0.a
0.6
S,
0.4
0.2
0
-0.2
S, - 0 4
-0.6
-0.8
TLJRBIJLENCE IN AN INTERNAL BOUNDARY LAYER
267
0
O
0
rn
4.0
A
A
2.0
3.0
2/6j
8
A
A
A
0
-I
-2 suu
-3
-4
Flu. 2. Skewness in smooth to rough internal layer. .v/6,, * 2.10; 0, S,; m, S, ; A, S”,,,.
x/fi0 3.14; 0, S,: 0 , S, : A, Suw.
The skewness of w (Fig. 2) remains positive across the internal layer and
shows a broad maximum near 2/15, = 1D while S, and S
, are negative in this
region. Near the outer edge of the external boundary layer @/a, > 210) the
negative S, and positive S , would be consistent with bulga d low momentum fluid in the external part of the boundary layst mrlring incursions into
higher momentum free stream fluid. The comparable Eeaturc at around
z/di = 1.0 similarly could be interpreted as incursions by the energetic
“new” turbulence from the sttonnlv retarded i n t e d layer into the (tired?)
“ old ” turbulence of the higher momantun external layer.
In contrast to the smooth to rough case, the skewnw aad flatness distributions in the rough to smooth internal layer (Figs. 3 and 4) at x/S, = 0.71