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Research Highlight Archive
Stability of relative equilibria of three vortices
Hassan Aref
Three point vortices on the unbounded plane have relative equilibria wherein the vortices either form an equilateral triangle or are collinear. While the stability analysis of the equilateral triangle configurations is straightforward, that of the collinear relative equilibria is considerably more involved.This paper gives analysis based on explicit formulas for the three eigenvalues determining the stability, including a new formula for the angular velocity of rotation of a collinear relative equilibrium.
Fluctuations and stratification in sedimentation of dilute suspensions of spheres
Daniel Chehata Gómez, Laurence Bergougnoux, Élisabeth Guazzelli, and John Hinch
Whether stratification can control velocity fluctuations in suspensions of sedimenting spheres is tested. The initial value and early decay of the velocity fluctuations are not affected by stratification. On the other hand, in the descending front where the stratification is strong and well defined, the velocity fluctuations are inhibited according to a previously proposed scaling. In between, after the initial decay and before the arrival of the front, the local value of the stratification does not always play a role.
Drag reduction in turbulent flows over superhydrophobic surfaces
Robert J. Daniello, Nicholas E. Waterhouse, and Jonathan P. Rothstein
This paper demonstrates that periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide laminar flow drag reduction, are capable of reducing drag in the turbulent flow regime.
Stick-slip dynamics of an oscillated sessile drop
Irina S. Fayzrakhmanova and Arthur V. Straube
Theoretical consideration is given to dynamics of an oscillated sessile drop of incompressible liquid and focus on the contact line hysteresis. The frequency response of surface oscillations on the substrate and at the pole of the drop are analyzed. It is shown that novel features such as the emergence of antiresonant frequency bands and nontrivial competition of different resonances are caused by contact line hysteresis.
Poiseuille flow and thermal creep based on the Boltzmann equation with the Lennard-Jones potential over a wide range of the Knudsen number
Felix Sharipov and Guilherme Bertoldo
The methodology to solve the linearized Boltzmann equation for an arbitrary potential of
intermolecular interaction described in our previous paper is used to calculate a rarefied gas flow between two parallel plates driven by pressure and temperature gradients over a wide range of the Knudsen number. As an example, the Lennard-Jones potential is applied. The calculations were carried out for all noble gases at the temperature equal to 300 K. A comparison with results for the same problem based on the kinetic model equations showed that the uncertainty of these equations has the same order that the Boltzmann equation based on the hard sphere particles.
Turbulent boundary layers up to Reθ =2500 studied through simulation and experiment
P. Schlatter,a_ R. Örlü, Q. Li, G. Brethouwer, J. H. M. Fransson, A. V. Johansson, P. H. Alfredsson, and D. S. Henningson
Direct numerical simulations (DNSs) and experiments of a spatially developing zero-pressure-gradient turbulent boundary layer are presented. Direct comparisons of DNS and experiments of turbulent boundary layers are given, showing excellent agreement in skin friction, mean velocity, and turbulent fluctuations. These results allow for a substantial reduction of the uncertainty of boundary-layer data, and cross validate the numerical setup and experimental technique.
