ME 312, F10, Laboratory #1 Drag of Five Objects
ME 312 LABORATORY #1
Flow Past Five Different Objects
Purpose: This experiment is intended to familiarize students with the low speed wind tunnel,
pitot-probes, pressure transducers, force transducers, barometers, and to give an introduction to
the aerodynamics of drag on objects.
Background: The aerodynamics of geometries has been of significant interest since the late
1800's when it was realized that manned flight was possible. Our objectives in this lab are to
gain experience with experimental tools used in fluid mechanics and to directly measure the
forces exerted on five different objects with the same projected frontal area at different wind
speeds. The diameter of all of the objects is 3 inches. Often times in fluid mechanics observed
behavior does not coincide with ones intuition. Thus, the results of our experiments and our
intuition will be evaluated.
Report: Turn in a copy of the attached laboratory summary sheet, a copy of your data in
tabulated form (drag force vs. wind speed) for each object, and all additional information
specified on the summary sheet. Please summarize your results into a one to two page document
with the above attachments.
Experimental Procedure: Measure the drag exerted on five different objects for a range of
speeds between 3 m/s (~5 Hz) to 40 m/s (~50 Hz).
Experimental Steps:
1. Record the atmospheric pressure and room temperature using the thermometer and
barometer in the laboratory. From these two values the density of the air in CB 110 can
be determined. The gas constant for air is 287 J/Kg-K.
2. Before taking any data predict which object will have the least drag and which will have
the greatest drag at the same air speed. (rank the objects from least (1) to greatest (5) on
the summary sheet)
3. Position the pitot-probe near the top of the wind tunnel and behind the object to be tested.
4. Mount the chamfered disk on the force balance.
5. Start the wind tunnel. Turn the main switch near the back of the tunnel to "on" and press
the local/remote button until the green LED is lit.
6. Set the fan speed to a frequency of 0 Hz on the key-pad controller. Measure the drag and
pressure difference using the drag balance and pressure transducer. Units of measured
drag are lbf and units of pressure are inches of water. These will be your reference values
and you will subtract these values from all of your other data. (Before computing velocity
using the pressure differential measurement you must first subtract off this value.)
7. Increase the fan speed to a frequency of 10 Hz and record the drag and pressure
differential. Repeat in increments of 10 Hz up to 50 Hz.
8. Stop the wind tunnel. Remove the access port cover to the test section and remove the
chamfered disk.
9. Mount the hemisphere (with flow into the cup) onto the drag balance and replace the
access cover.
10. Repeat steps 6—9 and obtain data at the same speeds for all five objects.
ME 312, F10, Laboratory #1 Drag of Five Objects
ME 312 LAB #1
Drag Measurements
Data Sheet
HZ
Disk
Drag
(lbs)
0
10
20
30
40
50
Pitot
Probe
ΔP
Hemisphere
(flow into
cup)
Drag
(lbs)
Pitot
Probe
ΔP
Hemisphere
Drag
(lbs)
Pitot
Probe
ΔP
Smooth Sphere
Drag
(lbs)
Pitot
Probe
ΔP
Rough Sphere
Drag
(lbs)
Pitot
Probe
ΔP
ME 312, F10, Laboratory #1 Drag of Five Objects
Name
ME 312 LAB #1
Drag on Five Objects
Laboratory Summary
1.
Record the atmospheric pressure and temperature: Patm=
2.
Using your intuition rank the objects in terms of amount of drag, from least to greatest.
Intuition
Actual
a.
Chamfered disk
b.
Hemisphere with flow into cup
c.
Hemisphere with flow around cup
d.
Smooth sphere
e.
Rough Sphere
3.
Assuming incompressible air flow at the measured laboratory conditions, develop a
conversion between air speed in m/s, the measured pressure difference in inches of water,
atmospheric pressure, and room temperature. (This should be an equation which when
ΔP is entered in units of inches of water returns velocity in m/s.)
4.
Using the equation you have developed above, determine the actual test section air speed
for all of your data. Plot on a full page the drag force in Newtons (convert from English
units-lbs.) for each object vs. air speed (m/s). Good practice is to use only markers for
experimental data. Use different markers for each object, and include a legend and
appropriate axis labels. Attach the graph and a table of the data (force vs. speed) to this
page. Keep a copy of your data since you will need it later in the course.
5.
In the space provided above rank the objects from least to greatest drag based on the
actual measurements. On a separate page summarize your observations from the data.
Some items to include are the shapes of the drag vs. speed curves (are they linear, second
order, exponential, etc.), any interesting or non-intuitive behavior, and an evaluation of
your intuition. A significant portion of your score will be based on this discussion.
Note: Make all plots and tables presentation quality
, Tatm =