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NEWS | April 5, 2021

Full speed ahead: Mach 18 now available to test customers at AEDC Tunnel 9

By Bradley Hicks AEDC/PA

Test customers in need of serious speed are lining up to take advantage of an unprecedented capability now available at Arnold Engineering Development Complex Hypervelocity Wind Tunnel 9 in White Oak, Md.

Calibration of the Mach 18 system was completed at Tunnel 9 in July 2020, less than two months after the mid-May initiation of the process. Performed to ensure the system would operate as expected, the calibration documented the flow properties and uniformity for four different test conditions based on Reynolds number, which expresses the relationship between inertial and viscous effects.

The system checked out, opening the door for Tunnel 9 to begin offering Mach 18 testing to customers. It wasn’t long before Tunnel 9 had its first patron. The first customer runs at Mach 18 occurred in August 2020.

The long-awaited capability, which allows for testing at speeds never before realized in an AEDC facility, has been in high demand since the calibration was completed.

“Every customer this fiscal year has a portion of their test matrix that is using Mach 18,” said John Lafferty, Tunnel 9 technical director. “They have been waiting for this.”

Prior to the calibration of Mach 18, the maximum speed offered at Tunnel 9, or at any AEDC facility, was Mach 14. Customers needing results at higher Mach simulations would be required to extrapolate the Mach 14 test conditions to the higher Mach numbers.

With Mach 18 now accessible, customers no longer have to do this.

“This allows them to build their aero database with more confidence at the high end of Mach numbers,” Lafferty said.

Lafferty added that Mach 18 not only benefits test customers, but is also ties into the National Defense Strategy since the capability better aligns with the maximum Mach numbers for hypersonic reentry systems and boost glide concepts.

The Mach 18 capability is the result of years of research, significant resource investments and technological advancements. Calls for testing at such speeds date back several decades. During the late 1980s and into the 1990s, the National Aerospace Plane Program was seeking data above Mach 14. Believing the technology was ready, those involved in this project provided funding to Tunnel 9 to develop Mach 18. However, the nozzle design methodology and diagnostics that would be used to examine the physics of the flow were immature. Because the flow quality of the nozzle was poor, the design was scrapped.

By the time higher Mach Number hypersonics again became a priority in the mid-2000s, computer-based modeling and simulation and diagnostic technologies had greatly advanced. A team was assembled at Tunnel 9 and a program aimed at achieving these higher Mach Numbers was designed.

Initial risk reduction efforts began in 2014 and focused on the development of a trio of state-of-the-art efforts: a new material for the nozzle, new laser diagnostics to verify the understanding of flow physics, and a new nozzle contour based on this understanding. This three-year effort leveraged a pair of Small Business Innovation Research programs and investment funds from AEDC to achieve its goals.

Following the risk reduction effort, Lafferty convinced the Office of the Secretary of Defense to construct the new capability for $6.5 million. The Tunnel 9 team then set out in 2017 to achieve Mach 18. Their goal was to accomplish this in three years.

With the help of AEDC counterparts in middle Tennessee, the Tunnel 9 team was able to incorporate their new understanding of flow physics into the design of a new high Mach Number wind tunnel nozzle.

With Mach 18 looking more feasible than ever, Tunnel 9 received additional funding from the Hypersonic Test Capability Improvement Project, an OSD investment program that aims to improve capabilities for hypersonic weapon systems development.

The nozzle design and fabrication, the successful incorporation of the new nozzle throat material, and the diagnostic demonstration all occurred within the three-year timeframe and were completed within budget and on-schedule.

“Successfully completing this project required the coordination of multiple, separate, highly-technical efforts,” said Nicholas Fredrick, Tunnel 9 chief engineer.

An initial calibration using the final Mach 18 hardware occurred in April 2019. By the middle of that year, there had been several test entries at Tunnel 9 to demonstrate the feasibility of the Mach 18 capability. These tests helped determine whether the new nozzle throat material could survive and remain shape-stable at both Mach 14 and Mach 18 nozzle supply conditions and validate the Mach 18 nozzle with the new nozzle throats at the design condition.

More work followed, leading up to the full-calibration completed last year.

“Initial testing of the new Mach 18 capability revealed deficiencies in the high-press, high-temperature nozzle throat section design,” Fredrick said. “Data from the first entry was analyzed by AEDC engineers and subcontractors and design revisions were analyzed and subsequently implemented prior to the start of the second test entry.”

Throughout the process of bringing Mach 18 to fruition, Tunnel 9 personnel gained knowledge that could be used to enhance other capabilities, Lafferty said.

“This development has forced us to better understand our system and the resulting flow physics,” he said. “Our understanding of the flow physics is much improved and, thus, the resultant flow quality is outstanding. The potential exists to apply the lessons learned to a new Mach 14 nozzle with improved flow quality that will provide lower uncertainties for our customers.”

The full calibration brought Mach 18 to full operating capability.

Lafferty said it is very gratifying to see the efforts that went into the development of Mach 18 pay off.

“I always felt it was possible to build the full-scale leg of Tunnel 9 that provided Mach 18. However, the devil is in the details, and it was a huge challenge.

“But the most satisfying thing is that customers are using it, and not just one or two. The first four customers following the calibration all are using it. We never anticipated that.”