Keita Receives Best Presentation Award

We are pleased to share that Mr. Keita Okano, a master’s student at the University of Tsukuba, has been recognized at the Multiphase Flow Symposium 2025, held at Kobe University from September 3–5, 2026. His presentation received both the:

• Best Presentation Award
• The Beauty of Multiphase Flow Award (awarded to only one presentation out of 117)
  

Presentation Title

“Rotational and mixing dynamics of an acoustically levitated droplet using phased array”

Authors:

• Keita Okano (University of Tsukuba, Graduate School)
• Akiko Kaneko (University of Tsukuba)
• Tatsuki Fushimi (University of Tsukuba)
• Asier Marzo (Public University of Navarra)

Mr. Okano conducted part of this collaborative research during his stay in Spain with Dr. Asier Marzo as part of the AsPIRE program.

About the Research

The study investigates how orbital angular momentum (OAM) can be used to enhance mixing inside acoustically levitated droplets. Acoustic levitation makes it possible to handle droplets without a container, avoiding contamination and wall effects, which is valuable for applications in chemistry and materials processing. However, efficient droplet mixing remains a challenge for practical use.

To address this, the team developed a phased array acoustic levitation system capable of switching between standing wave and vortex fields at high speed. This setup allowed droplets to remain levitated while simultaneously being rotated. High-speed imaging and Particle Image Velocimetry (PIV) were used to visualize the internal flow of the droplets, with tracer particles illuminated by a laser sheet.

The experiments showed that imposing OAM led to rotational motion, surface vibrations, and increasingly complex droplet deformations. Using the finite-time Lyapunov exponent (FTLE), the researchers confirmed that chaotic internal flow structures developed, indicating stronger mixing compared to conventional methods.

The results suggest that combining rotation and vibration is an effective approach for achieving high-efficiency internal mixing in levitated droplets, contributing to the advancement of container-less fluid processing technologies.