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1

Digitale Medien

Particle collision rate in fluid flows (1998)

Hu, Kevin C. ; Mei, Renwei

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 10 (1998), S. 1028-1030

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ISSN: 1089-7666

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The classical result of Smoluchowski [Z. Phys. Chem. 92, 129 (1917)] for the collision rate of monodisperse particles in a laminar shear flow is shown to be inaccurate due to the inclusion of the self-collision. In the present work we extend Smoluchowski's result by excluding the self-collision in the counting of collision pairs. A numerical simulation for particle collisions in a laminar shear flow at very low concentration is carried out to validate the extended result of Smoluchowski. Good agreement for the collision rate between the numerical simulation and the prediction based on the extended expression is obtained. © 1998 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.869622

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2

Digitale Medien

A note on the history force on a spherical bubble at finite Reynolds number (1994)

Mei, Renwei ; Klausner, James F. ; Lawrence, Christopher J.

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 6 (1994), S. 418-420

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ISSN: 1089-7666

Quelle: AIP Digital Archive

Thema: Physik

Notizen: An approximate expression for the history force on a spherical bubble is proposed for finite Reynolds number, Re. At small time, the history-force kernel is a constant, which decreases with increasing Re, and the kernel decays as t−2 for large time. For an impulsively started flow over a bubble, accurate finite difference results show that the history force on the bubble decays as t−2 at large time. Satisfactory agreement is observed between the presently proposed history force and the numerical solution.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.868039

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3

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Unsteady force on a spherical bubble at finite Reynolds number with small fluctuations in the free-stream velocity (1992)

Mei, Renwei ; Klausner, James F.

New York, NY : American Institute of Physics (AIP)

Physics of Fluids 4 (1992), S. 63-70

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ISSN: 1089-7666

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Unsteady flow over a stationary spherical bubble with small fluctuations in the free-stream velocity is considered for Reynolds number ranging from 0.1 to 200. Solutions to the Navier–Stokes equations of both steady and unsteady components are obtained using a finite-difference method and a regular perturbation scheme based on the amplitude of the fluctuations being small. The dependence of the unsteady drag on the frequency of the fluctuations is examined at finite Reynolds number. It is shown that the quasisteady drag can be represented by using the steady-state drag coefficient and the instantaneous velocity. Numerical results indicate that the unsteady force at low frequency, ω, increases linearly with ω rather than increasing linearly with ω1/2, which results from the creeping flow solution of the Stokes equation. The added-mass force at finite Reynolds number is found to be the same as in creeping flow and potential flow. The history force at finite Re is identified and carefully evaluated. The imaginary component of the history force increases linearly with ω when ω is small and decays as ω−1/2 as ω becomes large. The implication is that the history force has a much shorter memory in the time domain than predicted by the solution of the unsteady Stokes equation. Numerical results suggest that the history force, which is due to the combination of the viscous diffusion of the vorticity and the acceleration of the flow field, at low frequency is finite even at large Reynolds number.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.858501

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4

Digitale Medien

On boundary conditions in lattice Boltzmann methods (1996)

Chen, Shiyi ; Martínez, Daniel ; Mei, Renwei

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 8 (1996), S. 2527-2536

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ISSN: 1089-7666

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A lattice Boltzmann boundary condition for simulation of fluid flow using simple extrapolation is proposed. Numerical simulations, including two-dimensional Poiseuille flow, unsteady Couette flow, lid-driven square cavity flow, and flow over a column of cylinders for a range of Reynolds numbers, are carried out, showing that this scheme is of second order accuracy in space discretization. Applications of the method to other boundary conditions, including pressure condition and flux condition are discussed. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.869035

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