The Experts below are selected from a list of 471 Experts worldwide ranked by ideXlab platform
Hjh Herman Clercx - One of the best experts on this subject based on the ideXlab platform.
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an efficient second order method for the approximation of the Basset history Force
Journal of Computational Physics, 2011Co-Authors: M A T Van Hinsberg, J Ten Thije H M Boonkkamp, Hjh Herman ClercxAbstract:The hydrodynamic Force exerted by a fluid on small isolated rigid spherical particles are usually well described by the Maxey-Riley (MR) equation. The most time-consuming contribution in the MR equation is the Basset history Force which is a well-known problem for many-particle simulations in turbulence. In this paper a novel numerical approach is proposed for the computation of the Basset history Force based on the use of exponential functions to approximate the tail of the Basset Force kernel. Typically, this approach not only decreases the cpu time and memory requirements for the Basset Force computation by more than an order of magnitude, but also increases the accuracy by an order of magnitude. The method has a temporal accuracy of O ( Δ t 2 ) which is a substantial improvement compared to methods available in the literature. Furthermore, the method is partially implicit in order to increase stability of the computation. Traditional methods for the calculation of the Basset history Force can influence statistical properties of the particles in isotropic turbulence, which is due to the error made by approximating the Basset Force and the limited number of particles that can be tracked with classical methods. The new method turns out to provide more reliable statistical data.
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vertical dispersion of light inertial particles in stably stratified turbulence the influence of the Basset Force
Physics of Fluids, 2010Co-Authors: Van Marleen M Aartrijk, Hjh Herman ClercxAbstract:The dispersion of light inertial particles $\rho_p/\rho_f = \mathcal{O}(1)$ in statistically stationary stably stratified turbulence is studied by means of direct numerical simulations. The light particle dispersion behavior is found to be comparable to that of heavy particles when displayed as a function of the Stokes number. Deviations from fluid particle dispersion are found already for small Stokes numbers; the length of the typical plateau for vertical dispersion is shorter for the light inertial particles. All the Forces in the Maxey-Riley equation are taken into account and they are found to be of similar magnitude as the Stokes drag for particles with $\rho_p/\rho_f = \mathcal{O}(1)$. However, not all Forces directly influence the particle dispersion. It is shown that especially the often neglected Basset Force plays a considerable role in the vertical dispersion of light particles in stratified turbulence. Neglecting this Force results in an overprediction of the vertical dispersion by about 15%-20%.
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an efficient second order method for the approximation of the Basset history Force
CASA-report, 2010Co-Authors: M A T Van Hinsberg, Thije Boonkkamp Ten J H M, Hjh Herman ClercxAbstract:The hydrodynamic Forces exerted by a fluid on small isolated rigid spherical particles are usually well described by the Maxey-Riley (MR) equation. The most time-consuming contribution in the MR equation is the Basset history Force which is a well-known problem for many-particle simulations in turbulence. In this paper a novel numerical approach is proposed for the computation of the Basset history Force based on the use of exponential functions to approximate the tail of the Basset Force kernel. Typically, this approach not only decreases the cpu time and memory requirements for the Basset Force computation by more than an order of magnitude, but also increases the accuracy by an order of magnitude. The method has a temporal accuracy of O($\Delta t^2$) which is a substantial improvement compared to methods available in the literature. Furthermore, the method is partially implicit in order to increase stability of the computation. Traditional methods for the calculation of the Basset history Force can influence statistical properties of the particles in isotropic turbulence, which is due to the error made by approximating the Basset Force and the limited number of particles that can be tracked with classical methods. The new method turns out to provide more reliable statistical data. Keywords: Basset-history Force, numerical approximation, particle laden flow, Maxey- Riley equation, isotropic turbulence.
Ronald J. Adrian - One of the best experts on this subject based on the ideXlab platform.
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particle dispersion in isotropic turbulence under stokes drag and Basset Force with gravitational settling
Journal of Fluid Mechanics, 1991Co-Authors: Renwei Mei, Ronald J. Adrian, Thomas J HanrattyAbstract:An analysis that includes the effects of Basset and gravitational Forces is presented for the dispersion of particles experiencing Stokes drag in isotropic turbulence. The fluid velocity correlation function evaluated on the particle trajectory is obtained by using the independence approximation and the assumption of Gaussian velocity distributions for both the fluid and the particle, formulated by Pismen & Nir (1978). The dynamic equation for particle motion with the Basset Force is Fourier transformed to the frequency domain where it can be solved exactly. It is found that the Basset Force has virtually no influence on the structure of the fluid velocity fluctuations seen by the particles or on particle diffusivities. It does, however, affect the motion of the particle by increasing (reducing) the intensities of particle turbulence for particles with larger (smaller) inertia. The crossing of trajectories associated with the gravitational Force tends to enhance the effect of the Basset Force on the particle turbulence. An ordering of the terms in the particle equation of motion shows that the solution is valid for high particle/fluid density ratios and to 0 (1) in the Stokes number.
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UNSTEADY DRAG ON A SPHERE AT FINITE REYNOLDS NUMBER WITH SMALL FLUCTUATIONS IN THE FREE-STREAM VELOCITY
Journal of Fluid Mechanics, 1991Co-Authors: Renwei Mei, Christopher J. Lawrence, Ronald J. AdrianAbstract:Unsteady flow over a stationary sphere with small fluctuations in the free-stream velocity is considered at finite Reynolds number using a finite-difference method. The dependence of the unsteady drag on the frequency of the fluctuations is examined at various Reynolds numbers. It is found that the classical Stokes solution of the unsteady stokes equation does not correctly describe the behaviour of the unsteady drag at low frequency. Numerical results indicate that the Force increases linearly with frequency when the frequency is very small instead of increasing linearly with the square root of the frequency as the classical Stokes solution predicts. This implies that the Forces has a much shorter memory in the time domain. The incorrect behaviour of the Basset Force at large times may explain the unphysical results found by Reeks & McKee (1984) wherein for a particle introduced to a turbulent flow the initial velocity difference between the particle and fluid has a finite contribution to the long-time particle diffusivity. The added mass component of the Force at finite Reynolds number is found to be the same as predicted by creeping flow and potential theories. Effect of Reynolds number of the unsteady drag due to the fluctuating free-stream velocity are presented. The implications for particle motion in turbulence are discussed.
Renwei Mei - One of the best experts on this subject based on the ideXlab platform.
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particle dispersion in isotropic turbulence under stokes drag and Basset Force with gravitational settling
Journal of Fluid Mechanics, 1991Co-Authors: Renwei Mei, Ronald J. Adrian, Thomas J HanrattyAbstract:An analysis that includes the effects of Basset and gravitational Forces is presented for the dispersion of particles experiencing Stokes drag in isotropic turbulence. The fluid velocity correlation function evaluated on the particle trajectory is obtained by using the independence approximation and the assumption of Gaussian velocity distributions for both the fluid and the particle, formulated by Pismen & Nir (1978). The dynamic equation for particle motion with the Basset Force is Fourier transformed to the frequency domain where it can be solved exactly. It is found that the Basset Force has virtually no influence on the structure of the fluid velocity fluctuations seen by the particles or on particle diffusivities. It does, however, affect the motion of the particle by increasing (reducing) the intensities of particle turbulence for particles with larger (smaller) inertia. The crossing of trajectories associated with the gravitational Force tends to enhance the effect of the Basset Force on the particle turbulence. An ordering of the terms in the particle equation of motion shows that the solution is valid for high particle/fluid density ratios and to 0 (1) in the Stokes number.
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UNSTEADY DRAG ON A SPHERE AT FINITE REYNOLDS NUMBER WITH SMALL FLUCTUATIONS IN THE FREE-STREAM VELOCITY
Journal of Fluid Mechanics, 1991Co-Authors: Renwei Mei, Christopher J. Lawrence, Ronald J. AdrianAbstract:Unsteady flow over a stationary sphere with small fluctuations in the free-stream velocity is considered at finite Reynolds number using a finite-difference method. The dependence of the unsteady drag on the frequency of the fluctuations is examined at various Reynolds numbers. It is found that the classical Stokes solution of the unsteady stokes equation does not correctly describe the behaviour of the unsteady drag at low frequency. Numerical results indicate that the Force increases linearly with frequency when the frequency is very small instead of increasing linearly with the square root of the frequency as the classical Stokes solution predicts. This implies that the Forces has a much shorter memory in the time domain. The incorrect behaviour of the Basset Force at large times may explain the unphysical results found by Reeks & McKee (1984) wherein for a particle introduced to a turbulent flow the initial velocity difference between the particle and fluid has a finite contribution to the long-time particle diffusivity. The added mass component of the Force at finite Reynolds number is found to be the same as predicted by creeping flow and potential theories. Effect of Reynolds number of the unsteady drag due to the fluctuating free-stream velocity are presented. The implications for particle motion in turbulence are discussed.
A N Zakirov - One of the best experts on this subject based on the ideXlab platform.
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directional diagrams of the particle drift in a standing wave with account of the Basset Force
Journal of Engineering Physics, 2015Co-Authors: D A Gubaidullin, P P Osipov, A N ZakirovAbstract:A study is made of the threshold parametric values at which the direction of the particle drift in a standing wave is reversed, with account taken of the Basset Force at different Reynolds and Strouhal numbers. The dependences of the threshold value squared of the entrainment coeffi cient on the relative density of the particle with account and without account of the Basset Force are found. The infl uence of the Basset Force on the threshold value of the density parameter is investigated. It is shown that account taken of the Basset Force exerts a particularly strong infl uence on the threshold curves for nondense particles. The threshold values of density of the particle and of the coeffi cient of its entrainment decrease as the Strouhal number increases.
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impact of Basset Force on threshold values of particle drag coefficient and density parameter in standing sinusoidal wave
Journal of Physics: Conference Series, 2014Co-Authors: P P Osipov, A N Zakirov, D A GubaidullinAbstract:A one-dimensional drift of spherical particle in standing sinusoidal wave is studied numerically. The impact of stationary and non-stationary Forces of viscous drag, as well as Archimedes, added masses and Basset Forces on particle drift direction is investigated. For various Reynolds and Strouhal numbers the dependencies of the threshold particle drag coefficient on density parameter have been found. These dependencies show that with increasing Reynolds and Strouhal numbers the threshold value of the squared drag coefficient decreases markedly. Impact of Basset Force on threshold values is especially strong for low- density particles.
D A Gubaidullin - One of the best experts on this subject based on the ideXlab platform.
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directional diagrams of the particle drift in a standing wave with account of the Basset Force
Journal of Engineering Physics, 2015Co-Authors: D A Gubaidullin, P P Osipov, A N ZakirovAbstract:A study is made of the threshold parametric values at which the direction of the particle drift in a standing wave is reversed, with account taken of the Basset Force at different Reynolds and Strouhal numbers. The dependences of the threshold value squared of the entrainment coeffi cient on the relative density of the particle with account and without account of the Basset Force are found. The infl uence of the Basset Force on the threshold value of the density parameter is investigated. It is shown that account taken of the Basset Force exerts a particularly strong infl uence on the threshold curves for nondense particles. The threshold values of density of the particle and of the coeffi cient of its entrainment decrease as the Strouhal number increases.
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impact of Basset Force on threshold values of particle drag coefficient and density parameter in standing sinusoidal wave
Journal of Physics: Conference Series, 2014Co-Authors: P P Osipov, A N Zakirov, D A GubaidullinAbstract:A one-dimensional drift of spherical particle in standing sinusoidal wave is studied numerically. The impact of stationary and non-stationary Forces of viscous drag, as well as Archimedes, added masses and Basset Forces on particle drift direction is investigated. For various Reynolds and Strouhal numbers the dependencies of the threshold particle drag coefficient on density parameter have been found. These dependencies show that with increasing Reynolds and Strouhal numbers the threshold value of the squared drag coefficient decreases markedly. Impact of Basset Force on threshold values is especially strong for low- density particles.