The findings, published in Physics of Fluids, show that particles generated inside rocket motors can rapidly melt, deform and change shape while travelling through extreme high-temperature airflow, significantly altering how heat, energy and drag are transferred within propulsion systems.
The breakthrough has led Monash researchers to develop a new drag model capable of more accurately predicting particle behaviour under some of the harshest operating conditions encountered in aerospace and defence applications.
Associate Professor Qijun Zheng from Monash University’s Department of Mechanical and Aerospace Engineering and a co-author of the study said the research provides critical new insight into the complex physics occurring inside rocket engines.
“Inside rocket motors, these nanoparticles are exposed to enormous temperatures, pressures and speeds,” Zheng said.
“Our simulations show that once particles reach hypersonic velocities, they can rapidly heat up, melt and dramatically change shape while moving through the airflow.”
The research focused on microscopic alumina particles produced when aluminium fuel burns inside solid rocket motors. Despite being thousands of times smaller than the width of a human hair, these particles can travel through rocket nozzles at speeds approaching 10 kilometres per second.
Using advanced molecular dynamics simulations, which model interactions at the atomic level, the Monash-led team examined how individual nanoparticles respond to the extreme temperatures and pressures found inside rocket propulsion systems.
The simulations revealed a clear distinction between particles travelling at lower and higher speeds. Slower particles remained relatively stable, while those moving at hypersonic velocities experienced intense collisions with surrounding air molecules, causing them to heat rapidly and melt during flight.
Researchers also found that smaller particles reached higher temperatures more quickly because a greater proportion of their surface area was exposed to the surrounding environment.
Perhaps most surprisingly, the team observed molten particles stretching into thin, bag-like structures before collapsing and reforming into entirely new shapes as they travelled through the airflow.
According to Zheng, these transformations have important consequences for understanding how rocket systems perform under extreme conditions.
“These changing particle shapes affect how heat and energy move through the flow, which is important for predicting wear and performance inside rocket systems,” he said.
“Current engineering models often assume particles remain perfectly spherical, but our work shows that assumption no longer holds under these extreme conditions.”
The study also demonstrated that molten particles interact more strongly with the surrounding airflow than solid particles, creating larger regions of turbulence and energy transfer that can influence engine performance and material degradation.
Zheng said the new modelling approach could help engineers develop more reliable propulsion systems, improve predictions of material wear and enhance the design of future high-speed aerospace technologies.
“Understanding how these particles behave under extreme conditions is essential for improving the accuracy of future aerospace simulations and developing more resilient high-speed technologies,” he said.
While the research has immediate relevance to rocket propulsion, the findings could also benefit a range of other applications, including atmospheric re-entry systems, advanced energy technologies and industrial processes involving nanoparticles exposed to extreme temperatures.
The study was conducted by researchers from the Southeast University–Monash University Joint Research Institute, Monash University and Shanghai University, highlighting Monash’s growing role in advancing cutting-edge aerospace research and hypersonic science.
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