The program described covers development of sensors and sensing techniques for research applications on aeropropulsion systems. In general, the sensors are used in-situ to measure the environment at a given location within a turbine engine, or to measure the response of an engine component to the imposed environment. Locations of concern are generally in the gas path and, for the most part, are within the hot section. Specific parameters of concern are dynamic gas temperature, heat flux, airfoil surface temperature, and strain on airfoils and combustor liners. In order to minimize the intrusiveness of surface-mounted sensors, a considerable effort was expended to develop thin-film sensors for surface temperature, strain, and heat flux measurements. Most of the work described is sufficiently advanced that sensors were used and useful data were obtained. The notable exception is the work to develop a high-temperature static strain measuring capability; this work is still in progress

Englund, David R.

English

NASA Technical Reports Server

RESEARCH SENSORS 
D a v i d  I?. Englund 
ABSTRACT 
The program described here covers development of sensors and sensing techniques for 
research applications on aeropropulsion systems. In general, the sensors are used 
in situ to measure the environment at a given location within a turbine engine, or 
to measure the response of an engine component to the imposed environment. 
Locations of concern are generally in the gas path and, for the most part, are 
heat flux, airfoil surface temperature, and strain on airfoils and combustor 
I- within the hot section. Specific parameters of concern are dynamic gas temperature, 
ob 
h liners. In order to minimize the intrusiveness of surface-mounted sensors, a 
m 
cr) 
w 
I considerable effort has been expended to develop thin-film sensors for surface 
temperature, strain, and heat flux measurements. Most of the work described is 
sufficiently advanced that sensors have been used and useful data have been 
obtained. The notable exception is the work to develop a high-temperature static 
strain measuring capability; this work is still in progress. The work described 
here has been done in-house at the Lewis Research Center and via contracts and 
grants. 
PREEDmG PAGE BLANK NOT FILMED 
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https://ntrs.nasa.gov/search.jsp?R=19880006413 2020-03-20T07:56:00+00:00Z
RESEARCH SENSORS 
The program described here covers development of sensors and sensing techniques for 
research applications on aeropropulsion systems. In general, the sensors are used 
in situ to either measure the environment at a given location within a turbine engine 
or to measure the response of an engine component to the imposed environment. 
Locations of concern are generally in the gas path and, for the most part, are 
within the hot section of the engine. Since these sensors are used for research 
testing as opposed to operational use, a sensor lifetime of the order of 50 hours is 
considered sufficient. 
RESEARCH SENSORS 
MINIATURE DISCRETE SENSORS FOR IN SITU RESEARCH MEASUREMENTS IN 
AEROPROPULSION SYSTEMS: 
DYNAMIC GAS TEMPERATURE MEASURING SYSTEM 
TOTAL HEAT FLUX SENSORS 
THIN-FILM SENSORS 
HIGH-TEMPERATURE STRAIN MEASURING SYSTEMS 
CD-87-29396 
4- 8 
DYNAMIC GAS TEMPERATURE MEASURING SYSTEM 
One of the most important environmental parameters in a turbine engine hot section 
is gas temperature. Normally only time-average temperature is measured. 
Fluctuations in gas temperatures are, however, of great concern for hot section 
durability and combustor modeling activities. 
with two wire thermocouples with different diameters provides dynamic signals with 
limited frequency response. 
we can generate a compensation spectrum sufficient to provide compensated temperature 
data at frequencies up t o  1000 Hz. 
In this measuring system, a probe 
By comparing these signals over a range of frequencies, 
DYNAMIC GAS TEMPERATURE MEASURING SYSTEM 
MEASURES GAS TEMPERATURE 
FLUCTUATIONS AT THE EXIT OF A 
TURBINE ENGINE COMBUSTOR 
A TWO-ELEMENT PROBE PROVIDES 
DATA TO PERMIT ACCURATE 
FREQUENCY COMPENSATION 
CD-87-29397 
4-9 
DYNAMIC GAS TEMPERATURE MEASUREMENT 
This figure shows dynamic temperature data obtained from a probe at the turbine 
inlet of a PWA F-100 engine operating at an intermediate power setting. The plot on 
the left is the dynamic signal from a 0.003-in.-diameter wire thermocouple with no 
frequency compensation. The rms value of the temperature fluctuation is 74 O F .  The 
plot on the right is the compensated signal from the same thermocouple. The rms 
value of the temperature fluctuation is 390 O F  and the peak-to-peak fluctuation is 
2900 OF. Such a large temperature fluctuation implies that there are filaments of 
primary combustion gas and dilution gas within the combustor exhaust stream. 
I DYNAMIC GAS TEMPERATURE MEASUREMENT 
I TEMPERATURE AT TURBINE INLET 
TE M P E RAT U RE, 
"F 
TEMPERATURE, 
"F 
+ 400 
+ 200 
0 
- 200 
- 400 
390°F RMS 1 
I 
74°F RMS ] +1500 1 
+ 1000 
0 
- 1000 
4 -1500 1 J 
0 250 500 0 
TIME, msec 
250 500 
CD-87-29398 
4-  10 
TOTAL HEAT FLUX SENSORS 
Another environmental parameter of interest for hot section durability is total heat 
flux. 
combustor liners and built into cooled turbine airfoils. This figure shows one 
sensor configuration based on the Gardon Gage design. 
sensors is the use of the burner liner or airfoil material as part of a differential 
thermocouple circuit. 
technique could provide acceptable signals. The differential themocouple simplifies 
construction and permits a direct measurement of the differential temperature 
proportional to heat flux. 
over the temperature range in which they will be used. 
We have developed miniature total heat flux sensors which can be welded into 
An innovation in these 
Calibration tests on these materials showed that this 
These miniature heat flux sensors must be calibrated 
TOTAL HEAT FLUX SENSORS 
MEASURE TOTAL HEAT FLUX ON 
BURNER LINERS AND TURBINE 
AIRFOILS 
MINIATURE WIRE THERMOCOUPLE 
SENSOR: 
WELD INTO BURNER LINERS 
BUILD INTO AIRFOILS 
SENSOR BODY PART OF 
THERMOCOUPLE CIRCUIT 
CALIBRATION SYSTEM REQUIRED 
HIGH TEMPERATURE HEAT FLUX SENSOR 
\ \  
/ ... 
::::::.s..:i;r ...  
.... .. . .... .... .... ....... .... .... .... ...... 
WALL 
.:.>:.:.:.:.: ....... ....... ...... .............. I,.......... 
CD-87-29399 
4-11 
COMBUSTOR SEGMENT INSTRUMENTED WITH HEAT FLUX SENSORS 
This photograph shows a segment of a combustor liner which has been instrumented 
with six total heat f l u x  sensors. The sensors are 0.3-in.-diameter disks with 
thermocouple leads radiating from the edge of the disk. 
the unit is at the center of the disk and is only 0.06 in. in diameter. The sensors 
are individually calibrated and then welded into holes cut in the liner. 
combustors such as this one have produced useful heat flux data over a range of 
combustor operating conditions. 
have been less successful because of the sensitivity of these sensors to temperature 
and/or heat f l u  gradients which are more prevalent in turbine airfoils. 
designs which are less sensitive to gradients have been examined but have not yet 
been put into use. 
The actual sensor part of 
Tests on 
Similar sensors built into turbine airfoils 
Sensor 
I COMBUSTOR SEGMENT INSTRUMENTED WITH HEAT FLUX SENSORS 
4-12 
CD-07-29400 
HEAT FLUX SENSOR CALIBRATION SYSTEM 
This photograph shows a heat flux sensor calibration system developed at Lewis. The 
heat source is a 400-kW arc lamp. A reflector is used to focus the energy from the 
arc onto a ceramic sensor holder. This system can supply a maximum flux of 6 MW/m2, 
which is higher than the heat fluxes in present-day turbine engines. The system can 
operate in both steady-state and transient modes. 
calibration facilities exist in this country; efforts have been started to 
cross-compare calibration of test sensors. This is especially important since a 
national standard for heat f l u  sensor calibration does not exist. 
Two other roughly comparable 
4- 13 
CD-87-29401 
THIN-FILM SENSORS 
Lewis has been the major advocate and sponsor for development of thin-film sensors 
for turbine engine applications. Thin-film sensors applicable to turbine engines 
include temperature sensors, strain gages, and heat f l u  sensors. Thin-film sensors 
are formed directly on the component to be instrumented by first depositing a 
suitable insulating film and then depositing sensor and protective films as required. 
THIN-FILM SENSORS 
TEMPERATURE SENSORS 
r- INSULATING FILM 
\ COVER FILM 
\ \  
STRAIN GAGES: 
DYNAMIC 
STATIC 
HEAT FLUX SENSORS 
SENSOR STRUCTURE 
CD-87-29402 
4- 14 
THIN-FILM THERMOCOUPLES 
An excellent application for thin-film thermocouples is the measurement of the 
surface temperature of a cooled turbine airfoil such as shown here. The surface of 
the vane is covered with A1203 thermally grown from an anticorrosion coating and 
augmented with sputtered Al2O3. 
thermocouple junctions formed by overlapping the two films at the desired spot. The 
films extend to the base of the vane where 1eadwj.res are connected. The sensor is 
less than 0.001 in. thick. This technique has considerable advantages over the 
previous technology, which required swaged thermocouple wires to be buried in 
grooves cut in the surface. 
Pt and Pt-Rh films are sputter deposited with 
THIN-FILM THERMOCOUPLES 
MEASURE SURFACE TEMPERATURE 
OF COOLED TURBINE AIRFOILS 
FABRICATION: SPUTTER ALLOY 
FILM LEADS OVER INSULATING 
COATING ON AIRFOIL SURFACE 
SENSOR THICKNESS, ~ 0 . 0 0 1  in. 
CD-87-29403 
4-15 
I APPLICATIONS OF THIN-FILM SENSORS 
I Two types of thin-film sensors have been used in regularly scheduled test operations 
at some turbine engine facilities in the United States. Dynamic strain gages have 
been used on compressor blades, and thermocouples have been used to measure turbine 
airfoil surface temperatures. A thin-film, high-temperature static strain gage 
system and thin-film heat flux sensors are still under development. One of our 
goals is to make the thin-film sensor technology available to the entire United 
States turbine engine community. Impediments to wider use of this technology are 
many. One problem is that sensor fabrication is material specific; technology has 
not been established for a wide variety of materials. Another problem is that the 
investment required to establish a thin-film sensor fabrication capability is 
considerable; commercial services for custom fabrication of thin-film sensors are 
not yet available. 
APPLICATIONS OF THIN-FILM SENSORS 
I 
I 
I 
DYNAMIC STRAIN GAGES IN  USE ON COMPRESSOR BLADES AT SOME FACILITIES 
THERMOCOUPLES IN  USE ON TURBINE AIRFOILS AT SOME FACILITIES 
STATIC STRAIN GAGES AND HEAT FLUX SENSORS STILL UNDER DEVELOPMENT 
I 
I 
IMPEDIMENTS TO WIDER USAGE: 
TECHNOLOGY NOT ESTABLISHED FOR ALL MATERIALS 
LARGE INVESTMENT REQUIRED 
COMMERCIAL SERVICES FOR FABRICATING SENSORS NOT YET AVAILABLE 
I 
I 
CD-87-29404 
4- 16 
HIGH-TEMPERATURE STRAIN MEASURING SYSTEMS 
The most ambitious goal of the research sensor program is the development of 
high-temperature (1800 O F )  strain measuring systems. Approaches being followed in 
this work include both wire and thin-film resistance strain gages and remote 
measuring systems. Our resistance strain gage work has included work on new strain 
gage materials and testing of available strain gages, including the Chinese 700 OC 
gages. Work on remote strain measuring systems has involved three different system 
concepts based on laser speckle patterns. 
HIGH-TEMPERATURE STRAIN MEASURING SYSTEMS 
GOAL: 
MEASURE STATIC STRAIN ON TEST SAMPLES AND TURBINE ENGINE COMPONENTS AT 
TEMPERATURES UP TO 1800 OF 
APPROACHES: 
RESISTANCE STRAIN GAGES- 
WIRE GAGES 
THIN-FILM GAGES 
REMOTE STRAIN MEASURING SYSTEM- 
LASER SPECKLE BASED SYSTEM 
CD-87-29405 
4- 1 7  
FUTURE THRUSTS IN RESEARCH SENSORS 
Future work in research sensors will be strongly influenced by new materials being 
developed for turbine engine components. These materials are expected to be in the 
forms of metal- and ceramic-matrix composites. Both the nature of the materials and 
the significantly higher hot section temperatures that these materials are expected 
to make possible will influence our sensor work. If thin-film sensors are to be 
applied to these materials, methods for producing suitable insulating films must be 
developed. A s  surface temperatures rise, the temperature limits of available sensor 
materials will force more emphasis on remote noncontact sensing techniques. In 
addition, we will continue to search for new sensor materials with higher temperature 
capabilities. Work has already started in these directions relative to surface 
temperature, strain, and heat flux measurements on ceramic and ceramic-matrix 
composite materials. 
FUTURE THRUSTS IN RESEARCH SENSORS 
PROGRAM TO DEVELOP MATERIALS TO OPERATE AT SIGNIFICANTLY HIGHER HOT 
SECTION TEMPERATURES-METAL-AND CERAMIC-MATRIX COMPOSITES 
EFFECT ON SENSOR PROGRAMS: 
DEVELOP SENSOR MATERIALS FOR HIGHER TEMPERATURE RANGES 
IMPROVE REMOTE SENSING TECHNIQUES 
DEVELOP TECHNOLOGY FOR THIN-FILM SENSORS ON NEW SUBSTRATE MATERIALS 
CD-87-29406 
4-18 


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