252
2. ZARlC
Fro. 1. Velocity probability density distributions in the bulfer layer.
Velocity probability density distributions in the wall layers have been
presented by only a fcw authors (Klcbanofl, 1955; Marcillat, 1964; Eckelman, 1970), with Comtc-Bellot (1%3) presenting only measurements of the
skewness and the flatness factors. in all these studies the analogue technique
was employed. Our data on the distribution of the first four statistical
moments agree reasonably well with the results of Comte-Eellot (1963) and
Marcillat (1964). What is more important, the general shape of the complete
probability density distributions, as a function o f the distance from the wall,
agrees well with the shape of the distributions presented by Eckelman
(1970). It appears, therefore, that some features of these distributions are
general enough for wall turbulence. These include:
(1) Distributions are highly non-Gaussiaa throughout the inner layers. In
fact, some of the distributions presented in Fig. 1 are of a shape unlike any
known theoretical probability denaity distribution.
(2) Skewness and flatness factors have very high values in the viscous
sublayer. Asymmetry is such that an appreciable difference exists between
the average and the most probable velocity.
(3) At about Y+ = IS the distributions bccome symmetrical, with the
odd order moments being equal to zero. Approximately at the same distance
2. ZARlC
Fro. 1. Velocity probability density distributions in the bulfer layer.
Velocity probability density distributions in the wall layers have been
presented by only a fcw authors (Klcbanofl, 1955; Marcillat, 1964; Eckelman, 1970), with Comtc-Bellot (1%3) presenting only measurements of the
skewness and the flatness factors. in all these studies the analogue technique
was employed. Our data on the distribution of the first four statistical
moments agree reasonably well with the results of Comte-Eellot (1963) and
Marcillat (1964). What is more important, the general shape of the complete
probability density distributions, as a function o f the distance from the wall,
agrees well with the shape of the distributions presented by Eckelman
(1970). It appears, therefore, that some features of these distributions are
general enough for wall turbulence. These include:
(1) Distributions are highly non-Gaussiaa throughout the inner layers. In
fact, some of the distributions presented in Fig. 1 are of a shape unlike any
known theoretical probability denaity distribution.
(2) Skewness and flatness factors have very high values in the viscous
sublayer. Asymmetry is such that an appreciable difference exists between
the average and the most probable velocity.
(3) At about Y+ = IS the distributions bccome symmetrical, with the
odd order moments being equal to zero. Approximately at the same distance