Journal of Fluid Mechanics

Zonal winds on Jovian planets play an important role in governing the cloud dynamics, transport of momentum, scalars and weather patterns. Therefore, it is crucial to understand the evolution of zonal flows and their sustainability. Based on studies in two-dimensional $\beta$ -plane set-ups, zonal flow is believed to be forced at the intermediate scale via baroclinic instabilities, and the invers…

Non-equilibrium evaporative flows play a central role in many nanoporous membrane technologies, where transport of fluids is confined by solid surfaces at the nanoscale. In this work, we propose a molecular kinetic model that consistently resolves the coupled interactions among vapour, liquid and solid surfaces in such flows. As a direct consequence of this bottom-up approach, the liquid–vapour, …

Traditional Reynolds-averaged Navier–Stokes (RANS) closures, based on the Boussinesq eddy-viscosity hypothesis and calibrated on canonical flows, often yield inaccurate predictions of both mean flow and turbulence statistics. Here, we consider flow past a circular cylinder over a range of Reynolds numbers ( $3900$ – $100\,000$ ) and Mach numbers ( $0$ – $0.3$ ), encompassing incompressible and we…

Velocity measurement techniques, such as particle image velocimetry (PIV), face a trade-off between field of view, spatial resolution and sampling rate, so that small-scale vortices, shear layers and high-frequency turbulent motions are often under-resolved. Most physics-informed reconstructions use a velocity–pressure formulation, even though pressure is not measured in typical PIV experiments, …

The explosive dispersal of granular media, exemplified by the rapid radial expansion of a dense particle ring driven by internal pressurised gases, serves as a paradigmatic system for investigating multiphase blast dynamics. Despite the ubiquity of jetting and clustering phenomena in explosive dispersal scenarios, their governing mechanisms remain poorly resolved. In this work, we combine compres…

The hypersonic flow over 30 $^{\circ }$ –50 $^{\circ }$ double-cone configurations with three nose bluntness levels was experimentally investigated at Mach 6. High-speed schlieren photography, pressure sensors and pressure-sensitive paint were used to examine both global flow patterns and unsteady dynamics at a transitional Reynolds number. The experimental results indicate that the size of the s…

This study examines the cross-flow vortex-induced vibration (VIV) of a circular cylinder in combined current–oscillatory inflows, revealing a distinct multi-frequency response characterised by beat-like modulation. Systematic water-channel experiments were conducted across a range of reduced velocities, inflow oscillation intensities and frequency ratios to investigate the synchronisation mechani…

The interaction of a pair of unequal strength counter-rotating vortices is examined using a variety of visualization methods, including volumetric particle image velocimetry. Developed vortex cavitation in the cores of the vortices is also used to characterize the interaction of the initially parallel vortices. A pair of hydrofoils was used to generate two nearly parallel vortices with varying at…

The influence of hydrodynamic interactions on the schooling behaviour of fish is still poorly understood. This paper numerically investigates the collective motion of two parallel fish that move freely in both the longitudinal and lateral directions, focusing on the effects of wavelength and phase difference on their stable formations, swimming speed and energy efficiency. It is found that two pa…

The effectiveness of ultrasonic absorptive coatings (UACs) in achieving delay in turbulent transition on a hypersonic boundary layer over a 3 $^\circ$ half-angle cone was investigated under flight-like free-stream disturbance conditions. Tests were conducted at the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University for four free-stream Reynolds numbers ranging from $9.0\times 10^6\,$ to $14.3 …

A joint experimental–computational investigation was conducted to examine the aerodynamic behaviour of a partially closed cavity model in Mach-6 flow. The model, consisting of a flat plate with a rectangular cavity and a forward-facing hinged door, resulted in a strong 500 Hz fluctuation with a 7.5 $^\circ$ door and 25 mm cavity depth. The experiments revealed a recirculation bubble present upstr…

A theoretical study is made of steady, subcritical (Froude number $F \lt 1$ ) two-dimensional free-surface flow due to a uniform stream flowing over smooth, locally confined bottom topography of large horizontal extent ( $L \gg 1$ ) and finite peak height ( $\varepsilon = O(1)$ ). In earlier work, this flow was analysed based on the nonlinear shallow-water equations which neglect the effects of d…

An important category of microscale fluid–structure interactions concerns how flexible fibres deform and interact with flows. Many experimental and numerical studies have focused on the shape dynamics of fibres in linear shear flows. Here, instead, we consider a fully three-dimensional background flow with non-constant vorticity and study the shape evolution of fibres in a zero-Reynolds-number an…

Systematic deflection of microparticles off of initial streamlines is a fundamental task in microfluidics, aiming at applications including sorting, accumulation or capture of the transported particles. In a large class of set-ups, including deterministic lateral displacement and porous media filtering, particles in non-inertial (Stokes) flows are deflected by an array of obstacles. We show that …

Motivated by applications to underwater explosions and volcanic eruptions, this paper considers the evolution of an initial pressure disturbance in the ocean, including effects due to the dynamic and static compression of water and the free surface. In order to solve the equations of motion of a linear compressible ocean, a special inner product is introduced, which allows us to apply self-adjoin…

This paper examines two-dimensional liquid curtains ejected from a narrow horizontal outlet at an angle to the vertical. Curtains are characterised by the Froude number ${\textit{Fr}}=U/ ( gH ) ^{1/2}$ , Reynolds number ${\textit{Re}}=UH/\nu$ and Weber number ${\textit{We}}=\rho U^{2}H/\sigma$ , where $U$ is the ejection velocity, $g$ the gravity, $H$ the outlet’s half-width, $\nu$ the kinematic …

Richtmyer–Meshkov instability (RMI) at a single-mode interface separating an inert gas (N $_2$ ) and a reactive gas mixture (H $_2$ /O $_2$ /Xe) under reshock conditions is numerically investigated using a newly developed compressible reactive Navier–Stokes solver. The solver employs the Kéromnès mechanism (10 species, 21 reactions) for combustion modelling and a dual-flux algorithm to suppress n…

The forward leaning inclination angle, $\gamma$ , of coherent turbulent structures is a well-known feature of wall-bounded turbulent flows. Although invariant across friction Reynolds numbers within the range $\textit{Re}_\tau =10^3{-}10^6$ , $\gamma$ can vary significantly across turbulent scales within a high-Reynolds-number flow. Very-large-scale motions (VLSMs) are known to induce significant…

In this paper, the evaporation of neighbouring multi-component droplets or rivulets – often found in applications such as inkjet printing, spray cooling and pesticide delivery – is studied numerically and theoretically. The proximity induces a shielding effect that reduces individual evaporation rates and disrupts the symmetry of both the concentration profile and the flow field in the liquids. W…