Analysis of recent direct numerical simulations of wall-bounded turbulence with spanwise rotation find that even-order moments up to the 12th in the streamwise velocity fluctuations vary linearly with distance from the wall.

Brownian dynamics simulations of polymer molecules near bacterial flagella show that they experience a reduced viscosity in a long chain polymer solution. This can lead to an enhanced swimming speed when flagellum thickness is smaller than the radius of gyration of polymer molecules.

Pattern formation is an intriguing, and biologically important, feature of many motile microorganisms. A new study shows that gyrotatic swimmers can form complex patterns even in the presence of a chaotic background flow, through the local suppression of Lagrangian chaos.

We study Taylor dispersion in premixed combustion. Analytical formulas are derived which answer fundamental questions related to Damköhler’s second hypothesis of turbulent combustion and occurrence of the “bending-effect” of turbulent flame speed, when the questions are for laminar one-scale flows.

The interstitial squeeze flow between two approaching circular cylinders in a viscoplastic medium is studied numerically and semi-analytically. Yield stress effects external to the gap—not picked up by viscoplastic lubrication theory—are found to significantly affect the lubrication pressure.

Numerical simulation and theoretical analysis based on a model Boltzmann equation show that a plane shock wave in a polyatomic gas with large bulk viscosity exhibits three different types of structure, depending on the upstream Mach number.

When droplets roll down inclines, their velocities are affected by their characteristic size. Larger droplets will travel faster unless they’re too big. Droplets larger than a “critical” size travel more slowly. An investigation shows that this critical size is determined by the viscosity of the surrounding medium.

Numerical simulations show that the coalescence of a droplet on a liquid-air interface of lower surface tension manifests the nonmonotonic phenomena of emergence, disappearance, and re-emergence of “partial coalescence” with increasing surface-tension difference.

Experiments of hypopycnal and mesopycnal currents demonstrate that the microscopic transport of fresh water in viscous boundary layers surrounding the settling particles significantly impacts the macroscopic current evolution.

The potential of the nonlinear parabolized stability equations is examined to provide an accurate yet computationally efficient treatment of the laminar flow regime in direct and large-eddy simulations of transitional boundary layers.

Volatile viscous fluids on partially-wetting solid substrates can exhibit interesting dynamics and interfacial instabilities. A study of vapor condensation and fluid evaporation in a one-sided lubrication model incorporating surface tension, intermolecular effects, and evaporative fluxes is presented.

Inspired by nectar-drinking bats, an experimental and theoretical study investigates viscous entrainment in hairy textures. The trapped liquid is modeled using a Darcy-Brinkmann-like approach and the drainage flow solution is derived. The results reveal an optimal hair density to maximize fluid uptake.

Once a drop of water-soluble surfactant is deposited on a bare oil-water interface, flows are induced in water and in oil (Marangoni effect). An investigation shows that the interface is also deformed, with an upward water bump into the oil, and that the vertical shape of the interface is linked to the in-plane surface tension profile.

The boundary-layer separation produced by a small hump in a high-speed subsonic regime typical of civil aviation is studied. Different heights of the hump are considered, with the larger resulting in a fully nonlinear regime and the formation of a pair of streamwise counterrotating vortices.

Flow analysis in triple-helical micro-channels via µ-PIV experiments and 3D simulations show generation of strong secondary flow at the channel cross-section. Such flow is expected to significantly enhance mixing between liquids in the laminar regime useful for a host of microfluidic applications.

Vertical and transversal structures clearly change as interparticle interactions become more collisional. Bottom and lateral confinement prove to be decisive for friction and energy dissipation as experimental evidence shows.

An analysis shows that in 2D turbulence the nature of the irreversibility of two-particle dispersion inverts when the particle inertia exceeds a certain threshold. The results also imply that in turbulent flows with an inverse energy flux, inertial particle-pairs may yet exhibit a downscale flux of energy.

A large sphere moving through a fluid at rest collects small suspended particles. Estimating the efficiency of this process is of importance for wet aerosol deposition or planet formation. Multiple bounces do not lead to inelastic collapse but are still shown to significantly enhance accretion.

Fluid displacement in random piles of spheres occurs with strong hysteresis. Increasing heterogeneity (spheres with different wettability) is expected to increase hysteresis. Instead, we show that under certain conditions, hysteresis can be almost completely suppressed by adding heterogeneity.

3D flow measurements in the wake of a sphere positioned close to the wall in a turbulent boundary layer indicate that the wake deflects away from the wall as a result of induced motion of preferentially aligned, shed “hairpin” vortices. This is increasingly so with decreasing sphere-wall gap.

A crossover from a Kolmogorov decay of two decades in the inertial range to a stretched exponential in the dissipative range is unveiled in the experimental spatial energy spectrum of a turbulent swirling flow, as recently predicted based on nonperturbative renormalization group theory.

We find a strong degeneracy in the strain-rate tensor probability distribution in numerical simulations of isotropic turbulence in incompressible flows, reducing the distribution to a function of one variable. We also find a universal distribution for the ratio of strain tensor eigenvalues.

A computationally friendly morphing continuum theory for the energy cascade of compressible turbulence characterizes the statistical coupling of energy transfer at the length scale of eddies, with one-tenth of the computational costs required in the Navier-Stokes based DNS.

The statistics of velocity fluctuations in coflowing superfluid ${}^4$He are studied by direct numerical simulations. The statistics are highly non-Gaussian, generally more than in classical turbulence, with the maximal non-Gaussianity occurring when the super and normal fluid densities are comparable.

Inspired by recent theoretical advances in bridge scour research, a modeling framework is derived to predict the scour induced by Hydrokinetic turbines on erodible river bed surfaces. Using a mixed scaling formulation of the Reynolds stresses, the turbine performance is linked to the scour evolution.

Experimental and numerical studies reveal the hysteretic formation and decay of a water column extending from the bottom to the top of a sealed vertical cylinder filled with sunflower oil and water. The fluid motion is driven by the rotating lid and appears multicellular.

A new study shows that the motion of three interacting point vortices in the plane can be formulated in terms of the size and location of the circle that circumscribes the vortex triangle, the interior angles of the triangle, and the orientation of the triangle, giving an alternate perspective on this classic problem.

Low Prandtl number shell convection occurs in many geophysical and astrophysical scenarios. An exploration of the patterns that form at convective onset in this extreme regime finds new mode transitions and a triple point bifurcation.