# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 3 Search : Reynolds number
 large Reynolds number flow   تچان با عدد ِ بزرگ ِ رینولدز   tacân bâ adad-e bozorg-e ReynoldsFr.: écoulement à grand nombre de Reynolds   A turbulent flow in which viscous forces are negligible compared to nonlinear advection terms, which characterize the variation of fluid quantities. The dynamics becomes generally turbulent when the Reynolds number is high enough. However, the critical Reynolds number for that is not universal, and depends in particular on boundary conditions.→ large; → Reynolds number; → flow. magnetic Reynolds number   عدد ِ رینولدز ِ مغناتیسی   adad-e Reynolds-e meqnâtisiFr.: nombre de Reynolds magnétique   A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → magnetic advection to → magnetic diffusion. It is given by: Rm = σμ0νLU0, where σ is the → conductivity of the fluid, μ0 is the → magnetic permeability of the fluid, L is he characteristic length scale of the fluid flow, and U0 the characteristic velocity of the flow. A typical value for the Earth is Rm ~ 200. Reynolds number   عدد ِ رینولدز   adad-e Reynolds (#)Fr.: nombre de Reynolds   A dimensionless quantity that governs the conditions for hydrodynamic stability and the occurrence of turbulence in fluids. It is defined by the ratio, R, of the inertial force (ρ u2) and the viscous force (μ u / L), i.e. R = L u ρ/μ, where L is a typical dimension of the system, u is a measure of the velocities that prevail, ρ the density, and μ the kinematic viscosity. At low Reynolds numbers the flow is steady, since the viscous forces are predominant in controlling the flow. At a critical value of R, corresponding to a critical velocity, the flow becomes turbulent.Named after Osborne Reynolds (1842-1912), a British physicist who pioneered the study of turbulent flows; → number.