AOE 3104 Homework #2 Solutions
Problem 1.
In a wind tunnel, the speed changes as the cross sectional area of the tunnel changes. If the
speed in a circular test section with radius 5 feet is 100 miles per hour, what is the speed upstream of the
test section where the radius is 11 feet? Assume incompressible flow.
Solution.
The mass rate of flow is constant:
V A
= constant. Therefore
V
1
A
1
=
V
2
A
2
,
And, since density is constant:
V
1
=
V
2
A
2
A
1
.
Therefore:
V
1
= 100 mph
parenleftbigg
25 ft
2
121 ft
2
parenrightbigg
= 20
.
66 mph
Problem 2.
A model is being tested in a wind tunnel at a speed of 30 meters per second.
(a) If the flow in the test section is at sea level standard conditions, what is the pressure at the model’s
stagnation point?
(b) The tunnel speed is being measured by a pitotstatic tube connected to a Utube manometer. What is
the reading on the manometer in the inches of water?
(c) At one point on the model, a pressure of 100kPa is measured. What is the local airspeed at that point?
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 Spring '08
 DR.CRAIGWOOLSEY
 Fluid Dynamics, Wind Tunnel, test section, Stagnation Point, free stream, chord length

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