Fall 2008
Laboratory #4: The Hot Wire Anemometer
A data
report
is required for this laboratory. Please follow the instructions for data
report formats carefully, and include the items listing in the Additional
Instructions.
Additional Instructions
In step 14 of the procedure, pick your sampling frequency based on the assumption that important fluctuations in
the flow exist up to only 7 kHz. Also, choose your data
acquisition parameters so as to attain a resolution of at least 2 Hz. When
you perform the jet velocity survey, the LabView program will
ask
what types of data you want to save. Save all four types mean and
rms
(final), raw, histograms, and power spectra. Also, you should make sure
the power spectra is set to decibel (dB)
scaling before you acquire the data.
Using the information starting on page 8 of the lab manual, construct a
full wiring schematic for this lab. Starting with the output signal of
the anemometer and ending with all inputs to the data acquisition
system, oscilliscope and the DVM. You will need to BRING THIS TO LAB.
In step 18 of the procedure, make sure that one of the repeat points is
near the center of the jet, and the other is in the shear layer region
between the jet and freestream. For these repeats, you also need to
save all four types of data.
In the Results and Discussion
section, remember to include any calculations along with the results of
your
measurements. In addition to the results required in the lab manual,
you also need to present velocity
histograms for each of the ten locations in your profile, and power
spectra from the two repeated locations. For the spectra, first get an
average power spectrum at each of the two locations by finding the
average power at each frequency using the repeated data. Then plot the
averaged results as power (in dB) versus log10 of the
frequency(Hz). Don't forget the important narrative description section
required when you present data in formal reports. The "Error
Analysis" section should
include
a quantitative analysis of the measurement errors (systematic, random,
and combined) in as far as the
information available to you allows.
The jet flowfield studied in this Lab will be measured again in a
following lab. You will be asked to compare hot wire data from this Lab
with the
measurements in the laser Doppler velocimeter (LDV) lab. Therefore,
make sure
you
keep a copy of your data for this comparison. Also, you will need to be
careful how you set the motors for the wind tunnel and jet, so that you
can attempt to repeat the same flow in the LDV lab. At the end of your data acquisition
session (but before you recheck the hotfilm resistance), test
your ability to repeat the flow by placing the
probe at an appropriate
point in the flow and taking a velocity measurement - then change the
speed of the tunnel/jet (don't turn them off or you will have to turn
off the hotwire) and then return the controls to the original values
(as best you can). Take some new velocity
data at the repeated motor settings. Repeat this procedure as much as
you wish to check repeatability.
Questions
Your report must also include answers to the following questions in
the appropriate
sections:
- .