1 Foundation of Fluid Mechanics
45
Fig. 1.51 G. I. Taylor (1886–1975, British mechanist)
instantaneous physical quantities cannot be continuous differentiable from
the measurement results, at most a continuous function).
In 1937, Taylor (G. I. Taylor, 1886–1975, as shown in Fig. 1.51) and Von
Karman considered turbulence to be an irregular motion, which generally
occurs in fluids when fluids flow through solid surfaces or adjacent similar
fluids. In 1959, J. O. Hinze, the Dutch scholar, believed that turbulence was
an irregular flow state, but its various physical quantities varied randomly
with time and spatial coordinates, so that different statistical averages could
be distinguished. Zhou Peiyuan, the Chinese scholar, believes that turbulence
is an irregular eddy motion. The general textbook defines turbulence as an
irregular random motion that is disorderly and mixed with each other. At
present, it is generally accepted that turbulence is composed of vortices of
different sizes and frequencies, which make the changes in physical quantities
in time and space show irregular randomness. In the study of turbulence, the
engineering turbulence method represented by L. Prandtl and the turbulence
statistical theory represented by G. I. Taylor have been formed. With the
improvement of computational techniques in recent decades, the numerical
study of turbulence has been developed rapidly.
Compared with the definition of turbulence, the basic characteristics of
turbulence can be easily expressed as follows:
(1) Eddy in turbulence
Turbulence is accompanied by large and small vortices. Vortex is the main
cause of turbulence fluctuation. It is generally believed that large eddies
produce large fluctuations and small eddies produce small fluctuations during
45
Fig. 1.51 G. I. Taylor (1886–1975, British mechanist)
instantaneous physical quantities cannot be continuous differentiable from
the measurement results, at most a continuous function).
In 1937, Taylor (G. I. Taylor, 1886–1975, as shown in Fig. 1.51) and Von
Karman considered turbulence to be an irregular motion, which generally
occurs in fluids when fluids flow through solid surfaces or adjacent similar
fluids. In 1959, J. O. Hinze, the Dutch scholar, believed that turbulence was
an irregular flow state, but its various physical quantities varied randomly
with time and spatial coordinates, so that different statistical averages could
be distinguished. Zhou Peiyuan, the Chinese scholar, believes that turbulence
is an irregular eddy motion. The general textbook defines turbulence as an
irregular random motion that is disorderly and mixed with each other. At
present, it is generally accepted that turbulence is composed of vortices of
different sizes and frequencies, which make the changes in physical quantities
in time and space show irregular randomness. In the study of turbulence, the
engineering turbulence method represented by L. Prandtl and the turbulence
statistical theory represented by G. I. Taylor have been formed. With the
improvement of computational techniques in recent decades, the numerical
study of turbulence has been developed rapidly.
Compared with the definition of turbulence, the basic characteristics of
turbulence can be easily expressed as follows:
(1) Eddy in turbulence
Turbulence is accompanied by large and small vortices. Vortex is the main
cause of turbulence fluctuation. It is generally believed that large eddies
produce large fluctuations and small eddies produce small fluctuations during