Physics of Fluids: Most Cited articles
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Most cited articles from Physics of Fluidsen-usSun, 19 Mar 2023 10:59:16 GMTAtypon® Literatum™http://validator.w3.org/feed/docs/rss2.html10080Physics of Fluids: Most Cited articleshttps://aip.scitation.org/na101/home/literatum/publisher/aip/journals/covergifs/phf/cover.jpg
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A dynamic subgrid‐scale eddy viscosity model
https://aip.scitation.org/doi/10.1063/1.857955?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.857955?feed=most-citedOne major drawback of the eddy viscosity subgrid‐scale stress models used in large‐eddy simulations is their inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes. In the present work a new eddy viscosity model is presented which alleviates many of these drawbacks. The model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model is based on an algebraic identity between the subgrid‐scale stresses at two different filtered levels and the resolved turbulent stresses. The subgrid‐scale stresses obtained using theMassimo Germano, Ugo Piomelli, Parviz Moin, and William H. CabotThu, 04 Jun 1998 07:00:00 GMTA proposed modification of the Germano subgrid‐scale closure method
https://aip.scitation.org/doi/10.1063/1.858280?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.858280?feed=most-citedThe subgrid‐scale closure method developed by Germano et al. is modified by use of a least squares technique to minimize the difference between the closure assumption and the resolved stresses. This modification removes a source of singularity and is believed to improve the method’s applicability.D. K. LillyTue, 01 Sep 1998 07:00:00 GMTNumerical Calculation of Time‐Dependent Viscous Incompressible Flow of Fluid with Free Surface
https://aip.scitation.org/doi/10.1063/1.1761178?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.1761178?feed=most-citedA new technique is described for the numerical investigation of the time‐dependent flow of an incompressible fluid, the boundary of which is partially confined and partially free. The full Navier‐Stokes equations are written in finite‐difference form, and the solution is accomplished by finite‐time‐step advancement. The primary dependent variables are the pressure and the velocity components. Also used is a set of marker particles which move with the fluid. The technique is called the marker and cell method. Some examples of the application of this method are presented. All non‐linear effects are completely included, and the transient aspects can be computedFrancis H. Harlow and J. Eddie WelchThu, 09 Dec 2004 08:00:00 GMTDevelopment of turbulence models for shear flows by a double expansion technique
https://aip.scitation.org/doi/10.1063/1.858424?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.858424?feed=most-citedTurbulence models are developed by supplementing the renormalization group (RNG) approach of Yakhot and Orszag [J. Sci. Comput. 1, 3 (1986)] with scale expansions for the Reynolds stress and production of dissipation terms. The additional expansion parameter (η≡SK̄/■̄) is the ratio of the turbulent to mean strain time scale. While low‐order expansions appear to provide an adequate description for the Reynolds stress, no finite truncation of the expansion for the production of dissipation term in powers of η suffices−terms of all orders must be retained. Based on these ideas, a new two‐equation model and Reynolds stress transport model are developedV. Yakhot, S. A. Orszag, S. Thangam, T. B. Gatski, and C. G. SpezialeThu, 04 Jun 1998 07:00:00 GMTOn pressure and velocity boundary conditions for the lattice Boltzmann BGK model
https://aip.scitation.org/doi/10.1063/1.869307?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.869307?feed=most-citedPressure (density) and velocity boundary conditions are studied for 2-D and 3-D lattice Boltzmann BGK models (LBGK) and a new method to specify these conditions is proposed. These conditions are constructed in consistency with the wall boundary condition, based on the idea of bounceback of the non-equilibrium distribution. When these conditions are used together with the incompressible LBGK model [J. Stat. Phys. 81, 35 (1995)] the simulation results recover the analytical solution of the plane Poiseuille flow driven by a pressure (density) difference. The half-way wall bounceback boundary condition is also used with the pressure (density) inlet/outlet conditions proposed inQisu Zou and Xiaoyi HeThu, 04 Jun 1998 07:00:00 GMTEquation of motion for a small rigid sphere in a nonuniform flow
https://aip.scitation.org/doi/10.1063/1.864230?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.864230?feed=most-citedThe forces on a small rigid sphere in a nonuniform flow are considered from first prinicples in order to resolve the errors in Tchen’s equation and the subsequent modified versions that have since appeared. Forces from the undisturbed flow and the disturbance flow created by the presence of the sphere are treated separately. Proper account is taken of the effect of spatial variations of the undisturbed flow on both forces. In particular the appropriate Faxen correction for unsteady Stokes flow is derived and included as part of the consistent approximation for the equation of motion.Martin R. Maxey and James J. RileyTue, 01 Sep 1998 07:00:00 GMTOn coughing and airborne droplet transmission to humans
https://aip.scitation.org/doi/10.1063/5.0011960?feed=most-cited
https://aip.scitation.org/doi/10.1063/5.0011960?feed=most-citedOur understanding of the mechanisms of airborne transmission of viruses is incomplete. This paper employs computational multiphase fluid dynamics and heat transfer to investigate transport, dispersion, and evaporation of saliva particles arising from a human cough. An ejection process of saliva droplets in air was applied to mimic the real event of a human cough. We employ an advanced three-dimensional model based on fully coupled Eulerian–Lagrangian techniques that take into account the relative humidity, turbulent dispersion forces, droplet phase-change, evaporation, and breakup in addition to the droplet–droplet and droplet–air interactions. We computationally investigate the effect of wind speed on socialTalib Dbouk and Dimitris DrikakisTue, 19 May 2020 02:58:26 GMTA general classification of three‐dimensional flow fields
https://aip.scitation.org/doi/10.1063/1.857730?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.857730?feed=most-citedThe geometry of solution trajectories for three first‐order coupled linear differential equations can be related and classified using three matrix invariants. This provides a generalized approach to the classification of elementary three‐dimensional flow patterns defined by instantaneous streamlines for flow at and away from no‐slip boundaries for both compressible and incompressible flow. Although the attention of this paper is on the velocity field and its associated deformation tensor, the results are valid for any smooth three‐dimensional vector field. For example, there may be situations where it is appropriate to work in terms of the vorticity field or pressure gradient field.M. S. Chong, A. E. Perry, and B. J. CantwellThu, 04 Jun 1998 07:00:00 GMTDirect numerical simulation of turbulent channel flow up to Reτ=590
https://aip.scitation.org/doi/10.1063/1.869966?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.869966?feed=most-citedNumerical simulations of fully developed turbulent channel flow at three Reynolds numbers up to are reported. It is noted that the higher Reynolds number simulations exhibit fewer low Reynolds number effects than previous simulations at A comprehensive set of statistics gathered from the simulations is available on the web at http://www.tam.uiuc.edu/Faculty/Moser/channel.Robert D. Moser, John Kim, and Nagi N. MansourFri, 05 Mar 1999 08:00:00 GMTInertial Ranges in Two‐Dimensional Turbulence
https://aip.scitation.org/doi/10.1063/1.1762301?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.1762301?feed=most-citedTwo‐dimensional turbulence has both kinetic energy and mean‐square vorticity as inviscid constants of motion. Consequently it admits two formal inertial ranges, , where ε is the rate of cascade of kinetic energy per unit mass, η is the rate of cascade of mean‐square vorticity, and the kinetic energy per unit mass is . The range is found to entail backward energy cascade, from higher to lower wavenumbers k, together with zero‐vorticity flow. The −3 range gives an upward vorticity flow and zero‐energy flow. The paradox in these results is resolved by the irreducibly triangular nature of the elementary wavenumber interactions.Robert H. KraichnanThu, 09 Dec 2004 08:00:00 GMTCapillary effects during droplet impact on a solid surface
https://aip.scitation.org/doi/10.1063/1.868850?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.868850?feed=most-citedImpact of water droplets on a flat, solid surface was studied using both experiments and numerical simulation. Liquid–solid contact angle was varied in experiments by adding traces of a surfactant to water. Impacting droplets were photographed and liquid–solid contact diameters and contact angles were measured from photographs. A numerical solution of the Navier–Stokes equation using a modified SOLA‐VOF method was used to model droplet deformation. Measured values of dynamic contact angles were used as a boundary condition for the numerical model. Impacting droplets spread on the surface until liquid surface tension and viscosity overcame inertial forces, after which they recoiledM. Pasandideh‐Fard, Y. M. Qiao, S. Chandra, and J. MostaghimiWed, 02 Sep 1998 07:00:00 GMTAn eddy-viscosity subgrid-scale model for turbulent shear flow: Algebraic theory and applications
https://aip.scitation.org/doi/10.1063/1.1785131?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.1785131?feed=most-citedAn eddy-viscosity model is proposed and applied in large-eddy simulation of turbulent shear flows with quite satisfactory results. The model is essentially not more complicated than the Smagorinsky model, but is constructed in such a way that its dissipation is relatively small in transitional and near-wall regions. The model is expressed in first-order derivatives, does not involve explicit filtering, averaging, or clipping procedures, and is rotationally invariant for isotropic filter widths. Because of these highly desirable properties the model seems to be well suited for engineering applications. In order to provide a foundation of the model, an algebraic framework forA. W. VremanWed, 01 Sep 2004 07:00:00 GMTSparsity-promoting dynamic mode decomposition
https://aip.scitation.org/doi/10.1063/1.4863670?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.4863670?feed=most-citedDynamic mode decomposition (DMD) represents an effective means for capturing the essential features of numerically or experimentally generated flow fields. In order to achieve a desirable tradeoff between the quality of approximation and the number of modes that are used to approximate the given fields, we develop a sparsity-promoting variant of the standard DMD algorithm. Sparsity is induced by regularizing the least-squares deviation between the matrix of snapshots and the linear combination of DMD modes with an additional term that penalizes the ℓ1-norm of the vector of DMD amplitudes. The globally optimal solution of the resulting regularized convex optimization problemMihailo R. Jovanović, Peter J. Schmid, and Joseph W. NicholsThu, 06 Feb 2014 08:00:00 GMTEquations of state in a lattice Boltzmann model
https://aip.scitation.org/doi/10.1063/1.2187070?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.2187070?feed=most-citedIn this paper we consider the incorporation of various equations of state into the single-component multiphase lattice Boltzmann model. Several cubic equations of state, including the van der Waals, Redlich-Kwong, and Peng-Robinson, as well as a noncubic equation of state (Carnahan-Starling), are incorporated into the lattice Boltzmann model. The details of phase separation in these nonideal single-component systems are presented by comparing the numerical simulation results in terms of density ratios, spurious currents, and temperature ranges. A comparison with a real fluid system, i.e., the properties of saturated water and steam, is also presented.Peng Yuan and Laura SchaeferMon, 03 Apr 2006 07:00:00 GMTMomentum transfer of a Boltzmann-lattice fluid with boundaries
https://aip.scitation.org/doi/10.1063/1.1399290?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.1399290?feed=most-citedWe study the velocity boundary condition for curved boundaries in the lattice Boltzmann equation (LBE). We propose a LBE boundary condition for moving boundaries by combination of the “bounce-back” scheme and spatial interpolations of first or second order. The proposed boundary condition is a simple, robust, efficient, and accurate scheme. Second-order accuracy of the boundary condition is demonstrated for two cases: (1) time-dependent two-dimensional circular Couette flow and (2) two-dimensional steady flow past a periodic array of circular cylinders (flow through the porous media of cylinders). For the former case, the lattice Boltzmann solution is compared with the analytic solutionM’hamed Bouzidi, Mouaouia Firdaouss, and Pierre LallemandMon, 15 Oct 2001 07:00:00 GMTHairpin vortex organization in wall turbulence
https://aip.scitation.org/doi/10.1063/1.2717527?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.2717527?feed=most-citedCoherent 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 layerRonald J. AdrianWed, 18 Apr 2007 07:00:00 GMTGrid-point requirements for large eddy simulation: Chapman’s estimates revisited
https://aip.scitation.org/doi/10.1063/1.3676783?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.3676783?feed=most-citedResolution requirements for large eddy simulation (LES), estimated by Chapman [AIAA J. 17, 1293 (1979)], are modified using accurate formulae for high Reynolds number boundary layer flow. The new estimates indicate that the number of grid points (N) required for wall-modeled LES is proportional to , but a wall-resolving LES requires , where is the flat-plate length in the streamwise direction. On the other hand, direct numerical simulation, resolving the Kolmogorov length scale, requires .Haecheon Choi and Parviz MoinFri, 06 Jan 2012 08:00:00 GMTOn respiratory droplets and face masks
https://aip.scitation.org/doi/10.1063/5.0015044?feed=most-cited
https://aip.scitation.org/doi/10.1063/5.0015044?feed=most-citedFace mask filters—textile, surgical, or respiratory—are widely used in an effort to limit the spread of airborne viral infections. Our understanding of the droplet dynamics around a face mask filter, including the droplet containment and leakage from and passing through the cover, is incomplete. We present a fluid dynamics study of the transmission of respiratory droplets through and around a face mask filter. By employing multiphase computational fluid dynamics in a fully coupled Eulerian–Lagrangian framework, we investigate the droplet dynamics induced by a mild coughing incident and examine the fluid dynamics phenomena affecting the mask efficiency. The model takes intoTalib Dbouk and Dimitris DrikakisTue, 16 Jun 2020 02:48:47 GMTRortex—A new vortex vector definition and vorticity tensor and vector decompositions
https://aip.scitation.org/doi/10.1063/1.5023001?feed=most-cited
https://aip.scitation.org/doi/10.1063/1.5023001?feed=most-citedA vortex is intuitively recognized as the rotational/swirling motion of the fluids. However, an unambiguous and universally accepted definition for vortex is yet to be achieved in the field of fluid mechanics, which is probably one of the major obstacles causing considerable confusions and misunderstandings in turbulence research. In our previous work, a new vector quantity that is called vortex vector was proposed to accurately describe the local fluid rotation and clearly display vortical structures. In this paper, the definition of the vortex vector, named Rortex here, is revisited from the mathematical perspective. The existence of the possible rotational axisChaoqun Liu, Yisheng Gao, Shuling Tian, and Xiangrui DongTue, 20 Mar 2018 04:58:04 GMTVisualizing the effectiveness of face masks in obstructing respiratory jets
https://aip.scitation.org/doi/10.1063/5.0016018?feed=most-cited
https://aip.scitation.org/doi/10.1063/5.0016018?feed=most-citedThe use of face masks in public settings has been widely recommended by public health officials during the current COVID-19 pandemic. The masks help mitigate the risk of cross-infection via respiratory droplets; however, there are no specific guidelines on mask materials and designs that are most effective in minimizing droplet dispersal. While there have been prior studies on the performance of medical-grade masks, there are insufficient data on cloth-based coverings, which are being used by a vast majority of the general public. We use qualitative visualizations of emulated coughs and sneezes to examine how material- and design-choices impact the extentSiddhartha Verma, Manhar Dhanak, and John FrankenfieldTue, 30 Jun 2020 02:54:43 GMT