Strouhal Number

Strouhal number

[′strü·əl ‚nəm·bər] (mechanics) A dimensionless number used in studying the vibrations of a body past which a fluid is flowing; it is equal to a characteristic dimension of the body times the frequency of vibrations divided by the fluid velocity relative to the body; for a taut wire perpendicular to the fluid flow, with the characteristic dimension taken as the diameter of the wire, it has a value between 0.185 and 0.2 Symbolized S_r. Also known as reduced frequency.

Strouhal Number

a similarity criterion, or parameter, in the unsteady-state flow of liquids or gases. Symbolized S_r, Sh, or S, it expresses the similarity in the course of processes in time: S_r = l/vt = ωl/v, where v is the characteristic flow velocity, l is a characteristic linear dimension, t is a time interval characteristic of the unsteady-state flow, and w is the characteristic frequency. The inverse quantity vt/l is called the Thomson number N_Th

The Strouhal number has been found to be constant (S_r ≈ 0.2–0.3) over a wide range of Reynolds numbers. This empirical relation is used in calculating vibrations of elastic bodies, such as airplane wings and periscopes, in a liquid or gas flow and in determining pressure fluctuations in regions of flow separation—for example, behind a body past which a fluid is flowing, as at the tail of a rocket.

A similar number, H₀ = vt/l, is encountered in mechanical, thermal, and electromagnetic processes and is called the homochronous number. The Strouhal number is a special case, pertaining to hydroaeromechanics, of the inverse of the homochronous number.

The Strouhal number was named for the Czech scientist V. Strouhal (1850–1923).

S. L. VISHNEVETSKII

单词	strouhal number
释义	Strouhal Number Strouhal number [′strü·əl ‚nəm·bər] (mechanics) A dimensionless number used in studying the vibrations of a body past which a fluid is flowing; it is equal to a characteristic dimension of the body times the frequency of vibrations divided by the fluid velocity relative to the body; for a taut wire perpendicular to the fluid flow, with the characteristic dimension taken as the diameter of the wire, it has a value between 0.185 and 0.2 Symbolized S_r. Also known as reduced frequency. Strouhal Number a similarity criterion, or parameter, in the unsteady-state flow of liquids or gases. Symbolized S_r, Sh, or S, it expresses the similarity in the course of processes in time: S_r = l/vt = ωl/v, where v is the characteristic flow velocity, l is a characteristic linear dimension, t is a time interval characteristic of the unsteady-state flow, and w is the characteristic frequency. The inverse quantity vt/l is called the Thomson number N_Th The Strouhal number has been found to be constant (S_r ≈ 0.2–0.3) over a wide range of Reynolds numbers. This empirical relation is used in calculating vibrations of elastic bodies, such as airplane wings and periscopes, in a liquid or gas flow and in determining pressure fluctuations in regions of flow separation—for example, behind a body past which a fluid is flowing, as at the tail of a rocket. A similar number, H₀ = vt/l, is encountered in mechanical, thermal, and electromagnetic processes and is called the homochronous number. The Strouhal number is a special case, pertaining to hydroaeromechanics, of the inverse of the homochronous number. The Strouhal number was named for the Czech scientist V. Strouhal (1850–1923). S. L. VISHNEVETSKII AcronymsSeeslalom
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