publications
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AIP Publishing – Physics of Fluids, Kiss et al., 2026
Bridging shallow flow theory and microfluidics: The role of confinement in shaping wake lengths and pressure loss
Flow past obstacle clusters in micro-channels is central to a wide range of microfluidic applications, yet its fundamental hydrodynamics remain poorly understood under strong geometric confinement.
No-slip boundary conditions on all walls enforce inherently three-dimensional (3D) flow structures in fully confined micro-channels, fundamentally altering wake formation, momentum transport, and drag mechanisms. A combined experimental and numerical investigation of wake dynamics behind obstacle clusters in laminar micro-channel flows is presented. High-resolution micro-particle image velocimetry and resolved 3D computational fluid dynamics simulations are employed to systematically explore the effects of Reynolds number and cluster porosity. We demonstrate that full wall confinement suppresses classical wake–regime transitions commonly observed in shallow and unconfined flows, including shear layer instabilities and vortex shedding. Instead, wake recovery is governed primarily by secondary flows that promote rapid momentum redistribution across the channel depth. As a result, wake length exhibits only weak dependence on Reynolds number and is controlled predominantly by cluster porosity. We further introduce the relative bleeding velocity as a unifying metric to characterize the transition from macro-particle to individual particle behavior. The relative bleeding velocity is the ratio of the mean velocity through the cluster’s main axis perpendicular to the inflow and the mean inflow velocity. These findings establish a distinct physical regime of confined wake flows, bridging the gap between classical shallow flow theory and microfluidic hydrodynamics, and provide a foundation for improved prediction of pressure losses, transport, and mixing in micro-reactors and porous microfluidic systems.
Fully Additively Manufactured Wetted Foam Capsules for Inertial Confinement Fusion
In the pursuit of realizing reliable clean energy generation via inertial confinement fusion (ICF), wetted foam (WF) capsule targets have long been coveted due to their potential to simplify the target fielding process and suppress hydrodynamic instabilities and material mixing that limit achievable energy output, yet producing and deploying a WF target has proven challenging. In this work, we demonstrate the design, fabrication, metrology, and testing of fully additively manufactured (AM) foam-lined capsules using two-photon polymerization (2PP) for ICF. We successfully fielded an AM polymeric foam capsule with a 3-mm outer diameter, a nominally 15-µm-thick solid outer layer, a 120-µm-thick inner foam layer, and a 250-µm outer diameter copper fill tube on the National Ignition Facility for a polar direct-drive shot, and we showcase deuterium wetting of the capsule foam layer inside an ignition target proofing station. Our exploration showed that 2PP can produce fieldable targets with complex geometries and potentially shorten the design iteration turnaround time and the overall target fabrication time.
Probing ultrafast foam homogenization with grating-based X-ray dark-field imaging
Microstructured foams are emerging as a promising class of targets, with applications ranging from laser-driven particle acceleration to inertial confinement fusion. To unlock their full potential, a deeper understanding of their properties, especially the changes and behavior of the microstructure under extreme conditions, is required. While recently advancing 3D printed foam targets can be observed by X-ray radiography, the microstructure in chemically produced targets is far below the spatial resolution of conventional radiography. To overcome this limitation, we apply grating-based X-ray dark-field imaging to observe structural changes in foams that are rapidly heated by laser-accelerated proton pulses. The experimental data is compared to synthetic dark-field values obtained from hydrodynamic simulations of a simplified foam model. Both experimental and simulation results demonstrate the viability of utilizing grating-based dark-field imaging for observing microstructural changes in foam targets.
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