Figure 3-20. The effect of stratification on near-surface turbulence.
Although ] and Ri are both related to the stratified turbulent boundary
layer, ] is a function of the surface boundary conditions and Ri is a
function of the local density and velocity gradients. For a statistically steady
and homogeneous turbulent boundary layer, parameters ] and Ri are
related:
2
for 0
/ 1
for
0
m
m
Ri
U
]
] ]
] ]I ] I ]
]
E]
]
t t
­
®
!
¯
,
(3.85)
where E is a dimensionless constant, and U
I and m
I are the universal
functions for density and velocity respectively (see Chapter 1). According to
(3.85), Ri monotonically increases with ] , achieving an extreme as
] o f :
1
|
0 . 2 5
cr
Ri
Ri
9
]
E
of
|
(3.86)
Chapter 3: NEAR-SURFACE TURBULENCE
199