Defense

May 23, 2012

AEDC provides computational fluid dynamics expertise to Hill AFB engineers

by Patrick Ary
Arnold AFB, Tenn.

At its core, the Arnold Engineering Development Center at Arnold Air Force Base, Tenn., strives to test and evaluate aircraft to help customers develop, qualify and improve system designs and performance.

The center constantly researches and develops technology programs to develop advanced testing techniques and instrumentation to satisfy testing needs and keep pace with advancing aircraft, missile and space system requirements.

While business has focused on these aspects of the base’s mission, when opportunities arise to bring in money from other avenues, it’s considered. That recently happened when AEDC experts provided training to Hill Air Force Base, Utah, engineers in the area of computational fluid dynamics.

Specifically, three engineers from Hill came to AEDC for training in how to use a CFD software application known as Kestrel. Kestrel is a CFD application that will give fixed-wing aerodynamic flow field like pressures and temperatures on a fixed airframe. It is sponsored by the High Performance Computing Modernization Office’s Computational Research and Engineering Acquisition Tool Environment Program.

“We are part of a small team that does analysis for modifications and sustainment of the A-10, T-38 and other Mature and Proven Aircraft, such as the F-4 and F-5,” said Tristan Young, the T-38/MAPA aeroperformance engineer at Hill AFB. “Some T-38 modeling has been done in the past through contractors, but we were limited by our manpower and capabilities. The work that is being done at AEDC will provide us with models that can be run as is or modified to suit future problems.”

There are three steps in CFD analysis, according to Terrance Dubreus, AEDC project manager for the modeling and simulation capability. The first is building a computational grid, which serves as an input for the flow solver – in this case, Kestrel. Next, one has to determine the proper flow conditions and boundary conditions. The results will only be as good as the information provided to the flow solver. Then Kestrel is used to solve the aerodynamic equations – i.e. the continuity, Navier Stokes and energy equation which ultimately determine the change in pressure, temperature, Mach number, etc.

“It will solve the equations on all the data points that make up the computational grid,” Dubreus said. “That’s why we have to use supercomputers to do this type of application, because it’s very computationally intensive – usually millions of data points.”

Hill AFB engineers have had a relationship with AEDC for several years in the form of Flight Systems Branch analysis lead Dr. Don Malloy, who at the time worked for Aerospace Testing Alliance, AEDC’s operating contractor. Dubreus said the relationship developed initially when Hill AFB was investigating an increased drag on T-38 trainers caused by new inlets they bought from NASA.

“They were impressed with Don’s support, and keeping that two-way communication once he switched to a government employee in the [Air Force] Analysis Branch; he also made them aware of our CFD capability, which is unique within the Air Force,” Dubreus said.

Hill AFB had a CFD expert who was a contractor, but when he retired government engineers wanted to get some experience of their own. After talking with Malloy about their desire to get a handle on the basics of CFD, they decided to come to AEDC and learn the ropes. ATA’s Bill Sickles and Jim Masters provided the training.

Prior to the Hill engineers’ arrival, AEDC submitted a request to the HPCMO’s CREATE Program Office for a concurrent Kestrel demonstration workshop.

“The developers of Kestrel came to AEDC and went through the different capabilities of the flow solver,” Dubreus said. “They provided a day for the training, and the next day the Hill engineers met up with Bill and Jim and were able to ask more detailed questions.”

The training Hill engineers received will be used mostly for aircraft sustainment work.

“For example, occasionally a repair will require a doubler or external patch that changes the outer geometry of the aircraft,” Young said. “The goal is to be able to quickly modify and run a model to investigate what affect the repair has on aerodynamics.”

Young said the training they received at AEDC was excellent, and if they ever need more training they would like to come back.

“Most software training consists of working through tutorials that are ‘canned’ and work out perfectly with little effort,” Young said. “With this training we sat in a room with three experts and worked together to create a surface mesh on the actual T-38 geometry that we would be working on. We went through the same basic processes many times on different parts of the aircraft until we had created a complete surface mesh.

“Since CAD models tend to have defects each location provided a different challenge to overcome. Each day we had time to go work on our own projects with support from the AEDC engineers. That way we could use what we had learned.”

Other Air Force bases do work with CFD, but AEDC’s is more diverse because of the different mission areas served.

“We have three different mission areas,” Dubreus said. “We have flight, or the wind tunnels. We have space. We have propulsion. So we have tools capable of simulating the performance with regard to all three of those mission areas.”

Reimbursable Budget Authority (RBA) work has become more of an area of interest at AEDC in this time of tightening budgets, Dubreus said. Under RBA, AEDC can do work for other entities for which the base is reimbursed. In this case, about $50,000 went into AEDC’s budget from Hill AFB.

“This was a first for us, to provide training for another organization,” Dubreus said. “The work that we’ve done in the past was primarily focused on analysis, so this was the first of its kind where we were actually asked to provide training for engineers at another organization. That’s exploring new areas of providing support.”




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