Homogeneous cooling of mixtures of particle shapes
In this work, we examine theoretically the cooling dynamics of binary mixtures of spheres and rods. To this end, we introduce a generalized mean field analytical theory, which describes the free cooling behavior of the mixture. The relevant characteristic time scale for the cooling process is derived, depending on the mixture composition and the aspect ratio of the rods. We simulate mixtures of spherocylinders and spheres using a molecular dynamics algorithm implemented on graphics processing unit (GPU) architecture. We systematically study mixtures composed of spheres and rods with several aspect ratios and varying the mi...
Source: Physics of Fluids - July 1, 2016 Category: Physics Authors: R. C. Hidalgo, D. Serero and T. Pöschel Source Type: research
Phenomenology of a flow around a circular cylinder at sub-critical and critical Reynolds numbers
In this work, the flow around a circular cylinder is investigated at Reynolds numbers ranging from 79 000 up to 238 000 by means of a combined acquisition system based on Temperature Sensitive Paint (TSP) and particle velocimetry. The proposed setup allows simultaneous and time-resolved measurement of absolute temperature and relative skin friction fields onto the cylinder surface and near-wake velocity field. Combination of time-resolved surface measurements and planar near-field velocity data allows the investigation of the profound modifications undergone by the wall shear stress topology and its connections to the ...
Source: Physics of Fluids - July 1, 2016 Category: Physics Authors: Alessandro Capone, Christian Klein, Fabio Di Felice and Massimo Miozzi Source Type: research
Hybrid RANS/LES of turbulent flow in a rotating rib-roughened channel
In this paper, we investigate the effect of the Coriolis force on the flow field in a rib-roughened channel subjected to either clockwise or counter-clockwise system rotation using hybrid RANS/LES based on wall modelling. A simplified dynamic forcing scheme incorporating backscatter is proposed for the hybrid simulation approach. The flow is characterized by a Reynolds number of Re = 1.5 × 104 and a rotation number Ro ranging from −0.6 to 0.6. The mean flow speed and turbulence level near the roughened wall are enhanced under counter-clockwise rotation and suppressed under clockwise rotation. The Coriolis force signific...
Source: Physics of Fluids - July 1, 2016 Category: Physics Authors: Qian-Qiu Xun and Bing-Chen Wang Source Type: research
Parametric experimental studies on mixing characteristics within a low area ratio rectangular supersonic gaseous ejector
We use the rectangular gaseous supersonic ejector as a platform to study the mixing characteristics of a confined supersonic jet. The entrainment ratio (ER) of the ejector, the non-mixed length (LNM), and potential core length (LPC) of the primary supersonic jet are measures to characterize mixing within the supersonic ejector. Experiments are carried out on a low area ratio rectangular supersonic ejector with air as the working fluid in both primary and secondary flows. The design Mach number of the nozzle (MPD = 1.5–3.0) and primary flow stagnation pressure (Pop = 4.89–9.89 bars) are the parameters that are varied du...
Source: Physics of Fluids - July 1, 2016 Category: Physics Authors: S. K. Karthick, Srisha M. V. Rao, G. Jagadeesh and K. P. J. Reddy Source Type: research
Influence of the mixing parameter on the second order moments of velocity and concentration in Rayleigh–Taylor turbulence
The purpose of this paper is to highlight the existence of simple algebraic expressions linking the second order moments of velocity and concentration in Rayleigh–Taylor turbulence, in the Boussinesq limit. Focusing on the concentration variance, these relations allow to underline the influence of mixing on the remaining second order correlations, as well as on the growth rate of the mixing zone. (Source: Physics of Fluids)
Source: Physics of Fluids - June 29, 2016 Category: Physics Authors: Olivier Soulard, Jérôme Griffond and Benoît-Joseph Gréa Source Type: research
Poiseuille flow-induced vibrations of two tandem circular cylinders with different mass ratios
Flow-induced vibrations of two tandem circular cylinders with different mass ratios confined between two parallel walls are numerically studied via a lattice Boltzmann method. With fixed Reynolds number Re = 100 and blockage ratio β = 1/4, the effects of mass ratio m
* = [0.0625, 16] and streamwise separation between two cylinders S/D = [1.125, 10] on the cylinder motions and vortex wake modes are investigated. A variety of distinct cylinder motion regimes involving the symmetric periodic vibration, biased quasi-periodic vibration, beating vibration, and steady regimes, with the corresponding wake structure...
Source: Physics of Fluids - June 27, 2016 Category: Physics Authors: Ren-Jie Jiang and Jian-Zhong Lin Source Type: research
Precession-driven dynamos in a full sphere and the role of large scale cyclonic vortices
Precession has been proposed as an alternative power source for planetary dynamos. Previous hydrodynamic simulations suggested that precession can generate very complex flows in planetary liquid cores [Y. Lin, P. Marti, and J. Noir, “Shear-driven parametric instability in a precessing sphere,” Phys. Fluids
27, 046601 (2015)]. In the present study, we numerically investigate the magnetohydrodynamics of a precessing sphere. We demonstrate precession driven dynamos in different flow regimes, from laminar to turbulent flows. In particular, we highlight the magnetic field generation by large scale cyclonic v...
Source: Physics of Fluids - June 23, 2016 Category: Physics Authors: Yufeng Lin, Philippe Marti, Jerome Noir and Andrew Jackson Source Type: research
Turbulence generation through intense kinetic energy sources
Direct numerical simulations (DNS) are used to systematically study the development and establishment of turbulence when the flow is initialized with concentrated regions of intense kinetic energy. This resembles both active and passive grids which have been extensively used to generate and study turbulence in laboratories at different Reynolds numbers and with different characteristics, such as the degree of isotropy and homogeneity. A large DNS database was generated covering a wide range of initial conditions with a focus on perturbations with some directional preference, a condition found in active jet grids and passiv...
Source: Physics of Fluids - June 23, 2016 Category: Physics Authors: Agustin F. Maqui and Diego A. Donzis Source Type: research
Investigation on dip coating process by mathematical modeling of non-Newtonian fluid coating on cylindrical substrate
A mathematical model for the dip coating process has been developed for cylindrical geometries with non-Newtonian fluids. This investigation explores the effects of the substrate radius and hydrodynamic behavior of the non-Newtonian viscous fluid on the resulting thin film on the substrate. The coating fluid studied, Dymax 1186-MT, is a resin for fiber optics and used as a matrix to suspend 1 vol. % titanium dioxide particles. The coating substrate is a 100 μm diameter fiber optic diffuser. Ellis viscosity
model is applied as a non-Newtonian viscous
model for coating thickness prediction, i...
Source: Physics of Fluids - June 23, 2016 Category: Physics Authors: Mahyar Javidi, Michael A. Pope and Andrew N. Hrymak Source Type: research
LES investigation of the transport and decay of various-strengths wake vortices in ground effect and subjected to a turbulent crosswind
This study is concerned with the investigation of two-vortex systems (2VS) of various strengths that are released near the ground and evolve in the presence of a turbulent crosswind. We analyze the physics of the vortices
interactions with the turbulent wind and with the ground during the rebound phase, and that lead to the fully developed turbulent
flow and interactions. The transport and decay of the vortices are also analyzed. The turbulent wind itself is obtained by direct numerical simulation using a half channel flow. The flow is then supplemented with the 2VS, using vortices with a ci...
Source: Physics of Fluids - June 22, 2016 Category: Physics Authors: L. Bricteux, M. Duponcheel, I. De Visscher and G. Winckelmans Source Type: research
Effect of drop size on the impact thermodynamics for supercooled large droplet in aircraft icing
Supercooled large droplet (SLD), which can cause abnormal icing, is a well-known issue in aerospace engineering. Although efforts have been exerted to understand large droplet impact dynamics and the supercooled feature in the film/substrate interface, respectively, the thermodynamic effect during the SLD impact process has not received sufficient attention. This work conducts experimental studies to determine the effects of drop size on the thermodynamics for supercooled large droplet impingement. Through phenomenological reproduction, the rapid-freezing characteristics are observed in diameters of 400, 800, and 1300 μm....
Source: Physics of Fluids - June 21, 2016 Category: Physics Authors: Chen Zhang and Hong Liu Source Type: research
The role of fluid dynamics on compressed/expanded surfactant monolayers
We present a long wave theory that takes into account the fluid dynamics in the bulk phase coupled to the free surface elevation. In addition, apparent irreversibility is also discussed that may result from artifacts associated with the menisci
dynamics when surface tension is measured using a Wilhelmy plate. Instead, additional, purely chemical, non-equilibrium effects are ignored. Results from this theory are discussed for varying values of the parameters, which permit establishing specific predictions on experiments. On the other hand, these results compare fairly well with the available experimental obs...
Source: Physics of Fluids - June 21, 2016 Category: Physics Authors: Maria Higuera, Jose M. Perales and Jose M. Vega Source Type: research
Simulation of inertial fibre orientation in turbulent flow
The spatial and orientational behaviour of fibres within a suspension influences the rheological and mechanical properties of that suspension. An Eulerian-Lagrangian framework to simulate the behaviour of fibres in turbulent flows is presented. The framework is intended for use in simulations of non-spherical particles with high Reynolds numbers, beyond the Stokesian regime, and is a computationally efficient alternative to existing Stokesian models for fibre suspensions in turbulent flow. It is based on modifying available empirical drag correlations for the translation of non-spherical particles to be orientation depende...
Source: Physics of Fluids - June 21, 2016 Category: Physics Authors: Derrick O. Njobuenwu and Michael Fairweather Source Type: research
Electro-osmosis over inhomogeneously charged surfaces in presence of non-electrostatic ion-ion interactions
In this study, we attempt to bring out a generalized formulation for electro-osmotic flows over inhomogeneously charged surfaces in presence of non-electrostatic ion-ion interactions. To this end, we start with modified electro-chemical potential of the individual species and subsequently use it to derive modified Nernst-Planck equation accounting for the ionic fluxes generated because of the presence of non-electrostatic potential. We establish what we refer to as the Poisson-Helmholtz-Nernst-Planck equations, coupled with the Navier-Stokes equations, to describe the complete transport process. Our analysis shows that the...
Source: Physics of Fluids - June 21, 2016 Category: Physics Authors: Uddipta Ghosh and Suman Chakraborty Source Type: research
Resonances in the forced turbulent wake past a 3D blunt body
We study the resonances of a forced turbulent wake past a flat-based bluff body using symmetric and antisymmetric actuation modes. The natural, unforced wake flow exhibits broadband dynamics superimposed on oscillatory motions linked to the reminiscent laminar Bénard-von Kármán instability in the turbulent flow. Harmonic and subharmonic resonances can be controlled by the phase relationship of periodic forcing and are linked to the symmetry properties of vortex shedding. Symmetric forcing leads to a strong subharmonic amplification of vortex shedding in the wake, but no harmonic excitation. The robustness of the subharm...
Source: Physics of Fluids - June 21, 2016 Category: Physics Authors: Diogo Barros, Jacques Borée, Bernd R. Noack and Andreas Spohn Source Type: research
