Capability improvements at transonic wind tunnel leads to approximately $200,000 in savings annually.

ARNOLD AIR FORCE BASE, Tenn. – An annual savings of close to $200,000 is expected after the facility checkouts of the Arnold Engineering Development Complex 16-foot Transonic Wind Tunnel, or 16T, at Arnold Air Force Base last September.

By leveraging previous upgrades to the Propulsion Wind Tunnel facility’s main compressor drive, the 16T wind tunnel can be operated utilizing lower power consumption, according to Tyler McCamey, a program manager for Test Investment Planning and Programming funded capital improvement programs at Arnold.

“Flight team members Ron Lutz and Douglas Miller were overseeing a checkout of conditions of 16T, and during this test, the PWT main drive compressor was being used in a way that was not originally possible,” McCamey said. “But a Computational Fluid Dynamics analysis and a study of the compressor curves predicted that lower compressor speeds, combined with optimal blade angle settings, could safely and more efficiently generate test conditions for the 16T core operating envelope, where 85 percent of the tunnel’s testing occurs.”

Depending on the desired tunnel conditions, the test demonstrated an instantaneous savings of up to 10 megawatts, or the equivalent power of running 100,000 100-watt lightbulbs.

“Being the largest single-user on the TVA (Tennessee Valley Authority) grid, the team was able to demonstrate a way to be a better steward of power resources without any compromise in capability,” McCamey said.

Another way Flight team members determined they could improve test efficiency is by better maintaining air-velocity conditions during sweeps of wind tunnel model position. Precise air-velocity control is a crucial element of providing the highest quality data to customers. The Flight team determined that augmenting the system used to control air-velocity will increase the sweep-rate of model position without the need to slow down movement or repeat test points where the air velocity was not within tolerances. This improves productivity and reduces cost for repeat points.

Sid Ledbetter, an Instrumentation, Data and Controls engineer, and Sara Rhoades, a Facility Technology engineer, have been studying the predictive control of valves to help 16T stay on condition between changes to the test models.

“This control technique, which is already being employed by other AEDC facilities, shows promise of doing the same for 16T,” Ledbetter said. “Data collected during the facility checkouts will help our team in finalizing a predicative control algorithm that we will be able to deploy in the future.”

With the same intent of maintaining test conditions, AEDC controls engineers Drew Owen and Davy Ruehling took advantage of the same 16T capabilities tests to tune the load commutated inverter, or LCI, and found that the baseline tuning was good.

“The LCI is part of the system that controls the variable speed drive motors of the compressor,” Ruehling said. “By monitoring the LCI, it was determined that the lower speeds used for efficient compressor operation also resulted in near unity power factor, or when reactive power is reduced to zero. Operation away from unity power factor has historically resulted in about $101,000 annually in TVA penalties.”

Shelby Moorman, an electrical design engineer, is currently writing a new LCI control system specification that will use the knowledge gained through this recent testing to assure the upgraded system will avoid these penalties and improve upon the ability to operate at lower speeds.

Additionally, multiple test agendas were combined into an executed matrix of test points to minimize the cost of the testing on the facilities. Brian Edinger, a test project engineer, spearheaded this effort, along with engineers Joe Capps, Ethan Jobe and John Wright.

“This group found that some actions to improve power efficiency may compete with controllability and vice-versa, and the experiments improved understanding of these interactions.” McCamey said. “The facility characterization gained through the experiments will help test operations save the customer money, while also maximizing the amount of data they can collect within the program budgets on future tests.”

Because collecting data for test customers is a central mission of AEDC, McCamey explained that finding time to run the facilities for the sole purpose of discovering improvements can be difficult.

“The expense can occasionally be justified if there is an expected payback in improved capability or efficiency, and this certainly was the case for this cadre of experiments by the Test Operations group at PWT,” he said.