Physical Review Fluids

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Recent articles in Physical Review Fluids
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Driven active matter: Fluctuations and a hydrodynamic instability

Tue, 02/26/2019 - 10:00

Author(s): T. R. Kirkpatrick and J. K. Bhattacherjee

A new hydrodynamic instability in driven active matter is discussed. It is similar to the convective instability that occurs in passive fluids, but differs in several important ways. In particular, the transition to turbulence in the active matter system is expected to be novel.

[Phys. Rev. Fluids 4, 024306] Published Tue Feb 26, 2019

Fountain mixing in a filling box at low Reynolds numbers

Tue, 02/26/2019 - 10:00

Author(s): Nan Xue, Sepideh Khodaparast, and Howard A. Stone

Pouring a liquid down into a container of a denser liquid creates a fountain. We measure the penetration depth of such fountains and characterize the mixing based on the Reynolds (Re) and Froude (Fr) numbers.

[Phys. Rev. Fluids 4, 024501] Published Tue Feb 26, 2019

Multiscale analysis of the structure of homogeneous rotating turbulence

Mon, 02/25/2019 - 10:00

Author(s): Aurore Naso

Homogeneous rotating turbulence structure is investigated by analyzing instantaneous statistics of the scale-dependent perceived velocity gradient tensor. Rotation is shown to suppress some alignment properties of isotropic turbulence, decreasing enstrophy production and strain production rates.

[Phys. Rev. Fluids 4, 024609] Published Mon Feb 25, 2019

Dynamo effect in decaying helical turbulence

Fri, 02/22/2019 - 10:00

Author(s): Axel Brandenburg, Tina Kahniashvili, Sayan Mandal, Alberto Roper Pol, Alexander G. Tevzadze, and Tanmay Vachaspati

It is shown that decaying helical turbulence amplifies a weak magnetic field, which then itself becomes helical. However, it displays a transient behavior different from any other helical or nonhelical magnetic decaying field in a parametric representation between the temporal scaling exponents p(t) and q(t).

[Phys. Rev. Fluids 4, 024608] Published Fri Feb 22, 2019

Experiments on the low-Reynolds-number settling of a sphere through a fluid interface

Wed, 02/20/2019 - 10:00

Author(s): Paul A. Jarvis, Heidy M. Mader, Herbert E. Huppert, Katharine V. Cashman, and Jon D. Blundy

Experiments on the low-Reynolds number settling of a sphere through a fluid interface focus on the effect of the viscosity ratio and Bond number on the shape of the sphere position curve as a function of time, whether sinking occurs through a tailing or film drainage mode and the sinking timescale.

[Phys. Rev. Fluids 4, 024003] Published Wed Feb 20, 2019

Complex behavior very close to the pinching of a liquid free surface

Tue, 02/19/2019 - 10:00

Author(s): M. Rubio, A. Ponce-Torres, E. J. Vega, M. A. Herrada, and J. M. Montanero

High speed observations are made of the pinching off of a pendant drop.

[Phys. Rev. Fluids 4, 021602(R)] Published Tue Feb 19, 2019

Condensate in quasi-two-dimensional turbulence

Tue, 02/19/2019 - 10:00

Author(s): S. Musacchio and G. Boffetta

Three-dimensional numerical simulations of forced turbulence in a thin layer show the transfer from the forcing to larger scales is by two-dimensional modes, and to smaller scales by three-dimensional modes, the latter providing a viscosity-independent dissipation.

[Phys. Rev. Fluids 4, 022602(R)] Published Tue Feb 19, 2019

Two-dimensional isotropic turbulent inflow conditions for vortex particle method

Tue, 02/19/2019 - 10:00

Author(s): Sparsh Sharma and Ennes Sarradj

A genetic algorithm is used to optimally populate a random flow with two-dimensional Gaussian-shaped vortices subject to certain constraints.

[Phys. Rev. Fluids 4, 022701(R)] Published Tue Feb 19, 2019

Can small-scale turbulence approach a quasi-universal state?

Tue, 02/19/2019 - 10:00

Author(s): Shunlin Tang, Robert A. Antonia, Lyazid Djenidi, and Yu Zhou

Analytical considerations, based on the Navier-Stokes equations, which take into account the finite Reynolds number effect, together with all available experimental laboratory data, confirm a tendency towards the universal predictions of K41 as the Reynolds number continues to increase.

[Phys. Rev. Fluids 4, 024607] Published Tue Feb 19, 2019

Assessment of two vortex formulations for computing forces of a flapping foil at high Reynolds numbers

Tue, 02/19/2019 - 10:00

Author(s): A. Martín-Alcántara and R. Fernandez-Feria

Impulse-based vortex formulas are found appropriate for computing propulsion forces from experiments only when the vortices remain close to the moving foil, as in starting motions or in hovering flight, but are inaccurate in forward flight or swimming, where projection methods perform much better.

[Phys. Rev. Fluids 4, 024702] Published Tue Feb 19, 2019

Separation regimes of two spheres falling in shear-thinning viscoelastic fluids

Fri, 02/15/2019 - 10:00

Author(s): D. Freire, L. G. Sarasúa, A. Vernet, S. Varela, G. Usera, C. Cabeza, and A. C. Martí

Experiments show that the separation between two spheres settling down in viscoelastic shear-thinning solutions exhibit two different regimes depending on the fluids’ rheological properties. The existence of a previously reported elusive regime is corroborated.

[Phys. Rev. Fluids 4, 023302] Published Fri Feb 15, 2019

Shape factor of the turbulent boundary layer on a flat plate and the Reynolds shear stress in the outer region

Fri, 02/15/2019 - 10:00

Author(s): P. Phani Kumar and J. Dey

From the linear equation for the velocity defect in the outer boundary layer, the product of mean wall normal velocity and free stream velocity is shown to vary linearly with the Reynolds shear stress.

[Phys. Rev. Fluids 4, 024605] Published Fri Feb 15, 2019

Properties of the scalar variance transport equation in turbulent channel flow

Fri, 02/15/2019 - 10:00

Author(s): Ang Zhou, Joseph Klewicki, and Sergio Pirozzoli

We study the total scalar variance equation for fully developed turbulent channel flow subject to uniform scalar generation. We find a total scalar variance leading balance four-layer structure similar to total kinetic energy balance. Differences in the two Karman constants, k and k_θ, are clarified.

[Phys. Rev. Fluids 4, 024606] Published Fri Feb 15, 2019

Dynamics of long gas bubbles rising in a vertical tube in a cocurrent liquid flow

Wed, 02/13/2019 - 10:00

Author(s): M. Magnini, S. Khodaparast, O. K. Matar, H. A. Stone, and J. R. Thome

Long gas bubbles in a vertical tube do not rise in stagnant liquid if Bo < 0.842. An investigation shows that long bubbles rising in co-current liquid flow exhibit different asymptotic regimes at small liquid capillary numbers, as Bo transitions across this critical value.

[Phys. Rev. Fluids 4, 023601] Published Wed Feb 13, 2019

Sharp-edged geometric obstacles in microfluidics promote deformability-based sorting of cells

Wed, 02/13/2019 - 10:00

Author(s): Zunmin Zhang, Wei Chien, Ewan Henry, Dmitry A. Fedosov, and Gerhard Gompper

The application of the deterministic lateral displacement approach in microfluidics to deformability-based sorting of cells is explored. Mesoscale hydrodynamics simulations are employed to show that this requires large flow-induced cell deformation in the trajectory-distinguishing flow region.

[Phys. Rev. Fluids 4, 024201] Published Wed Feb 13, 2019

Wake characteristics of a utility-scale wind turbine under coherent inflow structures and different operating conditions

Tue, 02/12/2019 - 10:00

Author(s): Xiaolei Yang and Fotis Sotiropoulos

Large-eddy simulations show the similarity of turbine wakes for different tip speed ratios and suggest the coexistence of inflow large eddies and wake shear layer instability as the mechanism for the onset of wake meandering.

[Phys. Rev. Fluids 4, 024604] Published Tue Feb 12, 2019

Statistics of incompressible hydrodynamic turbulence: An alternative approach

Mon, 02/11/2019 - 10:00

Author(s): Nahuel Andrés and Supratik Banerjee

Using a recent alternative form of the 4/3 exact relation for fully developed hydrodynamic turbulence, the incompressible energy cascade rate ε is computed. The numerical results show that ε is in clear agreement with the cascade rates computed from the classical 4/3 law.

[Phys. Rev. Fluids 4, 024603] Published Mon Feb 11, 2019

Transition in swimming direction in a model self-propelled inertial swimmer

Fri, 02/08/2019 - 10:00

Author(s): Thomas Dombrowski, Shannon K. Jones, Georgios Katsikis, Amneet Pal Singh Bhalla, Boyce E. Griffith, and Daphne Klotsa

An inertial swimmer comprised of two unequal spheres oscillating in antiphase generates a steady streaming, which propels the swimmer in opposite directions depending on the Reynolds number.

[Phys. Rev. Fluids 4, 021101(R)] Published Fri Feb 08, 2019

Ice wicking

Fri, 02/08/2019 - 10:00

Author(s): Katherine E. Witt, S. Farzad Ahmadi, and Jonathan B. Boreyko

We observe silicone oils wicking across dendritic sheets of frost. The capillary action is found to be dependent upon both the surface orientation and the underlying surface wettability.

[Phys. Rev. Fluids 4, 024002] Published Fri Feb 08, 2019

Buoyant finite-size particles in turbulent duct flow

Fri, 02/08/2019 - 10:00

Author(s): Sagar Zade, Walter Fornari, Fredrik Lundell, and Luca Brandt

Many large spherical particles that sediment and resuspend from the bottom of a duct under fully developed turbulent conditions are studied. Optical experiments and direct numerical simulations are compared and used to investigate turbulence modulation and organization of particles.

[Phys. Rev. Fluids 4, 024303] Published Fri Feb 08, 2019