A research plan is currently being implemented by NASA to develop and validate the use of a commercial laser scanner to record and archive fully three-dimensional (3-D) ice shapes from an icing wind tunnel. The plan focused specifically upon measuring ice accreted in the NASA Icing Research Tunnel (IRT). The plan was divided into two phases. The first phase was the identification and selection of the laser scanning system and the post-processing software to purchase and develop further. The second phase was the implementation and validation of the selected system through a series of icing and aerodynamic tests. Phase I of the research plan has been completed. It consisted of evaluating several scanning hardware and software systems against an established selection criteria through demonstrations in the IRT. The results of Phase I showed that all of the scanning systems that were evaluated were equally capable of scanning ice shapes. The factors that differentiated the scanners were ease of use and the ability to operate in a wide range of IRT environmental conditions

Addy, Harold E., Jr.

Broeren, Andy P.

Lee, Sam

Pifer, Ellen M.

Sills, Robert

NASA Technical Reports Server

Development of 3-D Ice Accretion Measurement Method

Icing wind tunnels are designed to simulate in-flight icing environments. The chief product of such facilities is the ice accretion that forms on various test articles. Documentation of the resulting ice accretion key piece of data in icing-wind-tunnel tests. Number of currently used options for documenting ice accretion in icing-wind-tunnel testing

National Aeronautics and Space Administration 
www.nasa.gov 
Development of 3D Ice Accretion Measurement 
Method 
1 
Sam Lee 
Vantage Partners, LLC 
 
Andy Broeren 
Harold Addy, Jr. 
NASA Glenn Research Center 
 
Robert Sills 
Sierra Lobo, Inc. 
 
Ellen Pifer 
St. Louis University 
 
https://ntrs.nasa.gov/search.jsp?R=20130000320 2019-08-30T23:26:34+00:00Z
National Aeronautics and Space Administration 
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Outline 
• Introduction 
• Scanner Selection Methodology 
• Scanner Selection Results 
• Conclusion 
National Aeronautics and Space Administration 
www.nasa.gov 3 
Introduction 
• Icing wind tunnels are designed to simulate in-flight 
icing environments. 
• The chief product of such facilities is the ice 
accretion that forms on various test articles. 
• Documentation of the resulting ice accretion key 
piece of data in icing-wind-tunnel tests. 
• Number of currently used options for documenting 
ice accretion in icing-wind-tunnel testing. 
• Simple and quantitative photography 
• Pencil tracings 
• Mold and casting methods 
• Each method has limitations 
National Aeronautics and Space Administration 
www.nasa.gov 4 
Introduction (cont’d) 
• Method to accurately and efficiently digitize ice 
accretion in three dimensions is needed. 
• Laser-based scanning methods 
have been investigated. 
• Number of challenges with 
processing the raw point cloud data 
into a closed surface. 
• More recent research indicated new 
advances may allow complex three-
dimensional point cloud data be 
acquired and closed to form a “water 
tight” surface. 
• NASA incorporated development of three-
dimensional ice accretion digitization methods into 
its current research plans. 
National Aeronautics and Space Administration 
www.nasa.gov 5 
Laser Scanner – How it Works 
• Laser line projected on surface to be scanned 
• CCD camera uses triangulation to determine surface location 
From Wikipedia Commons 
 From Wikipedia Commons 
 
National Aeronautics and Space Administration 
www.nasa.gov 6 
Selection Methodology 
Objective: 
• Identify most suitable 3D laser scanner for further 
development 
Approach: 
• Establish selection criteria for scanner hardware and 
software. 
• Evaluate several commercially available 3D laser 
scanners and software using selection criteria. 
National Aeronautics and Space Administration 
www.nasa.gov 7 
Selection Methodology - Software Selection 
• A thorough evaluation of several commercially available 
3D scanning software was planned. 
• This was not possible due to cost and time constraints. 
• Required purchasing and becoming proficient on all of the 
software that were being considered. 
• Instead, two most widely used software packages were 
considered, Geomagic and Polyworks. 
• The most critical factor was the ability to create water-tight 
surfaces from the scan data. 
• Conversations with the scanner factory representatives 
indicated that Geomagic is better able to process and 
generate water-tight surfaces of “organic” shapes typical 
of ice accretion shapes.  
• This led to the decision to select Geomagic as the 
scanning software. 
National Aeronautics and Space Administration 
www.nasa.gov 8 
Selection Methodology – Hardware Evaluation 
IRT Test Procedure 
• All of the scanners were evaluated in NASA Glenn 
Icing Research Tunnel. 
• Four ice shapes on NACA 0012 chosen for evaluation: 
• Horn ice – 0 deg sweep, 21” chord 
• Roughness – 0 deg sweep, 21” chord 
• Streamwise ice – 0 deg sweep, 21” chord 
• Scallop ice – 45 deg sweep, 36” chord 
Ice Type V (kts)  (°) MVD (m) LWC (g/m
3
) T0 (°F) t (min) 
Horn 200 4 20 0.55 25 7 
Streamwise 200 4 20 0.55 1 7 
Roughness 200 4 20 0.55 25 1 
3D Scallop 200 0 32 0.45 20 19.9 
 
National Aeronautics and Space Administration 
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Selection Methodology – Hardware Evaluation 
IRT Test Procedure 
• The IRT scanner evaluation procedure consisted of the 
following six steps: 
1. Accrete ice on the test article 
2. Photograph the ice 
3. Spray the  ice with white paint 
4. Install and set up the scanner 
5. Scan the ice shape 
6. Make hand tracings of the ice shape 
National Aeronautics and Space Administration 
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Selection Methodology – Hardware Evaluation 
Scanners Evaluated 
• Three laser scanners were evaluated in the IRT during 
spring 2011 using the procedure described above. 
• Faro Quantum 
• Romer Absolute SI 
• NVision HandHeld 
From Hexagon Metrology 
 
• All arm-based laser scanning systems. 
• Faro Quantum 
• The body of the arm made of aluminum and 
used a temperature senor to compensate 
for the expansion/contraction of the tube. 
• Arm used relative position encoders 
• Could be operated directly from Geomagic 
National Aeronautics and Space Administration 
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Selection Methodology – Hardware Evaluation 
Scanners Evaluated 
• The Romer Absolute SI 
• Constructed of thermally stable carbon fiber. 
• Did not require any thermal compensation. 
• Arm employed absolute position encoders. 
• Could be operated directly from Geomagic. 
• The NVision HandHeld 
• Used a Romer arm with an NVision scanner head. 
• Carbon fiber arm with absolute encoders 
• Did not require any thermal compensation. 
• Could not be operated directly from Geomagic since a plug-in 
was not available. 
National Aeronautics and Space Administration 
www.nasa.gov 12 
Selection Methodology – Hardware Evaluation 
Scanners Evaluated 
• Two scanning systems manufactured by Creaform 
were evaluated but not as part of the standardized 
evaluation process. 
• HandyScan system - evaluated during an IRT icing test 
demonstration in 2008. 
• MetraScan system – evaluated with artificial ice shape in IRT 
with tunnel off (2011). 
• HandyScan system 
• Arm-free system 
• Used reflective targeting dots on the 
scanned objects for positioning. 
• Scan data from the HandyScan were 
referenced to these targeting dots. 
From Creaform 
 
National Aeronautics and Space Administration 
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Selection Methodology – Hardware Evaluation 
Scanners Evaluated 
• The MetraScan system 
• Used a “C-Track” base that 
tracked the position of the laser 
scanner optically using reflective 
dots on the scanner. 
• The scan data from the 
MetraScan were referenced to the 
location of the “C-track”. 
Manufacturer Model Type Max. Line 
Resolution 
Line 
Width 
Scan 
Rate 
Arm Encoder 
Type 
Geomagic 
Plug-in 
Faro Quantum Arm 0.002 in 2.5 in 30 Hz Relative Yes 
Romer Absolute Arm 0.002 in 2 in 30 Hz Absolute Yes 
NVision HandHeld Arm 0.002 in 2 in 30 Hz Absolute No 
Creaform HandyScan Armless 0.002 in 2.5 in 25 Hz N/A Yes 
Creaform MetraScan Armless 0.002 in 2.7 in 25 Hz N/A Yes 
 
From Creaform 
 
National Aeronautics and Space Administration 
www.nasa.gov 
Selection Results – General Findings 
14 
• The findings detailed below should not be viewed as a 
determination by NASA of one system being superior 
to another for general use. 
• All of the scanners demonstrated were able to scan ice 
shapes (or simulations) in the IRT test section 
• Quality of the ice shape scan depended greatly on the 
experience of the scanner operator. 
• Emphasis on the scanner evaluation was placed on 
usability, operability, and software compatibility. 
National Aeronautics and Space Administration 
www.nasa.gov 
Selection Results – Scanner Setup Procedure 
15 
• Arm-based systems 
• Set scanner up in test section 
• Begin scanning 
• Creaform arm-free systems 
• Handyscan - Wire mesh had to be 
installed after each icing spray before 
the ice shape could be scanned – time 
consuming process 
• MetraScan - Large access panel had 
to be created on the test section ceiling 
to provide a clear line of site between 
the C-track and the handheld scanner 
head. 
 
 
National Aeronautics and Space Administration 
www.nasa.gov 
Selection Results – Software Compatibility 
and Data Format 
16 
• All scanners except Nvision Handheld scanner could be 
operated directly from Geomagic 
• Geomagic plug-in not available for Nvision 
• Scan data format differences 
• All of the arm-based scanners outputted point cloud data. 
• Two Creaform scanners did not output point-cloud data.  Data 
already in a semi-processed triangular surface mesh 
• This was considered by NASA evaluators to be a significant 
limitation because it does not allow the user to work directly 
with raw, unprocessed data. 
 
National Aeronautics and Space Administration 
www.nasa.gov 
Selection Results – Operability in IRT Test 
Section 
17 
• Two Creaform arm-free systems easier to manipulate than 
arm-based systems 
• Two Romer-arm based systems easier to manipulate than 
Faro arm 
• All scanners except Faro arm demonstrated ability to 
operate at 0° F. 
• For Creaform scanners, the part of the scanning system that 
was brought into the test section did not have any moving 
parts. 
• Although no reliability issues were observed with the arm-
based scanners during the IRT evaluations, it is not known 
what effect (if any) repeated exposure to the IRT test section 
environment would have on the scanners.  
 
 
National Aeronautics and Space Administration 
www.nasa.gov 
Selection Results – Scanner Selection 
18 
• Romer Absolute system selected for further 
development in IRT. 
• Required minimal modifications to the test section, resulting in 
fewer risks in implementation for use. 
• It generated “raw” data in an unprocessed state, allowing 
more control over post-processing of the scan data. 
• Romer arm counterbalancing system was found to be more 
effective than Faro arm. 
• Romer system can operate at temperature down to 0° F. 
• Romer system can be operated directly from Geomagic 
National Aeronautics and Space Administration 
www.nasa.gov 
Selection Results – Sample Evaluation Data 
19 
• The data shown below were obtained during the 
evaluation of the Faro Quantum Arm. 
• The results are shown only as a general indication of 
typical results one would expect from a modern 3D 
laser scanning system and software. 
• More research is planned to improve quality of scan 
data 
National Aeronautics and Space Administration 
www.nasa.gov 20 
Selection Results – Sample Evaluation Data 
Horn Ice Shape 
National Aeronautics and Space Administration 
www.nasa.gov 21 
Roughness Ice Shape 
Selection Results – Sample Evaluation Data 
National Aeronautics and Space Administration 
www.nasa.gov 22 
Streamwise Ice Shape 
Selection Results – Sample Evaluation Data 
National Aeronautics and Space Administration 
www.nasa.gov 23 
Swept Wing Scallop Ice Shape 
Selection Results – Sample Evaluation Data 
National Aeronautics and Space Administration 
www.nasa.gov 
Comparison of 3D Scan to 2D Pencil Tracing 
24 
x (in)
-1 0 1 2 3 4
y
 (
in
)
-2
-1
0
1
2
Airfoil
3D Scan 
Hand Tracing
x (in)
-1 0 1 2 3 4
y
 (
in
)
-2
-1
0
1
2
Airfoil
3D Scan 
Hand Tracing
Horn Ice Shape Streamwise Ice Shape 
Selection Results – Sample Evaluation Data 
National Aeronautics and Space Administration 
www.nasa.gov 
Conclusion 
25 
• A research program is currently being implemented to 
develop and validate the use of a 3D laser scanning system to 
record ice accretion shapes in the NASA Icing Research 
Tunnel. 
• First step - identify the most suitable laser scanning hardware 
and software for further development.  
• Several scanning systems were evaluated against 
selection criteria 
• Arm-based system was found to be the most promising 
• Evaluation results showed that commercial 3D laser scanners 
were capable of recording many details of various types of ice 
shapes, and post-processing software were capable of 
generating “water-tight” surfaces. 
National Aeronautics and Space Administration 
www.nasa.gov 
Conclusion (cont’d) 
26 
• The selected scanner system will be used to implement and 
validate the use of this technology through a series of icing 
and aerodynamic tunnel tests. 
• With continued success of this research a suitable means of 
recording and archiving fully three-dimensional descriptions of 
experimental ice accretion geometry will have been 
developed.  


Development of 3-D Ice Accretion Measurement Method

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