AFOSR-Funded Team Makes Breakthrough in Hypersonic Computational Research

  • Published
  • By Erin Crawley
  • AFOSR Public Affairs
ARLINGTON, Va. --  An Air Force Research Laboratory Munitions Directorate science and engineering team, funded by the Air Force Office of Scientific Research here, has made a significant breakthrough in its hypersonic computational research. 

The team is studying the aerodynamic characteristics of projectiles that deform at hypersonic speeds at sea level conditions, which is a high-speed flight regime not commonly studied. Dr. Kirk Vanden, technical advisor for the computational mechanics branch, Air Force Research Laboratory Munitions Directorate, is the lead principal investigator on the project.

One of the goals of the research is to advance warhead technology and the team is getting closer to this goal. Recently, the team determined the level of chemistry modeling needed to model hypersonic flows at sea level conditions. They have determined that using a four-species frozen-flow chemistry model is an acceptable level of chemistry modeling for the particular types of explosively formed projectiles under study. This is a unique problem because the projectiles change shape in flight.

Because hypersonic vehicles normally fly at very high altitudes the research team had to answer some fundamentally new questions about hypersonic flight at sea-level conditions before proceeding with their broader research goals.

Dr. Vanden's team was awarded the grant to study hypersonic and unsteady flow science issues for explosively-formed penetrator warheads. Hypersonic speed is equal to or greater than five times the speed of sound. Dr. Vanden's work mostly concentrates on studying flows at speeds of around Mach 6, using highly advanced computational fluid dynamics codes.

Dr. John D. Schmisseur, an AFOSR program manager, oversees AFOSR'S boundary layers and hypersonics grant portfolio, which includes this research grant to Vanden. Schmisseur believes Vanden's work is truly cutting-edge.

"This is an exciting new application of nontraditional hypersonic computational analysis. We are really excited about Kirk applying these new tools to his problem," he said. "If we do that, we'll be able to hopefully revolutionize some of the analysis tools to help develop new warhead technologies for the warfighter."

Through this research, Vanden's team discovered that using a four-species frozen-flow chemistry model is an acceptable level of chemistry modeling. Dr. Vanden explained why this accomplishment is so important.

"Although the Air Force has done quite a bit of work in hypersonic vehicles, the vehicles often fly at altitudes of 60,000 feet and higher where the atmosphere is very thin," he said. "Researchers studying high altitude flight have a particular way of approximating how the molecules in the air behave. However, these approximations could not be used for sea level flight. At sea level, the air is very dense and behaves differently. As far as I know I'm the first person to look at hypersonic flight at sea-level conditions."

As a result, one of the first challenges for the team was to understand the level of chemistry modeling needed in order to measure the flow. In certain conditions air molecules will break down and start to chemically change character. The team had a lot of initial ideas, but Vanden said they were surprised to find out how much they would be challenged by the high density of the air at sea level.

"As it turned out we had some different changing chemistry in the air at sea-level conditions. And, that was something we didn't know before," said Dr. Vanden.

To understand the chemistry of these molecules the team used high performance super computers to run computational codes to study the flow physics and aerodynamics around the different projectiles. Currently the research team is using existing computational codes from both Air Force and NASA on super computers supplied by the Department of Defense. 

"We used their [NASA and Air Force] codes on DoD high performance super computers and simulated one of our shapes to get an idea of what level of chemistry would be needed. We had to look at it a lot of different ways until we saw at what level we no longer had chemistry changes and then we knew that was the proper level at which to simulate it," said Dr. Vanden.

"Kirk Vanden's work has the potential to take computational hypersonic methods to another stage by applying them to sea level flows and munitions warheads. These are arenas where computational hypersonics have not been previously employed," said Dr. Schmisseur.

Although Vanden's work in this arena is not ready for the application stage yet, Schmisseur said Vanden has a solid reputation for taking basic research to the next level.

"The key part about Kirk's research is that he's really building the bridge between our basic research programs and actual tools for application that will benefit the warfighter. He's a great transitioner of our technology and science," said Schmisseur.

AFOSR support has enabled Vanden not only to build bridges, but to position himself as a leading expert in computational analysis and develop relationships with major players in his field.

"The grant is significant in terms of our lab management, understanding that we are working with AFOSR and working with the universities. So the money was nice, but it was also the access to all the other people in AFOSR," said Vanden.

Next steps in this research, said Vanden, include development of new, more customized codes to enable the team to more closely study the rapidly changing shapes of penetrating warheads.

"We are interested in simulating massively deforming bodies [warheads] at high speeds, undergoing rapid acceleration or deceleration, and looking for computational techniques to do that. As far as we know, these computational methods don't exist to the level we need for this," said Vanden.

Dr. Vanden's research could lead to increasing the capability of existing warheads.

"Without going into specifics, this research already has a use in mind. We already have things in place with people who are doing the warhead work, so it is not something that we 'hope' to use someday, it is something that the warhead designers in my directorate have already given me problems to work on. We are now trying to develop the capability to go look at those problems," said Vanden.

By funding research programs like Vanden's hypersonic computational research project, AFOSR continues to expand the horizon of scientific knowledge through its leadership and management of the Air Force's basic research program. As a vital component of AFRL, AFOSR supports the Air Force's mission of control and maximum utilization of air and space. Many of the technological breakthroughs enjoyed by millions today, such as lasers, the Global Positioning System, and the computer mouse trace their scientific roots to research first funded by AFOSR.