Geometrical shock dynamics is used to predict that a converging cylindrical shock forms a singularity on the shock profile through nonlinear effects.

Simulations of a gas in a Minimal Couette unit at Re=500 using Direct Simulation Monte Carlo, a molecular method enforcing molecular chaos for gas-molecule collisions, reproduces the turbulence from DNS. Thus molecular chaos does not prevent development of long-range correlations in turbulence.

A full Koopman decomposition for the velocity field in the Burgers equation is presented by deriving explicit expressions for the Koopman modes and eigenfunctions.

A clear visualization of vortex breakdown is captured in a dividing microfluidic T-junction flow. This eye-catching structure can be greatly altered by slight outflow imbalances. Our results will guide the use of vortex breakdown to enhance flow control in lab-on-a-chip devices.

Three-dimensional Lattice Boltzmann simulations contrast backflow from an external reservoir into a confined microchannel in a dripping mode where the drop breaks off towards the end of the microchannel with a jetting mode at higher flows with drop break off further downstream inside the reservoir.

Simulations of Lagrangian turbulence with Fourier components removed (decimation) show no effect on the level of chaos but an emergent time reversality as indicated by the ratio of Lyapunov exponents shown in the figure.

Direct numercal simulations of fully developed turbulence in a rectangular duct are used to study the fluxes of vorticity.

Flowing trains of red blood cells are stable when tightly confined but can otherwise break down into an irregular flow. A linear stability formulation is developed to analyze this biological phenomena, advancing understanding of its origin and guiding the design of devices that process blood cells.

Experiments on a prototype flapping robotic wing show that a single design can propel in both air and water, as do puffins and other auks, by varying wing kinematics. We optimize for each fluid with a force measurement feedback scheme and determine the unsteady wakes through dye visualization.

Snapshot of a propagating shear front that transforms a dense suspension from a fluid into a jammed, solid-like state. A comprehensive description of this transformation is developed, which links the transient dynamics to parameters obtainable from steady-state rheology.

Experiments on single drop impacts on thin films of another liquid are analyzed theoretically over 8 orders of magnitude in viscosity ratio ${\nu }_f/{\nu }_d$. Away from ${\nu }_f\approxeq {\nu }_d$ we find that the K-numbers determine the splashing threshold and in that region a modified K-number, which we introduce, is needed.

Experiments on air bubbles nucleated on an inclined plate show the importance of the bubble foot shape. A new expression for the capillary force is proposed to predict the bubble detachment diameter.

We examine theoretically the break-up dynamics of a droplet in a sub-critical extensional flow. We find that it is analogous to other nonlinear dynamical systems with a finite basin of attraction, being governed by an unstable edge state equilibrium in the basin boundary of the base state.

Evaporation kinetics of surfactant-infused nanocolloidal droplets are studied using the pendant mode to understand the pure physics of evaporation in such complex fluids. Oscillatory solute-thermal convective currents are found to be responsible for evaporation rate enhancement in these complex fluids.

The coalescence of surfactant solutions on a substrate is studied. By varying both the contact angle of the droplets and their difference in surface tension, various regimes with distinct timescales of noncoalescence are identified.

For a pair of suspended leaky drops, the computed drop velocity (u) with varied permittivity-ratio (εin/εout) and two ‘outflow’ outer vortex pairs drive prolate and oblate deformation mechanisms. Two drops diverge for positive ‘u’ and move closer together and coalesce for negative ‘u’.

The drag coefficient of mangrove roots reveals a dependency on porosity and Reynolds number. By introducing the effective diameter via streamwise velocity and vortex shedding frequency, the effective drag coefficient of the root model can be predicted from a universal curve fit.

Cross-stream component of the optimal response at the natural shear layer frequency (solid black line: displacement thickness of the boundary layer, solid brown line: zero-streamwise mean velocity contour).

The dual roles of gravity and interfacial tension are experimentally studied. The existence of a crossover frequency, on either side of which gravity plays opposing roles, is confirmed. Faraday waves show a surprising stabilization with the reduction in interfacial tension.

High-speed imaging experiments and numerical simulations show that the minimum size of drops ejected after bubble bursting is determined by an interplay of viscous and inertial-capillary forces both prior and subsequent to jet formation. Implications for sea spray aerosol generation are discussed.

Motivated by ultrasound-induced pulmonary hemorrhage, we computationally study acoustic waves in water interacting with a perturbed water-air interface. We demonstrate that baroclinic vorticity due to the misaligned pressure (waves) and density (interface) gradients drives the perturbation growth.

There is considerable research to improve the displacement efficiency in buoyant two-fluid flow systems, e.g., when a heavy fluid is injected to displace a light one from a pipe. Experiments show that a pipe rotation helps to completely remove the displaced fluid.

Transient spreading of a viscous fluid beneath an adhered elastic sheet is controlled by the tip dynamics. Spreading occurs in two dynamical regimes: viscosity dominant and adhesion dominant. Experiments with elastic sheets made of PDMS confirm these regimes and the emergence of a vapor tip.

Molecular processes of contact line advancement in dynamic wetting is investigated for no-slip systems using computer simulations. The energy dissipation at the contact line is measured and shown to be large for mesoscopic systems. A model for the dissipation term is proposed.

Particles migrate towards the center or walls of a rectangular microchannel if they lead or lag a viscoelastic fluid flow due to positive and negative electrophoresis, respectively. This is opposite to a Newtonian fluid. We attribute this to the shear-induced extra lift in a viscoelastic fluid.

Our discrete element simulations and laboratory experiments revealed that density and friction are well-defined functions of the effective inertial number, which fully captures the effect of grain elongation.

Using a coupled lattice Boltzmann method/discrete element method model, the clogging of a pore with particles at microscopic scale is studied. We show that erosive bursts occur when the hydraulic pressure exceeds a critical point, which depends on the adhesive forces and the pores’ geometry.

What causes the rising or segregation of large particles at very low concentrations in dense bidisperse granular flows? The scaling of the lift force experienced by large particles with their downstream velocity lag suggests that the answer is a granular equivalent of the Saffman effect.

We analyze heat transfer between disperse and carrier phases in multiphase turbulent flows. We reduce the full characterization of the problem to two parameters: Stokes number based on large eddy time, and a dimensionless number indicating the ratio of gas thermal relaxation time to large eddy time.

Internal imaging shows that a granular bed consolidates and creeps under the action of fluid flow well below the bedload transport critical rate. The bed is shown to be armored with a systematic increase in erosion threshold depending on the duration and strength of applied subcritical shear.

A computational study shows that the viscosity contrast between the two phases of a multiphase fluid induces noticeable morphological changes to the geometry of the two phases during self-similar coarsening. Quantitative measures are specified.

A large-scale model for transport by secondary open wakes is proposed to describe the spatiotemporal evolution of the concentration field in a homogeneous bidimensional bubble swarm rising at high Reynolds number.

We investigate the effect of external intermittency on dissipation scales in turbulent boundary layer flow at $R{e}_{\tau }\approx 1000$ using a single hot wire probe for one point longitudinal velocity measurements. We find improved scaling universality by accounting for external intermittency throughout the flow.

We present a comprehensive framework for augmenting turbulence models with physics-informed machine learning, illustrating a complete workflow from identification of input/output to prediction of mean velocities. The learned model has Galilean invariance and coordinate rotational invariance.

There is a continued debate about the generation mechanism of turbulent spots in boundary-layer transition. We use the vortex-surface field to show that the sinuous distortion of vortex surfaces plays an important role in the rapid lateral growth of turbulent spots.

While the solid cylinder wake shows apparent and stable shedding frequency, the screen cylinder wake shows a broad-band peak with a trend of decreasing frequency, indicating that amalgamation of vortices has taken place. This trend implies that the merging process does not occur at a fixed location.

Measurements of pressure on the surface of a rigid wedge as it enters water find that, while the presence of the cylinder elicits a predictable increase in the pressure close to the keel, it is also responsible for a pressure drop in the vicinity of the pile-up.

We present a minimal approach to address the problem of ship hull optimization, and compare our theoretical results with existing data. We show that optimal hull aspect ratios result from a subtle balance between wave drag, pressure drag, and skin friction.