Suspensions of rotating particles near a floor can generate different types of density waves. Freely propagating waves and traveling fronts are observed and studied, and it is shown that the nonlocal nature of hydrodynamic interactions is responsible for the dispersive behavior of the system.

An integral analysis of the boundary layer equations under adverse pressure gradients finds estimates for the skin friction and mean wall-normal velocity in terms of the Rotta-Clauser parameter. These estimates are compared with experimental and numerical data even under nonequilibrium conditions.

Hysteretic transitions between statistically steady turbulent flows, quasi-two-dimensional flow, and three-dimensional flow, is found in forced rotating turbulence. It stems from the robustness of a large-scale columnar cyclonic vortex.

Numerical simulations of compressible two-dimensional turbulence find direct and inverse energy cascades involving vortices and waves.

Some bacteria enter mucus layers protecting epithelial cells by chemically changing the mucus rheological properties from a high-viscosity gel to a low-viscosity solution in which it may self-propel. An analytical two-fluid model is presented for this process of swimming in self-generated confinement.

A coarse-grained theory quickly and accurately estimates the cross-flow transport of red blood cells and platelets in pressure-driven channel flow. The deformability-induced cell migration and shear-induced diffusion are the keys to understanding blood suspensions at low Reynolds number.

Jammed suspensions of soft particles are shown to form crystalline or ordered structures depending on shear flow and suspension polydispersity, as in a state diagram. The disordered suspension to ordered structure transition is shear activated. Induction time depends on flow condition and material properties.

Starting with Doi-Onsager kinetic theory, an active nematic ”$Q$-tensor” model is built from the bottom up for suspensions of immotile, but mobile, particles exerting active extensile dipolar stresses on the fluid. The model exhibits collective dynamics and active flows, especially in confined domains.

Simple shear rheology of two-dimensional foam is investigated using the DySMaL model. Low shear rate results are consistent with existing data but at high shear rates the model range of applicability in the context of foams is reached with interesting consequences.

The impact of gas rarefaction on the acoustic field of a pulsating cylinder is studied for all Knudsen numbers. The continuum-limit far field exhibits thermoviscous exponential decay. Stronger attenuation occurs in the ballistic limit because of curvature-related geometric reduction of the affected layer.

We study doubly diffusive convection in a vertical slot when temperature and solute gradients balance and a stationary conduction state is present. A variety of disconnected spatially localized traveling states (both stable and unstable) are found and a procedure for locating them is described.

Shock wave emission is an important damaging event associated with cavitation. Simultaneous high-speed imaging and hydrophone measurements are combined to capture the multiple shock waves from nonspherically collapsing cavitation bubbles, and models are developed to predict their strengths.

The effect of a uniform electric field on shear rheology of a dilute emulsion comprised of Newtonian droplets is studied analytically. Non-Newtonian behavior is found for the dilute emulsion, such as shear-rate-dependent effective viscosity and nonzero first and second normal stress differences.

By modeling a drop as an octahedron whose vertices are connected by springs, a simple, efficient, physically accurate description of drop dynamics is presented. This model is applied to drops oscillating freely and to drops bouncing on solid or liquid surfaces.

In water electrolysis, a shear flow can be induced by magnetic fields. We study its effect on the dynamics of growing hydrogen bubbles. The hydrodynamic forces facilitating the bubble detachment and further observations on coalescence and Marangoni convection are discussed.

A model shows that equilibrium electroconvective instability is possible at a perfectly charge-selective solid with finite electrical conductivity. The transition to instability is supercritical, as opposed to the subcritical transition for the previously studied nonequilibrium instability.

Response to nonlinearities of instability waves traveling within subsonic turbulent jets is investigated downstream of the end of the potential core. The close match with a simplified model of the Orr mechanism suggests that a nonmodal growth of disturbances occurs in that region of the jet.

The Hadley circulation has been widely studied because of its involvement in various natural and industrial situations. In this work, we examine the effect of the Coriolis force on this type of flow. A basic flow is derived to include the rotation and then its linear stability is presented.

The leveling of a thin liquid film on a soft substrate represents an original example of elastocapillarity that is not mediated by the presence of a contact line. Experiments and theory show departures from the classical self-similarities observed for capillary leveling on rigid substrates.

The effect of topography on $\mu$-droplet spread is studied. Spreading is enhanced (hindered) with a positive (negative) topography gradient ahead of the contact line. A simple model combining quasistatic surface tension effects with a dynamic spreading law predicts the evolving morphology of the droplet.

Motivated by the need for understanding the boiling processes in three-phase microscopic systems, an experimental study aims to uncover the physics of forced dewetting of a soap film initially attached to a metal wire frame, which is heated impulsively.

Surface tension drives a liquid film lining a cylindrical tube to form annular collars or occlusive plugs, which can resist axial displacement under an imposed force when the tube wall is rough. The probability of displacement under a given force in a tube of given length is determined.

Results from a 2D numerical model of liquid-film flow on a rotating elliptical cylinder reveal that large variations in substrate curvature lead to strong capillary flows. With a suitably chosen time-dependent rotation rate, more liquid can be supported relative to the constant-rotation-rate case.

An analytical solution of the dynamics of an imbibition front (air displaced by oil) in a narrow channel with gap-thickness modulations can be obtained for persistent gap modulation in the direction of front advancement. It is in very good agreement with observed steady-state front morphologies.

Can a corrugated channel affect the entrapment of oil when it is displaced by water? We address this question by studying sequential flow of oil and water over corrugated triangular structures inside a microchannel.

In everyday fluids, viscosity is resistance to flow and is dissipative, but a quantum Hall (QH) fluid at zero temperature has nondissipative viscosity (“odd” viscosity). Using exact results we theoretically study observable consequences of odd viscosity in incompressible fluids in two dimensions.

The effects of gas viscosity, meniscus protrusion, and channel aspect ratio are captured in a numerical model for flow through textured microchannels. Spectral accuracy for the laminar flow field is obtained by using a Chebyshev collocation method with domain decomposition and singularity subtraction.

Just like a layered cake, fluid near a solid interface often arranges itself into clearly defined bands of density. The properties of this fluid layering are investigated, and a dimensionless group governing layer formation is introduced. A scaling relationship for high-density fluids is presented.

Subsurface explosions for ejecting low-density regolith from the surface of asteroids and comets are studied by solving two sets of coupled Euler equations. Formation and propagation of a granular shock is explored. The granular-shock radius exhibits a power-law relation with explosion time.

The effect of obstacle shape on clogging prevention in granular silo flow is studied with experiments and simulations. We find that a triangle or horizontal-bar obstacle is efficient for clogging prevention, detouring flow and resultant low packing fraction at the exit zone being principal factors.

How reversible is a sharp interface between a viscous suspension and clear fluid when subject to oscillatory flow? Simulations and experiments show minimal changes at the centerline but the front advances at the wall, with anomalous particle fluxes towards the wall within the bulk of the suspension.

With experiments and scaling analysis we study the effect of different Bond and Capillary numbers (Bo and Ca) for long bubbles in horizontol tubes. We find bubble inclination angle increasing with Bo and Ca which scaling suggests is due to gravity draining the thin film from channel top to bottom.

Self-propelled bodies of all scales generate a unique mechanical ‘swim stress’ and ‘Reynolds stress’ owing to their motility that impacts their large-scale collective motion.

A detailed and systematic investigation into the properties of steady streaming inside a fluid-filled container with oscillating deformable boundaries is presented. The results demonstrate and explain how flow reversal varies with the dimensionless vibration frequency.

Exact statistical equations (ESEs) allow precise direct numerical simulation (DNS) quantification. ESEs reveal quantities determining deviations from asymptotic relationships. Here, ESEs for small Schmidt-number scalar advection, in general and asymptotic cases, are obtained and compared with DNSs.

Mean velocity profiles in pipes and channels match the profile of the zero-pressure-gradient boundary layer up to $y^{+}=O({10}^3)$, where they change abruptly to flow-specific log laws.

The filtered density function closure is extended to a “self-contained” format to include the subgrid scale statistics of all of the hydro-thermo-chemical variables in turbulent flows. The model is comprehensive and facilitates large eddy simulation of flows at low and high compressibility levels.

Profiles of $\langle pp{\rangle }^{+}$ from direct numerical simulation calculations are correlated for various Reynolds numbers. The correlating functions are unusual; a single function in the outer region and a defect function in the inner region. This is exactly opposite of the correlating functions for the mean velocity.

The temporal dynamics of the coherent structures in a turbulent jet is studied using statistical tools and system identification. The dynamics is low-dimensional, and linear models optimally reproduce the input-output behavior. However, the full dynamics can be reproduced only partially.

Temporal evolution of the solution separation of two initially infinitesimally perturbed simulations for a turbulent flow. This metric provides assessment of the Lyapunov exponent as a measure for the predictability time and dynamic content of turbulent flow simulations.

The effects of a single vortex near a turbulent/nonturbulent interface (TNTI) layer are studied based on a Burgers’ vortex model and direct numerical simulation. The model describes the entrainment as a two-stage process, which is related to strain and vorticity fields, and predicts flow properties near the TNTI.

How does strictly axisymmetric turbulence behave? Numerical simulations indicate that large-scale structures are formed, in agreement with theoretical predictions based on statistical mechanics.

While previous studies mostly focused on wave refraction by a prescribed vortex, a new experiment looks at what happens when surface waves are strong enough to distort the background vortex. In the resulting nonlinear regime of wave refraction, strong waves are less refracted than weak ones.

The impact of Ekman pumping on the heat transfer in rapidly rotating Rayleigh-Bénard convection is examined. Direct numerical simulation and asymptotic simulation data are combined to map a range of parameter space within the geostrophic regime. This provides a benchmark for future low Ekman number experimental studies.

An experimental investigation reveals how the modification of a rectangular mixing turbine may alter its flow properties.

An experimental study of gravity-capillary wave turbulence in the case of weak nonlinearity is presented. By tuning the depth of water, dispersion is modified until compensating nonlinearity. A transition between weak wave turbulence and a solitonic regime is then observed.

The generation and effect of internal waves on convective motions are studied via direct numerical simulation. We show that the overall dynamics vary with the stratification strength of the stable fluid layer, and find two distinct convective regimes at weak and strong stratification limits.

Transmission (Trans.) and reflection (Ref.) coefficients of long waves are studied in a canal of abruptly changing cross section with background flow $U(x)$. All possible orientations of incident wave and a current have been considered for different regimes of a flow: sub-, trans- and super-critical.