November 22, 2017

CFD verifies new AEDC Hypervelocity Wind Tunnel 9 nozzle design

Deidre Ortiz
Arnold AFB, Tenn.

The new Mach 18 nozzle design at the AEDC Hypervelocity Wind Tunnel 9 at the AEDC site in White Oak, Md., near Silver Spring, has been successfully verified using computational fluid dynamic codes. This image shows computed contours of Mach number within the new Mach 18 nozzle design.

The new Mach 18 nozzle design at the AEDC Hypervelocity Wind Tunnel 9 in White Oak, Md., near Silver Spring, has been successfully verified using computational fluid dynamic codes.

A new nozzle was needed to extend the range of desired conditions from the Mach 7, 8, 10 and 14 conditions currently available.

According to Ken Tatum, AEDC modeling and simulation engineer, the nozzle had to be designed analytically to yield the near-uniform conditions in the test section required for the design of advanced future hypersonic weapons.

CFD analyses, performed by Tatum and Derick Daniel, AEDC aerospace engineer, assessed the physically complex hypersonic flows within the nozzle and showed that a high-quality flow within the test section that is undisturbed by excessive wave reflections is theoretically achievable.

“Ensuring that these facilities provide high-quality test results at the desired conditions and that the facilities are applicable to understanding extreme flow conditions requires advanced numerical analysis to fill in details that are unavailable from testing,” Tatum said.

“The thermodynamic chemistry model used in the CFD codes were validated with Coherent Anti-stokes Raman Scattering system test data taken by Andrew Alexander, instrumentation and diagnostics engineer,” he added. “Andrew’s measurements verified the existence of non-equilibrium effects at high Mach speeds. We also assessed the effects of pressure waves generated at nozzle joint locations and their effects on the test section for the new nozzle design at equilibrium and non-equilibrium extremes. Accurate modeling of both these effects are critical to building the best nozzle and test capability possible.”

The facilities at Tunnel 9 will be used to study advanced hypersonic system development. Part of these studies are continued advances in the understanding of turbulent boundary layers. High-quality flows will be necessary to provide useful data for such studies. One such diagnostic used to interrogate these boundary layers is particle-image velocimetry.

CFD analyses performed by Tatum were used to design a local particle injector nozzle for a PIV system in Tunnel 9.

“Particle-image velocimetry seeder designs have been shown to provide satisfactory particle distributions needed for future test programs,” Tatum said. “Studies of hypersonic boundary layers require careful design of injection flow paths for seeding high-speed boundary layers with satisfactory particle distributions for PIV techniques.”

Tatum performed analyses of numerous PIV seeder designs for both Mach 3 and 10 flows to assess boundary layer particle densities and disturbances on the boundary layer from particle injection into the stream.

These efforts are just two of many to expand the range of capabilities of the Tunnel 9 facilities and to add to the testing techniques available to Tunnel 9 researchers. The efforts are highly coupled in the sense that high-quality nozzle flows are essential to obtain high-quality data from new and improved test techniques.

AEDC team members are using innovative ideas to address issues that arise when taking on unique, and often challenging, work. It’s these ideas, according to Dr. Woodrow Whitlow, that “provide long-term benefits to test operations.”

Innovative ideas are also important to the U.S. Air Force because complex security and fiscal challenges demand that Airmen are innovative and find better and smarter ways to “fly, fight and win.” The Air Force leverages many channels to empower Airmen and industry partners to submit ideas as part of an overarching culture of innovation.

In a recent interview with Defense News, Air Force Secretary Heather Wilson commented on the Air Force’s focus on innovation and looking toward the future.

“What kind of an Air Force do we need in 2030, and how do we start ourselves on the process of getting there? We are a service whose roots and history are very deep in innovation, and I want to make sure that we’re not losing that,” she said.

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