The Arnold Engineering Development Complex Aeropropulsion Combined Test Force team at Arnold Air Force Base, Tenn., has become involved with AFWERX to explore ways to reduce the time required to prepare to test new U.S. Air Force turbine engines.
AFWERX is an Air Force initiative started in 2017 to foster a culture of innovation within the service.
Through AFWERX and a Small Business Innovative Research, or SBIR, project, the Aeropropulsion team is partnering with the small business Core Parts to design and build the hardware, refine the design of the Computational Fluid Dynamics model and test processes for this effort, known as Rapid Test Technique Development. Core Parts is a small business based in Mesa, Arizona.
“The AFWERX Rapid Test Technique Development project attempts to take advantage of emerging technologies, such as 3D printing and advanced CFD, to be better prepared to test new engine designs in altitude test cells,” said Steve Arnold, technical advisor for Aeropropulsion at Arnold. “Historically, when a new engine design is tested for the first time in an altitude test cell, unexpected interactions can occur between the engine and the test cell that take weeks to resolve before testing can continue.
“The AFWERX project uses improved CFD modeling predictions with 3D printing for reduced cost subscale prototyping to better understand the interaction problems and find solutions. Then when the engine arrives, less time is required to start productive testing.”
Yancee Burchett, Aeropropulsion test engineer, further explained that Rapid Test Technique Development is a program that seeks to quickly troubleshoot and understand issues from ground test through the use of rapid prototyping.
“The goal of the program is to understand ground test issues, in this case acoustic responses, early on so that we’ll be better prepared for future test programs,” he said. “This effort included exploring the use of additive manufacturing to reduce the cost and time.
“Once we receive the dimensions for a nozzle design, we can have an additively manufactured prototype made and shipped to us in a matter of days. In a week or two, we can flow air and gather valuable acoustic and flow data that we use to verify the CFD models that are being evaluated simultaneously.”
Burchett also added that this is a new capability.
“By using existing auxiliary air infrastructure that allows greater scheduling flexibility, we hope to use it to react quickly to issues that we see on the test stand,” he said. “We can run rapid prototype models independent of many of the integrated scheduling constraints of our larger test cells. Using the auxiliary air system also results in about 10 times the cost savings over using processed air. From the testing that we’ve accomplished so far, we’ve not encountered any airflow, pressure or temperature limitations from this system, meaning that we can better anticipate the expected conditions for our tests.”
As with all new efforts, the Rapid Test Technique Development program has not been without its challenges.
“Some of the challenges that we’ve noticed so far are the same ones that you’d expect with rapid response programs,” Burchett said. “We still have to navigate the same process for review boards as our larger test programs. In order to react quickly to test needs, we have had to create a process for combining review boards when possible and accelerating the signoff process to meet our desired test schedules.”
The Aeropropulsion team will be able to use this Rapid Test Technique Development effort as a way to train its new test engineers and test analysts.
“The process of preparing and executing these tests is very similar to our larger test programs,” Burchett said. “New hires learn about test instrumentation, data acquisition and analysis techniques in an environment where they can have greater flexibility to spend time delving into the foundational principles behind testing.”
Arnold added that through this program, engineers are more able to be involved with the design, build, test and analysis for future propulsion systems.
“When conducting tests on new engines, the USAF likely will not have access to all the needed information because of manufacturers’ proprietary concerns,” Arnold said. “For the Rapid Test project, Air Force engineers started with nozzles designed by Maj. Darrel Crowe at the Air Force Institute of Technology. Using their expertise in aircraft engine part design and manufacturing, Core Parts converted Maj. Crowe’s nozzle design to test hardware in less than seven days utilizing the additive manufacturing process.
“AEDC engineers then oversaw the CFD predictions, received and installed the hardware, conducted the test and are performing the analysis. Being involved in all phases of the effort instills a better understanding of the physics of the tests, as well as providing insight on ways to reduce test time and costs.”
Although there have only been four tests using the program to date, the benefits are already being seen.
“Lessons were learned with regard to the acoustic response of not only the new nozzle designs but also engine simulators that AEDC has many years of experience operating,” Burchett said.
“We’ve already gained a good understanding of how to efficiently test and make the most of our test periods. We anticipated seeing certain acoustic responses from our previous tests in SL-2 (Sea Level 2 Test Cell), but each nozzle presented its own unique characteristics that we were able to understand through further analysis. The new test engineers on the project were able to get hands-on with the hardware for a better understanding of the test process.”