Numerical simulations of viscoelastic flow around an isolated particle find that, while the particle contribution to bulk elongational viscosity of a suspension increases at small strains, at larger strains the particle is shielded by stretched polymers, leading to a decrease in relative viscosity.

Inverse-chevron interfaces with various initial amplitudes and wavelengths are used in shock tube experiments to study bubble competition in the Richtmyer-Meshkov instability. We find that width growth of the large interface is enhanced and that of the small interface is more affected and inhibited.

Simulations of synchronized spermatozoa reveal stable pairwise swimming, with swimmers speeding up as they approach each other from above. However, swimming side-by-side proves unstable, highlighting anisotropy in planar-beating flagellates that is not captured by simple singularity representations.

Theory and experiments explain why an inertial swimmer can swim more efficiently by flapping its tail slowly with a large amplitude than by doing so quickly with a small amplitude. The importance of drag is revealed as well as a fundamental tradeoff between thrust and efficiency.

A numerical study finds that bifrontal plug growth leading to the closure of a human lung airway induces high stress levels on the wall, which is the location of airway epithelial cells. Postcoalescence wall stresses can be from 300% to 600% greater than precoalescence values.

This work presents a unified physics-based reduced-order simulation framework for describing non-Boltzmann thermochemistry and radiative heating for hypersonic flows. The new approach is used to analyze afterbody flow dynamics and concomitant carbon dioxide IR radiation for the Mars 2020 mission.

It is shown that horizontal convection at an infinite Prandtl number will become time-dependent at sufficiently high Rayleigh numbers. The point of the transition is dependent on the heating configuration, and the scaling laws of heat flux and circulation strength are subsequently changed.

We study thermoelectric convection in a cylindrical annulus of dielectric liquid under rotation and a fixed temperature gradient. Convection onset is delayed and stationary helical vortices become oscillatory columnar vortices for a rotation rate above a value dependent on the radius ratio.

With multiscale simulations we study contracting filaments of aspect ratios O(1)-O(1000) and Ohnesorge numbers 0.0001-10. Breakup modes of inviscid, intermediately viscous, and highly viscous filaments are clarified, highlighting the key role of capillary wave interactions in the intermediate case.

An asymptotic analysis of a two-dimensional nonwetting drop rolling down an inclined plane at small Bond numbers shows, contrary to previous studies, that the leading-order contribution to the dissipation comes from the overlap region between the drop scale and the small neighborhood of the drop’s flat-spot.

Shear-induced gradient diffusivity in an emulsion of viscous drops is determined from direct numerical simulations of the system using a dynamic structure factor approach. A nonmonotonic variation of the gradient diffusivity with viscosity ratio and capillary number is observed.

A new analysis reveals distinctive features of the modeled evolution of the fluid nanofilm formed between two coalescing droplets: an attractor-type phase space, a non-Fickean behavior of the growing film, and a complexity measure larger than that expected for fractional Brownian motion.

Incipient motion of sediment particles is analyzed using a relation between a densimetric Froude number (Fr) and 6 decades of relative roughness ($N$). The universal character of the Fr-$N$ relation was recovered from the vertical velocity energy spectrum using a cospectral budget model.

The receptivity of pretransitional boundary layers is analyzed using the steady-state covariance of the stochastically forced linearized Navier-Stokes equations. Prevailing length scales captured by both locally parallel and global analyses provide insight into perturbation growth mechanisms.

Gliding is an energetically efficient mode of transportation. It is shown that reinforcement learning identifies gliding strategies with minimum energy expenditure and fastest time of arrival, with better performance than model-based optimal control, while being robust to perturbations.

Compressibility effects mean that fluctuation growth related to turbulence is suppressed as Mach number increases. An investigation that clarifies compressibility effects of the Batchelor vortex is presented. The findings indicate that entropy fluctuation in the vortex is strongly related to intrinsic compressibility.

We use direct numerical simulations of turbulent channel flows to model skin-friction drag reduction with wall rotating rings combined with hydrophobic surfaces or opposition control. We find rotating rings reduce drag 20%. Combining with opposition control adds 7.4% and hydrophobic surfaces 6.5%.

The effects of initial stratification on single-mode Rayleigh-Taylor instability are examined using fully compressible wavelet-based direct numerical simulations. Such instabilities are widespread and are found in inertial confinement fusion, supernova ignition fronts, x-ray bursts, and geophysics.

We study the action of spatial heat release modulation on wave patterns. In the case of multistability, the spatial modulation can be used for the creation of a pattern with a definite structure. The violation of the reflection symmetry of the pattern can lead to a quasiperiodic temporal evolution.

The long-wave oscillatory Marangoni instability in a heated liquid layer covered by insoluble surfactant is considered. It is shown that with the growth of the elasticity number the selected wave pattern is changed from the traveling waves to counterpropagating waves and then again to traveling waves.

Theory, simulations, and experiments are used to study liquid-air interfacial instability of lifted Hele Shaw cells (LHSCs) with a hole in the center. The stability map provides a design framework for using multihole LHSCs to generate stable meshlike patterns in the liquid film.

Transport and filtration of colloids through permeable materials is controlled by the underlying heterogeneous structure of the host medium. A stochastic model is proposed that takes into account pore-scale heterogeneity, which controls the macroscopic deposition.

An experimental investigation shows that thin liquid films can interconnect different parts of a porous network (like wet soils or rocks) and effectively enhance the overall connectivity of the system. The effect is large enough to allow for the drainage of fluid clusters that otherwise would be entirely trapped in the matrix.

We experimentally investigate the formation of coherent structures by finite-size particles in thermocapillary liquid bridges. Special attention is paid to particle accumulation structures in which suspended particles gather to form a solid-like-structure in the rotating frame of reference.

Direct numerical simulations are used to investigate forces on a stationary finite-sized particle in wall turbulence over a rough bed of hemispherical particles. Results show that lift is the main contributor of wall-normal force and can be well predicted with proper application of existing models.

An investigation of the impact of a nonlinear equation of state on the evolution of the Rayleigh-Taylor instability is presented. The nonlinear density relation introduces asymmetry in the growing plumes about the density interface, preferentially generating kinetic energy in the lower layer.

A Bayesian optimization framework is developed to optimize low-amplitude wall-normal blowing control of a turbulent boundary-layer flow in order to generate net energy savings.

Using signal processing of a large-eddy simulation based on flow-acoustic correlations and spectral proper orthogonal decomposition, we identify regions and mechanisms effective at generating sound in a turbulent flow around a NACA 0012 airfoil with zero angle of attack and Mach number of 0.115.

An experimental study of the pair separation of particles in turbulent thermal convection reveals the dramatic impact of the inhomogeneous large-scale flow on pair dispersion, without affecting the small-scale turbulent statistics. The Richardson-Obukhov regime is also revisited.

For a given stratification, the presence of a shear background current may significantly alter the wave form of internal waves. Depending on the direction and strength of background shear, it could prevent the formation of solitary waves but enable the formation of a dispersive wave train.

An investigation of a mode-2 internal solitary wave passing over a broad ridge finds that it is gradually adjusted into multiple waves of different form. The leading wave remains intact but is reduced in amplitude and energy. Incident amplitude, speed, and ridge height determine the strength of the resultant waves.

Simulation of density-stratified flow past an elongated body reveals substantial differences with respect to a sphere in flow separation, the near wake and internal waves. As stratification increases (Fr decreases), the fluid experiences vertical/sideways deflection and the separated region changes.