IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 35, NO. 3, JUNE 2007
693
Atmospheric Plasma Actuators for
Aeroacoustic Applications
Xun Huang, Sammie Chan, and Xin Zhang
Abstract—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.
Index Terms—Aeroacoustics, atmospheric pressure glow discharges, flow control.
I. I NTRODUCTION
P
LASMA, operating in atmospheric pressure air conditions,
holds the potential to reduce flow-induced noise generated
during the takeoff and approach-to-landing of aircraft that has
a significant environmental impact on the communities near
airports. A recent work [1] demonstrated the use of atmospheric
pressure air glow discharges [2] for attenuating the tonal noise
of a cavity that is similar to landing gear bay, which has been
frequently employed as a testbed in the study of flow-induced
noise control.
The actuator employed in this paper is able to generate
weakly ionized atmospheric plasma that mainly consists of
nitrogen/oxygen plasma components, which are coupled to
an electric field. Through Lorentzian collisions, momentum
is transferred to the neutral gas via charged particles in the
plasma thus affecting the flow field local to the plasma actuator
and subsequently serve flow control applications [3]–[5]. To
generate atmospheric glow discharges in air, a sufficiently high
potential is required to break down the surrounding species [2].
The potential is required at kilohertz frequency to sustain the
glow discharge and prevent electron avalanches that lead to
arcing [6]. The fast control response, simplicity and absence
of mechanical moving parts, e.g., pumps, make the plasma
actuator a promising option for aeroacoustic applications. Its
effectiveness under harsh working conditions, however, is still
an open problem.
In this paper, the plasma actuator consists of a series of
symmetrical electrodes that were manufactured to be aligned
with the oncoming mean flow. A continuous radio-frequency
driving signal at several kilohertz was applied on a small plasma
actuator (70 mm × 300 mm) and the consumed power exceeded
40 W. The electrodes on the bottom surface were wider than the
Manuscript received February 17, 2007; revised March 19, 2007.
The authors are with the School of Engineering Science, Southampton
University, SO17 1BJ Southampton, U.K. (e-mail: xunger@soton.ac.uk).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TPS.2007.896781
Fig. 1. Structure of the plasma actuator used in wind tunnel experiments.
electrodes on the upper flow facing surface (Fig. 1) in order to
introduce 3-D flow across the span of the cavity. The induced
fluid motion along the surface of the dielectric board led to the
formation of streamwise vortical structures, between a pair of
actuators, that convected downstream with the mean flow and
impeded the development of the vortices in the cavity shear
layer, disrupting and minimizing the feedback mechanism that
was required for sustaining fluid dynamic oscillations. More
details related to fluid dynamics and acoustics of the system
can be found in [1].
To improve the authority of plasma actuators, different
driving methods using unsteady actuation [7] and sawtooth
signal [8] have been presented. The former method was employed in this paper to improve the power efficiency. Rather
than using linear power amplifier [2], [8], our power supply
uses power switching circuit that restricts the plasma driving
signal to square wave. Fig. 1 shows that a driving signal with
an adjustable duty cycle (Cd ) is generated by a pulse width
modulation module of a dSPACE real-time system. Several
experiments using a signal generator indicated the optimal
driving frequency is 3.2 kHz for the present plasma actuator
in terms of its attenuation effect. The driving signal is subsequently modulated by a control signal with an adjustable
period (Cp ) and a variable duty cycle (Cd2 ). The duty cycles
of both square waves are set to 50%, unless otherwise stated.
The modulated driving signal is fed into a MOSFET driver to
reduce the switching loss of a power MOSFET. As the power
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IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 35, NO. 3, JUNE 2007
Fig. 2. Overall system working in a wind tunnel.
MOSFET is switched by the plasma driving signal, a step-up
transformer generates high voltage output sufficient to induce
discharges. The performance of the plasma actuator, therefore,
can be controlled by adjusting Cp and Cd , respectively.
Experiments were conducted in a wind tunnel facility at the
University of Southampton (Fig. 2). A cavity model manufactured from Perspex was used as a testbed to develop the plasma
actuator control system. The investigation was performed for
cavity geometries at flow speeds ranging from 10 to 20 m/s. The
tones generated by the cavity were recorded using a Panasonic
WM-60A omnidirectional condenser microphone that was flush
mounted to the surface of the front wall of the cavity. The
microphone’s signal was passed through an antialiasing filter and was subsequently sampled with a PC sound card at
44.1 kHz. A 4096 point fast Fourier transform with a Hanning
window function was applied to process the sampled data. The
sound pressure level (SPL) result was averaged over 300 signal
blocks for statistical confidence in the results. The experimental
procedure was adjusting Cp first and then adjusting Cd at the
proper Cp .
Fig. 3(a) shows that the flow-induced tones are attenuated
successfully with the system operating at Cd2 = 100%. Other
than attenuating flow-induced tones, the plasma actuator also
produces high-frequency acoustic tones and electromagnetic
radiations. If Cp = 500 µs, Fig. 3(b) shows that the switching power supply works ineffectively and the plasma actuator
generates insufficient plasma in the weak electric field, thus
affecting little over the flow field. The same phenomenon was
also discovered for conditions of Cd < 50% or Cd > 60%.
If Cp = 50 ms, given Cd2 = 50%, the flow-induced noise is
attenuated successfully in 25 ms, while it develops again in the
consecutive 25 ms. Fig. 3(c) shows that its overall attenuation
effect is not satisfactory. On the contrary, the flow-induced
noise fails to develop substantially if Cp < 20 ms. Fig. 3(d)
shows the result with the system operating at Cp = 5 ms and
Cd = 60% that is the optimal driving signal for this paper, in
terms of power efficiency and attenuation effect. As displayed
in Fig. 4, its attenuation effect is 6 dB higher than the baseline
result while approximately 50% of the system power is saved.
Fig. 3. SPL results at U∞ = 20 m/s: (a) Cd2 = 100%; (b) Cp = 500 µs;
(c) Cp = 50 ms; (d) Cp = 5 ms, Cd = 60%.
HUANG et al.: ATMOSPHERIC PLASMA ACTUATORS FOR AEROACOUSTIC APPLICATIONS
695
R EFERENCES
[1] S. Chan, X. Zhang, and S. Gabriel, “The attenuation of cavity tones using
plasma actuators,” presented at the 11th AIAA/CEAS Aeroacoustics Conf.,
Monterey, CA, 2005, AIAA Paper 2005-2802.
[2] J. R. Roth, “Aerodynamic flow acceleration using paraelectric and peristaltic electrohydrodynamic effects of a one atmosphere uniform glow
discharge plasma (OAUGDP),” Phys. Plasmas, vol. 10, no. 5, pp. 1166–
1172, 2003.
[3] J. R. Roth, “Electrohydrodynamically induced airflow in a one atmosphere
uniform glow discharge surface plasma,” in Proc. IEEE Int. Conf. Plasma
Sci., Jun. 1998, p. 291. no. 6P–67.
[4] J. R. Roth, D. M. Sherman, and S. P. Wilkinson, “Electrohydrodynamic
flow control with a glow-discharge surface plasma,” AIAA J., vol. 38, no. 7,
pp. 1166–1172, Jul. 2000.
[5] E. Moreau, “Airflow control by non-thermal plasma actuators,” J. Phys. D,
Appl. Phys., vol. 40, no. 3, pp. 605–636, Feb. 2007.
[6] J. R. Roth, Industrial Plasma Engineering: Applications to Nonthermal
Plasma Processing, vol. 2. London, U.K.: Inst. Phys. Publishing, 2001,
ch. 18.
[7] O. F. Thomas, A. Kozlov, and C. T. Corke, “Plasma actuators for landing
gear noise reduction,” presented at the 11th AIAA/CEAS Aeroacoustics
Conf., Monterey, CA, 2005, AIAA Paper 2005–3010.
[8] C. L. Enloe, T. E. McLaughlin, R. D. Van Dyken, K. D. Kachner, E. J.
Jumper, and T. C. Corke, “Mechanisms and responses of a single dielectric
barrier plasma actuator: Plasma morphology,” AIAA J., vol. 42, no. 3,
pp. 589–594, 2004.
Xun Huang was born in Hangzhou, China, in
1977. He received the B.Eng. degree in astronautics from the Northwestern Polytechnical University,
Xi’an, China, the M.Eng. degree in automatic control
from Tsinghua University, Beijing, China, and the
Ph.D. degree in aeronautics and astronautics from
the University of Southampton, Southampton, U.K.,
in 1999, 2002, and 2006, respectively.
He was a Research Engineer in the Shanghai Laboratory of the GE Global Research Center in 2003.
He was a Research Assistant in 2006 and became a
Research Fellow in 2007 in the School of Engineering Sciences, University
of Southampton. His research interests include control, plasma, and parallel
computation, especially for aerospace applications.
Dr. Huang received the Edison Technology Excellence Award in 2003.
Fig. 4. Relationships between the system power and the dominant amplitudes
of (a) the flow-induced tones and (b) the radiated plasma actuator noise.
Meanwhile, the radiated noise of the plasma actuator is still
lower than the flow-induced noise.
II. C ONCLUSION
In summary, the plasma actuator was applied to a flowinduced noise control problem to demonstrate its effectiveness
in aeroacoustic applications. The system was tested in the wind
tunnel. The results show that both the duty cycle of the driving
signal (Cd ) and the period of the control signal (Cp ) affect the
performance of the plasma actuator. The optimal values could
be achieved by several experiments with the present hardware
system rapidly. The results help to guide the selection of proper
parameters, leading to a more intelligent and efficient system
using closed-loop methodologies.
ACKNOWLEDGMENT
This work was performed under an extended studentship between October and December 2006 at Southampton University.
Sammie Chan was born in the U.K. in 1980. He
received the M.Eng. degree in aerospace engineering
and the Ph.D. degree, investigating the attenuation
of flow induced tonal noise using plasma actuators,
from the University of Southampton, Southampton,
U.K., in 2002 and 2006, respectively.
He is currently a Research Fellow with the Aerodynamics and Flight Mechanics Group, University
of Southampton, performing research with plasma
actuators applied to noise control.
Xin Zhang received the B.Eng. degree in aerospace
engineering from the Beijing University of Aeronautics and Astronautics, Beijing, China, and the
Ph.D degree in fluid mechanics from Cambridge
University, Cambridge, U.K.
He is a Professor of aerodynamics in the School of
Engineering Sciences, University of Southampton,
Southampton, U.K. His main research interests are in
the areas of unsteady aerodynamics, computational
aeroacoustics, engine and airframe noise, ground effect aerodynamics, race car aerodynamics, and flow
control. He has conducted studies of self-sustained fluid flow oscillations,
turbulent flow control through streamwise vortices, flow control jets, engine
and duct acoustics, etc. He is the Principal Investigator of many projects funded
by the U.K. government, EU, Airbus, and U.K. aerospace and motor-racing
industries, and has acted as a Consultant for a number of industrial companies.
Dr. Zhang is a Fellow of the Royal Aeronautical Society and an Associated
Fellow of the American Institute of Aeronautics and Astronautics.