PRODUCTS & SERVICES
HIGH-SPEED
IMAGING TECHNIQUES PROVEN QUALITY AND
POWERFUL RESULTS
AEROSPACETESTINGINTERNATIONAL.COM // SEPTEMBER 111
Aircraft hydraulic fluid monitoring is normally conducted
during C-checks, at an interval of one year or less. The
hygroscopic nature of hydraulic fluids can result in high
water concentration within the fluid, which potentially
results in hidden corrosion damage to aircraft control
systems. This can often be difficult to localize and is
expensive to repair. To combat water absorption, Test-
Fuchs has developed a small vehicle known as the Water
Separator WSS4. Aircraft maintenance teams simply
connect the Water Separator WSS4 to the return line
between the aircraft and a hydraulic ground power unit.
Water is extracted as the fluid circulates during concurrent
maintenance activities.
This procedure can potentially prolong the life of the
hydraulic medium, thus saving high costs for fluid
exchange and also avoids the need for unnecessary
hazardous waste fluid disposal. Additional cost savings
can also potentially be made by avoiding the replacement
of corrosion-damaged components and fluid lines.
When a number of airlines tested the Water Separator
WSS4, it was concluded that the quality of the hydraulic
medium improved significantly after a purification cycle of
only four hours.
The graph illustrates the results of the field tests,
illustrating water ppm versus time (hours). After a short
starting phase of 20 minutes, the oil circuit was closed
and the cleaning process began. Each dot represents a
documented ppm value on the display. The peaks around
hour 3 and 4 show movement of flight controls to get all
oil out of reservoirs. The water content was reduced from
2,351ppm to 831ppm after four hours. \\
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High-speed imaging is used in
various applications by
engineers in the aerospace
industry. Three very common
imaging techniques utilized are
Digital Image Correlation, Particle
Image Velocimetry, and Schlieren
Imaging. These imaging
techniques provide insight into
various aspects of the strength and
durability of materials, the
characteristics of engine
combustion processes, the
aerodynamics of objects in flight,
and much more.
Digital Image Correlation (DIC)
is used to determine the extent of
deformation, vibration and strain
on materials undergoing some
type of physical stress. DIC
analyzes high-speed video to
identify and measure movements,
some of which are incredibly small,
within a high-contrast speckle
pattern that has been applied to
the surface of the material being
tested. The speckle pattern
movements are examined to
provide automatic calculations and
visualization of the degree of
deformation, vibration or strain
found on the material.
Particle Image Velocimetry (PIV)
plays an important role in
understanding the fundamental
movement of liquids, gases and
plasmas (collectively known as
fluids). PIV analyzes high-speed
video to identify and measure the
movements of tracer particles that
have been added to the fluid being
tested. The particle movements are
examined to provide automatic
calculations and visualization of
the fluid flow.
Schlieren imaging is used as a
means of visualizing changes in
pressure and temperature, as well
as shock waves, moving through a
transparent fluid such as air. This
imaging technique relies on
differences in refractive index
caused by density gradients in the
fluid to bend light that is passing
through the fluid. The bending of
the light creates a spatial variation
in the intensity of light, and this
can be visualized with the use of a
high-speed camera.
There are a number of factors
that are important to consider
when purchasing a high-speed
camera for use with DIC, PIV, and
Schlieren imaging techniques.
These factors include frame rate,
light sensitivity, minimum exposure
time, and pixel resolution. All of
these factors contribute to the
overall image quality. \\
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