arXiv subjects

Chris Roh

Publications and source records attributed to Chris Roh.

4 recordsLinked to original sources

arXiv2026

A bent straw as a tool for an affordable student-safe experiment in vortex ring dynamics

Vortex dynamics are an important topic in fluid dynamics, explaining phenomena like drag and lift generation, jet propulsion, and corner flows. It is also often excluded from introductory or undergraduate fluid dynamics courses on account of its complexity and the inaccessibility of practical and engaging experiments. We present an affordable student-safe experiment to generate vortex rings and study their dynamics using a bent straw and dyed water that allows students to control key parameters, can be imaged using a smartphone camera, and explains the complex physics with simple and easily measured parameters. Vortex rings are produced that parallel seminal experiments, demonstrating secondary structures and the mirroring effect. Meanwhile, nonplanar and triangular jet exits are used to demonstrate asymmetric vortex rings and vortex ring inversion.

physics.flu-dyn↗

arXiv2026

Multi-pathline flow visualization using PIV images

One of the oldest flow visualization techniques is through multiple pathlines generated by the movement of seeding particles spatially distributed in the flow. In the computerized era, particle images are used in quantitative measurements, such as particle image and particle tracking velocimetry (PIV and PTV). Here, we present several methods for post-processing raw particle images to generate enhanced flow visualization without a need for conducting additional experiments. Three post-processing methods will be shown: 1) controlling the exposure time, 2) color-coding temporal information, and 3) changing the frame of reference. We showcase how employing these three methods can highlight different flow features in three canonical flow cases: vortex ring, leading edge vortex, and turbulent boundary layer. In addition to the quantitative flow field, the multi-pathline visualization is expected to augment our ability to observe fluid flow from many different perspectives.

physics.flu-dyn↗

arXiv2026

Scattering of Capillary Waves By a Cylindrical Meniscus

The propagation of water waves is altered when interacting with curved surfaces. Here, we consider the problem of capillary waves interacting with a 3D cylindrical meniscus. We show that when capillary waves scatter off an object surrounded by a meniscus, the resulting wavefield can be drastically altered by refraction to increase wave presence in the otherwise shadowed region behind a cylinder. This indicates that a meniscus acts as an effective coating around an object, slowing down the wave's propagation speed in its region of influence. Our results are not only an important step in surface tension dominated wave interactions, but may have implications in the biological communication of surface dwelling animals.

physics.flu-dyn↗

arXiv2023

Optimal free-surface pumping by an undulating carpet

Examples of fluid flows driven by undulating boundaries are found in nature across many different length scales. Even though different driving mechanisms have evolved in distinct environments, they perform essentially the same function: directional transport of liquid. Nature-inspired strategies have been adopted in engineered devices to manipulate and direct flow. Here, we demonstrate how an undulating boundary generates large-scale pumping of a thin liquid near the liquid-air interface. Two dimensional traveling waves on the undulator, a canonical strategy to transport fluid at low Reynolds numbers, surprisingly lead to flow rates that depend non-monotonically on the wave speed. Through an asymptotic analysis of the thin-film equations that account for gravity and surface tension, we predict the observed optimal speed that maximizes pumping. Our findings reveal a novel mode of pumping with less energy dissipation near a free surface compared to a rigid boundary.

physics.flu-dyn↗