984-01-01

304

Mechanical property measurements of plasma-sprayed thermal-barrier coatings subjected to oxidation  

SciTech Connect

Techniques have been developed for measuring the tensile properties of plasma-sprayed coatings which are used in thermal barrier applications. The measurements have included the average Young's modulus, bond strength and elongation at failure. The oxidation behavior of the bond coat plays an important role in the integrity and adhesion of plasma-sprayed thermal barrier coatings. This work studies the nature of the high temperature degradation on the mechanical properties of the coating. Furnace tests have been carried out on U-700 alloy with bond coats of NiCrAlY or NiCrAlZr and an overlay of ZrO2-8 percent Y2O3. Weight gain measurements on the coatings have been examined with relation to the adhesion strength and failure observations. The results from an initial study are reported in this work. 13 references.

Berndt, C.C.; Miller, R.A.

1984-07-01

305

On the nature and statistical properties of transport barriers in magnetospheric and laboratory plasma  

NASA Astrophysics Data System (ADS)

The transport barriers near magnetospheric cusp have a dualistic feature: being very effective in limitation of the momentum transfer, they display the super-diffusive statistical properties. We show an example from Interball-1 with a rare case of extremely quiet solar wind. The inbound magnetopause crossing, being inherently turbulent in this equilibrium case, is best seen from changes of the magnetic field component signs. The ion heating starts namely in the transport barrier and proceeds deeper inward magnetosphere. It agrees with the kinetic energy transformation into the thermal one inside the barrier - the turbulent dissipation of the magnetosheath kinetic energy - as simultaneously with the ion temperature rise the general velocity component drops from its model prediction. Fitting the log-Poisson model for 1D most- dissipative structures gives qualitatively similar result. In sense of the momentum transfer the Alfvenic turbulent barrier effectively isolates the high- ? part of the magnetospheric cusp, from rather fast- flowing (~ 200 km/s) magnetosheath. Contrary to that, several examples from different missions and different plasma parameters demonstrate the super-diffusive transport character. The individual Alfvenic 'collapsons' have similar scale chains to that of high kinetic pressure jets, showing mutual interaction features. We think that the interacting jets and barriers, accompanying by classic and/ or micro- reconnection, have rather general importance for the plasma physics, and for understanding of turbulence and mechanisms of magnetic field generation. These coherent, nonlinear interacting structures will be further explored in details by such missions as ROY and Cross-Scale/ SCOPE. We compare the statistical properties of transport barriers in space and fusion devices.

Savin, Sergey; Budaev, Viacheslav; Amata, Ermanno; Kozak, Liudmila; Korepanov, Valery; Buechner, Joerg; Romanov, Stanislav; Blecki, Jan; Balikhin, Mikhael; Lezhen, Liudmila

2010-05-01

306

Oxidation and degradation of a plasma-sprayed thermal barrier coating system  

SciTech Connect

The isothermal oxidation behavior of thermal barrier coating (TBC) specimens consisting of single-crystal superalloy substrates, vacuum plasma-sprayed Ni-22Cr-10Al-1Y bond coatings and air plasma-sprayed 7.5 wt.% yttria stabilized zirconia top coatings was evaluated by thermogravimetric analysis at 1150{degrees}C for up to 200 hours. Coating durability was assessed by furnace cycling at 1150{degrees}C. Coatings and reaction products were identified by x-ray diffraction, field-emission scanning electron microscopy and energy dispersive spectroscopy.

Haynes, J.A. [Univ. of Alabama, Birmingham, AL (United States). Dept. of Materials and Mechanical Engineering; Ferber, M.K.; Porter, W.D. [Oak Ridge National Lab., TN (United States)

1996-04-01

307

A dielectric-barrier discharge enhanced plasma brush array at atmospheric pressure  

SciTech Connect

This study developed a large volume cold atmospheric plasma brush array, which was enhanced by a dielectric barrier discharge by integrating a pair of DC glow discharge in parallel. A platinum sheet electrode was placed in the middle of the discharge chamber, which effectively reduced the breakdown voltage and working voltage. Emission spectroscopy diagnosis indicated that many excited argon atoms were distributed almost symmetrically in the lateral direction of the plasma. The concentration variations of reactive species relative to the gas flow rate and discharge current were also examined.

Li Xuemei; Zhan Xuefang; Yuan Xin; Zhao Zhongjun; Yan Yanyue; Duan Yixiang [Research Center of Analytical Instrumentation, Analytical Testing Center, College of Chemistry, Sichuan University, Chengdu (China); Tang Jie [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an (China)

2013-07-15

308

Optimization of a tunneling barrier in magnetic tunneling junction by tilted-plasma oxidation  

SciTech Connect

Oxidation of an AlO{sub x} insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 A thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer.

Nam, C.H.; Shim, Heejae; Kim, K.S.; Cho, B.K. [Center for Frontier Materials, Department of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712 (Korea, Republic of)

2004-10-01

309

Zero-dimensional states in submicron double-barrier heterostructures laterally constricted by hydrogen plasma isolation  

Microsoft Academic Search

The lateral dimensions of resonant tunneling AlGaAs-GaAs double barrier heterostructures have been restricted by hydrogen plasma exposure. Ohmic contacts to the submicron diodes have been made by solid phase epitaxial growth of Ge on GaAs. The current-voltage characteristics show a fine structure splitting that is inversely proportional to the lateral size of the diode. The results are interpreted as resonant

M. van Hove; R. Pereira; W. de Raedt; G. Borghs; R. Jonckheere; C. Sala; W. Magnus; W. Schoenmaker; M. van Rossum

1992-01-01

310

Plasma-deposited silicon oxide barrier films on polyethersulfone substrates: temperature and thickness effects  

Microsoft Academic Search

Silicon oxide (SiOx) films deposited on flexible polyethersulfone (PES) substrates by plasma-enhanced chemical vapor deposition (PEVCD) have been investigated for transparent barrier applications. Although the water vapor transmission rate (WVTR) of PES (?28 g\\/m2\\/day; thickness: 200 ?m) is higher than that of the polyethylene terephthalate (PET; ?16 g\\/m2\\/day; thickness: 188 ?m), the PES substrate can withstand process temperatures of up

D. S. Wuu; W. C. Lo; C. C. Chiang; H. B. Lin; L. S. Chang; R. H. Horng; C. L. Huang; Y. J. Gao

2005-01-01

311

Highly durable thermal barrier coatings made by the solution precursor plasma spray process  

Microsoft Academic Search

The solution precursor plasma spray (SPPS) process offers the prospect of depositing highly durable thermal barrier coatings (TBCs) of low thermal conductivity. In this study, a Taguchi design of experiments was employed to optimize the SPPS process. The spallation life of SPPS TBCs on a MCrAlY bond coated Ni-base superalloy substrate deposited under the optimized processing conditions was demonstrated to

Maurice Gell; Liangde Xie; Xinqing Ma; Eric H. Jordan; Nitin P. Padture

2004-01-01

312

Characterization of microstructural defects in plasma-sprayed thermal barrier coatings  

Microsoft Academic Search

Thermal barrier coatings with a NiCrAlY bond coating and a 1.5 mm thick zirconia top coating were air plasma sprayed onto\\u000a a nickel-base substrate. The top coatings were deposited with the same spraying parameters except for the amount of external\\u000a cooling, which varied from no cooling to the maximum available. This resulted in four sets of samples produced with different

P. Bengtsson; T. Johannesson

1995-01-01

313

Residual stresses in ceramic plasma-sprayed thermal barrier coatings: measurement and calculation  

Microsoft Academic Search

The present work concerns the residual stresses in plasma-sprayed ZrO2-7Y2O3 thermal barrier coatings deposited on Ni-base superalloy substrates which were kept at different temperatures. The stress measurements were carried out on as-sprayed specimens with X-ray diffraction equipment using the “sin2?” technique. It was found that the residual stresses in the ceramic layer changed from tensile to compressive with increasing substrate

M. Levit; I. Grimberg; B.-Z. Weiss

1996-01-01

314

Influence of isothermal and cyclic heat treatments on the adhesion of plasma sprayed thermal barrier coatings  

Microsoft Academic Search

The adhesion of thermal barrier coatings (TBC) has been studied using the standard method described in ASTM C633, which makes use of a tensile test machine to measure the adhesion. The studied specimens consist of air plasma sprayed (APS) TBC deposited on disc-shaped substrates of Ni-base alloy Hastelloy X. The bond coat (BC) is of a NiCoCrAlY type and the

Robert Eriksson; Håkan Brodin; Sten Johansson; Lars Östergren; Xin-Hai Li

2011-01-01

315

Modelled and measured residual stresses in plasma sprayed thermal barrier coatings  

Microsoft Academic Search

Thermal barrier coatings consisting of a NiCrAlY bond coating and a 1.4 mm thick partially stabilised zirconia top coating were air plasma sprayed onto grit blasted nickel-base substrates. Two samples were produced using different amounts of external cooling during spraying of the top coatings. The residual stress profiles in the samples were measured after each manufacturing process step with a

Per Bengtsson; Christer Persson

1997-01-01

316

Effect of residual stresses on air plasma sprayed thermal barrier coatings  

Microsoft Academic Search

Thermal barrier coating with a CoNiCrAlY bond coating and a 0.3 mm thick zirconia, (7% yttria stabilized) top coating were air plasma sprayed onto a Hastelloy-X nickel based super alloy substrate coupons. Substrate preparation is a key initial step in the production of quality thermal sprayed coatings. Grit blasting is usually used to roughen the substrate surface so that better

A. Nusair Khan; J. Lu; H. Liao

2003-01-01

317

Skeletal Cell Differentiation Is Enhanced by Atmospheric Dielectric Barrier Discharge Plasma Treatment  

PubMed Central

Enhancing chondrogenic and osteogenic differentiation is of paramount importance in providing effective regenerative therapies and improving the rate of fracture healing. This study investigated the potential of non-thermal atmospheric dielectric barrier discharge plasma (NT-plasma) to enhance chondrocyte and osteoblast proliferation and differentiation. Although the exact mechanism by which NT-plasma interacts with cells is undefined, it is known that during treatment the atmosphere is ionized generating extracellular reactive oxygen and nitrogen species (ROS and RNS) and an electric field. Appropriate NT-plasma conditions were determined using lactate-dehydrogenase release, flow cytometric live/dead assay, flow cytometric cell cycle analysis, and Western blots to evaluate DNA damage and mitochondrial integrity. We observed that specific NT-plasma conditions were required to prevent cell death, and that loss of pre-osteoblastic cell viability was dependent on intracellular ROS and RNS production. To further investigate the involvement of intracellular ROS, fluorescent intracellular dyes Mitosox (superoxide) and dihydrorhodamine (peroxide) were used to assess onset and duration after NT-plasma treatment. Both intracellular superoxide and peroxide were found to increase immediately post NT-plasma treatment. These increases were sustained for one hour but returned to control levels by 24 hr. Using the same treatment conditions, osteogenic differentiation by NT-plasma was assessed and compared to peroxide or osteogenic media containing ?-glycerolphosphate. Although both NT-plasma and peroxide induced differentiation-specific gene expression, neither was as effective as the osteogenic media. However, treatment of cells with NT-plasma after 24 hr in osteogenic or chondrogenic media significantly enhanced differentiation as compared to differentiation media alone. The results of this study show that NT-plasma can selectively initiate and amplify ROS signaling to enhance differentiation, and suggest this technology could be used to enhance bone fusion and improve healing after skeletal injury.

Zhang, Jun; Kurpad, Deepa S.; Fridman, Gregory; Fridman, Alexander; Freeman, Theresa A.

2013-01-01

318

Effect of atmospheric pressure dielectric barrier discharge plasma on the biological activity of naringin.  

PubMed

The biological activity of naringin treated with atmospheric pressure plasma was evaluated to investigate whether exposure to plasma can be used as a method to improve the biological activity of natural materials. Naringin was dissolved in methanol (at 500 ppm) and transferred to a container. A dielectric barrier discharge (DBD) (250 W, 15 kHz, ambient air) was then generated. Treatment with the plasma for 20 min increased the radical-scavenging activity, FRAP value, and the total phenolic compound content of naringin from 1.45% to 38.20%, from 27.78 to 207.78 ?M/g, and from 172.50 to 225.83 ppm, respectively. Moreover, the tyrosinase-inhibition effect of naringin increased from 6.12% to 83.30% upon plasma treatment. Naringin treated with plasma exhibited antimicrobial activity against foodborne pathogens, especially Salmonella Typhimurium; an activity that was absent before plasma treatment. Structural modifications induced in the naringin molecule by plasma might be responsible for improving the biological activity of naringin. PMID:24799234

Kim, Hyun-Joo; Yong, Hae In; Park, Sanghoo; Kim, Kijung; Kim, Tae Hoon; Choe, Wonho; Jo, Cheorun

2014-10-01

319

Controlled drug release through a plasma polymerized tetramethylcyclo-tetrasiloxane coating barrier.  

PubMed

A plasma polymerized tetramethylcyclo-tetrasiloxane (TMCTS) coating was deposited onto a metallic biomaterial, 316 stainless steel, to control the release rate of drugs, including daunomycin, rapamycin and NPC-15199 (N-(9-fluorenylmethoxy-carbonyl)-leucine), from the substrate surface. The plasma-state polymerized TMCTS thin film was deposited in a vacuum plasma reactor operated at a radio-frequency of 13.56 MHz, and was highly adhesive to the stainless steel, providing a smooth and hard coating layer for drugs coated on the substrate. To investigate the influence of plasma coating thickness on the drug diffusion profile, coatings were deposited at various time lengths from 20 s to 6 min, depending on the type of drug. Atomic force spectroscopy (AFM) was utilized to characterize coating thickness. Drug elution was measured using a spectrophotometer or high-performance liquid chromatography (HPLC) system. The experimental results indicate that plasma polymerized TMCTS can be used as an over-coating to control drug elution at the desired release rate. The drug-release rate was also found to be dependent on the molecular weight of the drug with plasma coating barrier on top of it. The in vitro cytotoxicity test result suggested that the TMCTS plasma coatings did not produce a cytotoxic response to mammalian cells. The non-cytotoxicity of TMCTS coating plus its high thrombo-resistance and biocompatibility are very beneficial to drug-eluting devices that contact blood. PMID:21294969

Osaki, Shigemasa; Chen, Meng; Zamora, Paul O

2012-01-01

320

Stress distributions in plasma-sprayed thermal barrier coatings as a function of interface roughness and oxide scale thickness  

Microsoft Academic Search

During thermal cyclic loading, plasma-sprayed thermal barrier coatings (TBCs) often show failure within the top coat close to the interface. In all cases this results from crack propagation of pre-existing cracks near the bond coat (BC)–top coat interface. Stresses developing on a microscopic scale near the BC–TBC interface of plasma-sprayed thermal barrier coatings govern crack growth in an initial phase

M Ahrens; R Vaßen; D Stöver

2002-01-01

321

Radio frequency plasma power dependence of the moisture permeation barrier characteristics of Al{sub 2}O{sub 3} films deposited by remote plasma atomic layer deposition  

SciTech Connect

In the present study, we investigated the gas and moisture permeation barrier properties of Al{sub 2}O{sub 3} films deposited on polyethersulfone films (PES) by capacitively coupled plasma (CCP) type Remote Plasma Atomic Layer Deposition (RPALD) at Radio Frequency (RF) plasma powers ranging from 100 W to 400 W in 100 W increments using Trimethylaluminum [TMA, Al(CH{sub 3}){sub 3}] as the Al source and O{sub 2} plasma as the reactant. To study the gas and moisture permeation barrier properties of 100-nm-thick Al{sub 2}O{sub 3} at various plasma powers, the Water Vapor Transmission Rate (WVTR) was measured using an electrical Ca degradation test. WVTR decreased as plasma power increased with WVTR values for 400 W and 100 W of 2.6 × 10{sup ?4} gm{sup ?2}day{sup ?1} and 1.2 × 10{sup ?3} gm{sup ?2}day{sup ?1}, respectively. The trends for life time, Al-O and O-H bond, density, and stoichiometry were similar to that of WVTR with improvement associated with increasing plasma power. Further, among plasma power ranging from 100 W to 400 W, the highest power of 400 W resulted in the best moisture permeation barrier properties. This result was attributed to differences in volume and amount of ion and radical fluxes, to join the ALD process, generated by O{sub 2} plasma as the plasma power changed during ALD process, which was determined using a plasma diagnosis technique called the Floating Harmonic Method (FHM). Plasma diagnosis by FHM revealed an increase in ion flux with increasing plasma power. With respect to the ALD process, our results indicated that higher plasma power generated increased ion and radical flux compared with lower plasma power. Thus, a higher plasma power provides the best gas and moisture permeation barrier properties.

Jung, Hyunsoo [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of) [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Samsung Display Co. Ltd., Tangjeong, Chungcheongnam-Do 336-741 (Korea, Republic of); Choi, Hagyoung; Lee, Sanghun [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)] [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Jeon, Heeyoung [Department of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)] [Department of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Jeon, Hyeongtag [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of) [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Department of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

2013-11-07

322

Rotary Actuator.  

National Technical Information Service (NTIS)

A rotary actuator suited for use in environments where rolling and sliding friction is to be avoided, such as in a high vacuum celestial space environment, is described. The actuator is characterized by the utilization of a plurality of spaced tri-flex pi...

C. Kallins J. Ostroff

1970-01-01

323

Internal Transport Barriers in Alcator C-Mod Ohmic H-Mode Plasmas  

NASA Astrophysics Data System (ADS)

Ohmic H-mode operation in Alcator C-Mod is often accompanied by a spontaneous peaking of the central density. The resulting electron density profile shows a ``foot'' at an r/a = 0.5, similar to most double transport barrier modes in this device. Analysis of the transport in these plasmas shows a reduction of the core thermal transport, decline of central toroidal rotataion velocity, and decrease of ?e in the barrier region. This is similar to the ITBs that are induced using off axis ICRF injection.(C. L. Fiore, et al., Phys. Plasmas), 8 2023.^,(S. J. Wukitch, et al., Phys. Plasmas), 9 2149.^,(J.E. Rice, et al., Nuclear Fusion), 42 510. The results of transport and stability code analysis of these plasmas will be presented. Recent experiments have been done to test the response and the performance of such Ohmic H-mode ITBs under the addition of varying amounts of central rf power. The results of these experiments will be also be presented.

Wolfe, S. M.; Fiore, C. L.; Bonoli, P. T.; Greenwald, M. J.; Hubbard, A. E.; Marmar, E. S.; Rice, J. E.; Wukitch, S. J.; Redi, M.

2002-11-01

324

Spatially resolved spectroscopic measurements of a dielectric barrier discharge plasma jet applicable for soft ionization  

NASA Astrophysics Data System (ADS)

An atmospheric pressure microplasma ionization source based on a dielectric barrier discharge with a helium plasma cone outside the electrode region has been developed for liquid chromatography/mass spectrometry and as ionization source for ion mobility spectrometry. It turned out that dielectric barrier discharge ionization could be regarded as a soft ionization technique characterized by only minor fragmentation similar to atmospheric pressure chemical ionization (APCI). Mainly protonated molecules were detected. In order to characterize the soft ionization mechanism spatially resolved optical emission spectrometry (OES) measurements were performed on plasma jets burning either in He or in Ar. Besides to spatial intensity distributions of noble gas spectral lines, in both cases a special attention was paid to lines of N 2+ and N 2. The obtained mapping of the plasma jet shows very different number density distributions of relevant excited species. In the case of helium plasma jet, strong N 2+ lines were observed. In contrast to that, the intensities of N 2 lines in Ar were below the present detection limit. The positions of N 2+ and N 2 distribution maxima in helium indicate the regions where the highest efficiency of the water ionization and the protonation process is expected.

Olenici-Craciunescu, S. B.; Müller, S.; Michels, A.; Horvatic, V.; Vadla, C.; Franzke, J.

2011-03-01

325

Surface treatment of para-aramid fiber by argon dielectric barrier discharge plasma at atmospheric pressure  

NASA Astrophysics Data System (ADS)

This paper is focused on influence of argon dielectric barrier discharge (DBD) plasma on the adhesive performance and wettability of para-aramid fibers and three parameters including treated power, exposure time and argon flux were detected. The interfacial shear strength (IFSS) was greatly increased by 28% with 300 W, 60 s, 2 L min-1 argon flux plasma treatment. The content of oxygen atom and oxygen-containing polar functional groups were enhanced after the argon plasma treated, so as the surface roughness, which contributed to the improvement of surface wettability and the decrease of contact angle with water. However, long-time exposure, exorbitant power or overlarge argon flux could partly destroy the prior effects of the treatment and damage the mechanical properties of fibers to some degree.

Gu, Ruxi; Yu, Junrong; Hu, Chengcheng; Chen, Lei; Zhu, Jing; Hu, Zuming

2012-10-01

326

Direct current dielectric barrier assistant discharge to get homogeneous plasma in capacitive coupled discharge  

NASA Astrophysics Data System (ADS)

In this paper, we propose a method to get more homogeneous plasma in the geometrically asymmetric capacitive coupled plasma (CCP) discharge. The dielectric barrier discharge (DBD) is used for the auxiliary discharge system to improve the homogeneity of the geometrically asymmetric CCP discharge. The single Langmuir probe measurement shows that the DBD can increase the electron density in the low density volume, where the DBD electrodes are mounted, when the pressure is higher than 5 Pa. By this manner, we are able to improve the homogeneity of the plasma production and increase the overall density in the target volume. At last, the finite element simulation results show that the DC bias, applied to the DBD electrodes, can increase the homogeneity of the electron density in the CCP discharge. The simulation results show a good agreement with the experiment results.

Du, Yinchang; Li, Yangfang; Cao, Jinxiang; Liu, Yu; Wang, Jian; Zheng, Zhe

2014-06-01

327

Surface modification of polypropylene non-woven fabric using atmospheric nitrogen dielectric barrier discharge plasma  

NASA Astrophysics Data System (ADS)

In this paper, a dielectric barrier discharge operating in nitrogen at atmospheric pressure has been used to improve the surface hydrophilic property of polypropylene (PP) non-woven fabric. The changes in the hydrophilic property of the modified PP samples are investigated by the contact angle measurements and the variation of water contact angle is obtained as a function of the energy density; micrographs of the PP before and after plasma treatment are observed by scanning electron microscopy (SEM) and the chemical composition of the PP surface before and after plasma treatment is also analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the surface hydrophilic property of the PP samples is greatly improved with plasma treatment for a few seconds, as evidenced by the fact that the contact angle of the treated PP samples significantly decreases after plasma treatment. The analysis of SEM shows that the surface roughness of the treated PP samples increases due to bonding and etching in plasma processing. The analyses of FTIR and the C1s peak in the high-resolution XPS indicate that oxygen-containing and nitrogen-containing polar functional groups are introduced into PP surface in plasma processing. It can be concluded that the surface hydrophilic property of the modified PP samples has been obviously improved due to the introduction of oxygen-containing and nitrogen-containing polar groups and the increase of the surface roughness on the PP surface.

Wang, Kunlei; Wang, Wenchun; Yang, Dezheng; Huo, Yan; Wang, Dezhen

2010-09-01

328

Development of a dielectric barrier discharge enhanced plasma jet in atmospheric pressure air  

SciTech Connect

A plasma jet equipped with dielectric barrier discharge (DBD) is developed to generate diffuse air plasma with fairly large gap and cross sectional area. The diffuse air plasma has two discharge modes under different gap widths from the nozzle to the ground plate electrode. For large gap width, a diffuse plume fills the whole space between the nozzle and the plate electrode after coaxial DBD is ignited when the applied voltage reaches a certain value. Rather than diffuse plasma plume, a bright plasma column bridges the nozzle and the plate electrode with further increasing the applied voltage under small gap width. By optical and electrical measurement, results show that the macroscopically diffuse discharge in air is obtained by the superimposition of radially distributed streamers that appear at different cycles of the applied voltage, and the bright plasma column belongs to atmospheric pressure glow discharge. The molecular vibrational temperature and the gas temperature are given as functions of the peak value of the applied voltage.

Li Xuechen; Chang Yuanyuan; Jia Pengying [College of Physics Science and Technology, Hebei University, Baoding 071002 (China); Xu Longfei; Fang Tongzhen; Wang Long [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2012-09-15

329

Effects of air dielectric barrier discharge plasma treatment time on surface properties of PBO fiber  

NASA Astrophysics Data System (ADS)

In this paper, the effects of air dielectric barrier discharge (DBD) plasma treatment time on surface properties of poly( p-phenylene benzobisoxazole) (PBO) fiber were investigated. The surface characteristics of PBO fiber before and after the plasma treatments were analyzed by dynamic contact angle (DCA) analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). DCA measurements indicated that the surface wettability of PBO fiber was improved significantly by increasing the fiber surface free energy via air DBD plasma treatments. The results were confirmed by the improvement of adhesion of a kind of thermoplastic resin to PBO fiber which was observed by SEM, showing that more resin was adhering evenly to the fiber surface. AFM measurement revealed that the surface topography of PBO fiber became more complicated and the surface roughness was greatly enhanced after the plasma treatments, and XPS analysis showed that some new polar groups (e.g. sbnd O sbnd C dbnd O) were introduced on plasma treated PBO fiber surface. The results of this study also showed that the surface properties of PBO fiber changed with the elongation of plasma treatment time.

Wang, Qian; Chen, Ping; Jia, Caixia; Chen, Mingxin; Li, Bin

2011-10-01

330

Development of a dielectric barrier discharge enhanced plasma jet in atmospheric pressure air  

NASA Astrophysics Data System (ADS)

A plasma jet equipped with dielectric barrier discharge (DBD) is developed to generate diffuse air plasma with fairly large gap and cross sectional area. The diffuse air plasma has two discharge modes under different gap widths from the nozzle to the ground plate electrode. For large gap width, a diffuse plume fills the whole space between the nozzle and the plate electrode after coaxial DBD is ignited when the applied voltage reaches a certain value. Rather than diffuse plasma plume, a bright plasma column bridges the nozzle and the plate electrode with further increasing the applied voltage under small gap width. By optical and electrical measurement, results show that the macroscopically diffuse discharge in air is obtained by the superimposition of radially distributed streamers that appear at different cycles of the applied voltage, and the bright plasma column belongs to atmospheric pressure glow discharge. The molecular vibrational temperature and the gas temperature are given as functions of the peak value of the applied voltage.

Li, Xuechen; Chang, Yuanyuan; Jia, Pengying; Xu, Longfei; Fang, Tongzhen; Wang, Long

2012-09-01

331

Electron temperature and plasma density distribution measurement along magnetic barrier in the PEGASES thruster  

NASA Astrophysics Data System (ADS)

The basic plasma parameter, electron temperature and plasma density were found as corresponding integrals of the measured EEDF in the PEGASES thruster. The measurements were carried out along the axis and off-axis of the magnetic barrier created with permanent magnets having their magnetic field lines normal to the plasma expansion. The plasma was generated with an induction coil on one end of the thruster, and diffused across magnetic field to the exit of the thruster. The experiments in argon gas were carried out for various parameters of magnetic field (strength, position and gradient). Previously, we showed that the electron temperature can be controlled by the magnetic field, and the degree of the temperature control depends on the gas pressure. In this study we measured the temperature off-axis to understand the influence of the wall conductivity on the electron transport across and along magnetic field. The off-axis probe measurements showed fine structures in the electron temperature and plasma density spatial distributions. A possible mechanism of the structures in the plasma density and the electron temperature distributions are discussed in this presentation.

Bredin, Jerome; Aanesland, Ane; Chabert, Pascal; Godyak, Valery

2012-10-01

332

Experimental Investigation of DBD Plasma Actuators Driven by Repetitive High Voltage Nanosecond Pulses with DC or Low-Frequency Sinusoidal Bias  

Microsoft Academic Search

Experimental studies were conducted of a flow induced in an initially quiescent room air by a single asymmetric dielectric barrier discharge driven by voltage waveforms consisting of repetitive nanosecond high-voltage pulses superimposed on DC or alternating sinusoidal or square-wave bias voltage. To characterize the pulses and to optimize their matching to the plasma, a numerical code for short pulse calculations

Dmitry F. Opaits; Gabriele Neretti; Alexandre V. Likhanskii; Sohail Zaidi; Mikhail N. Shneider; Richard B. Miles; Sergey O. Macheret

2007-01-01

333

Atmospheric plasma sprayed thermal barrier coatings with high segmentation crack densities: Spraying process, microstructure and thermal cycling behavior  

Microsoft Academic Search

Thermal barrier coatings (TBCs) with high strain tolerance are favorable for application in hot gas sections of aircraft turbines. To improve the strain tolerance of atmospheric plasma sprayed (APS) TBCs, 400?m–500?m thick coatings with very high segmentation crack densities produced with fused and crushed yttria stabilized zirconia (YSZ) were developed. Using a Triplex II plasma gun and an optimized spraying

M. Karger; R. Vaßen; D. Stöver

2011-01-01

334

Methane Conversion to Higher Hydrocarbons in the Presence of Carbon Dioxide Using Dielectric-Barrier Discharge Plasmas  

Microsoft Academic Search

Experimental investigation has been conducted to convert methane into higher hydrocarbons in the presence of carbon dioxide within dielectric-barrier discharge (DBD) plasmas. The objectives of cofeed of carbon dioxide are to inhibit carbon deposit and to increase methane conversion. The products from this plasma methane conversion include: (1) syngas (H2+CO), (2) gaseous hydrocarbons containing ethylene, acetylene, and propylene, (3) liquid

Chang-Jun Liu; Bingzhang Xue; Baldur Eliasson; Fei He; Yang Li; Gen-Hui Xu

2001-01-01

335

Dynamics of a potential barrier formed on the tail of a moving double layer in a collisionless plasma  

Microsoft Academic Search

A negative potential barrier on the low-potential side of a moving double layer gives rise to a current limitation in a collisionless plasma terminated by a positively biased cold collector plate in a Q machine. The double layer is produced in front of the plasma source and moves toward the collector during the limitation. When the double layer arrives at

S. Iizuka; P. Michelsen; J. J. Rasmussen; R. Schrittwieser; R. Hatakeyama; K. Saeki; N. Sato

1982-01-01

336

High-speed sterilization technique using dielectric barrier discharge plasmas in atmospheric humid air  

NASA Astrophysics Data System (ADS)

The inactivation of Bacillus atrophaeus spores by a dielectric barrier discharge (DBD) plasma produced by an ac voltage application of 1 kHz in atmospheric humid air was investigated in order to develop low-temperature, low-cost and high-speed plasma sterilization technique. The biological indicators covered with a Tyvek sheet were set just outside the DBD plasma region, where the air temperature and humidity as a discharge gas were precisely controlled by an environmental test chamber. The results show that the inactivation of Bacillus atrophaeus spores was found to be dependent strongly on the humidity, and was completed within 15 min at a relative humidity of 90 % and a temperature of 30 C. The treatment time for sterilization is shorter than those of conventional sterilization methods using ethylene oxide gas and dry heat treatment. It is considered that reactive species such as hydroxyl radicals that are effective for the inactivation of Bacillus atrophaeus spores could be produced by the DBD plasma in the humid air. Repetitive micro-pulsed discharge plasmas in the humid air will be applied for the sterilization experiment to enhance the sterilization efficiency.

Miyamae, M.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2010-11-01

337

Plasma-enhanced catalysis at atmospheric pressure, using a dielectric barrier discharge.  

NASA Astrophysics Data System (ADS)

The combination of plasmas and catalysis under moderate temperatures is an emerging area. The techniques are commonly combined in one of two ways. In the first of these the catalyst is introduced into the plasma while in the second, the catalyst is placed down-stream of the discharge. The introduction of a plasma to a catalysis system may produce a change in the distribution or type of reactive species available for reaction or a change of catalyst properties, such as an increase in dispersion or a change in catalyst structure. In the present work, a micro-reactor that allows the study of catalysis using temperature-programmed techniques. The reactor also allows a dielectric barrier discharge (DBD) to be generated over the whole length of the catalyst region or to precede it. The DBD produces a cool plasma at atmospheric pressure and generates surface modifications of the catalyst and is a source of ions and radicals for reaction processes. Test reactions have been studied to show differences in reaction product distributions and activation temperatures when compared with the catalyst alone. Reaction product distributions were measured using a Hiden, capillary-inlet, mass spectrometer. A molecular beam inlet, mass/energy spectrometer was also used to study the constituents of the DBD plasma.

Rees, J. A.; Lundie, D. T.; Seymour, D. L.; Whitmore, T. D.

2008-10-01

338

Rotary Actuator.  

National Technical Information Service (NTIS)

Rotary actuators and other mechanical devices incorporating shape memory alloys are provided herein. Shape memory alloys are a group of metals which when deformed at temperatures below their martensite temperatures, resume the shapes which they had prior ...

M. Brudnicki

1993-01-01

339

Process, properties, and environmental response of plasma sprayed thermal barrier coatings  

NASA Technical Reports Server (NTRS)

Experimental results are shown which demonstrate that the properties of plasma sprayed fully stabilized zirconia are strongly influenced by the process parameters. Properties of the coatings in the as-sprayed condition are shown to be additionally influenced by environmental exposure. This behavior is dependent on raw material considerations and processing conditions as well as exposure time and temperature. Process control methodology is described which can take into consideration these complex interactions and help to produce thermal barrier coatings in a cost effective way while meeting coating technical requirements.

Novak, Richard C.

1995-01-01

340

Plasma stability control using dielectric barriers in radio-frequency atmospheric pressure glow discharges  

SciTech Connect

It is widely accepted that electrode insulation is unnecessary for generating radio-frequency (rf) atmospheric pressure glow discharges (APGDs). It is also known that rf APGDs with large discharge current are susceptible to the glow-to-arc transition. In this letter, a computational study is presented to demonstrate that dielectric barriers provide an effective control over unlimited current growth and allow rf APGDs to be operated at very high current densities with little danger of the glow-to-arc transition. Characteristics of electrode sheaths are used to show that the stability control is achieved by forcing the plasma-containing electrode unit to acquire positive differential conductivity.

Shi, J. J.; Liu, D. W.; Kong, M. G. [Department of Electronic and Electrical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU (United Kingdom)

2006-08-21

341

Sintering and creep behavior of plasma-sprayed zirconia- and hafnia-based thermal barrier coatings  

Microsoft Academic Search

The sintering and creep of plasma-sprayed ceramic thermal barrier coatings under high temperature conditions are complex phenomena. Changes in thermomechanical and thermophysical properties and in the stress response of these coating systems as a result of the sintering and creep processes are detrimental to coating thermal fatigue resistance and performance. In this paper, the sintering characteristics of ZrO2–8wt%Y2O3, ZrO2–25wt%CeO2–2.5wt%Y2O3, ZrO2–6w%NiO–9wt%Y2O3,

Dongming Zhu; Robert A. Miller

1998-01-01

342

Fabrication of thin vertical mirrors through plasma etch and KOH:IPA polishing for integration into MEMS electrostatic actuators  

NASA Astrophysics Data System (ADS)

We developed a process for the fabrication of thin vertical mirrors as integrated structures of MEMS electrostatic actuators. The mirrors can be implemented as a vertical extension of the actuator sidewall, or can be positioned at any movable part of the actuator. The process involves the fabrication of a mesa structure on the handle layer of a silicon-oninsulator (SOI) wafer through deep reactive ion etching (DRIE). The etch/passivation cycles of the DRIE process were optimized to achieve vertical etch profiles with a depth of up to 200 ?m with an aspect ratio of 10:1. The DRIE process introduced typical etch scallops with peak-to-valley and rms roughnesses on the order of 100 nm and 30 nm, respectively. A mask layer was used to pattern a 2.1 ?m sacrificial oxide layer for the mesa structure. A second mask layer allowed us to define a large etch cavity for handle layer back-etch. The DRIE etched mesa structure was then etched with diluted potassium hydroxide (KOH) in isopropyl alcohol (IPA). Temperature and etch concentration were optimized for the removal of etch scallops without the formation of <111> etch facets. The etch scallops were almost completely removed and mirror quality surfaces were achieved. The developed mesa structures are suitable for integration into actuators that are patterned in the device layer. A third masking layer, aligned through infrared camera, was used to position the thin vertical mirror at the actuator sidewall. The process provides design flexibility in integrating vertical mirrors of adjustable dimensions to movable elements of MEMS structures.

Huda, M. Q.; Amin, T. M. F.; Ning, Y.; McKinnon, G.; Tulip, J.; Jäger, W.

2013-03-01

343

Decomposition of trifluoromethane in a dielectric barrier discharge non-thermal plasma reactor.  

PubMed

The decomposition of trifluoromethane (CHF3) was carried out using non-thermal plasma generated in a dielectric barrier discharge (DBD) reactor. The effects of reactor temperature, electric power, initial concentration and oxygen content were examined. The DBD reactor was able to completely destroy CHF3 with alumina beads as a packing material. The decomposition efficiency increased with increasing electric power and reactor temperature. The destruction of CHF3 gradually increased with the addition of O2 up to 2%, but further increase in the oxygen content led to a decrease in the decomposition efficiency. The degradation pathways were explained with the identified by-products. The main by-products from CHF3 were found to be COF2, CF4, CO2 and CO although the COF2 and CF4 disappeared when the plasma were combined with alumina catalyst. PMID:23513444

Gandhi, M Sanjeeva; Mok, Y S

2012-01-01

344

Deposition and Characteristics of Submicrometer-Structured Thermal Barrier Coatings by Suspension Plasma Spraying  

NASA Astrophysics Data System (ADS)

In the field of thermal barrier coatings (TBCs) for gas turbines, suspension plasma sprayed (SPS) submicrometer-structured coatings often show unique mechanical, thermal, and optical properties compared to conventional atmospheric plasma sprayed ones. They have thus the potential of providing increased TBC performances under severe thermo-mechanical loading. Experimental results showed the capability of SPS to obtain yttria stabilized zirconia coatings with very fine porosity and high density of vertical segmentation cracks, yielding high strain tolerance, and low Young's modulus. The evolution of the coating microstructure and properties during thermal cycling test at very high surface temperature (1400 °C) in our burner rigs and under isothermal annealing was investigated. Results showed that, while segmentation cracks survive, sintering occurs quickly during the first hours of exposure, leading to pore coarsening and stiffening of the coating. In-situ measurements at 1400 °C of the elastic modulus were performed to investigate in more detail the sintering-related stiffening.

Guignard, Alexandre; Mauer, Georg; Vaßen, Robert; Stöver, Detlev

2012-06-01

345

Development of dielectric barrier discharge plasma processing apparatus for mass spectrometry and thin film deposition.  

PubMed

Cost effective and a very simple dielectric barrier discharge plasma processing apparatus for thin film deposition and mass spectroscopic analysis of organic gas mixture has been described. The interesting features of the apparatus are the construction of the dielectric electrodes made of aluminum oxide or alumina (Al(2)O(3)) and glass and the generation of high ignition voltage from the spark plug transformer taken from car. Metal capacitor is introduced in between ground and oscilloscope to measure the executing power during the discharge and the average electron density in the plasma region. The organic polymer films have been deposited on Si (100) substrate using several organic gas compositions. The experimental setup provides a unique drainage system from the reaction chamber controlled by a membrane pump to suck out and remove the poisonous gases or residuals (cyanogens, H-CN, CH(x)NH(2), etc.) which have been produced during the discharge of CH(4)N(2) mixture. PMID:17672789

Majumdar, Abhijit; Hippler, Rainer

2007-07-01

346

Hybrid Plasma-Sprayed Thermal Barrier Coatings Using Powder and Solution Precursor Feedstock  

NASA Astrophysics Data System (ADS)

A novel approach of hybridizing the conventional atmospheric plasma spraying (APS) technique with the solution precursor plasma spray (SPPS) route to achieve thermal barrier coatings (TBCs) with tailored configurations is presented. Such a hybrid process can be conveniently adopted for forming composite, multi-layered and graded coatings employing simultaneous and/or sequential feeding of solution precursor as well as powder feedstock, yielding distinct TBC microstructures that bear promise to further extend coating durability. TBC specimens generated using conventional APS technique, the SPPS method and through APS-SPPS hybrid processing have been comprehensively characterized for microstructure, phase constitution, hardness and thermal cycling life, and the results were compared to demonstrate the advantages that can ensue from hybrid processing.

Joshi, S. V.; Sivakumar, G.; Raghuveer, T.; Dusane, R. O.

2014-04-01

347

Factors affecting the microstructural stability and durability of thermal barrier coatings fabricated by air plasma spraying  

SciTech Connect

The high-temperature behavior of high-purity, low-density (HP-LD) air plasma sprayed (APS) thermal barrier coatings (TBCs) with NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying is described. The high purity yttria-stabilized zirconia resulted in top coats which are highly resistant to sintering and transformation from the metastable tetragonal phase to the equilibrium mixture of monoclinic and cubic phases. The thermal conductivity of the as-processed TBC is low but increases during high temperature exposure even before densification occurs. The porous topcoat microstructure also resulted in good spallation resistance during thermal cycling. The actual failure mechanisms of the APS coatings were found to depend on topcoat thickness, topcoat density, and the thermal cycle frequency. The failure mechanisms are described and the durability of the HP-LD coatings is compared with that of state-of-the-art electron beam physical vapor deposition TBCs.

Helminiak, M. A.; Yanar, N. M.; Pettit, F. S.; Taylor, T. A.; Meier, G. H.

2012-10-01

348

Thermal barrier coatings on turbine blades by plasma spraying with improved cooling  

SciTech Connect

Turbine blades were coated with a thermal barrier coating system consisting of an MCrAlY bond coat about 100 [mu]m thick deposited by Low-Pressure Plasma Spraying (LPPS) and a 300 [mu]m thick ZrO[sub 2]-7 wt.% Y[sub 2]O[sub 3] top coat. The latter was manufactured by both Atmosphere and Temperature Controlled Spraying (ATCS) and Air Plasma Spraying (APS) using internal air cooling through the cooling holes of the turbine blades. Coated blades were submitted to thermal cycling tests in a burner rig with hot gas temperature of 1,485 C. In the case of ATCS coated blades the number of cycles until the first spallation at the leading edge of the blade was between 350 and 2,400. The number of cycles of the thermal barrier coatings sprayed with internal cooling was between 1,200 and 1,800. Furnace cycling tests were also carried out with ATCS coated blades at temperatures of 1,100 and 1,200 C. The results of thermal cycle tests and the investigations of the microstructure are discussed.

Cosack, T.; Schneiderbanger, S. (MTU Motoren- und Turbinen-Union, Munchen (Germany)); Pawlowski, L.; Sturlese, S. (CSM Centro Sviluppo Materiali, Pergine di Valsugana (Italy))

1994-01-01

349

Effects of Dielectric Barrier Discharge Plasma Treatment on Pentachlorophenol Removal of Granular Activated Carbon  

NASA Astrophysics Data System (ADS)

The pentachlorophenol (PCP) adsorbed granular activated carbon (GAC) was treated by dielectric barrier discharge (DBD) plasma. The effects of DBD plasma on the structure of GAC and PCP decomposition were analyzed by N2 adsorption, thermogravimetric, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and gas chromatography mass spectrometry (GC-MS). The experimental data of adsorption kinetics and thermodynamics of PCP on GAC were fitted with different kinetics and isotherm models, respectively. The results indicate that the types of N2 adsorption isotherm of GAC are not changed by DBD plasma, while the specific surface area and pore volume increase after DBD plasma treatment. It is found that the weight loss of the saturated GAC is the highest, on the contrary, the weight loss of DBD treated GAC is the least because of reduced PCP residue on the GAC. The XPS spectra and SEM image suggest that some PCP on the GAC is removed by DBD plasma, and the surface of GAC treated by DBD plasma presents irregular and heterogeneous morphology. The GC-MS identification of by-products shows that two main dechlorination intermediate products, tetrachlorophenol and trichlorophenol, are distinguished. The fitting results of experimental data of adsorption kinetics and thermodynamics indicate that the pseudo-first-order and pseudo-second order models can be used for the prediction of the kinetics of virgin GAC and DBD treated GAC for PCP adsorption, and the Langmuir isotherm model fits better with the data of adsorption isotherm than the Freundlich isotherm in the adsorption of PCP on virgin GAC and DBD treated GAC.

Ji, Puhui; Qu, Guangzhou; Li, Jie

2013-10-01

350

QUIESCENT DOUBLE BARRIER H-MODE PLASMAS IN THE DIII-D TOKAMAK  

SciTech Connect

High confinement (H-mode) operation is the choice for next-step tokamak devices based either on conventional or advanced tokamak physics. This choice, however, comes at a significant cost for both the conventional and advanced tokamaks because of the effects of edge localized modes (ELMs). ELMs can produce significant erosion in the divertor and can affect the beta limit and reduced core transport regions needed for advanced tokamak operation. Experimental results from DIII-D [J.L. Luxon, et al., Plasma Phys. and Contr. Nucl. Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987) Vol. I, p. 159] this year have demonstrated a new operating regime, the quiescent H-mode regime, which solves these problems. We have achieved quiescent H-mode operation which is ELM-free and yet has good density and impurity control. In addition, we have demonstrated that an internal transport barrier can be produced and maintained inside the H-mode edge barrier for long periods of time (>3.5 seconds or >25 energy confinement times {tau}{sub E}), yielding a quiescent double barrier regime. By slowly ramping the input power, we have achieved {beta}{sub N} H{sub 89} = 7 for up to 5 times the {tau}{sub E} of 150 ms. The {beta}{sub N} H{sub 89} values of 7 substantially exceed the value of 4 routinely achieved in standard ELMing H-mode. The key factors in creating the quiescent H-mode operation are neutral beam injection in the direction opposite to the plasma current (counter injection) plus cryopumping to reduce the density. Density and impurity control in the quiescent H-mode is possible because of the presence of an edge magnetic hydrodynamic (MHD) oscillation, the edge harmonic oscillation, which enhances the edge particle transport while leaving the energy transport unaffected.

K.H. BURRELL; M.E. AUSTIN; D.P. BRENNAN; J.C. DeBOO; E.J. DOYLE; C. FENZI; C. FUCHS; P. GOHIL; R.J. GROEBNER; L.L. LAO; T.C. LUCE; M.A. MAKOWSKI; G.R. McKEE; R.A. MOYER; C.C. PETTY; M. PORKOLAB; C.L.RETTIG; T.L. RHODES; J.C. ROST; B.W. STALLARD; E.J. STRAIT; E.J. SYNAKOWSKI; M.R. WADE; J.G. WATKINS; W.P. WEST

2000-11-01

351

Method and Process Development of Advanced Atmospheric Plasma Spraying for Thermal Barrier Coatings  

NASA Astrophysics Data System (ADS)

Over the last few years, global economic growth has triggered a dramatic increase in the demand for resources, resulting in steady rise in prices for energy and raw materials. In the gas turbine manufacturing sector, process optimizations of cost-intensive production steps involve a heightened potential of savings and form the basis for securing future competitive advantages in the market. In this context, the atmospheric plasma spraying (APS) process for thermal barrier coatings (TBC) has been optimized. A constraint for the optimization of the APS coating process is the use of the existing coating equipment. Furthermore, the current coating quality and characteristics must not change so as to avoid new qualification and testing. Using experience in APS and empirically gained data, the process optimization plan included the variation of e.g. the plasma gas composition and flow-rate, the electrical power, the arrangement and angle of the powder injectors in relation to the plasma jet, the grain size distribution of the spray powder and the plasma torch movement procedures such as spray distance, offset and iteration. In particular, plasma properties (enthalpy, velocity and temperature), powder injection conditions (injection point, injection speed, grain size and distribution) and the coating lamination (coating pattern and spraying distance) are examined. The optimized process and resulting coating were compared to the current situation using several diagnostic methods. The improved process significantly reduces costs and achieves the requirement of comparable coating quality. Furthermore, a contribution was made towards better comprehension of the APS of ceramics and the definition of a better method for future process developments.

Mihm, Sebastian; Duda, Thomas; Gruner, Heiko; Thomas, Georg; Dzur, Birger

2012-06-01

352

Flow Separation Control on Trailing Edge Radii using Single Dielectric Barrier Discharge Plasma Actuators: An Application to Vehicle Drag Control  

Microsoft Academic Search

As cruise speeds of ground vehicles has risen to as high as 70 miles per hour, overcoming the aerodynamic drag has become\\u000a a significant percentage of the total power required. Engines have been increased in power and fuel tanks made larger to provide\\u000a reasonable range between fuel stops. Heavy truck data in particular indicate that 2\\/3rds of the cruise power

R. Spivey; R. Hewitt; H. Othman; T. Corke

353

Thermally Actuated Hydraulic Pumps  

NASA Technical Reports Server (NTRS)

Thermally actuated hydraulic pumps have been proposed for diverse applications in which direct electrical or mechanical actuation is undesirable and the relative slowness of thermal actuation can be tolerated. The proposed pumps would not contain any sliding (wearing) parts in their compressors and, hence, could have long operational lifetimes. The basic principle of a pump according to the proposal is to utilize the thermal expansion and contraction of a wax or other phase-change material in contact with a hydraulic fluid in a rigid chamber. Heating the chamber and its contents from below to above the melting temperature of the phase-change material would cause the material to expand significantly, thus causing a substantial increase in hydraulic pressure and/or a substantial displacement of hydraulic fluid out of the chamber. Similarly, cooling the chamber and its contents from above to below the melting temperature of the phase-change material would cause the material to contract significantly, thus causing a substantial decrease in hydraulic pressure and/or a substantial displacement of hydraulic fluid into the chamber. The displacement of the hydraulic fluid could be used to drive a piston. The figure illustrates a simple example of a hydraulic jack driven by a thermally actuated hydraulic pump. The pump chamber would be a cylinder containing encapsulated wax pellets and containing radial fins to facilitate transfer of heat to and from the wax. The plastic encapsulation would serve as an oil/wax barrier and the remaining interior space could be filled with hydraulic oil. A filter would retain the encapsulated wax particles in the pump chamber while allowing the hydraulic oil to flow into and out of the chamber. In one important class of potential applications, thermally actuated hydraulic pumps, exploiting vertical ocean temperature gradients for heating and cooling as needed, would be used to vary hydraulic pressures to control buoyancy in undersea research vessels. Heretofore, electrically actuated hydraulic pumps have been used for this purpose. By eliminating the demand for electrical energy for pumping, the use of the thermally actuated hydraulic pumps could prolong the intervals between battery charges, thus making it possible to greatly increase the durations of undersea exploratory missions.

Jones, Jack; Ross, Ronald; Chao, Yi

2008-01-01

354

Improving Atmospheric Plasma Spraying of Zirconate Thermal Barrier Coatings Based on Particle Diagnostics  

NASA Astrophysics Data System (ADS)

Lanthanum zirconate (La2Zr2O7) has been proposed as a promising material for thermal barrier coatings. During atmospheric plasma spraying (APS) of La2Zr2O7 a considerable amount of La2O3 can evaporate in the plasma flame, resulting in a non-stoichiometric coating. As indicated in the phase diagram of the La2O3-ZrO2 system, in the composition range of pyrochlore structure, the stoichiometric La2Zr2O7 has the highest melting point and other compositions are eutectic. APS experiments were performed with a TriplexPro™-200 plasma torch at different power levels to achieve different degrees of evaporation and thus stoichiometry. For comparison, some investigations on gadolinium zirconate (Gd2Zr2O7) were included, which is less prone to evaporation and formation of non-stoichiometry. Particle temperature distributions were measured by the DPV-2000 diagnostic system. In these distributions, characteristic peaks were detected at specific torch input powers indicating evaporation and solidification processes. Based on this, process parameters can be defined to provide stoichiometric coatings that show good thermal cycling performance.

Mauer, Georg; Sebold, Doris; Vaßen, Robert; Stöver, Detlev

2012-06-01

355

Odor Removal Characteristics of Barrier-Type Packed-Bed Nonthermal Plasma Reactor  

NASA Astrophysics Data System (ADS)

Odor control has gained importance for ensuring a comfortable living environment. In this paper, the authors report the experimental results of a study of the detailed characteristics of a barrier-type packed-bed nonthermal plasma reactor used for odor control. This plasma reactor has been widely used for volatile organic compound (VOC) decomposition and NOx reduction. The reactor is energized by a low-cost 60 Hz AC power supply. Removal efficiency and the concentrations of byproducts are studied under various experimental conditions. The complete decomposition of the main odor component, namely, NH3, is obtained with minimal reaction byproduct formation (maximum N2O concentration, 10 ppm) in a dry environment. The decomposition is deteriorated by the addition of moisture. The minimum residence time is determined for the complete removal of NH3 in the case of the packed-bed plasma reactor. The pellet diameter has little effect on the removal tendency, and the reactor performed better than a silent corona. Mixing another odor component such as CH3CHO into the gas stream has little effect on the NH3 removal efficiency.

Okubo, Masaaki; Kametaka, Hidetaka; Yoshida, Keiichiro; Yamamoto, Toshiaki

2007-08-01

356

Actuated atomizer  

NASA Technical Reports Server (NTRS)

An actuated atomizer is adapted for spray cooling or other applications wherein a well-developed, homogeneous and generally conical spray mist is required. The actuated atomizer includes an outer shell formed by an inner ring; an outer ring; an actuator insert and a cap. A nozzle framework is positioned within the actuator insert. A base of the nozzle framework defines swirl inlets, a swirl chamber and a swirl chamber. A nozzle insert defines a center inlet and feed ports. A spool is positioned within the coil housing, and carries the coil windings having a number of turns calculated to result in a magnetic field of sufficient strength to overcome the bias of the spring. A plunger moves in response to the magnetic field of the windings. A stop prevents the pintle from being withdrawn excessively. A pintle, positioned by the plunger, moves between first and second positions. In the first position, the head of the pintle blocks the discharge passage of the nozzle framework, thereby preventing the atomizer from discharging fluid. In the second position, the pintle is withdrawn from the swirl chamber, allowing the atomizer to release atomized fluid. A spring biases the pintle to block the discharge passage. The strength of the spring is overcome, however, by the magnetic field created by the windings positioned on the spool, which withdraws the plunger into the spool and further compresses the spring.

Tilton, Charles (Inventor); Weiler, Jeff (Inventor); Palmer, Randall (Inventor); Appel, Philip (Inventor)

2008-01-01

357

Pneumatic Actuators  

NSDL National Science Digital Library

This learning object covers cylinders and motor pneumatic actuators. It is hosted by the University of Wisconsin-Madison and consists of cylinders operations such as: single, duel acting, factors for cylinder speed. The program require Macromedia Flash player, and presents a very nice overall presentation format.

2008-11-14

358

Mechanical Properties of Plasma-Sprayed ZrO2-8 wt% Y2O3 Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

Mechanical behavior of free standing, plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings, including strength, fracture toughness, fatigue, constitutive relation, elastic modulus, and directionality, has been determined under various loading-specimen configurations. This report presents and describes a summary of mechanical properties of the plasma-sprayed coating material to provide them as a design database.

Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

2004-01-01

359

Processing-structure-property relationships of thermal barrier coatings deposited using the solution precursor plasma spray process  

Microsoft Academic Search

This research is intended to develop a novel process, solution-precursor plasma-spray (SPPS), for the deposition of highly durable thermal barrier coatings (TBCs). In the SPPS process a solution precursor feedstock, that results in ZrO2-7 wt% Y2O3 ceramic, is injected into the plasma jet and the coating is deposited on a metal substrate. The formed coating has the following novel microstructural

Liangde Xie

2003-01-01

360

Microstructure and Thermal Properties of Plasma Sprayed Thermal Barrier Coatings from Nanostructured YSZ  

NASA Astrophysics Data System (ADS)

Nanostructured yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were produced by atmospheric plasma spraying. The microstructure of the sprayed coating was characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM). The nano-coating had a higher porosity of ~25% than the conventional coating, which is mainly attributed to the large amount of intersplat gaps in the nano-coating. The thermal conductivity for the nano-coating was in the level of 0.8-1.1 W/m·K, about 40% lower than that for the conventional coating, indicating a better thermal insulation performance. The nano-TBC exhibited a thermal cycling lifetime of more than 500 cycles, whereas spallation failure of the conventional TBC occurred within 200 cycles. Accelerated sintering could be one of the reasons for the failure of the nano-TBC.

Wu, Jing; Guo, Hong-Bo; Zhou, Le; Wang, Lu; Gong, Sheng-Kai

2010-12-01

361

A simple dielectric barrier discharge device for generating slot homogeneous plasma in atmospheric pressure air  

SciTech Connect

We report a simple dielectric barrier discharge device for generating slot homogeneous plasma in atmospheric pressure air. It consists of two parallel water electrodes with a distance adjusting micrometer. With increasing the applied voltage, the discharge becomes homogeneous. The electron temperature, vibrational temperature (T{sub V}) of N{sub 2}, and rotational temperature (T{sub R}) of N{sub 2}{sup +} are estimated by optical emission spectroscopy. Both T{sub V} and T{sub R} remain unchanged along the slot in the homogeneous discharge regime. The trend of the T{sub V} with respect to the applied voltage is opposite from that of T{sub R}, while the electron temperature keeps constant with the increasing applied voltage.

Dong Lifang; Zhang Yanzhao; Liu Weiyuan; Yang Li; Chen Junying [College of Physics Science and Technology, Hebei University, Baoding 071002 (China)

2009-03-02

362

Spray-dried porcine plasma influences intestinal barrier function, inflammation, and diarrhea in weaned pigs.  

PubMed

The objective of this study was to evaluate the effects of dietary inclusion levels of spray-dried porcine plasma (SDPP) on postweaning (PW) intestinal barrier function, mucosal inflammation, and clinical indices of gut health in pigs. Ex vivo Ussing chamber studies were conducted to measure Ileal and colonic barrier function in terms of transepithelial electrical resistance and paracellular flux of (3)H-mannitol and (14)C-inulin. Intestinal inflammation was assessed by histological analysis and mucosal levels of proinflammatory cytokines. Dietary inclusion of 2.5 and 5% SDPP reduced colonic paracellular permeability of (14)C-inulin compared with controls (0% SDPP) on d 7 PW. Both 2.5 and 5% dietary SDPP reduced ileal (3)H-mannitol and (14)C-inulin permeability on d 14 PW. The 5% SDPP diet reduced colonic short-circuit current, an index of net electrogenic ion transport, and fecal scores when measured on d 7 and 14 PW compared with the control and 2.5% SDPP groups (P < 0.05). Histological analysis revealed fewer lamina propria cells in ileum and colon from pigs fed diets containing 2.5 and 5% SDPP on d 7 and 14 PW. Levels of the proinflammatory cytokine TNF? were reduced in the colon but not ileum from pigs fed the 5% SDPP on d 7 and 14 PW compared with controls (P < 0.05). IFN? levels were lower than in controls in both of the SDPP-fed groups in the ileum and colon on d 7 but not on d 14 PW. Overall, this study demonstrated that dietary inclusion of SDPP had beneficial effects on intestinal barrier function, inflammation, and diarrhea in weaned pigs. PMID:21613450

Peace, Ralph Michael; Campbell, Joy; Polo, Javier; Crenshaw, Joe; Russell, Louis; Moeser, Adam

2011-07-01

363

Quiescent Double Barrier H-Mode Plasmas in the DIII-D Tokamak  

SciTech Connect

High confinement (H-mode) operation is the choice for next-step tokamak devices based either on conventional or advanced tokamak physics. This choice, however, comes at a significant cost for both the conventional and advanced tokamaks because of the effects of edge localized modes (ELMs). ELMs can produce significant erosion in the divertor and can affect the beta limit and reduced core transport regions needed for advanced tokamak operation. Experimental results from DIII-D this year have demonstrated a new operating regime, the quiescent H-mode regime, which solves these problems. We have achieved quiescent H-mode operation which is ELM-free and yet has good density and impurity control. In addition, we have demonstrated that an internal transport barrier can be produced and maintained inside the H-mode edge barrier for long periods of time (>3.5 seconds or >25 energy confinement times {tau}{sub E}), yielding a quiescent double barrier regime. By slowly ramping the input power, we have achieved {beta}{sub N} H89 = 7 for up to 5 times the {tau}{sub E} of 150 ms. The {beta}{sub N} H89 values of 7 substantially exceed the value of 4 routinely achieved in standard ELMing H-mode. The key factors in creating the quiescent H-mode operation are neutral beam injection in the direction opposite to the plasma current (counter injection) plus cryopumping to reduce the density. Density and impurity control in the quiescent H-mode is possible because of the presence of an edge magnetic hydrodynamic (MHD) oscillation, the edge harmonic oscillation, which enhances the edge particle transport while leaving the energy transport unaffected.

Burrell, K H; Austin, M E; Brennan, D P; DeBoo, J C; Doyle, E J; Fenzi, C; Fuchs, C; Gohil, P; Greenfield, C M; Groebner, R J; Lao, L L; Luce, T C; Makowski, M A; McKee, G R; Moyer, R A; Petty, C C; Porkolab, M; Rettig, C L; Rhodes, T L; Rost, J C; Stallard, B W; Strait, E J; Synakowski, E J; Wade, M R; Watkins, J G; West, W P

2000-11-01

364

Effect of Sintering on Mechanical and Physical Properties of Plasma-Sprayed Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

The effect of sintering on mechanical and physical properties of free-standing plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings (TBCs) was determined by annealing them at 1316 C in air. Mechanical and physical properties of the TBCs, including strength, modes I and II fracture toughness, elastic modulus, Poisson s response, density, microhardness, fractography, and phase stability, were determined at ambient temperature as a function of annealing time ranging from 0 to 500 h. All mechanical and physical properties, except for the amount of monoclinic phase, increased significantly in 5 to 100 h and then reached a plateau above 100 h. Annealing resulted in healing of microcracks and pores and in grain growth, accompanying densification of the TBC s body due to the sintering effect. However, an inevitable adverse effect also occurred such that the desired lower thermal conductivity and good expansivity, which makes the TBCs unique in thermal barrier applications, were degraded upon annealing. A model was proposed to assess and quantify all the property variables in response to annealing in a normalized scheme. Directionality of as-sprayed TBCs appeared to have an insignificant effect on their properties, as determined via fracture toughness, microhardness, and elastic modulus measurements.

Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

2004-01-01

365

Monitoring Delamination of Plasma-Sprayed Thermal Barrier Coatings by Reflectance-Enhanced Luminescence  

NASA Technical Reports Server (NTRS)

Highly scattering plasma-sprayed thermal barrier coatings (TBCs) present a challenge for optical diagnostic methods to monitor TBC delamination because scattering attenuates light transmitted through the TBC and usually degrades contrast between attached and delaminated regions of the TBC. This paper presents a new approach where reflectance-enhanced luminescence from a luminescent sublayer incorporated along the bottom of the TBC is used to identify regions of TBC delamination. Because of the higher survival rate of luminescence reflecting off the back surface of a delaminated TBC, the strong scattering exhibited by plasma-sprayed TBCs actually accentuates contrast between attached and delaminated regions by making it more likely that multiple reflections of luminescence off the back surface occur before exiting the top surface of the TBC. A freestanding coating containing sections designed to model an attached or delaminated TBC was prepared by depositing a luminescent Eu-doped or Er-doped yttria-stabilized zirconia (YSZ) luminescent layer below a plasma-sprayed undoped YSZ layer and utilizing a NiCr backing layer to represent an attached substrate. For specimens with a Eu-doped YSZ luminescent sublayer, luminescence intensity maps showed excellent contrast between unbacked and NiCr-backed sections even at a plasma-sprayed overlayer thickness of 300 m. Discernable contrast between unbacked and NiCr-backed sections was not observed for specimens with a Er-doped YSZ luminescent sublayer because luminescence from Er impurities in the undoped YSZ layer overwhelmed luminescence originating form the Er-doped YSZ sublayer.

Eldridge, Jeffrey I.; Bencic, Timothy J.

2006-01-01

366

Some observations on plasma-assisted combustion enhancement using dielectric barrier discharges  

NASA Astrophysics Data System (ADS)

We explore an effective way to promote propane combustion by applying a plasma discharge for efficiency enhancement. A coaxial-cylinder, dielectric barrier discharge is used to activate propane and air before they are mixed with each other and ignited for combustion. The characteristics of the combustion flame are well studied and evaluated by varying various operational parameters. It is found that the combustion process can be enhanced by applying a plasma on either the propane or air stream, and the combustion stability is found to be somewhat sensitive to the lean burning conditions and confined to a relatively narrow operating window. The temperature and spectrum of the flame in the main combustion zone are investigated with a 4 W plasma in the on or off state. The main components are identified, and the possible physical and chemical reaction mechanisms are discussed. A comparative analysis of these spectra and temperatures obtained in the main flame suggests that the energy generated from the 4 W plasma is partially used to heat the reaction gases in the flame, and another part of the energy is used to increase the luminosity, especially for activation of air. We also observe that combustion of high flow rate propane and/or air requires more discharge energy density under certain conditions. A comparison of combustion enhancement through different activation methods in flame blowout tests shows that reactive species derived from activation of air play a more critical role in the blowout limit of propane combustion flame than those generated by activation of propane at low equivalence ratio and propane flow.

Tang, Jie; Zhao, Wei; Duan, Yixiang

2011-08-01

367

Compartmentalisation of the sperm plasma membrane: a FRAP, FLIP and SPFI analysis of putative diffusion barriers on the sperm head  

Microsoft Academic Search

Spermatozoa are highly polarised cells with a compartmentalised distribution of lipids and proteins in their plasma membrane. It is not known how these compartments are stably maintained in what is essentially a fluid environment. In this investigation we have examined the hypothesis that intramembranous diffusion barriers selectively retain some components within compartments, while allowing free passage of others. A fluorescence

Peter S. James; Conor Hennessy; Torunn Berge; Roy Jones

2004-01-01

368

Characterization and Properties of Electroless Nickel Plated Poly (ethylene terephthalate) Nonwoven Fabric Enhanced by Dielectric Barrier Discharge Plasma Pretreatment  

Microsoft Academic Search

In order to develop a more economical pretreatment method for electroless nickel plating, a dielectric barrier discharge (DBD) plasma at atmospheric pressure was used to improve the hydrophilicity and adhesion of poly (ethylene terephthalate) (PET) nonwoven fabric. The properties of the PET nonwoven fabric including its liquid absorptive capacity (WA), aging behavior, surface chemical composition, morphology of the surface, adhesion

Yamin Geng; Canhui Lu; Mei Liang; Wei Zhang

2010-01-01

369

Role of environment deposits and operating surface temperature in spallation of air plasma sprayed thermal barrier coatings  

Microsoft Academic Search

Spallation of air plasma sprayed (APS) thermal barrier coatings (TBCs) was investigated on power generation combustors, military turboshaft engines, and commercial turboprop engines. In each case, irrespective of operating conditions or geographic location, spallation was linked to the presence and infiltration of high temperature molten phases of similar composition. Electron microprobe analysis found that, from all the possible oxides available

Marcus P. Borom; Curtis A. Johnson; Louis A. Peluso

1996-01-01

370

Isothermal Oxidation Behavior of Supersonic Atmospheric Plasma-Sprayed Thermal Barrier Coating System  

NASA Astrophysics Data System (ADS)

In this work, Y2O3 stabilized zirconia-based thermal barrier coatings (TBCs) were deposited by conventional atmospheric plasma spraying (APS) and high efficiency supersonic atmospheric plasma spraying (SAPS), respectively. The effect of Al2O3 layer stability on the isothermal growth behavior of thermally grown oxides (TGOs) was studied. The results revealed that the Al2O3 layer experienced a three-stage change process, i.e., (1) instantaneous growth stage, (2) steady-state growth stage, and (3) depletion stage. The thickness of Al2O3 scale was proved to be an important factor for the growth rate of TGOs. The SAPS-TBCs exhibited a higher Al2O3 stability and better oxidation resistance as compared with the APS-TBCs. Additionally, it was found that inner oxides, especially nucleated on the top of the crest, continually grew and swallowed the previously formed Al2O3 layer, leading to the granulation and disappearance of continuous Al2O3 scale, which was finally replaced by the mixed oxides and spinel.

Bai, Yu; Ding, Chunhua; Li, Hongqiang; Han, Zhihai; Ding, Bingjun; Wang, Tiejun; Yu, Lie

2013-10-01

371

Improving the thermal shock resistance of plasma sprayed CYSZ thermal barrier coatings by laser surface modification  

NASA Astrophysics Data System (ADS)

In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ) topcoat by air plasma spraying (APS). After that, the plasma sprayed CYSZ thermal barrier coatings (TBCs) were treated using a pulsed Nd:YAG laser. The effects of laser glazing on the microstructure and thermal shock resistance of the coatings were evaluated. Thermal shock test was administered by holding specimens at 950 °C for 5 min and then water quenching. More than 20% of the spalled region of the surface of the topcoat was adopted as the criterion for the failure of samples. The microstructures of both the as processed and the tested TBCs were investigated using scanning electron microscope (SEM). The phases of the coatings were analyzed with X-ray diffractometry (XRD). XRD analysis revealed that both as sprayed and laser glazed topcoats consisted of nonequilibrium tetragonal (T') phase. The results showed that the life times of the as sprayed TBCs were enhanced around fourfold by the formation of a continuous network of segmented cracks perpendicular to the surface and the increase in strain accommodation.

Ahmadi-Pidani, Raheleh; Shoja-Razavi, Reza; Mozafarinia, Reza; Jamali, Hossein

2012-05-01

372

Neutron and X-ray diffraction of plasma-sprayed zirconia-yttria thermal barrier coatings  

NASA Technical Reports Server (NTRS)

ZrO2-7.8mol. pct. YO1.5, a fused powder, and ZrO2-8.7mol. pct. YO1.5, a prereacted powder, were plasma-sprayed onto steel substrates. Neutron diffraction and X-ray diffraction of the as-received powder, the powder plasma sprayed into water, as-sprayed coatings, and coatings heat-treated for 10 and 100 h were carried out to study phase transformations and ordering of the oxygen ions on the oxygen sublattice. The as-received fused powder has a much lower monoclinic percentage than does the pre-reacted powder, this resulting in a much lower monoclinic percentage in the coating. Heat treatment increases the percentages of the cubic and monoclinic phases, while decreasing the tetragonal content. An ordered tetragonal phase is detected by the presence of extra neutron diffraction peaks. These phase transformations and ordering will result in volume changes. The implications of these transformations on the performance of partially stabilized zirconia thermal barrier coatings is discussed.

Shankar, N. R.; Herman, H.; Singhal, S. P.; Berndt, C. C.

1984-01-01

373

Generation of line-shaped atmospheric pressure plasma on planar surface with diffuse coplanar surface barrier discharge  

NASA Astrophysics Data System (ADS)

A line-shaped uniform atmospheric pressure plasma was generated by diffuse coplanar surface barrier discharge on a planar surface. In this work, the plate is assumed as a wall panel in operation rooms. In the wall panel sample, powered and grounded electrode lines were arranged alternately. Applying an negative high voltage pulse of V=?4 kV and f=13 kHz, a uniform atmospheric pressure plasma was observed between electrodes on the panel surface. The plasma had chemically active species of nitrogen molecule and nitrogen molecule ion which are effective for sterilization.

Akamatsu, H.

2014-06-01

374

Moisture barrier properties of thin organic-inorganic multilayers prepared by plasma-enhanced ALD and CVD in one reactor.  

PubMed

A widely used application of the atomic layer deposition (ALD) and chemical vapour deposition (CVD) methods is the preparation of permeation barrier layers against water vapour. Especially in the field of organic electronics, these films are highly demanded as such devices are very sensitive to moisture and oxygen. In this work, multilayers of aluminium oxide (AlO x ) and plasma polymer (PP) were coated on polyethylene naphthalate substrates by plasma-enhanced ALD and plasma-enhanced CVD at 80â"ƒ in the same reactor, respectively. As precursor, trimethylaluminium was used together with oxygen radicals in order to prepare AlO x , and benzene served as precursor to deposit the PP. This hybrid structure allows the decoupling of defects between the single AlO x layers and extends the permeation path for water molecules towards the entire barrier film. Furthermore, the combination of two plasma techniques in a single reactor system enables short process times without vacuum breaks. Single aluminium oxide films by plasma-enhanced ALD were compared to thermally grown layers and showed a significantly better barrier performance. The water vapour transmission rate (WVTR) was determined by means of electrical calcium tests. For a multilayer with 3.5 dyads of 25-nm AlO x and 125-nm PP, a WVTR of 1.2 × 10 (-3) gm (-2) d (-1) at 60â"ƒ and 90% relative humidity could be observed. PMID:24936155

Bülow, Tim; Gargouri, Hassan; Siebert, Mirko; Rudolph, Rolf; Johannes, Hans-Hermann; Kowalsky, Wolfgang

2014-01-01

375

Moisture barrier properties of thin organic-inorganic multilayers prepared by plasma-enhanced ALD and CVD in one reactor  

PubMed Central

A widely used application of the atomic layer deposition (ALD) and chemical vapour deposition (CVD) methods is the preparation of permeation barrier layers against water vapour. Especially in the field of organic electronics, these films are highly demanded as such devices are very sensitive to moisture and oxygen. In this work, multilayers of aluminium oxide (AlO x ) and plasma polymer (PP) were coated on polyethylene naphthalate substrates by plasma-enhanced ALD and plasma-enhanced CVD at 80℃ in the same reactor, respectively. As precursor, trimethylaluminium was used together with oxygen radicals in order to prepare AlO x , and benzene served as precursor to deposit the PP. This hybrid structure allows the decoupling of defects between the single AlO x layers and extends the permeation path for water molecules towards the entire barrier film. Furthermore, the combination of two plasma techniques in a single reactor system enables short process times without vacuum breaks. Single aluminium oxide films by plasma-enhanced ALD were compared to thermally grown layers and showed a significantly better barrier performance. The water vapour transmission rate (WVTR) was determined by means of electrical calcium tests. For a multilayer with 3.5 dyads of 25-nm AlO x and 125-nm PP, a WVTR of 1.2 × 10 ?3 gm?2d?1 at 60℃ and 90% relative humidity could be observed.

2014-01-01

376

Rotary actuator  

NASA Technical Reports Server (NTRS)

Rotary actuators and other mechanical devices incorporating shape memory alloys are provided herein. Shape memory alloys are a group of metals which when deformed at temperatures below their martensite temperatures, resume the shapes which they had prior to the deformation if they are heated to temperatures above their austensite temperatures. Actuators in which shape memory alloys are employed include bias spring types, in which springs deform the shape memory alloy (SMA), and differential actuators, which use two SMA members mechanically connected in series. Another type uses concentric cylindrical members. One member is in the form of a sleeve surrounding a cylinder, both being constructed of shape memory alloys. Herein two capstans are mounted on a shaft which is supported in a framework. Each capstan is capable of rotating the shaft. Shape memory wire, as two separate lengths of wire, is wrapped around each capstan to form a winding around that capstan. The winding on one capstan is so wrapped that the wire is in a prestretched state. The winding on the other capstan is so wrapped that the wire is in a taut, but not a prestretched, state. Heating one performs work in one direction, thus deforming the other one. When the other SMA is heated the action is reversed.

Brudnicki, Myron (inventor)

1995-01-01

377

A diffuse plasma generated by bipolar nanosecond pulsed dielectric barrier discharge in nitrogen  

NASA Astrophysics Data System (ADS)

In this study, a bipolar high-voltage pulse with 20 ns rising time is employed to generate diffuse dielectric barrier discharge plasma using wire-plate electrode configuration in nitrogen at atmospheric pressure. The gas temperature of the plasma is determined by comparing the experimental and the best fitted optical emission spectra of the second positive bands of N2(C3?u ? B3 ?g, 0-2) and the first negative bands of N2+ (B2 ?u+ ? X2 ?g+, 0-0). The effects of the concentration of argon and oxygen on the emission intensities of N2 (C3?u ? B3?g, 0-0, 337.1 nm), OH (A 2? ? X2?, 0-0) and N2+ (B2 ?u+ ? X2 ?g+, 0-0, 391.4 nm) are investigated. It is shown that the plasma gas temperature keeps almost constant with the pulse repetition rate and pulse peak voltage increasing. The emission intensities of N2 (C3?u ? B3?g, 0-0, 337.1 nm), OH(A2? ? X2?, 0-0) and N2+ (B2 ?u+ ? X2 ?g+, 0-0, 391.4 nm) rise with increasing the concentration of argon, but decrease with increasing the concentration of oxygen, and the influences of oxygen concentration on the emission intensities of N2(C3?u ? B3?g, 0-0, 337.1 nm) and OH (A2? ? X2?, 0-0) are more greater than that on the emission intensity of N2+ (B2 ?u+ ? X2 ?g+, 0-0, 391.4 nm).

Jia, Li; Yang, De-Zheng; Shi, Heng-Chao; Wang, Wen-Chun; Wang, Sen

2014-05-01

378

Mathematical analysis of thermoelastic characteristics in plasma-sprayed thermal barrier coatings.  

PubMed

The thermoelastic characteristics of plasma-sprayed thermal barrier coatings (TBCs) have been analyzed using mathematical modeling. Two types of TBC model, cylinder and circular disk which are commercial plasma-sprayed TBCs, subjecting to symmetric temperature distribution to the radial and longitudinal directions, respectively, were taken into consideration. Based on the thermoelastic theories, a second order ordinary differential equation was derived for the cylinder model and a pair of partial differential equations were set up for the circular disk model. The analytic solution was obtained from the ordinary differential equation, while a finite volume method was developed for numerical solutions to the pair of partial differential equations due to the complexity of governing equations. The thermoelastic characteristics of TBC models, such as temperature distributions, displacements, and stresses, were displayed according to the obtained solutions. The rate of heat conduction in the section of the top coat is relatively slow in comparison with the substrate, and no profound difference appears in the temperature distribution between two TBC models. The highest longitudinal tensile stress is expressed at the bond coat of both models, and the substrate is under the compressive stresses to the circumferential direction. While the cylinder expands to the positive longitudinal direction only, the expansion in the circular disk occurs to both the positive and negative longitudinal directions. Relatively large displacement and stresses exhibit in the cylinder as compared with the circular disk. In the circular disk, the stresses to the radial direction undulate at each section, and the displacement profile displays that the width of the circular disk is slightly narrowed. The results demonstrate that the mechanical and thermal properties of the top and bond coats are the crucial factors to be considered in controlling the thermoelastic characteristics of plasma-sprayed TBCs. PMID:22629912

Go, Jaegwi; Jungo, Yeon-Gil; Kim, Seokchan; Ali, Md Afsar; Paik, Ungyu

2012-02-01

379

Understanding crack formation in plasma sprayed thermal barrier coatings and their effects on coating properties  

NASA Astrophysics Data System (ADS)

As a key microstructural feature of plasma sprayed thermal barrier coatings (TBCs), microcracks determine the performance and service lifetimes of the coatings by influencing their thermal conductivity and compliance. The goal of this research is to obtain a fundamental understanding of crack formation in plasma sprayed microstructures, and their effect on mechanical and thermal properties through a synergistic combination of experimental and modeling efforts. Air plasma sprayed ZrO2-8wt%Y2O3 TBCs were deposited under tightly controlled conditions. The lengths and orientations of the horizontal cracks and vertical cracks in these coatings were characterized in detail, and process/crack microstructure maps of the crack distribution as a function of particle and substrate states were constructed. A fully coupled thermo-mechanical finite element, model was used to study the buildup of stresses during splat solidification; and to understand the effect of deposition conditions on crack formation during plasma spray deposition. Two stress components were considered, S11, oriented in the coating plane, which leads to vertical cracks; and S22, oriented normal to the coating plane, which leads to horizontal cracks. The model showed that both S11 and S22 scaled with the temperature difference between the superheated splat and the substrate. The model also showed that surface roughness plays a key role in determining the magnitude of maximum stresses, especially S 22. The maximum S11 occurred at the top of the splat, while the maximum S22 occurred at the bottom of the splat, both at surface roughness valleys. It was also found that the three geometric parameters, splat thickness, t, surface roughness wavelength; lambda, and surface roughness amplitude, A; scale with the stresses. Thus, two independent geometric parameters; psi = A/lambda, and zeta = t/lambda, were, defined. The simulation also showed that only roughness features on the scale of splat, thickness are important in providing locations of maximum stress concentration. A unique feature of this model is the incorporation of real surface roughness features obtained from the plasma sprayed TBCs, which are not sinusoidal. The elastic moduli (in-plane and out-of plane) and thermal conductivity (out-of-plane) of select samples were measured by a non-destructive ultrasonic technique and by a laser flash technique, respectively. It was found that out-of-plane thermal and mechanical properties were dominated by horizontal cracks and that all properties scaled with the sum of the cube of the crack lengths.

Ye, Guosheng

380

Flow Control over a Conical Forebody by Duty-Cycle Actuations  

NASA Astrophysics Data System (ADS)

Duty-cycle modulation alternately blowing from two opposite-facing plasma actuators on the leeward surface near the apex of a cone with a 10° semi-apex angle is adopted to control mean lateral force and moment, and the flow control mechanisms are presented. Pressure distributions over the forebody of the cone are measured by steady pressure tappings. The experiments are performed in a 3.0×1.6 m open-circuit wind tunnel at a wind speed of 20 m/s, a 45° angle of attack and a Reynolds number of 2×105, based on the diameter of the base of the cone. Almost linearly proportional control of the lateral forces and moments over a slender conical forebody at a high angle of attack has been demonstrated by employing a pair of single dielectric barrier discharge plasma actuators near the apex of the cone, combined with a duty-cycle technique. The pressure distribution measurements indicate that the bi-stable vortex pattern appears to be shifted in the opposite direction when the port or starboard actuator is activated, while the other is kept off during the test. It is shown that the reduced pulse-repetition frequency based on the local diameter at the plasma actuator equal to one yields the highest effectiveness among the cases considered.

Zheng, Borui; Gao, Chao; Li, Yibin; Liu, Feng; Luo, Shijun

2012-01-01

381

Modeling of dielectric barrier discharge-induced fluid dynamics and heat transfer  

Microsoft Academic Search

A dielectric barrier discharge, operating at kHz and kV conditions, can generate largely isothermal surface plasma and induce wall-jet-like fluid flow. It can serve as an aerodynamic actuator, and has advantages of no moving parts. In order to better understand the mechanism of the momentum coupling between the plasma and the fluid flow, both computational modeling and experimental information are

Balaji Jayaraman; Wei Shyy

2008-01-01

382

Improved Electrohydraulic Linear Actuators  

NASA Technical Reports Server (NTRS)

A product line of improved electrohydraulic linear actuators has been developed. These actuators are designed especially for use in actuating valves in rocket-engine test facilities. They are also adaptable to similar industrial uses. Advantageous features of the electrohydraulic linear actuators with respect to shortcomings of prior electrohydraulic linear actuators are described.

Hamtil, James

2002-01-01

383

Removal of priority pollutants from water by means of dielectric barrier discharge atmospheric plasma.  

PubMed

Two different nonthermal plasma reactors at atmospheric pressure were assessed for the removal of organic micropollutants (atrazine, chlorfenvinfos, 2,4-dibromophenol, and lindane) from aqueous solutions (1-5 mg L(-1)) at laboratory scale. Both devices were dielectric barrier discharge (DBD) reactors; one was a conventional batch reactor (R1) and the other a coaxial thin-falling-water-film reactor (R2). A first-order degradation kinetics was proposed for both experiments. The kinetic constants (k) were slightly faster in R1 (0.534 min(-1) for atrazine; 0.567 min(-1) for chlorfenvinfos; 0.802 min(-1) for 2,4-dibromophenol; 0.389 min(-1) for lindane) than in R2 (0.104 min(-1) for atrazine; 0.523 min(-1) for chlorfenvinfos; 0.273 min(-1) for 2,4-dibromophenol; 0.294 min(-1) for lindane). However, energy efficiencies were about one order of magnitude higher in R2 (89 mg kW(-1) h(-1) for atrazine; 447 mg kW(-1) h(-1) for c hlorfenvinfos; 47 mg kW(-1) h(-1) for 2,4-dibromophenol; 50 mg kW(-1) h(-1) for lindane) than in R1. Degradation by -products of all four compounds were identified in R1. As expected, when the plasma treatment (R1) was applied to industrial wastewater spiked with atrazine or lindane, micropollutant removal was also achieved, although at a lower rate than with aqueous solutions (k = 0.117 min(-1) for atrazine; k = 0.061 min(-1) for lindane). PMID:24121639

Hijosa-Valsero, María; Molina, Ricardo; Schikora, Hendrik; Müller, Michael; Bayona, Josep M

2013-11-15

384

Reduction of NO{sub x} from combustion flue gases by superimposed barrier discharge plasma reactors  

SciTech Connect

NO{sub x} reduction from combustion flue gases by superimposed barrier discharge plasma reactors is experimentally investigated. The experiments are conducted for applied voltages from 0 to 28 kV, flue gas rates from 0.5 to 2 L/min, ammonia mixture concentrations from 0.7 to 2.65 stoichiometry, and applied voltage phase differences from 0 to 180{degree}, where two 60-Hz ac power supplies are used. The results show the following: (1) NO{sub x} reduction rate decreases with increasing discharge power for surface discharge operations, however, NO{sub x} reduction rate increases with increasing discharge power for silent and superimposing discharge operating modes; (2) NO{sub x} reduction rate increases with increasing discharge power, gas flow rate and ammonia stoichiometry under in-phase operations; (3) NO{sub x} reduction rate for out-of-phase operations is much higher compared with inphase operations, however, NO{sub x} reduction rate has an optimum condition on ammonia stoichiometry, discharge power, and gas flow rate; and (4) energy efficiency of NO{sub x} reduction increases with increasing ammonia mixture and gas flow rate and decreases with increasing discharge power.

Urashima, Kuniko [McMaster Univ., Hamilton, Ontario (Canada). Dept. of Engineering Physics] [McMaster Univ., Hamilton, Ontario (Canada). Dept. of Engineering Physics; [Musashi Inst. of Tech., Tokyo (Japan). Dept. of Electrical and Electronic Engineering; Chang, J.S. [McMaster Univ., Hamilton, Ontario (Canada). Dept. of Engineering Physics] [McMaster Univ., Hamilton, Ontario (Canada). Dept. of Engineering Physics; Ito, Tairo [Musashi Inst. of Tech., Tokyo (Japan). Dept. of Electrical and Electronic Engineering] [Musashi Inst. of Tech., Tokyo (Japan). Dept. of Electrical and Electronic Engineering

1997-07-01

385

[Influence of pressure on plasma temperature of octagon structure in dielectric barrier discharge].  

PubMed

Octagon structure consisting of the spots and lines was firstly observed in discharge in argon and air mixture by using a dielectric barrier discharge device with water electrodes. Plasma temperatures of the spots and lines in octagon structure at different gas pressure were studied by using optical emission spectra. The emission spectra of the N2 second positive band (C3IIu-->B3IIg)were measured, and the molecule vibrational temperatures of the spots and lines were calculated by the emission intensities. Based on the relative intensity of the line at 391.4 nm and the N2 line at 394.1 nm, the average electron energy of the spots and lines were investigated. The spectral lines of Ar I 763.26 nm ((2)P6-1Ss) and 772.13 nm ((2)P2-->1S3) were chosen to estimate electron excitation temperature of the spots and lines by the relative intensity ratio method. The molecule vibrational temperature, average electron energy, and electron excitation temperature of the lines are higher than those of the spots at the same pressure. The molecule vibrational temperature, average electron energy, and electron excitation temperature of the spots and lines decrease with pressure increasing from 40 to 60 kPa. PMID:24369624

Dong, Li-fang; Zhao, Long-hu; Wang, Yong-jie; Tong, Guo-liang; Di, Cong

2013-09-01

386

Acetamiprid removal in wastewater by the low-temperature plasma using dielectric barrier discharge.  

PubMed

Degradation of acetamiprid in wastewater was studied in a dielectric barrier discharge (DBD) reactor. This reactor produces ultraviolet light and reactive species like ozone (O3) can be used for the treatment of wastewater. We examined the factors that could affect the degradation process, including the discharge power, and the initial concentrations of acetamiprid, and O3 which is generated by the DBD reactor. We also investigated the effect of adding Na2B4O7 as a radical scavenger to probe the role of hydroxyl radical in the reaction. The results indicated that acetamiprid could be removed from aqueous solution effectively and hydroxyl radicals played an important role during the degradation by the low temperature plasma. The degradation process of acetamiprid fits the first-order kinetics. The degradation efficiency was 83.48 percent at 200min when the discharge power was 170W and the initial acetamiprid concentration was 50mg/L. The removal efficiency of acetamiprid decreased with the increasing concentration of Na2B4O7 because B4O7(2-) is an excellent radical scavenger that inhibited the generation of OH during the DBD process. The removal efficiency of acetamiprid improved in the presence of O3. The main reason was that O3 can oxidize certain organic compounds directly or indirectly by generating hydroxyl radicals. The degradation products of acetamiprid were characterized qualitatively and quantitatively using high performance liquid chromatography, mass spectrometry and UV-vis spectroscopy. PMID:24840877

Li, Shanping; Ma, Xiaolong; Jiang, Yanyan; Cao, Xiaohong

2014-08-01

387

Sintering and Creep Behavior of Plasma-Sprayed Zirconia and Hafnia Based Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

The sintering and creep of plasma-sprayed ceramic thermal barrier coatings under high temperature conditions are complex phenomena. Changes in thermomechanical and thermophysical properties and in the stress response of these coating systems as a result of the sintering and creep processes are detrimental to coating thermal fatigue resistance and performance. In this paper, the sintering characteristics of ZrO2-8wt%y2O3, ZrO2-25wt%CeO2-2.5wt%Y2O3, ZrO2-6w%NiO- 9wt%Y2O3, ZrO2-6wt%Sc2O3-2wt%y2O3 and HfO2-27wt%y2O3 coating materials were investigated using dilatometry. It was found that the HfO2-Y2O3 and baseline ZrO2-Y2O3 exhibited the best sintering resistance, while the NiO-doped ZrO2-Y2O3 showed the highest shrinkage strain rates during the tests. Higher shrinkage strain rates of the coating materials were also observed when the specimens were tested in Ar+5%H2 as compared to in air. This phenomenon was attributed to an enhanced metal cation interstitial diffusion mechanism under the reducing conditions. It is proposed that increased chemical stability of coating materials will improve the material sintering resistance.

Zhu, Dongming; Miller, Robert A.

1998-01-01

388

Quasistatic vs. Dynamic Modulus Measurements Of Plasma-Sprayed Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

Plasma-sprayed 8wt% yttria-stabilized zirconia (8YSZ) thermal barrier coatings (TBCs) have been demonstrated to exhibit nonlinear hysteretic elastic behavior by quasistatic cyclic compression and cylindrical punch indentation measurements. In particular, the instantaneous (tangential) elastic modulus increases with applied stress and exhibits significant hysteresis during cycling. Sound velocity (dynamic) measurements also show an increase in TBC modulus with applied compressive stress, but in contrast show no significant hysteresis for the modulus during cycling. The nonlinear elastic behavior of the TBCs evidenced by these tests is attributed to coating compaction and internal sliding. The differences between the quasistatic and dynamic measurements are explained by the relative absence of the effect of internal sliding in the dynamic modulus measurements. By incorporating short load reversals into the larger loading cycle and measuring the instantaneous modulus at the start of each load reversal, the effects of internal sliding can be substantially reduced in the quasistatic measurements, and the resulting modulus values show good agreement with the modulus values determined by dynamic sound velocity measurements.

Eldridge, J. I.; Morscher, G. N.; Choi, S. R.

2002-01-01

389

Atmospheric pressure plasma jets beyond ground electrode as charge overflow in a dielectric barrier discharge setup  

SciTech Connect

With a proper combination of applied voltage and the width of ground electrode, atmospheric pressure plasma jets extending beyond the ground electrode, whether it sits on the downstream or the upstream side, can be equally obtained with a dielectric barrier discharge setup, which can be ascribed to the overflow of deposited charges [J. Appl. Phys. 106, 013308 (2009)]. Here, we show that, by using narrower ground electrodes, such an overflow jet can be successfully launched at a much reduced voltage (down to below 10 kV). Moreover, by using transparent and triadic ground electrodes, development of charge overflow beneath the ground electrode was temporally and spatially resolved. Temporal evolution of discharge currents measured on the severed ground electrode helps establish the propagation dynamics of discharges along the dielectric surface beneath ground electrode, and also reinforces the conception that the streamer's head is in connection to the active electrode via a conducting channel. A small propagation velocity of 3.3x10{sup 3} m/s was measured for the ''overflow'' jet inside the dielectric tube. The availability of such overflow jets is enormously advantageous concerning their application to living bodies, to which the high voltage at active electrode is lethally dangerous.

Jiang Nan; Ji Ailing; Cao Zexian [Beijing National Laboratory for Condensed Matters, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190 (China)

2010-08-15

390

New Material Concepts for the Next Generation of Plasma-Sprayed Thermal Barrier Coatings  

NASA Astrophysics Data System (ADS)

In application as a thermal barrier coating (TBC), partially stabilized zirconia (Zr) approaches some limits of performance. To further enhance the efficiency of gas turbines, higher temperature capability and a longer lifetime of the coating are needed for the next generation of TBCs. This paper presents the development of new materials and concepts for application as TBC. Materials whose compositions have the pyrochlore structure or doped Zr are presented in contrast with new concepts like nanolayers between the top and bond coat, metal-glass composites, and double-layer structures. In the last concept, the new compositions are used in a combination with Zr, as a double, multi, or graded layer coating. In this case, the benefits of Zr will be combined with the promising properties of the new top coating. In the case of metal-glass composites, the paper will be focused on the influences of different plasma spraying processes on the microstructure. The performance of all these different coating systems has been evaluated by burner rig tests. The results will be presented and discussed.

Stöver, D.; Pracht, G.; Lehmann, H.; Dietrich, M.; Döring, J.-E.; Vaßen, R.

2004-03-01

391

Lanthanum hexaaluminate—a new material for atmospheric plasma spraying of advanced thermal barrier coatings  

NASA Astrophysics Data System (ADS)

One of the main application fields of the thermal spraying process is thermal barrier coatings (TBCs). Today, partially stabilized zirconia (YSZ or MSZ) is mainly used as a TBC material. At temperatures above 1000 °C, zirconia layers age distinctively, including phenomena shrinkage and microcrack formation. Therefore, there is a considerable interest in TBCs for higher temperature applications. In this paper, lanthanum hexaaluminate, a newly developed TBC material with long-term stability up to 1400 °C, is presented. It ages significantly more slowly at these high temperatures than commercial zirconia-based TBCs. Its composition favors the formation of platelets, which prevent a densification of the coating by postsintering. It consists of La2O3, Al2O3, and MgO. Its crystal structure corresponds to a magnetoplumbite phase. Lanthanum hexaaluminate powders were produced using two different fabrication routes, one based on salts and the other one based on oxides. To optimize the granulate, various raw materials and additives were tested. The slurry was spray dried in a laboratory spray drier and calcined at 1650 °C. Using these two powders, coatings were produced by atmospheric plasma spraying (APS). The residual stresses of the coatings were measured by the hole drilling method, and the deposition process was optimized with respect to the residual stresses in the TBC. The coatings were extensively analyzed regarding phase composition, thermal expansion, and long-term stability, as well as microstructural properties.

Friedrich, C.; Gadow, R.; Schirmer, T.

2001-12-01

392

Optical emission characteristics of surface nanosecond pulsed dielectric barrier discharge plasma  

SciTech Connect

This paper reports an experimental study of the optical emission characteristics of the surface dielectric barrier discharge plasma excited by nanosecond pulsed voltage. N{sub 2}(C{sup 3}{Pi}{sub u}) rotational and vibrational temperatures are almost the same with upper electrode powered with positive polarity and lower electrode grounded or upper electrode grounded and lower electrode powered with positive polarity. While the electron temperature is 12% higher with upper electrode powered with positive polarity and lower electrode grounded. When the frequency is below 2000 Hz, there is almost no influence of applied voltage amplitude and frequency on N{sub 2}(C{sup 3}{Pi}{sub u}) rotational, vibrational temperature and electron temperature. As the pressure decreases from 760 Torr to 5 Torr, N{sub 2}(C{sup 3}{Pi}{sub u}) rotational temperature remains almost unchanged, while its vibrational temperature decreases initially and then increases. The discharge mode changes from a filamentary type to a glow type around 80 Torr. In the filamentary mode, the electron temperature remains almost unchanged. In the glow mode, the electron temperature increases while the pressure decreases.

Wu Yun; Li Yinghong; Jia Min; Song Huimin; Liang Hua [Science and Technology on Plasma Dynamics Lab, Aeronautics and Astronautics Engineering College, Air Force Engineering University, Xi'an 710038 (China)

2013-01-21

393

A homogeneous dielectric barrier discharge plasma excited by a bipolar nanosecond pulse in nitrogen and air  

NASA Astrophysics Data System (ADS)

In this paper, a nanosecond bipolar pulse voltage with 20 ns rise time is employed to generate a low gas temperature homogeneous dielectric barrier discharge plasma both in nitrogen and air at atmospheric pressure. Images of the discharge, waveforms of pulse voltage and discharge current, and the optical emission spectra emitted from the discharge are recorded successfully under severe electromagnetic interference. The effects of pulse peak voltage, pulse repetition rate and the gap distance between electrodes on gas temperature and the emission intensities of NO (A 2? ? X 2?), OH (A 2? ? X 2?) and N2 (C\\,^3\\Pi _u \\to B\\,^3\\Pi _g ) are discussed. It is found that the emission intensities of NO (A 2? ? X 2?), OH (A 2? ? X 2?) and N2 (C\\,^3\\Pi _u \\to B\\,^3\\Pi _g ) rise with increasing both pulse peak voltage and pulse repetition rate but decrease with gap distance between the electrodes when it is above 2.5 mm. The effect of concentrations of O2 on the emission intensities of NO (A 2? ? X 2?), OH (A 2? ? X 2?) and N2 (C\\,^3\\Pi _u \\to B\\,^3\\Pi _g ) is also investigated, and it is found that the emission intensities of both NO (A 2? ? X 2?) and OH (A 2? ? X 2?) reach maximum values when the O2 concentration is 0.3%.

Yang, De-Zheng; Yang, Yang; Li, Shou-Zhe; Nie, Dong-Xia; Zhang, Shuai; Wang, Wen-Chun

2012-06-01

394

Thermal and plasma flow control  

NASA Astrophysics Data System (ADS)

Electrical and thermal actuators are devices in the flow field which are used for flow control by electric or thermal action, examples can be presented by discharges (dielectric barrier discharge, sliding discharge, glow discharge, high-frequency capacitive discharge, etc). Today much work is devoted to the interaction of discharge with air flow. This work presents a theoretical study of the thermal and plasma effects of the influence of discharge on air flow. Investigation of a plasma actuator is very difficult because of the multiscale nature of the problem, which follows from some order differences in space and time differences in space charge, ion and electrons kinetics and plasma chemistry dynamics. However, on the thermal and hydrodynamic scales the natures of thermal and plasma actuators are similar. The electron energy distribution function is found from a solution of the Boltzmann equation in a two-term approximation. Numerical simulation of thermal and plasma actuators has been carried out with a parallel gas dynamics tool (GDT) package.

Son, E. E.; Tereshonok, D. V.

2010-12-01

395

Development of a diffuse air-argon plasma source using a dielectric-barrier discharge at atmospheric pressure  

SciTech Connect

A stable diffuse large-volume air plasma source was developed by using argon-induced dielectric-barrier discharges at atmospheric pressure. This plasma source can be operated in a filamentary discharge with the average areal power density of 0.27 W/cm{sup 2} and the gas temperature of 315{+-}3 K. Spatial measurement of emission spectrum and temperature indicates that this plasma is uniform in the central region along the transverse direction. It is also found that the formation of diffuse air plasma mainly lies in the creation of sufficient seed electrons by the Penning effect through collisions between two argon or nitrogen metastables at low electric fields.

Tang Jie; Jiang Weiman; Zhao Wei; Wang Yishan; Li Shibo; Wang Haojing [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119 (China)] [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119 (China); Duan Yixiang [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119 (China) [State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119 (China); Research Center of Analytical Instrumentation, Sichuan University, Chengdu 610064 (China)

2013-01-21

396

Reduction of Copper Oxide Thin Films with Hydrogen Plasma Generated by a Dielectric-Barrier Glow Discharge  

Microsoft Academic Search

The reduction behavior of sputtered thin Cu2O films withhydrogen plasma generated by a dielectric-barrier glow discharge wasinvestigated by means of surface characterization and hydrogen plasmadiagnosis using the vacuum ultraviolet (VUV) line absorptiontechnique. The reduction model was derived by assuming that thediffusion of atomic hydrogen in the reduced layer is therate-determining step. This reduction model provides a goodapproximation of the Cu2O

Yasushi Sawada; Noriyuki Taguchi; Kunihide Tachibana

1999-01-01

397

Application of Cr 3+ photoluminescence piezo-spectroscopy to plasma-sprayed thermal barrier coatings for residual stress measurement  

Microsoft Academic Search

Cr3+ photoluminescence piezo-spectroscopy (CPLPS) is being developed as a non-destructive inspection technique for the measurement of residual stresses within the thermally grown oxide (TGO; consisting of ?-Al2O3 with Cr3+ solute) layer buried under Y2O3-stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs). In this study, CPLPS experiments were performed to measure residual stresses in TGOs buried under four different types of plasma-sprayed

K. W Schlichting; K Vaidyanathan; Y. H Sohn; E. H Jordan; M Gell; N. P Padture

2000-01-01

398

Improvement of oxygen barrier of PET film with diamond-like carbon film by plasma-source ion implantation  

Microsoft Academic Search

Plasma-source ion implantation is employed to deposit amorphous carbon layers on polyethylene terepthalate (PET) film as a means of improving the oxygen barrier characteristics. This process is performed using pulsed, high negative voltage (?15 kV, 10 ?s pulse width, 300 pulses\\/s) and C2H2 gas at 5.5 Pa. The effect of adding Ar or CH4 to the gas mixture is also

Mitsuhiro Yoshida; Takeshi Tanaka; Satoshi Watanabe; Masaru Shinohara; Jong-Wan Lee; Toshinori Takagi

2003-01-01

399

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work  

Microsoft Academic Search

A review is presented of how heat transfer takes place in plasma-sprayed (zirconia-based) thermal barrier coatings (TBCs)\\u000a during operation of gas turbines. These characteristics of TBCs are naturally of central importance to their function. Current\\u000a state-of-the-art TBCs have relatively high levels of porosity (~15%) and the pore architecture (i.e., its morphology, connectivity,\\u000a and scale) has a strong influence on the

I. O. Golosnoy; A. Cipitria; T. W. Clyne

2009-01-01

400

Crack initiation and propagation in air plasma sprayed thermal barrier coatings, testing and mathematical modelling of low cycle fatigue behaviour  

Microsoft Academic Search

In the present paper failure mechanisms in air plasma sprayed thermal barrier coatings for land-based gas turbines have been studied. This has been done by finite element simulations and fractographic investigations of low cycle fatigue (LCF) tested material, here chosen as an 350?m thick partially stabilised zirconia top coat (TC) together with a 150?m thick Ni?Co?Cr?Al?Y bond coat (BC) on

Magnus Jinnestrand; Håkan Brodin

2004-01-01

401

A mechanistic study of oxidation-induced degradation in a plasma-sprayed thermal barrier coating system  

Microsoft Academic Search

A parametric study is conducted to quantify the effects of different microstructural variables and service conditions on the local stresses induced by oxidation, sintering processes and thermal cycling in a typical plasma sprayed thermal barrier coating (PS-TBC) system. The study relies on the numerical results obtained from a continuum mechanics-based mechanistic study of the oxidation-induced degradation of the PS-TBC system.

E. P Busso; J Lin; S Sakurai

2001-01-01

402

Damage mechanisms and lifetime behavior of plasma-sprayed thermal barrier coating systems for gas turbines — Part II: Modeling  

Microsoft Academic Search

A phenomenological lifetime prediction tool for plasma-sprayed ZrO2 based thermal barrier coating systems with MCrAlY bondcoat is presented. The analytical model uses a two step approach for calculating the development of delamination cracks: The initial crack growth is considered to be proportional to the thickness of the thermally grown oxide (TGO) scale on the bondcoat. After exceeding a critical TGO

Tilmann Beck; Roland Herzog; Olena Trunova; Marita Offermann; Rolf W. Steinbrech; Lorenz Singheiser

2008-01-01

403

Failure of thick, low density air plasma sprayed thermal barrier coatings  

NASA Astrophysics Data System (ADS)

This research was directed at developing fundamental understandings of the variables that influence the performance of air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBC). Focus was placed on understanding how and why each variable influenced the performance of the TBC system along with how the individual variables interacted with one another. It includes research on the effect of surface roughness of NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying, the interdiffusion behavior of bond coats coupled to commercial superalloys, and the microstructural and compositional control of APS topcoats to maximize the coating thicknesses that can be applied without spallation. The specimens used for this research were prepared by Praxair Surface Technologies and have been evaluated using cyclic oxidation and thermal shock tests. TBC performance was sensitive to bond coat roughness with the rougher bond coats having improved cyclic performance than the smoother bond coats. The explanation being the rough bond coat surface hindered the propagation of the delamination cracks. The failure mechanisms of the APS coatings were found to depend on a combination of the topcoat thickness, topcoat microstructure and the coefficient of thermal expansion (CTE) mismatch between the superalloy and topcoat. Thinner topcoats tended to fail at the topcoat/TGO interface due to bond coat oxidation whereas thicker topcoats failed within the topcoat due to the strain energy release rate of the thicker coating exceeding the fracture strength of the topcoat. Properties of free-standing high and conventional purity YSZ topcoats of both a lowdensity (LD) and dense-vertically fissure (DVF) microstructures were evaluated. The densification rate and phase evolution were sensitive to the YSZ purity and the starting microstructure. Increasing the impurity content resulted in enhanced sintering and phase decomposition rates, with the exception of the conventional-purity DVF which exhibited a density decrease during sintering. A combination of the DVF and LD topcoat microstructures (dual TBC) resulted in significant increase in cyclic durability. A 1275 mum thick dual TBC coating was found to have a comparable furnace cyclic life to that of a 100 im LD TBC.

Helminiak, Michael Aaron

404

Sintering and Fracture Behavior of Plasma-Sprayed Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. There is a need to characterize the fundamental sintering and fracture behavior of the current ZrO2-(7 to 8)wt%Y2O3 coating, in order to fully take advantage of the coating capability. In addition, a thorough evaluation of the coating behavior and temperature limits will be useful for more accurately assessing the benefit gained from future advanced coating systems. In this study, the sintering behavior of plasma-sprayed ZrO2-8wt%Y2O3 coatings was systematically investigated as a function of temperature and time using a dilatometer in the temperature range of 1200-1500 C. The coating sintering kinetics obtained by dilatometry were compared with the coating thermal conductivity increase kinetics, determined by a steady-state laser heat-flux testing approach, under high temperature and thermal gradient sintering conditions. The mode I, mode II, and mixed mode I-mode II fracture behavior of as-processed and sintering-annealed coatings was determined in asymmetric flexure loading at ambient and elevated temperatures in order to evaluate the coating sintering effects on the fracture envelope of K(sub I) versus K(sub II). The coating thermal conductivity cyclic response associated with the interface delamination of the coating systems under simulated engine heat-flux conditions will be discussed in conjunction with the sintering and fracture testing results.

Zhu, Dongming; Choi, Sung R.; Miller, Robert A.

2004-01-01

405

Plasma-sprayed duplex and graded partially stabilized zirconia thermal barrier coatings: deposition process and properties  

NASA Astrophysics Data System (ADS)

Atmospheric plasma spraying of duplex and graded ZrO2 (8% Y2O3) thermal barrier coatings (TBCs) on Inconel 617 substrate with a NiCrAlY bond coat is described in terms of a deposition process of con-trolled coating structure. Special attention is devoted to the dominant spray parameters and the injector configuration for powder feeding, which play a fundamental role in graded coating deposition with con-trolled formation of a graded metal-ceramic (GMC) intermediate zone. The results of the graded coating spraying allow: (a) suppression of step-interface effects, (b) suppression of large differences (misfit) be-tween physical and mechanical constants of the coating and those of the substrate material, and (c) favor-able intergrowth of crystallites for a microstructurally integrated structure. Sprayed TBCs were investigated and compared with regard to their thermal cycling, oxidation behavior, and mechanical properties. The influence of crystal anisotropy changes on the resulting coating structure and properties is shown. On the basis of finite element (FE) calculations, the stress distribution within thermally cycled coating systems was analyzed. It is confirmed that the graded coating structure relaxes considerably the stresses resulting from the internal constraint due to thermal expansion difference between both metallic and ce-ramic materials. This stress distribution also decreases the gradient of elastic deformation and/or resid-ual stresses between the metal bond coat and top ceramic coating, and hence leads to a better thermal cycling behavior of the graded TBC systems. However, this advantage is not practical in every case, since the rapid oxidation of the metallic lamellae causes the ceramic phase in the GMC zone to undergo tensile stresses within a short thermal exposure time. The lifetime of duplex TBC systems that are under steady-state thermal load conditions is much higher than that of graded ones.

Musil, J.; Alaya, M.; Oberacker, R.

1997-12-01

406

Flight control actuation system  

NASA Technical Reports Server (NTRS)

A flight control actuation system comprises a controller, electromechanical actuator and a pneumatic actuator. During normal operation, only the electromechanical actuator is needed to operate a flight control surface. When the electromechanical actuator load level exceeds 40 amps positive, the controller activates the pneumatic actuator to offset electromechanical actuator loads to assist the manipulation of flight control surfaces. The assistance from the pneumatic load assist actuator enables the use of an electromechanical actuator that is smaller in size and mass, requires less power, needs less cooling processes, achieves high output forces and adapts to electrical current variations. The flight control actuation system is adapted for aircraft, spacecraft, missiles, and other flight vehicles, especially flight vehicles that are large in size and travel at high velocities.

Wingett, Paul T. (Inventor); Gaines, Louie T. (Inventor); Evans, Paul S. (Inventor); Kern, James I. (Inventor)

2006-01-01

407

Reduction of Copper Oxide Thin Films with Hydrogen Plasma Generated by a Dielectric-Barrier Glow Discharge  

NASA Astrophysics Data System (ADS)

The reduction behavior of sputtered thin Cu2O films withhydrogen plasma generated by a dielectric-barrier glow discharge wasinvestigated by means of surface characterization and hydrogen plasmadiagnosis using the vacuum ultraviolet (VUV) line absorptiontechnique. The reduction model was derived by assuming that thediffusion of atomic hydrogen in the reduced layer is therate-determining step. This reduction model provides a goodapproximation of the Cu2O reduction process. The surface hydrogenconcentration estimated from this model is higher by an order of105 106 than the hydrogen atom concentration in the plasma phasemeasured by means of the plasma diagnosis. It is verified that the number ofhydrogen atoms transported onto the solid surface satisfactorilyagrees with that consumed in the Cu2O layer.

Sawada, Yasushi; Taguchi, Noriyuki; Tachibana, Kunihide

1999-11-01

408

Preferential killing of human lung cancer cell lines with mitochondrial dysfunction by nonthermal dielectric barrier discharge plasma  

PubMed Central

The distinctive cellular and mitochondrial dysfunctions of two human lung cancer cell lines (H460 and HCC1588) from two human lung normal cell lines (MRC5 and L132) have been studied by dielectric barrier discharge (DBD) plasma treatment. This cytotoxicity is exposure time-dependent, which is strongly mediated by the large amount of H2O2 and NOx in culture media generated by DBD nonthermal plasma. It is found that the cell number of lung cancer cells has been reduced more than that of the lung normal cells. The mitochondrial vulnerability to reactive species in H460 may induce distinctively selective responses. Differential mitochondrial membrane potential decrease, mitochondrial enzymatic dysfunction, and mitochondrial morphological alteration are exhibited in two cell lines. These results suggest the nonthermal plasma treatment as an efficacious modality in lung cancer therapy.

Panngom, K; Baik, K Y; Nam, M K; Han, J H; Rhim, H; Choi, E H

2013-01-01

409

Possibility of internal transport barrier formation and electric field bifurcation in LHD plasma.  

National Technical Information Service (NTIS)

Theoretical analysis of the electric field bifurcation is made for the LHD plasma. For given shapes of plasma profiles, a region of bifurcation is obtained in a space of the plasma parameters. In this region of plasma parameters, the electric field domain...

H. Sanuki K. Itoh M. Yokoyama A. Fujisawa K. Ida

1999-01-01

410

A dielectric barrier discharge (DBD) plasma reactor: an efficient tool to prepare novel RuO2 nanorods  

NASA Astrophysics Data System (ADS)

One-dimensional (1D) nanostructured materials have attracted a great deal of interest owing to their potential applications in various industries. Due to the limitations and cost associated with conventional low-pressure plasma systems, atmospheric-pressure plasma techniques such as dielectric barrier discharges (DBDs) are investigated as an alternative approach for inducing specific chemical reactions. RuO2 nanomaterials are widely used as supercapacitor electrodes, in field-emission devices and for catalytic applications. In such applications, size and shape dependent properties of nanomaterials play critical roles in improving the performance. In this paper, an attempt is made to prepare 1D RuO2 nanostructured materials using a DBD plasma. It is reported here that the composition of feed gas is an important factor in determining the final morphology. For example, an Ar + H2 plasma yields aggregated RuO2 nanostructures, whereas ‘nanopillar’ and ‘nanorod’ morphologies are obtained when using Ar + O2 and Ar, respectively. Possible mechanisms behind the morphological differences are elucidated on the basis of the temperature variations inside the plasma reactor and the chemistry of the gaseous reactive species. The application of a DBD plasma to the synthesis of RuO2 nanorods is reported for the first time in this paper.

Ananth, Antony; Sanjeeva Gandhi, Mani; Mok, Young Sun

2013-04-01

411

Superconducting linear actuator  

NASA Technical Reports Server (NTRS)

Special actuators are needed to control the orientation of large structures in space-based precision pointing systems. Electromagnetic actuators that presently exist are too large in size and their bandwidth is too low. Hydraulic fluid actuation also presents problems for many space-based applications. Hydraulic oil can escape in space and contaminate the environment around the spacecraft. A research study was performed that selected an electrically-powered linear actuator that can be used to control the orientation of a large pointed structure. This research surveyed available products, analyzed the capabilities of conventional linear actuators, and designed a first-cut candidate superconducting linear actuator. The study first examined theoretical capabilities of electrical actuators and determined their problems with respect to the application and then determined if any presently available actuators or any modifications to available actuator designs would meet the required performance. The best actuator was then selected based on available design, modified design, or new design for this application. The last task was to proceed with a conceptual design. No commercially-available linear actuator or modification capable of meeting the specifications was found. A conventional moving-coil dc linear actuator would meet the specification, but the back-iron for this actuator would weigh approximately 12,000 lbs. A superconducting field coil, however, eliminates the need for back iron, resulting in an actuator weight of approximately 1000 lbs.

Johnson, Bruce; Hockney, Richard

1993-01-01

412

Measurement of Turbulence Decorrelation during Transport Barrier Evolution in a High Temperature Fusion Plasma  

SciTech Connect

A low power polychromatic beam of microwaves is used to diagnose the behavior of turbulent fluctuations in the core of the JT-60U tokamak during the evolution of the internal transport barrier. A continuous reduction in the size of turbulent structures is observed concomitant with the reduction of the density scale length during the evolution of the internal transport barrier. The density correlation length decreases to the order of the ion gyroradius, in contrast to the much longer scale lengths observed earlier in the discharge, while the density fluctuation level remain similar to the level before transport barrier formation.

R. Nazikian; K. Shinohara; G.J. Kramer; E. Valeo; K. Hill; T.S. Hahm; G. Rewoldt; S. Ide; Y. Koide; Y. Oyama; H. Shirai; W. Tang

2005-03-29

413

Plasma-assisted atomic layer deposition of Al{sub 2}O{sub 3} moisture permeation barriers on polymers  

SciTech Connect

Thin Al{sub 2}O{sub 3} films of different thicknesses (10-40 nm) were deposited by plasma-assisted atomic layer deposition on substrates of poly(2,6-ethylenenaphthalate) (PEN), and the water vapor transmission rate (WVTR) values were measured by means of the calcium test. The permeation barrier properties improved with decreasing substrate temperature and a good WVTR of 5x10{sup -3} g m{sup -2} day{sup -1} (WVTR{sub PEN}=0.5 g m{sup -2} day{sup -1}) was measured for a 20 nm thick Al{sub 2}O{sub 3} film deposited at room temperature using short purging times. Such ultrathin, low-temperature deposited, high-quality moisture permeation barriers are an essential requirement for the implementation of polymeric substrates in flexible electronic and display applications.

Langereis, E.; Creatore, M.; Heil, S. B. S.; Sanden, M. C. M. van de; Kessels, W. M. M. [Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands)

2006-08-21

414

Sintering and Fracture Behavior of Plasma-Sprayed Thermal Barrier Coatings.  

National Technical Information Service (NTIS)

Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. There is a need to characterize the fundamental sintering and ...

D. Zhu S. R. Choi R. A. Miller

2004-01-01

415

Influence of the RF plasma polymerization process on the barrier properties of coil-coating  

Microsoft Academic Search

The work is devoted to the investigation of the influence of silica-based plasma polymer films deposition on the protective properties of polyurethane coil-coating. Different locations and different deposition stages were investigated for radio frequency (rf) plasma deposition reactor to establish relations between deposition stages and coating properties. The surface evolution of the plasma treated samples was assessed by atomic force

R. Serra; M. L. Zheludkevich; M. G. S. Ferreira

2005-01-01

416

Columnar-Structured Thermal Barrier Coatings (TBCs) by Thin Film Low-Pressure Plasma Spraying (LPPS-TF)  

NASA Astrophysics Data System (ADS)

The very low-pressure plasma Spray (VLPPS) process has been developed with the aim of depositing uniform and thin coatings with coverage of a large area by plasma spraying. At typical pressures of 100-200 Pa, the characteristics of the plasma jet change compared to conventional low-pressure plasma-spraying processes (LPPS) operating at 5-20 kPa. The combination of plasma spraying at low pressures with enhanced electrical input power has led to the development of the LPPS-TF process (TF = thin film). At appropriate parameters, it is possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This technique offers new possibilities for the manufacturing of thermal barrier coatings (TBCs). Besides the material composition, the microstructure is an important key to reduce thermal conductivity and to increase strain tolerance. In this regard, columnar microstructures deposited from the vapor phase show considerable advantages. Therefore, physical vapor deposition by electron beam evaporation (EB-PVD) is applied to achieve such columnar-structured TBCs. However, the deposition rate is low, and the line-of-sight nature of the process involves specific restrictions. In this article, the deposition of TBCs by the LPPS-TF process is shown. How the evaporation of the feedstock powder could be improved and to what extent the deposition rates could be increased were investigated.

Hospach, Andreas; Mauer, Georg; Vaßen, Robert; Stöver, Detlev

2011-01-01

417

Nonthermal Dielectric-Barrier Discharge Plasma-Induced Inactivation Involves Oxidative DNA Damage and Membrane Lipid Peroxidation in Escherichia coli?  

PubMed Central

Oxidative stress leads to membrane lipid peroxidation, which yields products causing variable degrees of detrimental oxidative modifications in cells. Reactive oxygen species (ROS) are the key regulators in this process and induce lipid peroxidation in Escherichia coli. Application of nonthermal (cold) plasma is increasingly used for inactivation of surface contaminants. Recently, we reported a successful application of nonthermal plasma, using a floating-electrode dielectric-barrier discharge (FE-DBD) technique for rapid inactivation of bacterial contaminants in normal atmospheric air (S. G. Joshi et al., Am. J. Infect. Control 38:293-301, 2010). In the present report, we demonstrate that FE-DBD plasma-mediated inactivation involves membrane lipid peroxidation in E. coli. Dose-dependent ROS, such as singlet oxygen and hydrogen peroxide-like species generated during plasma-induced oxidative stress, were responsible for membrane lipid peroxidation, and ROS scavengers, such as ?-tocopherol (vitamin E), were able to significantly inhibit the extent of lipid peroxidation and oxidative DNA damage. These findings indicate that this is a major mechanism involved in FE-DBD plasma-mediated inactivation of bacteria.

Joshi, Suresh G.; Cooper, Moogega; Yost, Adam; Paff, Michelle; Ercan, Utku K.; Fridman, Gregory; Friedman, Gary; Fridman, Alexander; Brooks, Ari D.

2011-01-01

418

Characterisation of thermal barrier coatings and ultra high temperature composites deposited in a low pressure plasma reactor  

Microsoft Academic Search

A low pressure plasma process working at 600–800Pa was used to deposit from aqueous solution ZrO2–4mol% Y2O3 (Yttria partially stabilized Zirconia–YpSZ) layers and stacks of Ta2O5\\/YpSZ layers for use as thermal barrier coatings (TBC). The observation of the cross section revealed a high porosity. The thermal diffusivity of the layers (1×10?7m2s?1) was measured by a laser flash technique and compared

C. Fourmond; G. Da Rold; F. Rousseau; C. Guyon; S. Cavadias; D. Morvan; R. Mévrel

2011-01-01

419

Influence of wall-charge accumulation on the gas dielectric barrier discharge in alternating current plasma display panel  

SciTech Connect

Influences of wall-charge accumulation on gas dielectric barrier discharge (DBD) breakdown threshold and sustaining voltage margin of alternating current plasma display panel (AC-PDP) were investigated. It is observed that wall-charge accumulation results in a remarkable increase of gas DBD breakdown threshold during sustaining discharge period. Sustaining voltage margin is reduced by the threshold increase. A larger margin can be obtained when the threshold is decreased by removing unfavorable influence of wall-charge accumulation. Compared with normal margin, improved margin has a larger value and a faster linear increase with increasing wall-charge voltage. That indicates a way to improve AC-PDP performances remarkably.

Guo Bingang; Wei Wei; Shinoda, Tsutae; Liu Chunliang [Advanced Display Research Center, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba Meguro-Ku, Tokyo 153-8505 (Japan); Key Laboratory for Physical Electronics and Devices of the Ministry of Education of China, Xi'an Jiaotong University, Xi'an, Shaanxi Province, 710049 (China)

2007-03-05

420

Catalytic Effects of Metal-loaded Membrane-like Alumina Tubes on Ammonia Synthesis in Atmospheric Pressure Plasma by Dielectric Barrier Discharge  

Microsoft Academic Search

Plasma synthesis of ammonia was studied at atmospheric pressure using a dielectric-barrier-discharge-plasma reactor equipped\\u000a with a metal-loaded membrane-like alumina tube as a catalyst between the electrodes. Introducing the pure alumina into N2–H2 plasma resulted in an increase in the ammonia yield and the further improvement was achieved by loading the alumina with\\u000a Ru, Pt, Ni, and Fe. These results clearly

Takanori Mizushima; Kazumi Matsumoto; Hironobu Ohkita; Noriyoshi Kakuta

2007-01-01

421

Collective phenomena in volume and surface barrier discharges  

NASA Astrophysics Data System (ADS)

Barrier discharges are increasingly used as a cost-effective configuration to produce non-equilibrium plasmas at atmospheric pressure. This way, copious amounts of electrons, ions, free radicals and excited species can be generated without significant heating of the background gas. In most applications the barrier is made of dielectric material. Major applications utilizing mainly dielectric barriers include ozone generation, surface cleaning and modification, polymer and textile treatment, sterilization, pollution control, CO2 lasers, excimer lamps, plasma display panels (flat TV screens). More recent research efforts are devoted to biomedical applications and to plasma actuators for flow control. Sinusoidal feeding voltages at various frequencies as well as pulsed excitation schemes are used. Volume as well as surface barrier discharges can exist in the form of filamentary, regularly patterned or diffuse, laterally homogeneous discharges. The physical effects leading to collective phenomena in volume and surface barrier discharges are discussed in detail. Special attention is paid to self-organization of current filaments and pattern formation. Major similarities of the two types of barrier discharges are elaborated.

Kogelschatz, U.

2010-11-01

422

Mach 5 bow shock control by a nanosecond pulse surface dielectric barrier discharge  

Microsoft Academic Search

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

M. Nishihara; K. Takashima; J. W. Rich; I. V. Adamovich

2011-01-01

423

Silicon oxide barrier films deposited on PET foils in pulsed plasmas: influence of substrate bias on deposition process and film properties  

NASA Astrophysics Data System (ADS)

A widely used plastic for packaging, polyethylene terephtalate (PET) offers limited barrier properties against gas permeation. For many applications of PET (from food packaging to micro electronics) improved barrier properties are essential. A silicon oxide barrier coating of PET foils is applied by means of a pulsed microwave driven low-pressure plasma. While the adjustment of the microwave power allows for a control of the ion production during the plasma pulse, a substrate bias controls the energy of ions impinging on the substrate. Detailed analysis of deposited films applying oxygen permeation measurements, x-ray photoelectron spectroscopy and atomic force microscopy are correlated with results from plasma diagnostics describing the deposition process. The influence of a change in process parameters such as gas mixture and substrate bias on the gas temperature, electron density, mean electron energy, ion energy and the atomic oxygen density is studied. An additional substrate bias results in an increase in atomic oxygen density up to a factor of 6, although plasma parameter such as electron density of ne = 3.8 ± 0.8 × 1017 m-3 and electron temperature of kBTe = 1.7 ± 0.1 eV are unmodified. It is shown that atomic oxygen densities measured during deposition process higher than nO = 1.8 × 1021 m-3 yield in barrier films with a barrier improvement factor up to 150. Good barrier films are highly cross-linked and show a smooth morphology.

Steves, S.; Ozkaya, B.; Liu, C.-N.; Ozcan, O.; Bibinov, N.; Grundmeier, G.; Awakowicz, P.

2013-02-01

424

Low Thermal Conductivity Yttria-Stabilized Zirconia Thermal Barrier Coatings Using the Solution Precursor Plasma Spray Process  

NASA Astrophysics Data System (ADS)

The primary function of thermal barrier coatings (TBCs) is to insulate the underlying metal from high temperature gases in gas turbine engines. As a consequence, low thermal conductivity and high durability are the primary properties of interest. In this work, the solution precursor plasma spray (SPPS) process was used to create layered porosity, called inter-pass boundaries, in yttria-stabilized zirconia (YSZ) TBCs. IPBs have been shown to be effective in reducing thermal conductivity. Optimization of the IPB microstructure by the SPPS process produced YSZ TBCs with a thermal conductivity of 0.6 W/mK, an approximately 50% reduction compared to standard air plasma sprayed (APS) coatings. In preliminary tests, SPPS YSZ with IPBs exhibited equal or greater furnace thermal cycles and erosion resistance compared to regular SPPS and commercially made APS YSZ TBCs.

Jordan, Eric H.; Jiang, Chen; Roth, Jeffrey; Gell, Maurice

2014-06-01

425

Micromachined electrostatic vertical actuator  

DOEpatents

A micromachined vertical actuator utilizing a levitational force, such as in electrostatic comb drives, provides vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control. The micromachined electrostatic vertical actuator provides accurate movement in the sub-micron to micron ranges which is desirable in the phase modulation instrument, such as optical phase shifting. For example, compact, inexpensive, and position controllable micromirrors utilizing an electrostatic vertical actuator can replace the large, expensive, and difficult-to-maintain piezoelectric actuators. A thirty pound piezoelectric actuator with corner cube reflectors, as utilized in a phase shifting diffraction interferometer can be replaced with a micromirror and a lens. For any very precise and small amplitudes of motion` micromachined electrostatic actuation may be used because it is the most compact in size, with low power consumption and has more straightforward sensing and control options.

Lee, Abraham P. (Walnut Creek, CA); Sommargren, Gary E. (Santa Cruz, CA); McConaghy, Charles F. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

1999-10-19

426

Control of Smart Actuators.  

National Technical Information Service (NTIS)

Hysteresis in smart materials hinders wider applicability of such materials in actuators and sensors. In this dissertation we study modeling, identification and control of hysteresis in smart actuators. While the approaches are applicable to control of a ...

X. Tan

2002-01-01

427

Electromagnetic rotational actuation.  

SciTech Connect

There are many applications that need a meso-scale rotational actuator. These applications have been left by the wayside because of the lack of actuation at this scale. Sandia National Laboratories has many unique fabrication technologies that could be used to create an electromagnetic actuator at this scale. There are also many designs to be explored. In this internship exploration of the designs and fabrications technologies to find an inexpensive design that can be used for prototyping the electromagnetic rotational