Technology project at Range G focuses on boundary layer transition testing

  • Published
  • By Deidre Ortiz
  • AEDC/PA
ARNOLD AIR FORCE BASE, TENN. --  Boundary layer transition tests have not occurred in the hypervelocity ballistic Range G facility at Arnold Engineering Development Complex (AEDC) for many years but this is changing as a result of a new technology project.

The purpose of a boundary layer transition test is to measure the location on a model where transition from laminar to turbulent flow occurs.

"These tests can be conducted in wind tunnels, ballistic ranges like the G Range, or in flight," Taylor Swanson, AEDC aerospace engineer in the Test Technology Branch, said.

Swanson explained the current technology project in Range G has two primary purposes: determine a suite of instruments for boundary layer transition tests and gain the experience necessary to conduct such tests. 

"An investments branch project is planned as a follow-on to this effort to acquire the specified instrument suite," he said.

In addition to the immediate use of these results for the follow-on project, results will be shared with the hypersonic transition community.

Swanson said, "An N factor from the eN method is an integrated disturbance growth rate. If high N factor transition is achieved, that would be a key accomplishment and selling point for this facility."

As part of the project, testing on cones at hypersonic speeds will be conducted in Range G.

"Cones are a standard geometry similar to others reported in the literature," Swanson said. "Several diagnostics are used to visualize the surrounding flow field, including the laminar or turbulent condition of the boundary layer."

Flow visualization techniques like Schlieren and shadowgraph image density gradients in the flow field allow the test team to see shock waves, vortices and the boundary layer. Infrared cameras determine model surface temperature by viewing thermal radiation emitted by the model. From flow field information and surface temperature, boundary layer transition is determined.

Swanson mentioned that boundary layer transition testing has always been important for any object flying at hypersonic speeds.

"The high heat transfer to the vehicle in the transition region impacts the thermal protection system design," he said.

G Range has a history of hypersonic testing including tests on the Apollo models and the space shuttle. Much of the formative work in the field of boundary layer transition testing was conducted at AEDC by pioneers such as J. Leith Potter, Jack Whitfield and Samuel Pate, among others.

Swanson said he's confident the technology project will be successful in preparing G-range for upcoming testing.

"With the push towards hypersonic vehicles, we anticipate renewed requirement for this capability."