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Top 20 Most Read Articles
October 2010
The 20 articles with the most full-text downloads during the month, in descending order.
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A short wave instability caused by the approach of a vortex pair to a ground plane Phys. Fluids 22, 091106 (2010); http://dx.doi.org/10.1063/1.3483215 (1 page) Online Publication Date: 30 September 2010
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Fluid-structure interaction of two bodies in an inviscid fluid Phys. Fluids 22, 107101 (2010); http://dx.doi.org/10.1063/1.3485063 (12 pages) Online Publication Date: 1 October 2010
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The interaction of two arbitrary bodies immersed in a two-dimensional inviscid fluid is investigated. Given the linear and angular velocities of the bodies, the solution of the potential flow problem with zero circulation around both bodies is reduced to the determination of a suitable Laurent series in a conformally mapped domain that satisfies the boundary conditions. The potential flow solution is then used to determine the force and moment acting on each body by using generalized Blasius formulas. The current formulation is applied to two examples. First, the case of two rigid circular cylinders interacting in an unbounded domain is investigated. The forces on two cylinders with prescribed motion (forced-forced) is determined and compared to previous results for validation purposes. We then study the response of a single “free” cylinder due to the prescribed motion of the other cylinder (forced-free). This forced-free situation is used to justify the hydrodynamic benefits of drafting in aquatic locomotion. In the case of two neutrally buoyant circular cylinders, the aft cylinder is capable of attaining a substantial propulsive force that is the same order of magnitude of its inertial forces. Additionally, the coupled interaction of two cylinders given an arbitrary initial condition (free-free) is studied to show the differences of perfect collisions with and without the presence of an inviscid fluid. For a certain range of collision parameters, the fluid acts to deflect the cylinder paths just enough before the collision to drastically affect the long time trajectories of the bodies. In the second example, the flapping of two plates is explored. It is seen that the interactions between each plate can cause a net force and torque at certain instants in time, but for idealized sinusoidal motions in irrotational potential flow, there is no net force and torque acting at the system center.
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Phys. Fluids 22, 091102 (2010); http://dx.doi.org/10.1063/1.3479926 (1 page) Online Publication Date: 30 September 2010
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Phys. Fluids 22, 091107 (2010); http://dx.doi.org/10.1063/1.3483217 (1 page) Online Publication Date: 30 September 2010
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Self-propelled jumping drops on superhydrophobic surfaces Phys. Fluids 22, 091110 (2010); http://dx.doi.org/10.1063/1.3483222 (1 page) Online Publication Date: 30 September 2010
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Phys. Fluids 22, 101701 (2010); http://dx.doi.org/10.1063/1.3491511 (4 pages) Online Publication Date: 14 October 2010
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The present letter is a thorough study of the flow regime where an asymmetry of the mean axial velocity profiles is observed for shear-thinning fluids flow in a pipe. This study is based on a statistical analysis of the axial velocity fluctuations. It is shown that this flow regime exhibits features of a weak turbulence: chaotic in time and regular in space. More precisely, (i) power spectra of axial velocity fluctuations decay following a power law with an exponent very close to −3, (ii) large-scale coherent structures are generated, and (iii) there is essentially no intermittency in this flow regime.
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Particle motion between parallel walls: Hydrodynamics and simulation Phys. Fluids 22, 103301 (2010); http://dx.doi.org/10.1063/1.3487748 (16 pages) Online Publication Date: 11 October 2010
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The low-Reynolds-number motion of a single spherical particle between parallel walls is determined from the exact reflection of the velocity field generated by multipoles of the force density on the particle’s surface. A grand mobility tensor is constructed and couples these force multipoles to moments of the velocity field in the fluid surrounding the particle. Every element of the grand mobility tensor is a finite, ordered sum of inverse powers of the distance between the walls. These new expressions are used in a set of Stokesian dynamics simulations to calculate the translational and rotational velocities of a particle settling between parallel walls and the Brownian drift force on a particle diffusing between the walls. The Einstein correction to the Newtonian viscosity of a dilute suspension that accounts for the change in stress distribution due to the presence of the channel walls is determined. It is proposed how the method and results can be extended to computations involving many particles and periodic simulations of suspensions in confined geometries.
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Numerical studies of flow over a circular cylinder at ReD = 3900 Phys. Fluids 12, 403 (2000); http://dx.doi.org/10.1063/1.870318 (15 pages)
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Flow over a circular cylinder at Reynolds number 3900 is studied numerically using the technique of large eddy simulation. The computations are carried out with a high-order accurate numerical method based on B-splines and compared with previous upwind-biased and central finite-difference simulations and with the existing experimental data. In the very near wake, all three simulations are in agreement with each other. Farther downstream, the results of the B-spline computations are in better agreement with the hot-wire experiment of Ong and Wallace [Exp. Fluids 20, 441–453 (1996)] than those obtained in the finite-difference simulations. In particular, the power spectra of velocity fluctuations are in excellent agreement with the experimental data. The impact of numerical resolution on the shear layer transition is investigated. © 2000 American Institute of Physics. |
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The height of a static liquid column pulled out of an infinite pool Phys. Fluids 22, 102101 (2010); http://dx.doi.org/10.1063/1.3484275 (8 pages) Online Publication Date: 5 October 2010
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We consider a solid cone whose vertex points down and dips in an infinite pool of liquid. If the cone is slowly lifted, a liquid column with its top attached to the cone is pulled out of the pool. In this paper, we compute the maximum height of the cone before the column ruptures. Two reasons for rupturing are identified. In some cases, no solution for a higher position of the cone exists. In other cases, a solution does exist, but is unstable.
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Dynamics within surfactant monolayers Phys. Fluids 22, 091113 (2010); http://dx.doi.org/10.1063/1.3492833 (1 page) Online Publication Date: 30 September 2010
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Transitional and turbulent boundary layer with heat transfer Phys. Fluids 22, 085105 (2010); http://dx.doi.org/10.1063/1.3475816 (8 pages) Online Publication Date: 26 August 2010
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We report on our direct numerical simulation of an incompressible, nominally zero-pressure-gradient flat-plate boundary layer from momentum thickness Reynolds number 80–1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number Pr = 1. Skin-friction coefficient and other boundary layer parameters follow the Blasius solutions prior to the onset of turbulent spots. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cf deviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Mean velocity and Reynolds stresses agree with experimental data over an extended turbulent region downstream of transition. Normalized rms wall-pressure fluctuation increases gradually with the streamwise growth of the turbulent boundary layer. Wall shear stress fluctuation, τw,rms′+, on the other hand, remains constant at approximately 0.44 over the range, 800<Reθ<1900. Turbulent Prandtl number Prt peaks at around 1.9 at the wall, and decreases monotonically toward the boundary layer edge with no near-wall secondary peak, in good agreement with previous boundary layer heat transfer experiments. In the transitional region, turbulent spots are tightly packed with numerous hairpin vortices. With the advection and merging of turbulent spots, these young isolated hairpin forests develop into the downstream turbulent region. Isosurfaces of temperature up to Reθ = 1900 are found to display well-resolved signatures of hairpin vortices, which indicates the persistence of the hairpin forests.
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Introduction: 27th Annual Gallery of Fluid Motion (Minneapolis, Minnesota, USA, 2009) Phys. Fluids 22, 091101 (2010); http://dx.doi.org/10.1063/1.3483224 (1 page) Online Publication Date: 30 September 2010
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Collapse of nonaxisymmetric cavities Phys. Fluids 22, 091104 (2010); http://dx.doi.org/10.1063/1.3481432 (1 page) Online Publication Date: 30 September 2010
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Lagrangian feature extraction of the cylinder wake Phys. Fluids 22, 091108 (2010); http://dx.doi.org/10.1063/1.3483220 (1 page) Online Publication Date: 30 September 2010
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Phys. Fluids 22, 091109 (2010); http://dx.doi.org/10.1063/1.3483221 (1 page) Online Publication Date: 30 September 2010
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Hairpin vortex organization in wall turbulence Phys. Fluids 19, 041301 (2007); http://dx.doi.org/10.1063/1.2717527 (16 pages) Online Publication Date: 18 April 2007
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Coherent structures in wall turbulence transport momentum and provide a means of producing turbulent kinetic energy. Above the viscous wall layer, the hairpin vortex paradigm of Theodorsen coupled with the quasistreamwise vortex paradigm have gained considerable support from multidimensional visualization using particle image velocimetry and direct numerical simulation experiments. Hairpins can autogenerate to form packets that populate a significant fraction of the boundary layer, even at very high Reynolds numbers. The dynamics of packet formation and the ramifications of organization of coherent structures (hairpins or packets) into larger-scale structures are discussed. Evidence for a large-scale mechanism in the outer layer suggests that further organization of packets may occur on scales equal to and larger than the boundary layer thickness.
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Preferential concentration of heavy particles: A Voronoï analysis Phys. Fluids 22, 103304 (2010); http://dx.doi.org/10.1063/1.3489987 (10 pages) Online Publication Date: 14 October 2010
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We present an experimental characterization of preferential concentration and clustering of inertial particles in a turbulent flow obtained from Voronoï diagram analysis. Several results formerly obtained from various data processing techniques are successfully recovered and further analyzed with Voronoï tesselations as the main single tool. We introduce a simple and nonambiguous way to identify particle clusters. We emphasize the maximum preferential concentration for particles with Stokes numbers around unity and the self-similar nature of clustering and we report new unpredicted results concerning clusters inner concentration dependence on Stokes number and global seeding density. Some of these experimental observations can be consistently interpreted in the context of the so-called sweep-stick mechanism. Finally, we stress the great potential of Voronoï analysis that offers important openings for new investigations of particle laden flows in terms, for instance, of simultaneous Lagrangian statistics of particle dynamics and local concentration field.
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Grid-independent large-eddy simulation using explicit filtering Phys. Fluids 22, 105103 (2010); http://dx.doi.org/10.1063/1.3485774 (11 pages) Online Publication Date: 21 October 2010
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The governing equations for large-eddy simulation are derived from the application of a low-pass filter to the Navier–Stokes equations. It is often assumed that discrete operations performed on a particular grid act as an implicit filter, causing results to be sensitive to the mesh resolution. Alternatively, explicit filtering separates the filtering operation, and hence the resolved turbulence, from the underlying mesh distribution alleviating some of the grid sensitivities. We investigate the use of explicit filtering in large-eddy simulation in order to obtain numerical solutions that are grid independent. The convergence of simulations using a fixed filter width with varying mesh resolutions to a true large-eddy simulation solution is analyzed for a turbulent channel flow at Reτ = 180, 395, and 640. By using explicit filtering, turbulent statistics and energy spectra are shown to be independent of the mesh resolution used.
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A numerical simulation of a plunging breaking wave Phys. Fluids 22, 091111 (2010); http://dx.doi.org/10.1063/1.3487758 (1 page) Online Publication Date: 30 September 2010
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Large-eddy simulations of Richtmyer–Meshkov instability in a converging geometry Phys. Fluids 22, 091112 (2010); http://dx.doi.org/10.1063/1.3491373 (1 page) Online Publication Date: 30 September 2010
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