The Experts below are selected from a list of 40062 Experts worldwide ranked by ideXlab platform
Hossein Parishani - One of the best experts on this subject based on the ideXlab platform.
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effects of Gravity on the acceleration and pair statistics of inertial particles in homogeneous isotropic turbulence
Physics of Fluids, 2015Co-Authors: Hossein Parishani, Orlando Ayala, Bogdan Rosa, Lianping Wang, Wojciech W GrabowskiAbstract:Within the context of heavy particles suspended in a turbulent airflow, we study the eff ects of Gravity on acceleration statistics and radial relative velocity (RRV) of inertial particles. The turbulent flow is simulated by direct numerical simulation (DNS) on a 256 3 grid and the dynamics of O(10 6 ) inertial particles by the point-particle approach. For particles/droplets with radius from 10 to 60 µm, we found that the Gravity plays an important role in particle acceleration statistics: (a) a peak value of particle acceleration variance appears in both the horizontal and vertical directions at a particle Stokes number of about 1.2, at which the particle horizontal acceleration clearly exceeds the fluid-element acceleration; (b) Gravity constantly disrupts quasi-equilibrium of a droplet’s response to local turbulent motion and amplifies extreme acceleration events both in the vertical and horizontal directions and thus eff ectively reduces the inertial filtering mechanism. By decomposing the RRV of the particles into three parts: (1) diff erential sedimentation, (2) local flow shear, and (3) particle diff erential acceleration, we evaluate and compare their separate contributions. For monodisperse particles, we show that the presence of Gravity does not have a significant e ff ect on the shear Term. On the other hand, Gravity suppresses the probability distribution function (pdf) tails of the diff erential acceleration Term due to a lower particle-eddy interaction time in presence of Gravity. For bidisperse cases, we find that Gravity can decrease the shear Term slightly by dispersing particles into vortices where fluid shear is relatively low. The di ff erential acceleration Term is found to be positively correlated with the Gravity Term, and this correlation is stronger when the diff erence in colliding particle radii becomes smaller. Finally, a theory is developed to explain the eff ects of Gravity and turbulence on the horizontal and vertical acceleration variances of inertial particles at small Stokes numbers, showing analytically that Gravity aff ects particle acceleration variance both in horizontal and vertical directions, resulting in an increase in particle acceleration variance in both directions. Furthermore, the eff ect of Gravity on the horizontal acceleration variance is predicted to be stronger than that in the vertical direction, in agreement with our DNS results. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4915121]
Wojciech W Grabowski - One of the best experts on this subject based on the ideXlab platform.
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effects of Gravity on the acceleration and pair statistics of inertial particles in homogeneous isotropic turbulence
Physics of Fluids, 2015Co-Authors: Hossein Parishani, Orlando Ayala, Bogdan Rosa, Lianping Wang, Wojciech W GrabowskiAbstract:Within the context of heavy particles suspended in a turbulent airflow, we study the eff ects of Gravity on acceleration statistics and radial relative velocity (RRV) of inertial particles. The turbulent flow is simulated by direct numerical simulation (DNS) on a 256 3 grid and the dynamics of O(10 6 ) inertial particles by the point-particle approach. For particles/droplets with radius from 10 to 60 µm, we found that the Gravity plays an important role in particle acceleration statistics: (a) a peak value of particle acceleration variance appears in both the horizontal and vertical directions at a particle Stokes number of about 1.2, at which the particle horizontal acceleration clearly exceeds the fluid-element acceleration; (b) Gravity constantly disrupts quasi-equilibrium of a droplet’s response to local turbulent motion and amplifies extreme acceleration events both in the vertical and horizontal directions and thus eff ectively reduces the inertial filtering mechanism. By decomposing the RRV of the particles into three parts: (1) diff erential sedimentation, (2) local flow shear, and (3) particle diff erential acceleration, we evaluate and compare their separate contributions. For monodisperse particles, we show that the presence of Gravity does not have a significant e ff ect on the shear Term. On the other hand, Gravity suppresses the probability distribution function (pdf) tails of the diff erential acceleration Term due to a lower particle-eddy interaction time in presence of Gravity. For bidisperse cases, we find that Gravity can decrease the shear Term slightly by dispersing particles into vortices where fluid shear is relatively low. The di ff erential acceleration Term is found to be positively correlated with the Gravity Term, and this correlation is stronger when the diff erence in colliding particle radii becomes smaller. Finally, a theory is developed to explain the eff ects of Gravity and turbulence on the horizontal and vertical acceleration variances of inertial particles at small Stokes numbers, showing analytically that Gravity aff ects particle acceleration variance both in horizontal and vertical directions, resulting in an increase in particle acceleration variance in both directions. Furthermore, the eff ect of Gravity on the horizontal acceleration variance is predicted to be stronger than that in the vertical direction, in agreement with our DNS results. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4915121]
Lianping Wang - One of the best experts on this subject based on the ideXlab platform.
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effects of Gravity on the acceleration and pair statistics of inertial particles in homogeneous isotropic turbulence
Physics of Fluids, 2015Co-Authors: Hossein Parishani, Orlando Ayala, Bogdan Rosa, Lianping Wang, Wojciech W GrabowskiAbstract:Within the context of heavy particles suspended in a turbulent airflow, we study the eff ects of Gravity on acceleration statistics and radial relative velocity (RRV) of inertial particles. The turbulent flow is simulated by direct numerical simulation (DNS) on a 256 3 grid and the dynamics of O(10 6 ) inertial particles by the point-particle approach. For particles/droplets with radius from 10 to 60 µm, we found that the Gravity plays an important role in particle acceleration statistics: (a) a peak value of particle acceleration variance appears in both the horizontal and vertical directions at a particle Stokes number of about 1.2, at which the particle horizontal acceleration clearly exceeds the fluid-element acceleration; (b) Gravity constantly disrupts quasi-equilibrium of a droplet’s response to local turbulent motion and amplifies extreme acceleration events both in the vertical and horizontal directions and thus eff ectively reduces the inertial filtering mechanism. By decomposing the RRV of the particles into three parts: (1) diff erential sedimentation, (2) local flow shear, and (3) particle diff erential acceleration, we evaluate and compare their separate contributions. For monodisperse particles, we show that the presence of Gravity does not have a significant e ff ect on the shear Term. On the other hand, Gravity suppresses the probability distribution function (pdf) tails of the diff erential acceleration Term due to a lower particle-eddy interaction time in presence of Gravity. For bidisperse cases, we find that Gravity can decrease the shear Term slightly by dispersing particles into vortices where fluid shear is relatively low. The di ff erential acceleration Term is found to be positively correlated with the Gravity Term, and this correlation is stronger when the diff erence in colliding particle radii becomes smaller. Finally, a theory is developed to explain the eff ects of Gravity and turbulence on the horizontal and vertical acceleration variances of inertial particles at small Stokes numbers, showing analytically that Gravity aff ects particle acceleration variance both in horizontal and vertical directions, resulting in an increase in particle acceleration variance in both directions. Furthermore, the eff ect of Gravity on the horizontal acceleration variance is predicted to be stronger than that in the vertical direction, in agreement with our DNS results. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4915121]
S Markoff - One of the best experts on this subject based on the ideXlab platform.
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linking accretion flow and particle acceleration in jets ii self similar jet models with full relativistic mhd gravitational mass
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Peter Polko, David L Meier, S MarkoffAbstract:We present a new, semi-analytic formalism to model the acceleration and collimation of relativistic jets in a gravitational potential. The gravitational energy density includes the kinetic, thermal and electromagnetic mass contributions. The solutions are close to self-similar throughout the integration, from very close to the black hole to the region where Gravity is unimportant. The field lines are tied to the conditions very close to the central object and eventually overcollimate, possibly leading to a collimation shock. This collimation shock could provide the conditions for diffusive shock acceleration, leading to the observed electron populations with a power-law energy distribution in jets. We provide the derivation, a detailed analysis of a solution and describe the effects the parameters have on the properties of the solutions, such as the Lorentz factor and location of the collimation shock. We also discuss the deviations from self-similarity. By comparing the new Gravity Term with the Gravity Term obtained from a non-relativistic formalism in a previous work, we show they are equivalent in the non-relativistic limit. This equivalence shows the approach taken in that work is valid and allows us to comment on its limitations.
Gedeon Dagan - One of the best experts on this subject based on the ideXlab platform.
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Mixing at the interface between two fluids in porous media: a boundary-layer solution
Journal of Fluid Mechanics, 2007Co-Authors: Amir Paster, Gedeon DaganAbstract:A lighter fluid (fresh water) flows steadily above a body of a standing heavier one (sea water) in a porous medium. If mixing by transverse pore-scale dispersion is neglected, a sharp interface separates the two fluids. Solutions for interface problems have been derived in the past, particularly for the case of interest here: sea-water intrusion in coastal aquifers. The Peclet number characterizing mixing, Pe=b'/α T , where b' is the aquifer thickness and α T is transverse dispersivity, is generally much larger than unity. Mixing is nevertheless important in a few applications, particularly in the development of a transition layer near the interface and in entrainment of sea water within this layer. The equations of flow and transport in the mixing zone comprise the unknown flux, pressure and concentration fields, which cannot be separated owing to the presence of density in the Gravity Term. They are nonlinear because of the advective Term and the dependence of the dispersion coefficients on flux, the latter making the problem different from that of mixing between streams in laminar viscous flow. The aim of the study is to solve the mixing-layer problem for sea-water intrusion by using a boundary-layer approximation, which was used in the past for the case of uniform flow of the upper fluid, whereas here the two-dimensional flux field is non-uniform. The boundary-layer solution is obtained in a few steps: (i) analytical potential flow solution of the upper fluid above a sharp interface is adopted; (ii) the equations are reformulated with the potential and streamfunction of this flow serving as independent variables; (iii) boundary-layer approximate equations are formulated in Terms of these variables; and (iv) simple analytical solutions are obtained by the von Karman integral method. The agreement with an existing boundary-layer solution for uniform flow is excellent, and similarly for a solution of a particular case of sea-water intrusion with a variable-density code. The present solution may serve for estimating the thickness of the mixing layer and the rate of sea-water entrainment in applications, as well as a benchmark for more complex problems.
