Exploration of Acoustic Trap Stability Limit at Sub-Atmospheric Pressures and Reduced Temperatures

Micrometer-sized chain aggregates of atmospheric ice crystals are commonly observed in high-altitude clouds. They attach to each other in different orientations, producing varied geometries, yet their formation mechanisms remain poorly understood. Recent aircraft field campaigns have captured 2D images of these intricate ice structures, revealing large, chain-like aggregates. These ice crystals pose significant risks to hypersonic flight through the atmosphere, including re-entry vehicles, missiles, or jet aircraft, by causing structural damage. Despite this, their behavior under shock wave conditions remains underexplored due to lack of laboratory techniques capable of producing atmospherically realistic ice in controlled conditions. To explore realistic atmospheric ice crystals’ thermodynamic and mechanical changes in hypersonic environments, we investigate the formation and behavior of ice crystal aggregates using levitation methods that avoid physical contact and better replicate freezing processes in clouds. We recently successfully demonstrated the generation of atmospheric ice crystals using two levitation devices: An acoustic levitator and an electrodynamic balance. In this work, we explore acoustic levitation at sub-zero temperatures (down to -30 ℃) and sub-atmosphere pressures (down to 0.4 atm), paving the way for future shock interaction experiments. The long-term experimental objective is to integrate acoustic levitation with high-speed flow facilities, such as shock tubes. By matching the lowest pressure regime of the acoustic levitator with the driven section of a shock tube, we aim to overcome a key technical barrier to studying ice crystal-shockwave interactions under realistic atmospheric conditions.