New Tunnel 9 paint lab providing convenience for staff and savings for customers
By Bradley Hicks, AEDC/PA
/ Published February 05, 2019
ARNOLD AIR FORCE BASE, Tenn. -- When those at AEDC Hypervelocity Tunnel 9 in White Oak, Maryland, determined that a new space was needed for the application of Temperature-Sensitive Paint, an unused area of the facility received a proverbial and literal fresh coat of paint.
The result of this multi-month refurbishment effort - the Tunnel 9 Temperature-Sensitive Paint Application Lab – has been operational for the better part of the past year, and both Tunnel 9 personnel and test customers are reaping the benefits.
Tunnel 9 Test & Evaluation Engineer Inna Kurits said the advantages of the new lab include improved efficiency and a cleaner environment in which to apply TSP.
“Having the lab at Tunnel 9 gives us a greater control over the quality of the coating, lowers costs and allows us to meet the customer schedule,” Kurits said. “Having the space has also greatly simplified the logistics of applying the TSP to sensitive test articles.”
The lab is not only used to apply TSP to wind tunnel test articles but also to continue the development and refinement of TSP formulations and application techniques.
Prior to establishment of the lab, a section of the Tunnel 9 Machine Shop was used as the TSP application area. According to Kurits, this not only impaired efficient Machine Shop operations, but the location of the application area also impacted the quality of the paint jobs. She explained the Machine Shop environment is “inherently dusty,” adding the air in the facility is also full of residual vaporized and atomized oils and cutting fluids.
“Machine shop operations had to be halted days before and during paint application and curing to minimize the possibility of contaminating the paint,” Kurits said. “Even with these precautions, a clean environment is hard to maintain in the Machine Shop area. Additionally, the proper temperature and humidity are difficult to maintain in the Machine Shop due to the size and openness of the area.”
It was decided that a space that could more suitably meet the TSP application needs was required.
“The requirements included a dedicated HVAC system to maintain required temperature and humidity, an environment relatively free of dust and oil, a space large enough to house all the equipment and supplies, and a large access door for ease of getting models in and out,” Kurits said. “The space had to be removed from offices and foot traffic areas to avoid the inadvertent exposure of personnel to volatile organic compound spray mists or residual vapors and odors and to minimize the impact on other ongoing work around the site. Also, the space had to be relatively easy to secure for sensitive operations.”
The former “Gun Room/Pilot Tank” building at Tunnel 9 was identified as the best space that could meet these requirements with a minimal investment and in the shortest amount of time. Work to convert this unutilized area began in September 2017 and was completed in early February 2018.
The TSP Application Lab occupies two floors of the former Gun Room/Pilot Tank. The lab itself houses two large spray booths and a booth used for paint mixing and paint gun cleaning. The space also includes equipment and chemical storage areas and model cleaning and preparation areas, as well as desk space and safety equipment.
“TSP has revolutionized the way we obtain aerothermal data,” said Tunnel 9 Director Dan Marren. “Our team has innovated their way to having class-leading capabilities, and this new application facility has permitted them to take it to the next level just in time to support hypersonic customers working on the Department of Defense’s number one priority.”
TSP is a global temperature and heat transfer measurement technique. It provides 3D maps of heating on a model’s surface and, according to Kurits, is “invaluable at characterizing complex flow phenomena such as boundary layer transition and shock-boundary layer interactions.”
Through the TSP mixing process, luminescent molecules called luminophores are combined with a polymer binder. The resulting mixture is sprayed onto a test article. The luminophores in the coating are excited by the illumination of a particular wavelength of light, typically ultraviolet. The process by which the luminophores return to the ground state is characterized by the emission of photons with a wavelength that is redshifted relative to the excitation wavelength.
The emission intensity is inversely proportional to the local temperature of the coating. As the temperature is raised, an increased number of molecules take thermal paths to de-excitation rather than emitting photos. This results in a measurable decrease in emission intensity.
“In other words, the paint gets dark as it heats up and gets brighter as it cools off,” Kurits said. “A unique relationship between the emission intensity and paint temperature can be established through a calibration process and allows the paint to be used as a global surface temperature sensor. The measured surface temperature time histories can be used to compute surface heat transfer.”
The lab has seen plenty of use since going online, as the space has been utilized for the painting of several test models and numerous samples. It is a trend that is likely to continue.
“TSP is now requested by customers on almost every wind tunnel test conducted at Tunnel 9, which means the lab is used prior to almost every wind tunnel test to apply the coating to the model prior to installation in the tunnel,” Kurits said.