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A new study suggests that aircraft design may not have to be changed drastically for hypersonic flight.
Air behaves differently around aircraft at low speeds compared to high speeds. Air density below 225 miles per hour remains constant. This is called incompressible flow and helps simplify aircraft design. At higher speeds, especially above the speed of sound, it switches to compressible flow. The air density changes significantly due to variations in pressure and temperature, affecting how an aircraft flies.
Aerospace engineers already understand how airflow works with aircraft that fly at low Mach speeds. Military aircraft already fly at double and triple the speed of sound, which is known as Mach 2 and 3, respectively. Mach 1 is the speed of sound at 760 mph. However, airflow at greater Mach numbers, such as Mach 5 or 10, is still rather unknown.
Professor Nicholaus Parziale at the Stevens Institute of Technology released a new study titled "Hypersonic Turbulent Quantities in Support of Morkovin's Hypothesis". The study hypothesizes that when air moves at around Mach 5 or 6 speeds, turbulence behavior does not change significantly compared to slower speeds, even if the air density and temperature do. That means that hypersonic aircraft do not need to be designed significantly differently from current slower aircraft.
Parziale's research focuses on hypersonic flight. In January, he received the Presidential Early Career Award for Scientists and Engineers for his research into fluid mechanics that affect high-speed flight.
The study was based on Morkovin's hypothesis, which was introduced in the 20th century. The research team sent an ionized krypton gas through a wind tunnel as part of the experiment. While the gas initially formed a straight glowing line, it did move and bend with the air flow of the tunnel.
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"As that line moves with the gas, you can see crinkles and structure in the flow, and from that, we can learn a lot about turbulence," said Parziale, who spent 11 years building the setup. "And what we found was that at Mach 6, the turbulence behavior is pretty close to the incompressible flow."
The hypothesis is not confirmed yet, but the Institute states that the study brings hypersonic flight one step closer to reality.
"Today, we must use computers to design an airplane, and the computational resources to design a plane that will fly at Mach 6, simulating all the tiny, fine, little details would be impossible," said Parziale. "The Morkovin's hypothesis allows us to make simplifying assumptions so that the computational demands to design hypersonic vehicles can become more doable."