Until now, experiments were limited to 2D observations due to technological constraints. (Representational image)
Hypersonic flight, with speeds exceeding Mach 5, pushes the boundaries of engineering. But as vehicles slice through the atmosphere at these incredible velocities, complex interactions occur between the gases and the vehicle’s surface.
Boundary layers, shock waves, and unpredictable flow patterns create immense challenges.
Researchers at the University of Illinois Urbana-Champaign, led by Professor Deborah Levin and Ph.D. student Irmak Taylan Karpuzcu, have conducted advanced simulations.
Using powerful supercomputers and cutting-edge software, they have conducted the first-ever fully 3D simulations of hypersonic flow around cone-shaped models.
This 3D approach revealed unexpected new disturbances, breaking away from the standard understanding of concentric flow patterns.
“We have those data to compare, but having the full picture now in 3D, it’s different. Normally, you would expect the flow around the cone to be concentric ribbons, but we noticed breaks in the flow within shock layers both in the single and double cone shapes,” said Karpuzcu.
The cone shape, though seemingly basic, serves as a crucial simplified model for a wide range of hypersonic vehicles.
Until now, experiments were limited to 2D observations due to technological constraints.
The team was able to capture the full 3D complexity by leveraging the high processing power of the Frontera supercomputer at the Texas Advanced Computing Center and specialized in-house software.
At Mach 16, they observed breaks in the flow within the shock layers, near the cone’s tip, where air molecules become more viscous. Interestingly, these breaks were absent at Mach 6, highlighting the crucial role of speed in these instabilities.
“As you increase the Mach number, the shock gets closer to the surface and promotes these instabilities. It would be too expensive to run the simulation at every speed, but we did run it at Mach 6 and did not see the break in the flow,” Karpuzcu said.
The most challenging aspect of the research was determining the cause of the flow disruption.
They found that a linear stability analysis using triple-deck theory, a complex mathematical approach, could be applied to this situation. To confirm their hypothesis, they developed a new computer code to simulate the flow again and test analysis.
“We set up a second computer program to make sure everything works and is within the limits for our flow conditions. When we did that, we saw the break in two big chunks in 180-degree periodicity around the cone,” added Karpuzcu.
Furthermore, the team also used the Direct Simulation Monte Carlo method, which tracks billions of individual air molecules and simulates their collisions.
“The Monte Carlo method does random, repetitive attempts. It’s more extensive than classical computational fluid dynamics methods and we’re tracking billions of particles. This makes sure there are enough particles within the flow field and collisions are captured properly,” the author concluded in the press release.
This research sheds new light on the intricate behavior of hypersonic flows by revealing previously unseen 3D instabilities. It paves the way for improved vehicle designs and safer, more efficient hypersonic travel.
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