Consistent post-reaction vibrational energy redistribution in DSMC simulations using TCE model
The direct simulation Monte Carlo (DSMC) method has been widely applied to study shockwaves, hypersonic reentryflows, and other nonequilibriumflow phenomena. Although there is currently active research on high-fidelitymodels based onab initio data, the total collisionenergy (TCE) and Larsen-Borgnakke (LB)models remain the most often used chemistry and relaxationmodels in DSMC simulations, respectively. The conventional implementation of the discrete LBmodel, however, may not satisfy detailed balance when recombination andexchange reactions play an important role in theflowenergy balance. This issue can become even more cri...
Source: Physics of Fluids - October 19, 2016 Category: Physics Authors: Israel Borges Sebasti ão and Alina Alexeenko Source Type: research
Puddle jumping: Spontaneous ejection of large liquid droplets from hydrophobic surfaces during drop tower tests
Largedroplets and puddles jump spontaneously from sufficientlyhydrophobicsurfaces during routinedrop tower tests. The simple low-cost passive mechanism can in turn be used as an experimental device to investigate dynamicdroplet phenomena fordrops up to 104 times larger than their normal terrestrial counterparts. We provide and/or confirm quick and qualitative design guides for such “drop shooters” as employed indrop tower tests including relationships to predictdroplet ejection durations and velocities as functions ofdrop volume,surface texture,surface contour, wettability pattern, and fluid properties including contac...
Source: Physics of Fluids - October 18, 2016 Category: Physics Authors: B. Attari, M. Weislogel, A. Wollman, Y. Chen and T. Snyder Source Type: research
Direct numerical simulation of heat transfer in a spatially developing turbulent boundary layer
Direct numerical simulation has been performed to investigate heat transfer in a zero-pressure-gradientspatially developingturbulent boundary layer with realistic thermal inflowboundary conditions. The temperature is considered as a passive scalar and the molecular Prandtl number is set to be 0.71. Theturbulence statistics for both the velocity and temperature fields show good agreement with previous numerical and experimental data in the literature. The present study provides a valuable database for thespatially developingturbulent thermal boundary layer over a wide range ofReynolds numbers fromReθ = 1100 to 1940. The si...
Source: Physics of Fluids - October 18, 2016 Category: Physics Authors: Dong Li, Kun Luo and Jianren Fan Source Type: research
Spatial-temporal and modal analysis of propeller induced ground vortices by particle image velocimetry
During the ground operation ofaircraft, there is potentially a system ofvortices generated from the ground toward the propulsor, commonly denoted as groundvortices. Although extensive research has been conducted on groundvortices induced by turbofans which were simplified by suction tubes, these studies cannot well capture the properties of groundvortices induced by propellers, e.g., theflow phenomena due to intermittent characteristics of blade passing and the presence of slipstream of the propeller. Therefore, the investigation of groundvortices induced by a propeller is performed to improve understanding of these phenom...
Source: Physics of Fluids - October 18, 2016 Category: Physics Authors: Y. Yang, A. Sciacchitano, L. L. M. Veldhuis and G. Eitelberg Source Type: research
Stable state of Mode A for flow past a circular cylinder
A stable three-dimensional (3D) wake structure forflow past a circular cylinder has been discovered through 3D direct numerical simulations (DNS). The stable 3D wake structure occurs over a small range ofReynolds number (Re) below the criticalRe for Mode A∗ (i.e., Mode A with large-scalevortex dislocations, where Mode A is the first 3Dinstability mode which will evolve into Mode A∗)instability. It is believed that the stable 3D wake structure discovered in this study is the stable state of Mode A wake structure inferred by Williamson [ “Three-dimensional wake transition,” J. Fluid Mech.328, 345 –407 (1996)]. This...
Source: Physics of Fluids - October 18, 2016 Category: Physics Authors: Hongyi Jiang, Liang Cheng, Feifei Tong, Scott Draper and Hongwei An Source Type: research
Similarity transformation approach for ferromagnetic mixed convection flow in the presence of chemically reactive magnetic dipole
A simple model of chemical reactions for two dimensionalferrofluidflows is constructed. The impact of magnetic dipole and mixed convection is further analyzed.Flow is caused by linear stretching of the sheet. Similarity transformation is adopted to convert the partial differential equations into ordinary differential equations and then solved by Euler ’s explicit method. The characteristics of sundry parameters on the velocity,temperature, and concentration fields are graphically elaborated. It is noted that the impact of magneto-thermomechanical interaction is to slow down the fluid motion. The skinfriction coefficient ...
Source: Physics of Fluids - October 18, 2016 Category: Physics Authors: Tasawar Hayat, Muhammad Ijaz Khan, Maria Imtiaz, Ahmed Alsaedi and Muhammad Waqas Source Type: research
Review of literature on local scour under plane turbulent wall jets
Stability ofhydraulic structures is threatened by persistent scour downstream of the apron, which renders their foundations exposed.Jets issuing under the sluice gate are turbulent enough to cause significant scour. Extensive study of thejets is, therefore, necessary in order to understand the underlyinghydraulics and provide remedialmeasures. In this paper, a comprehensive review of the investigations on local scour caused by walljets is presented, including both the classical as well as the prevalent approach. Various aspects of the scour under walljets have been explained, including the process of scouring, different pa...
Source: Physics of Fluids - October 17, 2016 Category: Physics Authors: Mohammad Aamir and Zulfequar Ahmad Source Type: research
Modeling of conductive particle motion in viscous medium affected by an electric field considering particle-electrode interactions and microdischarge phenomenon
Up and down motion of a spherical conductive particle in dielectricviscous fluid driven by a DCelectric field between two parallelelectrodes was investigated. A nonlinear differential equation, governing the particle dynamics, was derived, based on Newton ’s second law of mechanics, and solved numerically. All the pertaining dimensionless groups were extracted. In contrast to similar previous works,hydrodynamic interaction between the particle and theelectrodes, as well as image electric forces, has been taken into account. Furthermore, the influence of themicrodischarge produced between theelectrodes and the approaching...
Source: Physics of Fluids - October 17, 2016 Category: Physics Authors: Ghiyam Eslami, Esmaeil Esmaeilzadeh and Alberto T. P érez Source Type: research
Tidal energy redistribution among vertical modes in a fluid with a mid-depth pycnocline
We modeled internaltide generation above a high sinusoidal ridge in a fluid with a mid-depth pycnocline and developed an original method to quantify internaltide vertical mode amplitude in two-dimensional-vertical simulations. Since lowest modes can propagate over considerable distances, while high modes are more likely to dissipate locally, estimating thetidal energy distribution among vertical modes is necessary to investigate the spatial redistribution of thetidal energy. Our numerical approach allows expansion and verification of previous analytical studies over a larger range of configurations. Thetidal energy distrib...
Source: Physics of Fluids - October 17, 2016 Category: Physics Authors: L. Bordois, F. Auclair, A. Paci, Y. Dossmann, T. Gerkema and C. Nguyen Source Type: research
On the response of nonlinear viscoelastic materials in creep and stress relaxation experiments in the lubricated squeeze flow setting
Rigorous analysis of the response of nonlinear materials to step inputs requires one to simultaneously handle the discontinuity, differentiation, and nonlinearity. This task is however beyond the reach of the standard theories such as the classical theory of distributions and presents a considerable mathematical difficulty. New advanced mathematical tools are necessary to handle the challenge. An elegant and relatively easy-to-use framework capable of accomplishing the task is provided by the Colombeau algebra, which is a generalisation of the classical theory of distributions to the nonlinear setting. We use the Colombeau...
Source: Physics of Fluids - October 14, 2016 Category: Physics Authors: Martin Řehoř, Vít Průša and Karel Tůma Source Type: research
Erratum: “Spatial evolution of supersonic streamwise vortices” [Phys. Fluids 26, 074102 (2014)]
(Source: Physics of Fluids)
Source: Physics of Fluids - October 12, 2016 Category: Physics Authors: Toshihiko Hiejima Source Type: research
The impact of heating the breakdown bubble on the global mode of a swirling jet: Experiments and linear stability analysis
This study investigates the dynamics of non-isothermal swirling jets undergoingvortex breakdown, with an emphasis on helicalcoherent structures. It is proposed that the dominant helicalcoherent structure can be suppressed by heating the recirculation bubble. This proposition is assessed with stereo Particle ImageVelocimetry(PIV)measurements of thebreakdown region of isothermal and heated swirling jets. Thecoherent kinetic energy of the dominant helical structure was derived fromPIV snapshots via proper orthogonal decomposition. For one set of experimental parameters, mild heating is found to increase the energy content of ...
Source: Physics of Fluids - October 12, 2016 Category: Physics Authors: Lothar Rukes, Moritz Sieber, C. Oliver Paschereit and Kilian Oberleithner Source Type: research
Drop generation from a vibrating nozzle in an immiscible liquid-liquid system
Dropgeneration from an axially vibrating nozzle exhibits a transition indrop diameter when varying the vibration amplitude. Below a threshold amplitude, forcing has essentially no effect ondrop size anddrops form in dripping mode. Above the threshold,drop size is controlled by forcing:drops detach at resonance, i.e., when the first eigenfrequency of the growingdrop coincides with the forcing frequency. We experimentally study the impact of the nozzle inner diameter, dispersed phaseflow rate,interfacial tension, and dispersed phaseviscosity on this transition.Drop diameter is well correlated to the mode 1 eigenfrequency of ...
Source: Physics of Fluids - October 12, 2016 Category: Physics Authors: A. Bertrandias, H. Duval, J. Casalinho and M. L. Giorgi Source Type: research
Numerical study on the freely falling plate: Effects of density ratio and thickness-to-length ratio
A numerical study on two-dimensional (2D) rectangular plates falling freely in water is carried out in the range of 1.2 ≤ρs/f≤ 5.0 and 1/20 ≤β≤ 1/4, whereρs/f is the solid-to-water density ratio andβ is the plate thickness-to-length ratio. To study this problem, the immersed boundary-latticeBoltzmann flux solver in a moving frame is applied and validated. For the numerical result, aphase diagram is constructed for fluttering, tumbling, and apparent chaoticmotions of the plate parameterized usingρs/f andβ. The evolution of vortical structures in both modes is decomposed into three typical stages of initial tra...
Source: Physics of Fluids - October 11, 2016 Category: Physics Authors: Y. Wang, C. Shu, C. J. Teo and L. M. Yang Source Type: research
Natural solutal convection in magnetic fluids: First-order phase transition aspect
Concentration stratification ofmagnetic fluids under the action of externalmagnetic field can disturb mechanical equilibrium in the system and cause intensive solutalconvection. The current paper is devoted to the study of free solutalconvection inmagnetic fluids undergoing first-orderphase transition. Simulation of solutalconvection in OpenFOAM package makes it possible to compare numeric results with physicalexperiment observations. The numeric simulation of convective hydrodynamic flows was carried out in the framework of several theories of first-orderphase transition in ferrocolloids. The numerical results are compare...
Source: Physics of Fluids - October 10, 2016 Category: Physics Authors: Aleksey S. Ivanov Source Type: research
