ROMER Absolute Arm with integrated laser scanner
Hexagon Metrology
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While air travel is considered the safest form of transportation, research continues to better understand ice buildup and its affects on aerodynamics. At NASA’S Glenn Research Center in Cleveland, OH, engineers in the Icing Branch have been studying the mechanics of ice buildup since the 1940s.

Early on, the team’s method of studying this phenomenon was to physically recreate ice forms and test their performance. At the team’s disposal is NASA’S Icing Research Tunnel (IRT) at Glenn, one of the world’s largest refrigerated wind tunnels with the capability to generate airspeeds of more than 400 miles per hour.

NASA has been tasked with creating software to help predict ice growth. To do so, the researchers investigated the subject of acquiring quantitative data using non-contact 3D laser scanning. The crew chose a ROMER Absolute Arm portable coordinate measuring machine (CMM) with integrated laser scanner. The stiff carbon fiber construction eliminates the need for temperature compensation since, for this application, it is routinely used in an environment where temperatures range from 0 to 28°F (-18 to -2°C).

The team then changed their procedure. After accreting ice, a researcher brings the portable CMM and computer into the wind tunnel. The ice is painted with a custom titanium dioxide fast-evaporating paint. While maintaining temperatures of 0 to 30 °F, the operator scans the ice using a slow, smooth motion.

The scanning process takes approximately 15 to 20 minutes. The difficulty in scanning the shapes is ensuring all the small gaps within them are measured. When the scan is complete, the researchers have a 0.5 to 1.0 GB data file. They are able to scan up to seven ice shapes during a day of testing due to the time it takes to initially accrete the ice.

Though the specifications of the portable CMM boast far better accuracies, this was not a primary concern for NASA since the tolerances the team needs to achieve are 4 to 5 thousandths of an inch. The importance of the work is not the absolute accuracy, but in capturing the finer details of the ice shapes. In this application, the laser scanner’s resolution of 0.046 mm between points allows them to document those details.

One of the biggest benefits when reverse-engineering with a laser scanner is the savings of time and materials. Although the savings are a definite benefit, faster data acquisition is the most important gain. The laser-scanning method can now be used to increase the utility of icing wind-tunnel tests by improving the documentation of ice accretions.

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NASA Tech Briefs Magazine

This article first appeared in the December, 2014 issue of NASA Tech Briefs Magazine.

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