AEROLAB MODULE 4

Question 1

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.

Answer 1

flow
characteristics

Question 2

Wind Tunnel instruments that uses pressure

Answer 2

Manometer, Barometer, Transducers

Question 3

Pressure is balanced by the
weight of the liquid
column.

Answer 3

Manometer

Question 4

Used to measure
atmospheric pressure.

Answer 4

Barometer

Question 5

Converts pressure to an
analog electrical signal.

Answer 5

Transducers

Question 6

Why do we calibrate?

Answer 6

To ensure the accuracy

To control errors

Help assure precise
measurements

Question 7

While doing the
Calibration, some
properties are to be
measured:

Answer 7

Air Speed

Flow Angularity

Turbulence Measurement

Question 8

Setting the speed of the
wind tunnel is done when
the is _______ the
test section.

Answer 8

no model inside

Question 9

This can be put
inside the test section to
determine the airspeed.

Answer 9

Pitot Tube

Question 10

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.

Answer 10

measuring either static or total pressure

Question 11

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.

Answer 11

dynamic pressure ; density

Question 12

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.

Answer 12

0.50% ; 0.25%

Question 13

_________ 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.

Answer 13

screens

Question 14

The flow has to be uniform across the cross section with all stream lines _______ to the tunnel axis when the test section is empty.

Answer 14

parallel

Question 15

The flow direction can be calculated by using _____________________.

Answer 15

Sphere type and Claw type yaw meter

Question 16

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 _______.

Answer 16

posneg0.10° ; posneg0.20°.

Question 17

_________ is a measurement of irregularity in the flow.

Answer 17

Turbulence

Question 18

__________ is used to identify whether the flow is
laminar or turbulent.

Answer 18

Reynolds Number

Question 19

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 “___________”

Answer 19

effective Reynolds
number.

Question 20

Before the now common use of hot-wire anemometry, a ____________ was the primary way to measure the relative turbulence of a wind tunnel.

Answer 20

turbulence sphere

Question 21

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.

Answer 21

indicated effect

Question 22

The critical Reynolds number
for the sphere can be measured
in two ways. What are those?

Answer 22

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.

Question 23

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:

Answer 23

critical Reynolds number

Question 24

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

Answer 24

tunnel boundary layers