关于热力学、热量传递和质量传递,以及流体工程的 A-Z 指南
中文 English Русский Português Español Français Deutsch 关于我们 编辑 联系我们 访问 Begell House
View in Semantic Map View in A-Z Index

The friction velocity (also known as the shear-stress velocity), u*, of a flow is defined by the relation:

(1)

where τ is the shear stress and r the fluid density. This quantity has the dimensions of velocity and is frequently encountered in the study of Boundary Layers. For turbulent flow it is approximately constant in the region near to a wall, and in the atmosphere, this region extends over the lowest several metres. The flow velocity in the boundary layer is commonly expressed in terms of the friction velocity and the height, z, as:

(2)

where z0 is the roughness length. κ is an empirical constant known as the von Kármán constant and is found to have a value of κ ≈ 0.35 for all cases of turbulent flow. The derivation of this formula is given in, for example, Holton (1979) and Streeter and Wylie (1983).

REFERENCES

Holton, J. R. (1979) An Introduction to Dynamic Meterorology, Academic Press, New York.

Streeter, V. L. and Wylie, E. B. (1983) Fluid Mechanics, McGraw-Hill, Singapore.

References

  1. Holton, J. R. (1979) An Introduction to Dynamic Meterorology, Academic Press, New York. DOI: 10.1119/1.1987371
  2. Streeter, V. L. and Wylie, E. B. (1983) Fluid Mechanics, McGraw-Hill, Singapore.
浏览次数: 62401 创建日期: 2 February 2011 最后修改日期: 16 March 2011 © Copyright 2010-2021 返回顶部
A-Z 索引 作者/编辑 语义地图 视觉画廊 贡献 Guest