arXiv subjects

Chien-chia Liu

Publications and source records attributed to Chien-chia Liu.

4 recordsLinked to original sources

arXiv2026

Unified Hydrodynamic Analogue of Aharonov-Bohm and Lense-Thirring Effects

We show that surface waves in a draining-bathtub vortex provide a hydrodynamic realization of both Aharonov-Bohm phase shifts and Lense-Thirring frame dragging within a single system. A static time transformation maps the flat (2+1)-dimensional wave equation onto the convected shallow-water equation, yielding an effective vector potential set by the background flow. In this geometry, the circulation defines a global phase holonomy that controls wave structure. Traveling waves exhibit wavefront dislocations characteristic of Aharonov-Bohm scattering, while standing-wave superpositions produce nodal patterns that rotate at an angular velocity fixed by the circulation, providing a direct analogue of frame dragging. For noninteger circulation, the problem is naturally defined on the universal cover, ensuring single-valued partial-wave solutions. Experiments on a controlled vortex confirm these predictions and establish a laboratory platform in which topological phase and inertial effects, central to gauge and gravitational physics, emerge from a measurable velocity field.

physics.flu-dyn↗

arXiv2017

Generating the Log Law of the Wall with Superposition of Standing Waves

Turbulence remains an unsolved multidisciplinary science problem. As one of the most well-known examples in turbulent flows, knowledge of the logarithmic mean velocity profile (MVP), so called the log law of the wall, plays an important role everywhere turbulent flow meets the solid wall, such as fluids in any kind of channels, skin friction of all types of transportations, the atmospheric wind on a planetary ground, and the oceanic current on the seabed. However, the mechanism of how this log-law MVP is formed under the multiscale nature of turbulent shears remains one of the greatest interests of turbulence puzzles. To untangle the multiscale coupling of turbulent shear stresses, we explore for a known fundamental tool in physics. Here we present how to reproduce the log-law MVP with the even harmonic modes of fixed-end standing waves. We find that when these harmonic waves of same magnitude are considered as the multiscale turbulent shear stresses, the wave envelope of their superposition simulates the mean shear stress profile of the wall-bounded flow. It implies that the log-law MVP is not expectedly related to the turbulent scales in the inertial subrange associated with the Kolmogorov energy cascade, revealing the dissipative nature of all scales involved. The MVP with reduced harmonic modes also shows promising connection to the understanding of flow transition to turbulence. The finding here suggests the simple harmonic waves as good agents to help unravel the complex turbulent dynamics in wall-bounded flow.

physics.flu-dyn↗

arXiv2017

Hidden Order behind Two Dimensional Random Vortices

The vortices that appear repeatedly and suggest turbulent dynamics are crucial to the understanding of sheared turbulence. These vortices produce order out of chaos, benefiting the turbulence modelling that focuses only on statistically stable quantities. In three dimensions, the hairpin vortices [J. Zhou, R. Adrian, S. Balachandar, T. Kendall, J. Fluid Mech., 387, 353 (1999); R. Adrian, Phys. Fluids, 19, 041301 (2007)] play such a fundamental role in the transport of momentum and energy for wall bounded sheared turbulence. In two dimensions where the atmospheric flow has a great play, the fundamental vortices have yet to be observed. Here we report the experimental finding of the slanted vortices in the quasi-two-dimensional sheared soap-film turbulence. We also demonstrate how these slanted fundamental vortices, which result from the interaction between the sheared mean flow and the random turbulent vortices, could possibly connect to the turbulent transport. The finding here might introduce another means of understanding the planetary turbulence where the mean flow is commonly existent and nonuniform.

nlin.AO↗

arXiv2017

Kolmogorovian turbulence in transitional pipe flows

As everyone knows who has opened a kitchen faucet, pipe flow is laminar at low flow velocities and turbulent at high flow velocities. At intermediate velocities there is a transition wherein plugs of laminar flow alternate along the pipe with "flashes" of a type of fluctuating, non-laminar flow which remains poorly known. We show experimentally that the fluid friction of flash flow is diagnostic of turbulence. We also show that the statistics of flash flow are in keeping with Kolmogorov's phenomenological theory of turbulence (so that, e.g., the energy spectra of both flash flow and turbulent flow satisfy small-scale universality). We conclude that transitional pipe flows are two- phase flows in which one phase is laminar and the other, carried by flashes, is turbulent in the sense of Kolmogorov.

physics.flu-dyn↗