Aerospace Application Brief
Turbine Power
The Solution
Wiedner's group copes with the hostile environment they need to measure
by using a wind tunnel with a bend in it to simulate the air movement
inside an engine, and by using the graphic display data processing
software
DADiSP, by
DSP Development Corporation, to get the most out of
the data they collect.
Heat Transfer Rate
The wind tunnel has a square cross-sectioned 90-degree turning duct
test section which produces some of the same complex aerodynamic and
heat transfer phenomena present in an actual turbine passage.
Fluctuations in velocity, or turbulence, have been found to play a
large role in the rate of heat transfer from free-flowing air to the
tunnel wall, so Wiedner collects data from the turbulence of the air
stream passing through the tunnel and uses DADiSP to analyze and
correlate those measurements with heat transfer rates at various test
section surfaces. Data are collected with a hot-wire anemometer system
consisting of a hot-wire sensor controlled by an anemometer. A data
acquisition card controlled by a personal computer samples the sensor
output at a rate of 15 KHz. The sampled signal is converted to a free
stream velocity history and stored. The data are logged to the
computer's hard disk and are then ready for processing with DADiSP.
Waveform Analysis
DADiSP is used to extract the fluctuating component of the waveform,
calculate the autocorrelation function of the fluctuations, and
normalize the function with respect to its maximum value. Next, the
peak value and first zero-crossing of the function are located and used
for integration and multiplication by the mean velocity to get the
integral length scale. DADiSP's RMS (root mean square) function is
used to find the intensity level of the fluctuations as a percent of
the mean velocity. This analysis procedure is repeated for each set of
data acquired at each of several positions in the flow fields of the
wind tunnel and in other turbulent conditions. The products of the
analyses are compared to heat transfer measurements taken at the same
sites. The resulting correlations give some idea of the way air flow
affects heat transfer.
DADiSP, A Great Advantage
One of the features Wiedner appreciates most about DADiSP is its
ability to read in large data files. "We have several time series of
data taken for several seconds at high sampling rates, so we end up
with great big files that need to be loaded in and analyzed as a
continuous group." Wiedner also notes that appreciation for DADiSP is
widespread in his lab, and says that "having one software package that
integrates a lot of functions we need" is "a great advantage." Wiedner
states that research like his will ultimately provide turbine design
engineers with answers to questions that will allow them to design more
effective cooling and protection schemes, so that turbines will one day
be able to operate at even greater efficiency. This kind of work, he
says, will "propel the gas turbine industry into the 21st century."