Cavitation bubbles generated by focused ultrasound can mechanically destroy tissues, as in histotripsy, where tissue damage scales with maximum bubble size. We extend an energy budget analysis to include viscoelastic and compressibility effects and derive an analytical expression for the maximum radius of a spherical bubble. The maximum radius decreases with increasing shear modulus but increases with pulse amplitude and wavelength. Our model accurately predicts the maximum radius under explosive growth conditions, established from pulse amplitude and frequency. These findings clarify the physics governing bubble growth and may inform the design of ultrasound-based therapies.

The inertial layer is a cornerstone of wall-turbulence theory and is characterized by a balance dominated by Reynolds shear stress. Using direct numerical simulation of turbulent channel flow at Re${}_{\tau }\approx 16000$, we identify a wall-normal region where the Reynolds shear stress approaches its expected constant value and where additional inertial-layer predictions for velocity fluctuations and dissipation are simultaneously satisfied. These observations provide strong evidence for the emergence of inertial-layer dynamics at this Reynolds number.

The free surface of thin film of a yield stress fluid has been shown to develop undulations when subject to uniaxial compression. In this paper, using a novel experimental setup, we characterize this surface instability for the first time. We show that the amplitude of the undulations depends linearly on the Bingham number, the non-dimensional yield stress, whereas the wavelength scales with the initial thickness of the compressed layer. These experiments enhance our understanding of surface instabilities in related systems, such as recent experimental work scraping a thin layer of a viscoplastic fluid.

Classical shock-wave theory relies on ideal-gas assumptions that fail in dense and supercritical fluid regimes. By coupling the Navier–Stokes equations with a real-fluid thermophysical model for supercritical CO${}_2$, this study resolves the internal spatial structure and non-ideal jump relations across shocks. Surprisingly, while non-ideal thermodynamics strongly alters pressure–density jumps, the physical shock thickness remains primarily governed by the upstream Mach number. These results reveal how dense- fluid thermodynamics reshapes compressive discontinuities, defining the limits of classical shock theory.

Conductivity differences can trigger electrokinetic instabilities (EKI) in electrically driven microflows. Building on theories for Newtonian fluids, we propose a scaling analysis that predicts suppression of EKI in viscoelastic fluids through combined viscous and elastic effects, consistent with earlier experiments and simulations. Experiments with hyaluronic acid (a viscoelastic polymer) solutions further show that adding polymer to one stream can suppress EKI more strongly than adding it to both. The findings identify polymer placement as an additional way to control flow stability.

This study presents a systematic investigation of the second-shock induced micro jetting from sinusoidally perturbed tin surfaces using a combined smoothed particle hydrodynamics (SPH) and molecular dynamics (MD) approach. The key contributions of this work are: 1) identification of three distinct bubble morphologies after the first shock, controlled by $k_0{h}_0$; 2) revealing that two dimensional unloading and weak Richtmyer-Meshkov instability at the bubble base drive the morphological transition; 3) development of a novel predictive model for second-shock ejecta mass by treating the post shock interface as a multi mode perturbation and incorporating explicit mode coupling effects.

The classical Graetz-Nusselt framework forms the foundation of laminar forced convection theory, but becomes inaccurate at the nanoscale, where axial conduction, viscous dissipation and interfacial transport grow comparable to bulk convective transport. We extend the generalized Graetz model by incorporating axial conduction, bulk and slip-induced interfacial dissipation, velocity slip, temperature jump, and thermal conductivity anisotropy. A dimensionless resistance ratio Π is introduced that delineates the transition from bulk- to interface-controlled heat transfer. Molecular-scale observations and continuum theory are linked, providing a unified framework for nanoscale thermal transport.

Population-balance models offer a route to connect dispersed vapor bubbles with macroscopic cavitation, but their closures require experimental constraints. Here, point-by-point optical probe measurements reveal self-similar void-fraction and bubble-velocity profiles, yielding an effective Schmidt number for the bubbly/non-bubbly transition. The measurements further show that bubble-size distributions and bubble velocities depend strongly on the local flow region, providing new guidance for region-dependent population-balance closures in cavitating flows.

Collisions between inertial particles in turbulence are often treated as a sequence of uncorrelated events, yet coalescence fundamentally removes particles and their future collision trajectories. We show that the statistical differences between coalescing and noninteracting “ghost” particles can be traced to this finite-time collision memory. By filtering ghost-particle trajectories to remove particles with recent collision histories, we reproduce the collision rates and pair statistics of coalescing systems, revealing coalescence as a form of history filtering in turbulent particle dynamics.

Several problems are related to the behavior of aerosol particles around a porous screen, from fog collectors to the limitation of virus transmission by a facemask. The droplet size distribution in fog or human respiratory flows is wide enough that it can become relevant to consider the inertia of the largest droplets at the scale of the screen. The purpose of this work is thus to propose a model for such an aerodynamic effect and quantify the collection efficiency depending on screen parameters such as its size, solidity, and local Reynolds number at pore scale. The present computation is performed for water droplets around a square textile composed of fibers, providing optimal parameters.

Experiments have shown that subcritical fluid flows can strengthen granular beds in the flow direction, while weakening them in the opposite direction. However, the grain-scale mechanisms for this anisotropy of bed strength remain unclear. Using discrete element method simulations in two and three dimensions, we show that the stress history-dependent anisotropy of bed strength arises primarily from changes in the surface grain positions, which causes variations in the fraction of surface grains that are susceptible to becoming dislodged in different flow directions.

Enstrophy dynamics is investigated in homogeneous isotropic turbulence, revealing the interplay between vortex stretching, diffusion, and interscale transport. Using direct numerical simulations and a two-point statistical framework, the interscale enstrophy transfer is shown to simultaneously transfer longitudinal vorticity increments towards larger scales and transverse vorticity increments towards smaller scales, resulting in a net transfer towards smaller scales. Conditional correlation coefficients are used to provide further insights into the role of pressure in energy and enstrophy interscale transport events.

Rheoscopic flow visualization is widely used to study turbulent decay in wall-bounded flows, although the physical interpretation of the measured decay times has received less attention. By comparing rheoscopic visualization with particle image velocimetry in plane Couette–Poiseuille flow, we show that the measured decay times are closely associated with the slower decay of streamwise streaks rather than the faster decay of vortical rolls. These findings improve our understanding of rheoscopic measurements in transition to turbulence in plane shear flows.

Prior work has established frequency lock-in in cylinder wakes under streamwise oscillatory forcing, but how wall proximity affects three-dimensional mode competition remains unclear. Three-dimensional simulations at Re${}_D$ = 500 reveal distinct desynchronized and locked-in regimes, including a torsional A mode, localized switching between A and S modes, and a single-row vortex street under strong confinement. Higher forcing frequencies suppress spanwise instabilities and promote a nearly two-dimensional wake. These findings demonstrate that gap ratios and forcing frequency jointly control near-wall wake topology and three-dimensional stability.

In turbulent flows energy cascades, on average, from large scales to small, yet locally it sometimes flows backward—”backscatter”—a stubborn complication for subgrid models. Using high-resolution direct numerical simulations from the Johns Hopkins database at three Reynolds numbers, we show that the probability of local backscatter is suppressed as the local dissipation rises, following a single scale-invariant law. The measured suppression matches the form predicted by a coherence-based closure, with a steepness that stays well below the naive slope. The result turns a qualitative intuition into a directly tested, quantitative rule.

In the late 1970s, J.S. and S.E. Tsakadze carefully monitored the long-term spin down of a vessel containing superfluid helium initially set into rotation. They occasionally observed short spontaneous spin-up events followed by relaxation. These strange events are still a mystery, but it is thought that they are due to the quantum nature of the rotating superfluid (the presence of quantized vortex lines). If so, Tsakadzes’ experiments shed light onto another mystery: the observed glitches of the rotation of neutron stars. We revisit Tsakadzes’ experiments and discuss them in view of the current understanding of quantized vortex lines and quantum turbulence.

Can a floating ring protect offshore structures from impactful ocean waves? This study presents how a floating annular viscoelastic plate can significantly reduce wave-induced forces and wave run up on a vertical cylinder by combining elastic deformation with viscous energy dissipation. The results reveal that tuning the plate’s flexibility and damping can provide appreciable protection to the central structure. These findings provide a promising passive strategy for enhancing the resilience of offshore structures.

We report on a suite of direct numerical simulations of rotating plumes interacting with a pre-existing density interface. For an experimentally realizable range of rotation rates and buoyancy source sizes we find evidence of long-lived plumes that bifurcate from the source region and twist around each other as they descend. These plumes are a novel example of coherent structure formation at intermediate Reynolds number.

Data-driven closure modeling of transport systems is limited by the difficulty of generating diverse training data. We develop the Generalized Forcing Method, which uses prescribed forcings to excite the dynamics in the reduced space while preserving the target closure relation. Applications to linear transport problems, from shear dispersion to passive-scalar transport in homogeneous isotropic turbulence, demonstrate that the framework can identify accurate and stable reduced models.