Two experiments for verifying the frequency response of a previously-developed dynamic gas temperature measurement system were performed. In both experiments, fine-wire resistance temperature sensors were used as standards. The compensated dynamic temperature sensor data will be compared with the standards to verify the compensation method. The experiments are described in detail

Elmore, D. L.

Robinson, W. W.

Watkins, W. B.

English

NASA Technical Reports Server

N88- 11141
Further Development of The
Dynamic Gas Temperature Measurement System*
D. L. Elmore, W. W. Robinson, W. B. Watkins
Pratt and Whitney Engineering Division
West Palm Beach, Florida 33402
SUMMARY
Two experiments for verifying the frequency response of a
previously-developed dynamic gas temperature measurement
system have been performed. The first involves a rotating
wheel and gas manifolds alternately introducing heated and
ambient air to the sensors. The second involves a
high-temperature atmospheric pressure burner which produces
a wide band temperature spectrum. In both experiments,
fine-wire resistance temperature sensors were used as stand-
ards, and the compensated dynamic temperature sensor data
will be compared with the standards to verify the compen-
sation method. In the rotating wheel experiment, knowledge
of the air supply temperatures and repetition frequency pro-
vides an additional check on the compensated data. In the
burner experiment redundant sensors were employed, and
uncompensated data from different combinations of sensors
will be used in the compensation algorithm. The two exper-
iments are described in detail. A short description of the
numerical compensation method and software revisions in the
past year are described.
INTRODUCTION
The measurement system developed in reference 1 uses a com-
pensated two-element thermocouple probe. The compensation
technique uses the ratio of signal amplitudes from the two
thermocouples' passive responses to gas temperature vari-
ations. Comparisons with a numerical heat transfer model
allow compensation of temperature fluctuations to above
IKHz. Two-element sensors were used in atmospheric pressure
burners and gas turbine engines in reference i, and demon-
strated durability required for these test environments. In
addition, compensated data were generated.
The objectives of the present program are to: I) verify
experimentally the frequency response of the dynamic gas
temperature measurement system; 2) optimize the computer
compensation method for execution speed; and 3)
* Work performed under NASA Contract NAS3-24228
37
https://ntrs.nasa.gov/search.jsp?R=19880001759 2020-03-20T08:34:55+00:00Z
to implement the reference 1 computer code in Fortran IV for
use on generally available computers.
The program is organized into four basic tasks including (i)
frequency response experimental verification: (2) compen-
sation code execution streamlining; (3) implementation of
the compensation code in Fortran IV; and (4) data acquisi-
tion at NASA Lewis Research Center. This progress report
will describe progress since the October 1984 HOST meeting
(reference 2). Efforts in tasks 2 and 3 are complete. The
experiments of task 1 have been performed and data analysis
is underway. The numerical compensation method has been
streamlined for execution on an IBM3081 computer in Fortran.
FREQUENCY RESPONSE VERIFICATION EXPERIMENTS
Reference 2 describes twelve conceptual experiments for ver-
ifying the measurement system compensation system. From the
twelve, two were selected for detailed design, fabrication
and execution. Both set-ups have capability to generate
minimum peak-to-peak fluctuations of 278K (500°F) at Mach
numbers greater than 0.I and frequency content to 250Hz.
The experiments are described in detail below.
Rotating Wheel
The rotating wheel experiment consists of a hot gas manifold
supplying 568K (563°F) air, a cold gas manifold supplying
ambient air at 291K (63°F), a wheel with eight holes in the
periphery, a bifurcated collection manifold, and the dynamic
temperature sensor (Figure I). The wheel is driven by an
electric motor at rotation rate N revolutions per second.
The hot gas and adjacent ambient air manifolds exhaust into
the plane of the wheel such that one opens into a hole on
the wheel and the gas is collected by one leg of the col-
lection duct as the other manifold and collection duct leg
are blocked. Then, as the hole rotates beneath the adjacent
manifold, its gas flows to the second leg of the bifurcation
duct, and the first gas supply is blocked. The common leg
of the collection duct in turn exhausts alternate hot and
ambient air streams onto the dynamic temperature sensor.
The resultant flow generated consists of an approximate
square wave pulse train of frequencies from 20Hz to 250Hz
and peak to peak amplitude of the hot air supply temperature
minus the ambient air supply temperature.
The dynamic temperature sensor and a fine-wire anemometer
resistance thermometer are mounted in the collection duct
discharge stream. The fine wire anemometer is used as a
temperature measurement standard. Uncompensated frequency
response of the fine wire thermometer was computed from a
38
theoretical model, the probe geometry, and the gas path
parameters to be approximately 350Hz (ist order response).
An existing Pratt and Whitney-designed analog compensation
amplifier was set up to provide the inverse function (Ist
order RC high pass filter with Fc = 350Hz) for use in
extending the frequency roll-off of the sensor. Dynamic
temperature sensor and fine wire thermometer data were
recorded on FM tape. The dynamic temperature sensor data
will then be compensated using the method described in ref-
erence i. Comparison between the fine wire resistance sig-
nals, known frequency and amplitude inputs generated by the
apparatus, and the compensated dynamic temperature sensor
signals will then be made.
Figures 2 through 4 show three views of the experiment.
Figure 5 shows the two-wire dynamic temperature sensor used
in these experiments. The two-wire sensor consists of two
thermocouple elements constructed using Type K material.
The junctions were formed using a technique that produces no
bead and thus a uniform cylindrical cross section, which
simplifies the analysis and compensation. The two elements
were fabricated using 76 Nm (.003 inch) and 254 _m (.010
inch) diameter wire. The support wires are 381 _m (.015
inch) and 508 _m (.020 inch) in diameter. The probe was
inspected prior to testing to determine actual dimensions
and the results are presented in Figure 6.
Atmospheric Pressure Burner
Measurements taken under the previous contract (reference I)
characterized the atmospheric burner flowfield as having
large (> 500°F p-p) temperature fluctuations. Verification
of the compensation algorithm using burner data by compen-
sating both small (76 _m) and large (254 _m) thermocouple
signals and comparing results was done. This comparison is
to be extended under this effort by adding an intermediate
size thermoelement (127 N m) and a fine-wire resistance ther-
mometer. Compensations then may be done with three combina-
tions of thermocouples: 76 Nm-254 _m; 76 _m-127 _m; and 127_
m-254 _m. Compensated spectra for the three pairs may also
be compared with the fine-wire resistance thermometer.
The dynamic temperature sensors shown in Figure 7 consist of
one probe with 127 _m (.005 inch) and 254 _m (.010 inch)
diameter elements and another probe with a single 76 _m
(.003 inch) diameter element. The elements were constructed
with Type B thermocouple material and have beadless junc-
tions. The probes tested were inspected and the results are
shown in Figure 8. The fine-wire resistance thermometer was
fabricated using 8.3 _m (.00025 inch) and 12.7 _m (.0005
inch) diameter elements.
39
Figure 9 is a diagram of the burner setup. The dynamic tem-
perature sensors, a fine wire resistance thermometer, and a
total pressure impact tube were mounted together to obtain a
close spatial relationship as shown in Figure I0. The sen-
sors were then mounted downstream of the burner which was
run at the minimum operating combustion temperature due to
the structural limits of the fine-wire thermometer sensor.
Figure ii is a photograph of the experiment with approxi-
mately 1367K (2000°F) flowfield. The sensors were located
approximately 28 cm (II inches) from the burner nozzle exit
plane.
COMPUTERCODEOPTIMIZATION
Task 2, involving compensation code execution streamlining,
and Task 3, involving implementation of the compensation
code in Fortran, are both complete. The reference 1 numer-
ical method calculates thermocouple response at several fre-
quencies, and the compensation spectrum is obtained by
cumulating results of several calculations (Figure 12).
This approach was originally implemented on a Hewlett-Pack-
ard 5451C Fourier Analyzer, and reprogramming into Fortran
and optimization for execution time was required for practi-
cal, repeated use. The reference 1 approach was retained in
the reprogramming software. Execution time for a typical
data set was reduced to about 3 minutes of IBM 3081 computer
time as compared with about 2 hours on the HP5451C. The
upgraded compensation software is now in routine use, and
will be used to compensate data from the previously
described experiments.
DATA ANALYSIS
Data taken in the two experiments described above will be
analyzed and results will be presented at the next HOST
meeting.
REFERENCES
I •
•
Elmore, D.L., Robinson, W.W., and Watkins, W.B., "Dynam-
ic Gas Temperature Measurement System", NASA CR-168207
(May, 1983). This work is summarized in ISA Trans-
actions 24, No. 2, P. 73-82•
Elmore, D.L., Robinson, W.W., and Watkins, W.B., "Fur-
ther Development of the Dynamic Gas Temperature Measure-
ment System", in Turbine Engine Hot Section Technoloqy,
NASA CP-2339 (October, 1984).
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Further development of the dynamic gas temperature measurement system

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