Air Force Is Developing Mach 18 Wind Tunnel

Mike Smith, AEDC optical diagnostic physicist, verifies the Coherent Anti-Stokes Raman Spectroscopy system is functioning properly prior to conducting tests in support of risk reduction for a new test capability that will increase Mach number of AEDC Hypervelocity Wind Tunnel 9 at White Oak, Md. (U.S. Air Force photo/A.J. Spicer)

The Arnold Engineering Development Center (AEDC) Hypervelocity Wind Tunnel 9 team is conducting tests in support of risk reduction for a new test capability that will be revolutionary for AEDC and the U.S. Air Force. The capability involves increasing the Mach number of what AEDC is currently able to achieve at Tunnel 9 in White Oak, Md., from Mach 14 to Mach 18.

Dan Marren, director of AEDC White Oak, explained the testing is in response to national strategy and requests from high priority customers. “AEDC is in the process of transforming hypersonic test and evaluation,” he said. Ed Tucker, High Speed Systems Test chief at AEDC, is managing the Hypersonic Test and Evaluation Investment Program for the U.S. Air Force, which will improve evaluation of hypersonic technologies through improving our test capabilities, advancing modeling efforts and diagnostics and finding ways to prepare the next generation testing workforce.”

The program is expected to bring hundreds of millions of investment dollars to AEDC over the Future Years’ Defense Program. As part of the coordinated plan, the Tunnel 9 test team is doing its part to extend the existing Mach capability of the hypervelocity wind tunnel. “This will require advances in material technologies and a deeper physics-based understanding of the flow quality in the test cell,” Marren said.

The risk reduction runs are aimed at evaluating the new test environment needed for Mach 18 prior to building a new nozzle. John Lafferty, Tunnel 9 technical director said, “In the existing facility nozzle, we are creating the conditions we will experience at Mach 18 to determine the exact thermodynamic state of the gas to achieve the best design. Several optical diagnostic techniques not typically deployed in a major T&E (test and evaluation) facility are being operated to help prosecute the physics and calibrate the flow.”

In order to achieve this, collaboration is occurring across the aerospace testing enterprise. Andrew Alexander, AEDC engineer and scientist, Jeff Bala, of NASA Langley, and Richard Kennedy, a University of Maryland student, have been working together to configure operations and analyzing data from several non-intrusive instruments.

Alexander stated that the work has been challenging, but the combined efforts have proved successful. “Especially when considering the high number of optics in the laser system, the ps-CARS (pico-second Coherent anti-Stokes Raman Scattering) portion of the test operated very smoothly,” he said. “I was pleasantly surprised at how well the system stayed in alignment throughout the duration of the test with only minor tweaking of the optics.”

George Moraru, project engineer at AEDC White Oak, agreed the test was unique for Tunnel 9, largely because of the number of non-standard diagnostic measurements.

“The successful coordination of the various test components was critical towards obtaining a complete data product that will serve as risk-reduction towards extending the maximum Tunnel 9 capability to Mach 18,” he said. “Each system faced its own minor challenges, ranging from ensuring proper alignment to successful communication between the hardware and the data acquisition systems.

Marren noted engineers and researchers have been working towards achieving higher Mach capability for decades now, and coincidentally it was one of AEDC’s very own that helped lead the effort. “The fascinating part of all this is that today's measurements and the ability to go to Mach 18 is rooted almost 25 years ago when two young engineers, one being current Tunnel 9 Tech Director John Lafferty, took a data set that at the time they didn’t have the sophisticated tools to analyze sufficiently. They did, however, publish their results conclusions and hypothesis anyway,” he said. “That original data set, and a few others along the way, served to form a foundation and hypothesis that others, including researchers at NASA, picked up and with modern tools and techniques, unlocked some of the physics-challenges required to get to Mach 18.”

Lafferty added even in the 1990s the objective was the same: to provide the maximum Mach number possible. But at that time, the tools were not adequate to provide a complete understanding of the flow physics. “Now with modern computational fluid dynamic simulations and modern diagnostics I believe we will be able to provide new maximum Mach number test capability that is needed to support advanced hypersonic system development,” he said. “Although we still face many challenges the recent testing goes a long way toward verifying the design assumptions and answering many of the open questions regarding the state of the flow from 25 years ago.”