Invited Lecturers

Plenary Lecturers

• Dr. Tetsuro Tsuji, Graduate School of Informatics, Kyoto University, Japan

Tetsuro Tsuji received his Ph.D. degree from the Department of Mechanical Engineering and Science at Kyoto University, Japan, in 2013. After obtaining his Ph.D., he became an Assistant Professor at the Graduate School of Engineering Science, Osaka University. In 2019, he was appointed Assistant Professor at the Graduate School of Informatics, Kyoto University. Since 2021, he has been an Associate Professor in the same department.

His current research areas include molecular fluid dynamics, rarefied gas dynamics, and microfluidics. From the beginning of his career, he has worked on numerical analysis and theoretical modeling of non-equilibrium gaseous systems. More recently, he has also focused on microfluidic and optofluidic experiments. In particular, thermally induced microflows and microparticle motion, as well as their interconnection, are among the main topics of his recent publications.

 Title of the Plenary Lecture: Thermally-induced flows in microfluidic systems: from optothermal fluidic experiments to non-equilibrium gaseous modeling

In this talk, some recent experimental and theoretical studies on thermally-induced microflows will be introduced. In the experimental part, we focus on thermophoresis, namely, a microparticle motion along a temperature gradient in fluids. Using an optothermal microfluidic system combined with optical trapping, thermally-induced flows around microparticles are detected, and the connection between the thermally-induced flows and the thermophoresis is discussed [1]. Optothermal microfluidic systems are found to be effective, feasible, and convenient experimental setup to investigate thermal microflows, and thus a semianalytical model has been developed recently [2]. In the modeling part, a kinetic model on thermally-induced non-equilibrium gas flows will be introduced. The model is shown to reproduce the sign reversal of the thermal slip coefficients according to gas-surface interaction, regardless of its simplicity [3]. These outcomes on thermally-induced microflows are expected to contribute to the development of novel microfluidic functions such as separation and concentration.
[1]    T. Tsuji, S. Mei, and S. Taguchi, “Thermo-osmotic slip flows around a thermophoretic microparticle characterized by optical trapping of tracers,” Physical Review Applied 20, 054061 (2023)
[2]    T. Tsuji, S. Saito, and S. Taguchi, “Semianalytical model of optothermal fluidics in a confinement,” Physical Review Fluids 9, 124202 (2024)
[3]    T. Tsuji, K. Takita, and S. Taguchi, in preparation

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• Dr. Benjamin Schafer, John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, and Rarefied Technologies, Albuquerque, NM, USA

Ben Schafer is the CEO and Co-Founder of Rarefied Technologies and an Associate Researcher at the Harvard University John A. Paulson School of Engineering and Applied Sciences. Rarefied Technologies is a startup based in Albuquerque, New Mexico, USA, dedicated to developing photophoretic levitation for near-space flight.

Ben's research focuses on innovative designs for photophoretically flying structures, the experimental fabrication and testing of flying devices, and the application of this technology to address challenges in climate science, atmospheric sensing, and telecommunications. He is a Breakthrough Energy Fellow and was recognized in Forbes 30 Under 30 as a leader in climate-focused technology. He received his Ph.D. in Applied Physics from Harvard University in 2024.

 Title of the Plenary Lecture: Photophoretic levitation: from aerosols to aircraft

Photophoresis, or light-driven motion, of aerosols in Earth’s upper atmosphere has been studied since the 1960s. When sunlight warms an aerosol particle surrounded by rarefied gas, an asymmetry in the temperature or accommodation coefficient on the aerosol’s surface creates a photophoretic force on the aerosol, allowing it to levitate. With recent advancements in nanofabrication, could we build engineered devices that are bigger than aerosols, yet lightweight enough to fly on their own? Using aerosols as a starting point, I will discuss advancements in the field of photophoretic levitation, which include holographic displays, particle traps, and macroscopic platforms for near-space flight. The promise of photophoretic aircraft for atmospheric sensing, telecommunications, and Martian exploration has spurred new research into ultra-lightweight 2D materials that generate photophoretic gas flows.

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• Pr Thierry Magin, Université Libre de Bruxelles, von Karman Institute for Fluid Dynamics, Belgium

Thierry Magin is a professor at the Université Libre de Bruxelles (ULB) and the von Karman Institute for Fluid Dynamics (VKI). He earned his PhD from ULB and VKI in 2004. Following his doctorate, he spent two years at École Centrale Paris, where he investigated nonequilibrium radiation for the Huygens mission. He then joined Stanford and NASA for three years, contributing to the development of aerothermodynamic models for the Orion spacecraft. In 2010, he established a research team at VKI with support of the European Research Council, focusing on multiscale and multiphysics models and computational methods for reacting and plasma flows. Prof. Magin’s research interests are related to hypersonics and very low Earth orbit applications. Together with his team, they study both fundamental principles and aerospace technology, in collaboration with space agencies, defense organizations, and industry partners.

 Title of the Plenary Lecture: Aerothermochemistry, coupling fluid mechanics and physical chemistry to simulate aerospace flows

Modeling and simulating hypersonic flows present significant challenges, many of which arise from the field of aerothermochemistry, a multidisciplinary domain coined by von Kármán, that integrates fluid mechanics, thermodynamics, and physical chemistry. Accurate modeling of gas-surface interactions, such as the ablation of thermal protection materials, is critical in simulating heat shields for atmospheric entry spacecraft. Another key application is the prediction of electron concentrations in the plasma sheath surrounding hypersonic vehicles, which affects electromagnetic wave propagation. Beyond spacecraft reentry, aerothermochemistry plays a key role in analyzing meteor phenomena, the demise of artificial space debris, and the aerodynamics of space platforms operating in very low Earth orbit (below 150 km), where rarefied gas dynamics dominate. This presentation reviews the physico-chemical models and computational methods used to simulate reacting and plasma flows in this aerospace context. We explore non-equilibrium gas dynamics across both continuum and rarefied regimes, focusing on the coupling of chemical mechanisms with fluid and kinetic equations. Accurate multiphysics simulations demand rigorous model validation and calibration, often using uncertainty quantification techniques informed by experimental data obtained in ground-based facilities and in-flight. We will illustrate these concepts with two examples: (1) high-order computational fluid dynamics simulations of atmospheric entry flows, accounting for the thermal protection system's material response; and (2) stochastic particle simulations of rarefied flows in a low-density test facility designed for air-breathing electric propulsion systems.