AEROLAB MODULE 4 Flashcards
After a tunnel is designed, the next
step is to decide its _____________ and, of course, to
modify that which is unsatisfactory
for the intended purposes.
flow
characteristics
Wind Tunnel instruments that uses pressure
Manometer, Barometer, Transducers
Pressure is balanced by the
weight of the liquid
column.
Manometer
Used to measure
atmospheric pressure.
Barometer
Converts pressure to an
analog electrical signal.
Transducers
Why do we calibrate?
To ensure the accuracy
To control errors
Help assure precise
measurements
While doing the
Calibration, some
properties are to be
measured:
Air Speed
Flow Angularity
Turbulence Measurement
Setting the speed of the
wind tunnel is done when
the is _______ the
test section.
no model inside
This can be put
inside the test section to
determine the airspeed.
Pitot Tube
The tunnel speed is usually determined by
__________________ in
the settling chamber in front of the
contraction tube, as station L indicates,
and a static pressure in front of the test
section as station S indicates.
measuring either static or total pressure
The ___________ is usually measured
throughout selected regions of the test
section by means of a pitot-static tube.
The __________ is calculated from a
barometric pressure measurement, and a
test-section temperature determination
along with the equation of state.
dynamic pressure ; density
The variation of q in the working range of
the jet should be less than _____ from the
mean, which corresponds to a _____
variation in velocity.
0.50% ; 0.25%
_________ may be added in the largest section
of the tunnel with spatial mesh densities
varied so that they are more dense in the
sections that correspond to high-velocity
regions in the jet.
screens
The flow has to be uniform across the cross section with all stream lines _______ to the tunnel axis when the test section is empty.
parallel
The flow direction can be calculated by using _____________________.
Sphere type and Claw type yaw meter
It would be desirable to have the variation less than
________. but it is often necessary to accept the best values
that can be achieved. The maximum variation should be
held to _______.
posneg0.10° ; posneg0.20°.
_________ is a measurement of irregularity in the flow.
Turbulence
__________ is used to identify whether the flow is
laminar or turbulent.
Reynolds Number
It has been argued that this turbulence causes flow patterns in
the tunnel to be similar to the flow pattern in free air at a
higher Reynolds number. Hence the tunnel test Reynolds
number could be said to be a higher “___________”
effective Reynolds
number.
Before the now common use of hot-wire anemometry, a ____________ was the primary way to measure the relative turbulence of a wind tunnel.
turbulence sphere
It’s useful to characterize the turbulent environment in a tunnel and to check if there is an ________
following changes in the tunnel configuration or special installations that might affect the flow quality.
indicated effect
The critical Reynolds number
for the sphere can be measured
in two ways. What are those?
One method is to plot the
measured CD based on
cross-sectional area versus
Reynolds number
The second method is to
take the average of the
four pressures on the
aft surface of the
sphere and subtract this
value from the
stagnation value at the
leading edge of the
sphere, yielding ΔP.
The ___________ as defined by either force or pressure measurements is then used to define a turbulence factor for the tunnel by comparing the tunnel’s critical Reynolds number to the atmospheric free-air Reynolds number:
critical Reynolds number
The __________ can be measured using
rakes of pitot tubes (left figure), which are specially
configured for the purpose or traversing devices (right
figure) fitted with pitot tubes, static tubes, or hot wire
tunnel boundary layers