st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Aerodynamic drag reduction of 3D train model using dielectric barrier discharge plasma actuators
T. Kim1, S. Yun2
1
Department of Aerospace Engineering, Chosun University, Gwangju, Republic of Korea
2
Korea Railroad Institute, Uiwang, Republic of Korea
Abstract: DBD (dielectric barrier discharge) plasma actuator was used to control the flow
properties. The flexible DBD actuator was designed to be installed on an arbitrary shape.
Wind-tunnel tests were performed to measure a drag reduced by the flow control using the
DBD actuators. At the wind velocity of 5 m/s, the drag on the 3-D train model was reduced by
5.35%, whereas the degree of drag reduction decreased as the wind velocity increased.
Keywords: Aerodynamic drag, Drag reduction, Dielectric barrier discharge, Plasma actuator
1. Introduction
Passive flow control, such as shape improvements, has
been mainly employed to reduce aerodynamic drag but
reached the limitation. Active flow control is needed to
reduce more and more the aerodynamic drag.
Recently, plasma was used to control actively the flow,
so called “Plasma flow control.” The electrons are accelerated by the plasma and collided with gas particles, generating the induced flow [1]. DBD (dielectric barrier discharge) plasma actuator was used to generate the plasma
in the flow stream. The DBD actuator generating a glow
discharge at the atmospheric temperature and pressure has
merits such as low power consumption, no moving parts,
long lifetime, easy maintenance, high reliability, good
dynamic characteristics and compactness. DBD actuator
has a simple structure as shown in Fig. 1.
Upper and bottom electrodes are placed unsymmetrically on the surface of a dielectric barrier. The plasma
discharge between electrodes generates a body force orienting from upper to bottom electrode. Consequently, the
body force generates an ionic wind [2]. The plasma flow
control using the ionic wind by the DBD actuator is employed for reducing the aerodynamic drags by controlling
a turbulent boundary layer and flow separation.
Recently, feasibility study of the plasma flow control
using DBD actuators has been carried out. Velkoff et al.
[3] and Thomas et al. [4] reported that the aerodynamic
drags were reduced by controlling the flow separation on
Fig.1 Conceptual structure of DBD actuator
the flat-plate and the cylindrical body. Pond et al. [2] reported the performance characteristics in term of a geometric structure of the DBD actuator and plasma discharge conditions such as voltage and frequency. Roth [5]
used the plasma flow control to improve aerodynamic
performances of an airfoil for aeronautical applications.
Thomas et al. [6] controlled the flow separation on turbine
blades using DBD actuators.
The performance characteristics of the DBD actuator
according to the geometric and discharge parameters were
already carried out. In the present study, the flow separation on 2-D and 3-D train models was controlled using
DBD actuators. First, the flow motion on the 2-D model
was visualized when the plasma was discharged. Next,
Wind-tunnel tests were performed to verify the plasma
flow control reducing the aerodynamic drag of the 2-D
and 3-D train models.
2. Experiments
In the previous study [7], a DBD actuator was designed
as various parameters including the electrode geometry
and discharge conditions. Based on the result of performance characteristics, the DBD actuator for controlling
the flow separation on the train models was designed.
Table 1 shows the specification of a DBD actuator. Cupper tape having a high electric conductivity was used as
electrodes, and an acryl was selected as a dielectric mate-
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Fig.2 DBD actuators attached on 2-D model.
rial. Two electrodes were attached on upper and bottom
surfaces of dielectric material, respectively. The gap between electrodes and the dielectric material thickness
were 2 and 5 mm, respectively.
Fig. 2 shows a photograph of DBD actuators attached
on 2-D model. DBD1 and DBD2 locating in the incline
plane of 2-D model were DBD actuators to control the
flow separation of upper and lower flow streams. DBD3
was not used in this study. Fig. 3 shows a photograph of
DBD actuators attached on 3-D model. The 9 DBD actuators in total were attached on the head part of the 3-D
model.
Fig. 4 shows the schematic of wind-tunnel test setup for
the plasma flow control. High voltage for the plasma discharge was generated by a high-voltage amplifier (Trek
20/20C). The maximum amplifying magnitude is 2,000
times as high as amplitude of an input signal. Voltage,
frequency and waveform of the input signal were controlled by a function generator (Agilent 33220A). The
voltage and current were measured using a high-voltage
and current sensors and recorded by an oscilloscope
(WaveSurfer 424, LeCory).
Wind-tunnel tests were performed at wind velocities of
2, 5, 10, 15 and 20 m/s. The aerodynamic drag was measured using a load cell before and after the plasma dis-
Fig.3 DBD actuators attached on 3-D model.
Fig.4 Wind-tunnel test setup.
Fig.5 Flow visualization on the test model.
charge. Test sequence is as follows: (1) The wind-tunnel
is operated and the wind velocity is stabilized, (2) The
drag is measured without the plasma discharge, (3) The
DBD actuators are operated and then the drag is measured,
and (4) The on and off of DBD actuators are repeated.
Before the wind-tunnel tests, the flow passing though
the test model was visualized using a smoke. In the flow
visualization, a scale-down model with the same geometry was used.
3. Results and discussion
Flow visualization using a smoke was performed to
verify the possibility of the flow separation control using
the DBD actuator. The flow stream lines were observed
with the plasma discharge as the discharge voltage varied.
Fig. 5 shows the flow profile on the test model at 7 kV
and 5 kHz as the time elapsed. It was observed that the
flow stream was attached on the surface of the test model.
Fig. 6 shows the wind-tunnel test results of the 2-D
model as increasing the wind velocity. The DBD1 and
DBD2 actuators were simultaneously operated at 13 kV
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Fig.6 Flow visualization on the test model.
and 1 kHz. D* is a dimensionless drag and defined as the
reduced drag with the plasma discharge divided by the
actual drag without the plasma discharge. For example,
D*=1 means that the DBD actuator is not operated, and
D*<1 means the drag is reduced by the DBD actuators.
D*
Dwith plasma dischrage
Dwithout plasma discharge
(1)
DBD actuator induces the momentum change generating a thrust. Thus, it seems that the drag can be reduced
by the thrust that generated by the DBD actuator but not
by the plasma flow control. Fig. 6 (a) shows the drag
change when the DBD actuator was operated at zero velocity. The flow separation is not occurred because the
flow is not existed. Therefore, the drag should be constant
because the DBD actuator did not control the flow separation. If the drag is reduced at zero velocity, it will be obviously because of a thrust by the DBD actuator. As a
result, however, the drag was not changed as shown in Fig.
6 (a). Consequently, the thrust was not generated by the
DBD actuator.
Fig. 6 (b)-(f) shows the drag change as increasing the
wind velocity. It was validated that the drag was reduced
by controlling the flow separation using the DBD actuator.
At the wind velocity of 2 m/s, the drag was reduced by
9.7%. The degree of the drag reduction was decreased as
increasing the wind velocity. The drag was reduced by
3.3% at the wind velocity of 15 m/s. At the wind velocity
greater than 20 m/s, the drag change was not clear. The
flow separation is more intensive as the wind velocity
increased. Therefore, the ionic wind of the DBD actuator
should be enhanced to control the flow separation at a
high wind velocity [7]. High voltage and frequency are
required to increase the intensity of the plasma discharge
on the DBD actuator.
Fig. 7 shows the aerodynamic drag reduction of 3-D
model using DBD actuators as the wind velocity varied.
The DBD actuators were installed on a scale-down model
of Korea next-generation high-speed train as shown in Fig.
3. The DBD actuators were operated at 19 kV and 2 kHz;
then the ionic wind velocity and power consumption were
4.7 m/s and 3.29 W/cm. Wind-tunnel tests were performed to measure a drag reduced by the flow control
using the DBD actuators. DBD actuating can generate a
thrust, which can be observed as a drag is reduced. At the
zero wind velocity, however, drag reduction was not observed. At the wind velocity of 5 m/s, the drag was reduced by 5.35%, whereas the degree of drag reduction
decreased as the wind velocity increased as shown in Fig.
7.
4. Conclusion
In the present study, the aerodynamic drag was reduced
using the DBD actuator for controlling the flow separation. The 2-D and 3-D models were designed as the test
Fig.7 Aerodynamic drag reduction of 3-D model.
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
models. The DBD actuators were attached on the incline
plane of the test models. The wind-tunnel tests were performed at the various wind velocities and the reduced
drag was measured. At the zero wind velocity, where the
flow separation was not occurred, the drag was not
changed because the effect of the electric wind generated
by the DBD actuator on the drag measurement was negligible. At the wind velocity of 2 m/s, the drag was reduced
by 9.7% in the test of 2-D model, while at the wind velocity of 5 m/s, the drag was reduced by 5.35% in the test of
3-D model. The drag reduction decreased as the wind
velocity increased.
5. Acknowledgement
This research was supported by research funds from
Korea Railroad Research Institute, “Development of the
core technologies for wheel-rail type ultra high-speed
train.”
6. References
[1] E. Moreau, J. Phys. D: Appl. Phys., 40, 605 (2007).
[2] J. Pons, E. Moreau, G. Touchard, J. Phys. D: Appl.
Phys., 38, 3635 (2005).
[3] H. Velkoff, J. Ketchman, AIAA J., 16, 1381 (1968).
[4] F.O. Thomas, A. Kozlov, T.C. Corke, AIAA Meeting
(San Francisco, USA, June 2006), paper #2006-2845.
[5] J. Reece Roth, Phys. Plasmas, 10, 1227 (2003).
[6] C. Thomas, O. Flint, J. Huang, NASA Technical
Report, NASA/ CR-2007-214677.
[7] S. Yun, H. Kwon, T. Kim, KSAS Journal, 40, 492
(2012).
[8] C. Kwing-So, T. Jukes, R. Whalley, Phil. Trans. R.
Soc. A, 369, 1443 (2011).