Some of the areas of research conducted at Lewis on optical measurement techniques are described. Two laser anemometer systems developed at Lewis are used to illustrate the special instrumentation needs encountered in aeropropulsion research. Velocity measurements to be made through small viewing ports, close to surfaces within the propulsion system components, and in turbulent or highly-accelerating flows are some of the significant challenges. The application to research facilities of two advanced optical systems, the rainbow schlieren and the combustor viewing system, is presented. The calibration and verification of commercial optical measuring systems, such as droplet sizing systems, are also discussed. Calibration techniques capable of simulating moving droplets for flight-type sizing systems are being developed at Lewis. The presentation concludes with a brief look at the forces driving future research on optical instrumentation

Lesco, Daniel J.

English

NASA Technical Reports Server

OPTICAL MEASUREMENT SYSTEMS 
/ D a n i e l  J .  Lesco 
ABSTRACT 
This presentation describes some of the areas of research conducted at Lewis on 
optical measurement techniques. Two new laser anemometer systems developed at Lewis 
are used to illustrate the special instrumentation needs encountered in aeropro- 
pulsion research. Velocity measurements to be made through small viewing ports, 
close to surfaces within the propulsion system components, and in turbulent or 
highly-accelerating flows are some of the significant challenges. The application to 
research facilities of two advanced optical systems, the rainbow schlieren and the 
combustor viewing system, is presented. The calibration and verification of commer- 
cial optical measurement systems, such as droplet sizing systems, are also discussed. 
New calibration techniques capable of simulating moving droplets for flight-type 
sizing systems are being developed at Lewis. The presentation concludes with a brief 
look at the forces driving future research on optical instrumentation. 
4-19 
https://ntrs.nasa.gov/search.jsp?R=19880006414 2020-03-20T07:56:02+00:00Z
OPTICAL MEASUREMENT SYSTEMS 
The goal of our research is to enhance the capabilities of non-intrusive research 
instrumentation used in aeropropulsion research. This instrumentation is needed to 
validate analytical codes and to verify the performance of aeropropulsion components 
and systems. Listed here are the primary areas of current research, together with 
two recently completed efforts. I will describe several of the areas in more detail 
in this presentation to illustrate the aeropropulsion instrumentation needs we are 
trying to fill. The fluid and structural parameters measured by the measurement 
techniques are also shown. 
NON-INTRUSIVE RESEARCH INSTRUMENTATION 
FOR AEROPROPULSION SYSTEMS 
LASER ANEMOMETRY 
HOLOGRAPHIC INTERFEROMETRY 
LASER SPECTROSCOPY 
PARTICLE SIZING 
LASER SPECKLE SYSTEMS 
RAINBOW SCHLIEREN 
HOT SECTION VIEWING SYSTEM 
- FOR AVERAGE FLOW VELOCITY, FLOW ANGLE, TURBULENCE INTENSITY 
- FOR GAS DENSITY CHANGES, SURFACE DISPLACEMENTS 
- FOR GAS TEMPERATURE, CONSTITUENTS, VELOCITY, PRESSURE 
- FOR FUEL SPRAY AND CLOUD DROPLET DIAMETERS 
- FOR SURFACE STRAIN 
- FOR FLOW VISUALIZATION 
- MONITORING HOT SECTION PHENOMENA 
CD-87-29408 
4-20 
ADVANCES IN LASER ANEMOMETRY FOR AEROPROPULSION RESEARCH 
Applying laser anemometry to aeropropulsion research facilities presents many 
challenges for the instrumentation researcher. Desired characteristics include the 
ability to measure flow in three axes through a very limited viewport, to make 
velocity measurements near surfaces, and to efficiently make measurements in a 
turbulent or highly accelerating flow. 
needs will be described. 
currently being investigated to meet the problem of high vibration and acoustic 
noise levels. 
Two systems developed to meet these special 
The use of fiber-optics in laser anemometry systems is 
ADVANCES IN LASER ANEMOMETRY 
FOR AEROPROPULSION RESEARCH 
THREE-AXIS LA FOR LIMITED VIEW APPLICATIONS 
FOUR-SPOT LASER-TRANSIT-ANEMOMETER FOR 
NEAR-SURFACE TURBULENT FLOWS 
FIBER-OPTIC LA FOR HIGH-VIBRATION ENVIRONMENTS 
CD-87-29409 
4-21 
THREE COMPONENT LASER ANEMOMETRY SYSTEM 
The system was developed at Lewis to measure the radial component of flow in 
addition to the axial and circumferential components in a turbine stator cascade 
facility, through a single optical viewing port. 
interferometer technique in conjunction with the more common dual-beam fringe 
configuration. 
radial velocity component. 
in the figure and compared with the predicted values obtained with a computer code. 
The system uses a Fabry-Perot 
The annular vane ring shown has a contoured hub to enhance the 
Velocity data for each axis and total velocity are shown 
1 THREE COMPONENT LASER ANEMOMETRY SYSTEM 
THREE COMPONENT LASER ANEMOMETER LA SURVEY DATA AND DENTON 
CODE RESULTS 
l.o r 
ANNULAR VANE RING VNCR 
DENTON CODE I VoNCR 
t I  I I I  1 
6 8 10 12 14 
CIRCUMFERENTIAL POSITION, deg 
CD-87-29410 
4-22 
FOUR-SPOT LASER ANEMOMETER 
This system was developed at Lewis in conjunction with Case Western Reserve 
University. It is a laser transit anemometer (LTA) wherein velocity is determined 
by measuring the time it takes for seed particles to cross the gap between closely- 
spaced laser beams. 
angle (necessary for measurements in turbulent flows) while retaining the LTA 
advantages of close-to-wall and small seed particle compatibility. 
The four-spot system has the feature of wide flow acceptance 
FOUR-SPOT LASER ANEMOMETER 
FEATURES 
WIDE FLOW ACCEPTANCE ANGLE NECESSARY FOR MEASUREMENTS IN 
TURBULENT FLOWS 
HIGH SPATIAL SELECTIVITY FOR MEASUREMENTS CLOSE TO SURFACES AND WITH 
SMALL SEED PARTICLES NECESSARY TO FOLLOW HIGH VELOCITY/HIGHLY 
ACCELERATING FLOWS 
TEST RESULTS 
VELOCITY SURVEYS OBTAINED TO WITHIN 200 MICROMETERS OF SURFACE IN 
700 "C FLOW 
VELOCITIES TO MACH 1.3 MEASURED WITH 0.5 MICROMETER SEED PARTICLES 
CD-87-29411 
4-23 
TESTING OF FOUR-SPOT LASER ANEMOMETER IN OPEN JET BURNER FACILITY 
The four-spot LA was tested in a facility capable of generating hot (700 "C)  
turbulent flows. Velocity surveys were obtained to within 200 micrometers of a 
turbine vane surface inserted into the test flow. 
measurements to Mach 1.3 with 0.5 micrometer seed particles. 
Other tests demonstrated velocity 
ORIGINAL PAGE IS 
OE POOR QUALITY 
TESTING OF FOUR-SPOT LASER ANEMOMETER 
IN OPEN JET BURNER FACILITY 
CD-87-29412 
4-24 
RAINBOW SCHLIEREN 
The rainbow schlieren system, developed at Lewis, uses a bull's-eye color filter to 
add a continuous color spectrum to the classical flow visualization technique for 
enhancing index-of-refraction gradients such as those accompanying supersonic shock 
waves. Not only does the color aid the eye's sensitivity in perceiving minor flow 
features, it adds a potential for quantitative flow analysis by coding the magnitude 
of refractive index changes in those flows exhibiting simple geometries. 
RAINBOW SCHLIEREN 
BULL'S-EYE FILTER ADDS CONTINUOUS COLOR SPECTRUM TO CLASSICAL FLOW 
VISUALIZATION TECHNIQUES 
POTENTIAL FOR QUANTITATIVE INFORMATION ON FLOW DENSITY GRADIENTS 
SYSTEM INSTALLED IN LEWIS WIND TUNNELS AND COMPONENT FACILITIES 
CD-87-29413 
4-25 
RAINBOW SCHLIEREN SYSTEM IN THE 10 x 10 WIND TUNNEL AT LEWIS 
A technician is shown aligning the rainbow schlieren system in the 10 x 10 Wind 
Tunnel. 
D!GINAL PAGE I8 
EKx>R QTJALITY 
RAINBOW SCHLIEREN SYSTEM IN THE 
10x10 WIND TUNNEL AT LEWIS - 
CD-87-29414 
4-26 
RAINBOW SCHLIEREN PHOTOGRAPH OF A SUPERSONIC INLET TESTED 
IN THE 10 x 10 WIND TUNNEL AT LEWIS 
This color photograph illustrates the flow visualization enhancement achieved with 
the rainbow schlieren system. 
(wherein flow features to the bottom of the photo are artifacts of the lack of a 
mounting body). 
It shows a top view of a supersonic side inlet 
The red color indicates maximum index-of-refraction changes. 
~ C I N A L  PAGE t9 
DF POOR QUALIm 
RAINBOW SCHLIEREN PHOTOGRAPH OF A SUPERSONIC INLET 
TESTED IN THE 10x10 WIND TUNNEL AT LEWIS 
CD-07- -2941 5 
4-2 7 
COMBUSTOR VIEWING SYSTEM 
The combustor viewing system was designed as a diagnostic tool for use in studying 
internal processes in high temperature, high pressure combustors. One of the 
primary goals was to study the onset of combustor liner failures such as cracking. 
The images of the combustor interior are transmitted to a photographic or video 
camera through a coherent bundle of 75,000, 10-micrometer fibers. Also included are 
two 1-mm fibers to provide illumination from a laser or arc lamp. The rotatable, 
retractable probe is purged with N2 to keep the tip clean and water cooled to allow 
operation at environmental temperatures above 2000 K. 
AN OPTICAL SYSTEM TO VIEW THE INTERIOR OF HIGH PRESSURE COMBUSTORS 
TO STUDY COMBUSTION PROCESSES 
TO RECORD LINER FAILURE MECHANISMS 
USES COHERENT IMAGE BUNDLE OF 75,000 IO-MICROMETER FIBERS TOGETHER 
WITH TWO 1-MM FIBERS FOR ILLUMINATION 
ROTATABLE PROBE PURGED WITH N2 AND COOLED WITH WATER FOR OPERATION IN 
OPERATING EXPERIENCE AT PRATT 81 WHITNEY ON PW 2037 ENGINE, AT LEWIS IN 
ENVIRONMENTS AT 2000 K 
HIGH PRESSURE FACILITY, AND AT NAPC IN HOT GAS FACILITY 
CD-87-29416 
4-28 
COMBUSTOR VIEWING SYSTEM PROBE 
In this photograph of the combustor viewing system probe, the two illumination- 
carrying fibers and the angled tip of the imaging bundle can be identified by the 
backlighting. 
COMBUSTOR VIEWING SYSTEM PROBE 
CD-87-29417 
4-29 
PW 2037 ENGINE FUEL NOZZLE AT FULL POWER I 
This photograph of a combustor fuel nozzle in a PW 2037 engine was recorded through 
the combustor viewing system while the engine was operating at full power. 
PW 2037 ENGINE FUEL NOZZLE AT FULL POWER 
CD-87-29418 
OORIGINAL PAGE IS 
Dl ]eOOR QUALITY 
4-30 
VERIFICATION OF OPTICAL DROPLET SIZING SYSTEMS' ACCURACY 
In many areas of measurement technology, the available commercial instrument systems 
satisfy research needs. Optical droplet sizing systems appear to be adequate for 
most aeropropulsion-related applications such as fuel-spray and icing research. But 
important questions remain on the proper use and calibration of these instruments. 
We are conducting comparison tests on the most useful systems to better define their 
operating regimes (droplet size, droplet concentration, droplet velocity, etc.) and 
are also developing adequate calibration tools and techniques. 
VERIFICATION OF OPTICAL DROPLET SIZING SYSTEMS' ACCURACY 
AEROPROPULSION-RELATED APPLICATIONS 
FUEL-SPRAY MEASUREMENTS 
ICING CLOUD AND SPRAY MEASUREMENTS 
MENU OF COMMERCIAL INSTRUMENTS APPEARS TO SATISFY NEEDS OF RESEARCHERS 
THERE ARE IMPORTANT QUESTIONS OF PROPER USE AND CALIBRATION OF 
WE ARE CONDUCTING COMPARISON TESTS ON THESE INSTRUMENTS TO DEFINE 
WE ARE DEVELOPING NEW CALIBRATION TOOLS 
THESE INSTRUMENTS 
OPERATING REGIMES 
CD-87-29419 
4-31 
DROPLET SIZING INSTRUMENT USED IN THE ICING FLIGHT RESEARCH PROGRAM 
Shown is a cloud droplet sizing instrument used on the Lewis Twin Otter aircraft 
during icing research. Techniques to better calibrate this instrument are being 
developed and evaluated. 
DROPLET SIZING INSTRUMENT USED IN THE ICING 
FLIGHT RESEARCH PROGRAM 
CD-87-29420 
4 - 3 2  
CALIBRATION RETICLE FOR DROPLET SIZING INSTRUMENTS 
Shown is a rotatable calibration reticle with qrecisely-sized -pots used to simulate 
droplets passing through the probe volume of a flight-type droplet sizing instrument. 
CALIBRATION RETICLE FOR DROPLET SIZING INSTRUMENTS 
CD-87-29421 
4-33 
OPTICAL DIFFRACTION-BASED DROPLET SIZING SYSTEM 
IN AN AEROPROPULSION FACILITY 
I 
A commercial diffraction-based multiple droplet sizing system has been adapted 
through the use of additional optics to meet the research needs of a hypersonic- 
related research facility. 
OPTICAL DIFFRACTION-BASED DROPLET SIZING SYSTEM 
IN AN AEROPROPULSION FACILITY 
CD-87-29422 
4-34 
FUTURE RESEARCH IN OPTICAL MEASUREMENT SYSTEMS 
Our present program in optical instrumentation research is driven by the needs of 
the aeropropulsion researcher and aided by the advances in optical and electronic 
technology. Prevalent needs ate dynamic data, including the time correlation 
between two or more parameters, and rapidly acquired whole-field data maps. 
optics and new solid-state lasers are two of the important ingredients for rugged 
didgnostic systems t o  be used in aeropropulsion facilities. 
Fiber 
FUTURE RESEARCH IN OPTICAL MEASUREMENT SYSTEMS 
NEED FOR DYNAMIC DATA 
ADVANCES IN FIBER OPTICS 
MATURING OF LASER SPECTROSCOPY FROM LAB TO FACILITY ENVIRONMENTS 
POTENTIAL FOR APPLICATION OF ARTIFICIAL INTELLIGENCE 
ADVANTAGES OF WHOLE-FIELD DATA ACQUISITION (VERSUS POINT-BY-POINT) 
DEVELOPMENTS IN RUGGED, EFFICIENT SOLID-STATE LASERS 
CD-07-29423 
4-35 


Optical measurement systems

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