MATEC Web of Conferences 31 , 0 7 0 0 4 (2015)
DOI: 10.1051/ m atec conf/ 201 5 3 10 7 0 0 4
C Owned by the authors, published by EDP Sciences, 2015
Development of coaxial speaker-like non-contact electrostatic sensor for
aviation engine exhaust electrostatic character research
Zhaoheng Du
1
1&2,a
1
1
Xiaofeng Hu Ming Wei Lei Wang
1
Research Institute of Electrostatic and Electromagnetic Protection , Mechanical Engineering College in Shijiazhuang, China
2
Northwest Institute of Nuclear Technology in Xi’an, China
Abstract. Electrostatic sensor is the most important equipment in aero-engine exhaust electrostatic character research.
By comparing a variety of sensor test programs, the coaxial speaker-like noncontact electrostatic sensor program is
proposed. Numerical simulation analysis indicates the electric field distribution of electrostatic sensor, the influence
principle of gap width, outer diameter, center diameter, angle and other factors on the sensor capacitance values
which identify the key indicators of electrostatic sensor. The experiment test shows that the simulation analysis is in
good agreement with the experimental results.
1 Introduction
Aero-engine exhaust electrostatic will charge aircraft to
very high potential which causes a lot of electromagnetic
interference to navigation system and communication
system[1]. So, it is very important to research the
electrostatic character of aero-engine exhaust and its
electrification effect. Electrostatic sensor is the most
important equipment of aero-engine exhaust electrostatic
character research[2].
In order to measure the electrostatic character of aeroengine exhaust, it seems a easy approach: Insulate the
engine from the earth, drive the engine to work in
different conditions, test the charging current between the
engine and the earth directly or the amount of
electrostatic charge on aero-engine directly. However,
due to the huge and complex of aviation engine test
platform, the basic conditions of aviation engine test
platform can not meet the test requirement[3]. So, an
alteration is prerequisite. According to the special
requirements of electrostatic testing, the leak resistance of
aviation engine test platform should be 1012Ω or bigger.
It requires all the leak resistance of aviation engine test
platform should be 1012Ω or bigger. In fact, the quality
of such a big aviation engine test platform is so great that
the resistance of insulating material which having a high
volume resistivity will drop rapidly and is difficult to
maintain 1012Ω or bigger. It is, actually, impossible to
insulate all the part of aero-engine test platform from the
earth with a resistance larger than 1012Ω . Therefore,
many consideration suggests that the easy approach is not
suitable for the electrostatic character research of jet
aircraft engines. And electrification is can not be
measured directly[4,5].
a
2 Principle of electrostatic sensor
influence factors of coaxial speaker-like
non-contact electrostatic sensor
According to the principle of conservation of charge, if
aero-engine’s working produces exhaust electrostatic
electrification, there is bound to be a positive and
negative charge separation and transfer. If the aeroengine carries some kind polarity charge, the aero-engine
exhaust is bound to carry the opposite polarity charge. So
if the exhaust charged state is measured, the electrical
conditions of aircraft engines are naturally clear.
Although the engine combustion chamber is in high
temperature and pressure, and the physical and chemical
changes are complex, the temperature of the tail nozzle is
lower, the pressure is relatively smaller, the overall
charge state is relatively stable, which make the exhaust
can be considered as a stable gas-solid two-phase flow.
High-speed charged aero-engine exhaust can be
approximately considered as uniformly charged cylinder.
Directional movement of positive and negative charge of
aero-engine exhaust airflow forms current. And the
current can be measured with the help of Rogowski coil
type sensor. The current at the center of Rogowski coil
type sensor generates magnetic field, and the output
signal of Rogowski coil is the differential of the current.
When the engine operating condition is stable, the current
is kept constant or relatively slow change, so the sensor
output signal is very small which make it not conducive
to the test and has a poor dynamic performance. On the
other hand, the Rogowski coil type sensor has a complex
structure, costly and long design cycles. Therefore, it is
not suitable for aero-engine exhaust electrostatic
character research.
Zhaoheng Du: duzhaoheng188@163.com
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits XQUHVWULFWHGXVH distribution, and reproduction in any medium, provided the original work is properly cited.
Article available at http://www.matec-conferences.org or http://dx.doi.org/10.1051/matecconf/20153107004
MATEC Web of Conferences
Table 1. Main parameters of coaxial speaker-like non-contact
electrostatic sensor
Parameters
d_in
dis
Lin
LL1
LL2
zeta
Value
0.6m
0.1m
0.5m
0.5m
0.5m
11°
LL2
Lin
zeta
Inner
Cylinder
Airflow
d_in
Pr
Outer
Cylinder
dis
LL1
Pl
Figure1.Diagram of
electrostatic sensor.
coaxial
speaker-like
non-contact
The main design parameters are as follow: Central
radius (d_in, meters), spacing between the inner and outer
cylinder (dis, meters), the inner cylinder half-chord (Lin,
meters), the outer cylinder on the left side chord length
(LL1, meters), the outer on the right cylinder chord (LL2,
meters) and wall angle with the central axis (zeta, angle
degrees) equal to the inner and outer tube.
3 Influence factors of coaxial speakerlike electrostatic sensor
The output voltage of the coaxial speaker-like noncontact electrostatic sensor is analyzed by the finite
element analysis. Simulation results with different mesh
grid settings are shown in Figure 2.Among numerical
calculation, the point charge is equivalent to a charged
conductor sphere with radius of CBr (m) in order to
simulate conditions under point charge sensor output
voltage.
-2.0650
? ?Sensor
? ? output
? ? ? voltage
( V) (V)
For the special requirements of the aero-engine
exhaust electrostatic character research, a sensor with
high sensitive area and output signal is required to be
designed. After comprehensive consideration, the
electrostatic sensor designed to be non-contact coaxial
speaker-like (Fig. 1). The electrostatic sensor is installed
behind the engine nozzle, and is coaxial with the aeroengine exhaust airflow. Taking into account the rapid
spread of the engine jet, the sensor is designed to be
speaker-like in the actual test in order to prevent the
damage caused by the spread of the aero-engine exhaust
airflow.
The outer cylinder of the electrostatic sensor is
connected to the ground and its length is bigger than the
inner cylinder, so that the electrostatic sensor can be
considered as an ideal Faraday cylinder. At the same time,
the inner cylinder gets a good electrostatic shielding. The
inner cylinder is the test electrode, and is directly
connected with the electrostatic test apparatus. The inner
cylinder is separated from the outer cylinder by a certain
number of special electrostatic insulation support rod.
The static insulation support rod adopts a multilayer
composite structure, which not only ensures the reliability
of internal and external cylinder connections, but also
ensures the high resistance at high temperature. This
coaxial speaker-like non-contact electrostatic sensor not
only has high stability and sensitivity, but also has the
advantages of simple structure, compact and convenient
assembly and disassembly. And it will not damage the
original engine system. In order to simplify the analysis
of aero-engine exhaust’s electrostatic electricity,
In order to simplify the analysis and discussion of the
influence of aero-engine exhaust’s electrostatic charge on
the output voltage of the engine, the aero-engine exhaust
is reduced to an uniformly charged finite length cylinder
with a radius and a half lengths are Pr (meters) and Pl (in
meters),which is shown at Table 1.
? ? ? 1
? ? ? 1
? ? ? 2
Coarse grid
-2.0655
-2.0660
Fine grid
Middle grid
-2.0665
1E-4
1E-3
0.01
0.1
CBr
Figure 2.Sensor output voltage changes with the radius of
the conductor CBr.
By comparing the results of three kinds of grid step
size, it can be found that the results of the coarse grid
computing are slightly greater than that of the fine grid
and the middle grid. This is due to the poor accuracy of
the coarse mesh, and the voltage drop of small conductor
near the sphere is larger. Because the potential drop
occurs mainly in the space region near the conductor
sphere, and the distance from the conductor sphere is
smaller, the output voltage of the sensor is smaller. So,
the middle mesh grid is a better setup for numerical
calculation.
The radius of the internal and external cylinder of the
sensor and the distance between them are an important
factor affecting the output voltage of the sensor. When
the outer wall of the LL1 and the outer wall of the right
size LL2 have the same value, the dis changes as 0.05,
0.1, 0.2, 0.25 respectively. The sensor output voltage with
different gap width changes with the outer wall
size(Fig.3 ). From Fig.3, the output voltage of the sensor
decreases with the increase of the length of the outer wall,
and decreases with the increase of LL1. When the LL1
reaches 1m ˈits increase will not lead to a significant
decrease of the output voltage of the sensor. This shows
that although the external wall length of the sensor can be
improved, the anti-interference ability of the sensor can
be improved, but the increase of the external wall size
will result in the increase of the internal and external wall
capacitance.
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ICMEE 2015
9E-10
9E-10
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.13
0.14
8E-10
-0.4
-0.8
-1.0
-1.2
-1.4
-1.6
-1.8
0.05
0.1
0.2
0.25
dis
-2.0
-2.2
0.0
0.5
1.0
1.5
2.0
2.5
-0.6
-
6E-10
C(F)
(V)
? Sensor
? ? ? output
? ? ? voltage
( V)
(V)
?Sensor
? ? ? output
? ? ? voltage
( V)
7E-10
-0.6
5E-10
0.2
0.4
0.5
1
1.5 LL1
2
3
-1.8
-
4E-10
0.05
0.10
9x10-10
0.20
7.00E-010
d_in??increase
?
6.00E-010
C(F)
C(F)
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.13
0.14
8.00E-010
7x10-10
5.00E-010
-10
4.00E-010
-10
3.00E-010
2x10-10
0.04
dis ?increase
?
2.00E-010
0.06
0.08
0.10
dis
0.12
0.14
0.16
11
12
13
14
0.04
0.06
0.08
0.10
0.12
0.14
dis
0.25
9.00E-010
d_in=0.5
d_in=0.6
d_in=0.7
3x10
5E-10
Figure 5.The sensor output voltage with different zeta and dis..
0.15
As one of the key parameters of the coaxial
speaker-like non-contact electrostatic sensor, the
variation of the capacitance value of the capacitance
value of the static sensor with the distance between
different medium and different diameters is shown in
Fig. 4. By the increase of the inner and outer cylinder
spacing, the sensor capacitance can be reduced. The
increase of the diameter will lead to the increase of
capacitance, which is not difficult to explain with the
law of the ideal plate capacitor.
4x10
10
zeta? ?
Figure3.The sensor output voltage with different dis and
LL1.
5x10
6E-10
-2.4
3.0
-10
7E-10
4E-10
9
? ? ? ? dis
6x10-10
8E-10
-1.2
-
? ? ? ? LL1
8x10-10
zeta=9
zeta=10
zeta=11
zeta=12
zeta=13
dis ?increase
?
0.0
C(F)
-0.2
0.50
0.55
0.60
0.65
0.70
0.75
d_in
Figure 4.The sensor output voltage with different dis and
d_in.
Under different spacing and angle, the capacitance
value of the non-contact type coaxial horn-shaped
electrostatic sensor shown in Figure 5 below. As
suggested by the Fig.5, when the angle value are
between 9~13 degrees, the sensor capacitance value
is almost not affected by the change of the angle, the
basic remain constant. The effect of the angle can be
found in the range of a larger variation range, with
the increase of the angle, the capacitance value of the
sensor is only slightly increased, but the increase
range is no more than 1%. The influence of the
change of the internal and external wall spacing on
the capacitance value is negligible.
4 Discussions and conclusions
The results of the coarse grid computing are slightly
greater than that of the fine grid and the middle grid. This
is due to the poor accuracy of the coarse mesh, and the
voltage drop of small conductor near the sphere is larger.
Because the potential drop occurs mainly in the space
region near the conductor sphere, and the distance from
the conductor sphere is smaller, the output voltage of the
sensor is smaller. So, the middle mesh grid is a better
setup for numerical calculation.
The output voltage of the sensor decreases with the
increase of the length of the outer wall, and decreases
with the increase of LL1. When the LL1 reaches 1m ˈits
increase will not lead to a significant decrease of the
output voltage of the sensor. This shows that although the
external wall length of the sensor can be improved, the
anti-interference ability of the sensor can be improved,
but the increase of the external wall size will result in the
increase of the internal and external wall capacitance.
By the increase of the inner and outer cylinder
spacing, the sensor capacitance can be reduced. The
increase of the diameter will lead to the increase of
capacitance, which is not difficult to explain with the law
of the ideal plate capacitor.
When the angle value are between 9~13 degrees, the
sensor capacitance value is almost not affected by the
change of the angle, the basic remain constant. The effect
of the angle can be found in the range of a larger
variation range, with the increase of the angle, the
capacitance value of the sensor is only slightly increased,
but the increase range is no more than 1%. The influence
of the change of the internal and external wall spacing on
the capacitance value is negligible.
References
1. Liu, S., et al, (2014) Gaodianya Jishu/High Voltage
Engineering. Mechanism analysis and experimental
research of aero-engine exhaust electrostatic charging,
40(9), (2014)
2. Du, Z., et al, Gaodianya Jishu/High Voltage
Engineering. Modeling and simulation analysis of
aerial vehicle charging and discharging process,
40(9),(2014)
3. Fu, Y., et al, Transactions of Nanjing University of
Aeronautics and Astronautics. Gas path elec-trostatic
sensor monitoring and comparison experiment on
turbojet engine, 30(4) ,(2013).
07004-p.3
MATEC Web of Conferences
4. Du, Z., S. Liu and W. Lei,(2010) Selection of the
optimal wavelet bases for wavelet de-noising of partial
discharge signal. In: International Conference on
Signal Processing Systems, ICSPS 2010, 5-7 July
2010,Dalian, China: IEEE Computer Society. (2010).
5. Liu, P., H. Zuo and J. Sun, (2014)IEEE Sensors
Journal. The electrostatic sensor applied to the online
monitoring experiments of combustor carbon
deposition fault in aero-engine, 14(3), (2014).
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