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Army Works Toward ‘Sandphobic’ Coatings

Monday, November 14, 2016

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When it comes to military coatings, the Department of Defense has a new target in its sights: sand.

Scientists and engineers with the U.S. Army Research Laboratory are experimenting with coatings in high-temperature environments at the Aberdeen Proving Ground (APG) site in Maryland. Their goal is to create a material that will make sand slide off the inside of a turbine engine with ease.

Referred to as “sandphobic coatings,” such a technology would have the capacity to save pilots’ lives.

Destructive Sand Particles

It’s common knowledge that sand can create low-visibility situations, but the smallest particles of sand and dust can also wreak havoc inside aircraft engines. Molten sand accumulates inside gas turbine engines, researchers say, restricting air flow and leading to engine loss.

Blowing sand
U.S. Army photo

In environments with lots of sand and dust, Army aviators risk engine loss; Army researchers are searching for a sandphobic coating to protect those gas turbine engines.

“We are facing, especially in Southwest Asia, and other places, brown-out conditions,” says Dr. Anindya Ghoshal, chief scientist for the laboratory’s Vehicle Technology Directorate.

Particularly when a helicopter is hovering, he explains, a lot of dust particles are blown around, and these sand and dust particulates end up getting sucked into the engine.

Although helicopters have filtration systems to filter out larger particles, micron-sized particles can get through the turbine’s combustor and adhere to the blades, Ghoshal says.

“Our goal is to have the particles strike the blades or vanes [inside a gas turbine engine] and then flake off,” he adds.

Ghoshal explains that they first want to understand the physical chemical behavior behind the process, then use that model and to help predict the type of material that would enable the team to develop the sandphobic coating.

Test Rig, Computer Simulations

“We have a unique rig here,” says Dr. Michael Walock, a physicist on the sandphobic coatings team. “The hot particulate ingestion rig allows us to shoot sand into the hot-gas flow at small level components and rapidly prototype new coating materials.”

According to Walock, the team is reportedly the first in the in the global scientific community to have used high-speed imaging to confirm the sand particles are in a molten state when impacting onto thermal barrier coatings.

At the Army’s Vehicle Research Laboratory, the team shot high-speed videos, showing the molten sand particles splattering on turbine blade material targets and then vaporizing.

Computer simulations also play a role in finding a technology solution, the scientists add, as computer modeling will help them observe the interactions between particles and the surface.

“The particles go through a phase change from solid to liquid and then they deposit onto the surface,” says Dr. Muthuvel Murugan, acting team lead for the lab’s Turbomachinery Research Team.

Computer modeling of this phenomena will help them understand how damage occurs, he says, adding that he anticipates using the powerful supercomputers at the DOD High Performance Computing Center, also located at APG.

Murugan notes that the team will also use advanced computational fluid dynamics together with particle ingestion to gain a better understanding of how sand particles interact at the high temperatures of a gas turbine engine.

sand particles
U.S. Army photo by David McNally

During brown-out conditions when a helicopter flies into a cloud of sand, micron-sized particles go through the turbine's combustor and adhere to the blades of the engine, restricting air flow and causing power loss. Army scientists use samples to discover a potential sandphobic coating for the inside of engines.

“When we simulate how particles go through the flow-field and impact and adhere to the surface, then we can understand the vulnerable parts of the turbine blade and engineer a sandphobic coatings solution,” he explains.

Keeping Soldiers Safe

“I strongly believe that in the next three to five years we will have not only one, but several solutions,” Ghoshal says of the sandphobic coatings research.

“It will definitely save a lot of soldiers’ lives in the long run,” he adds. “Our solutions will make our soldiers’ lives safe and will make our Army stronger.”

Sandphobic coatings research is part of a larger strategic effort called the Sciences for Maneuver Campaign, which is working toward innovative science and solutions to significantly increase the force effectiveness and global responsiveness of the Army. This includes developing technology that will make improvements in aviation responsiveness and minimize vulnerabilities.

New research from the team will also be published in the January 2017 Advances in Aircraft and Spacecraft Sciences, an international journal.


Tagged categories: Aerospace; Coating Materials; Coatings Technology; Department of Defense (DOD); Military; North America; Protective Coatings; Research and development; U.S. Army

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