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Robyn Macdonald is pushing the limits of hypersonic research with a new NASA grant.

Macdonald, an assistant professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences at the University of Colorado Boulder, has been awarded a to improve computational modeling of turbulence at hypersonic speeds.

“If you’re flying at Mach 25, there is a lot of kinetic energy present in the gas that gets converted into other forms of energy before reaching the surface of your spacecraft, aircraft, or entry capsule,” Macdonald said. “Fully understanding this process is a really hard problem and is important for things like heat shield design and post-flight reconstruction.”

During hypersonic flight, the temperature of air and other gases around a vehicle can reach thousands of degrees, triggering chemical reactions. Despite recent developments in hypersonic vehicle design, the interaction of these chemical reactions with the surrounding hypersonic turbulent flow is not well understood.

“You need very detailed information, and you’re looking at a variety of scales in both time and space. The calculations become very expensive,” Macdonald said. “As a result there are deficiencies in the current models.”

Most current computational work for design of hypersonic vehicles uses a turbulence model called a Reynolds-averaged Navier–Stokes solution (RANS). RANS is computationally efficient, making it attractive for design processes, but Macdonald said it relies on models which may be invalid for certain hypersonic regimes.

“It’s the current design paradigm, but its applicability is not well characterized for hypersonic flows, and we need better predictions as space missions go further into our solar system to places we don’t understand as well as Earth,” Macdonald said. “We can’t run dozens of experiments in a simulated Mars or Jupiter’s moon Titan environment in advance, so these models are really important.”

Macdonald intends to develop a Wall Modeled Large Eddy Simulation (WMLES) model which includes the relevant chemistry for hypersonic flows. WMLES provides an improvement over RANS by predicting the larger scale turbulent structures while making simplifying assumptions about the small scales of turbulence. However, there does not currently exist a WMLES model which includes the chemical reactions relevant for hypersonic flows. The innovation of this work is the inclusion of the chemistry within WMLES.

It is a significant undertaking requiring supercomputers; Macdonald expects to use CU Boulder’s Blanca Condo Cluster as well as NASA’s

Over the course of the three-year grant, Macdonald and her team will formulate equations, write and verify software to conduct the analysis, and then run test cases to validate their results.

“It’s a big project, and I’m really excited. I like the chemistry. I like turbulence. This is exactly my area,” Macdonald said.

This is Macdonald’s second major hypersonics grant in as many years. She previously received a from the Air Force Office of Scientific Research to study gas-phase chemical reactions in the boundary layer at the surface of hypersonic vehicles.