The significance of coherent flow structures for the turbulent mixing ...

]
õ
õ>
I
]
Û
W
õ>U:
é
ˆ
]
"
R
]
Û
]
5 Investigation of the xy-plane
namely &~€ W
the parameter R
Î¥ÆË0¾ and 16080. The friction velocity
§QP
Ø—õ>
fàÛ in equation (5.20) to ¾ÁÃË0Û¿½ß0Î m/s and ÆÁþÞÆÞ0Î m/s.
fàÛ was determined from
f
f
f
(5.20)
Figure 5.2 reveals the mean velocity profile of the turbulent boundary layer flow in outer- and
inner-law scaling. The agreement between the stereoscopic PIV results with the analytical
law-of-the-wall and the log-law, derived on page 71, is excellent and also the hot-wire measurements
match nicely. Only : T Þ¾¾ for a progressing departure of the HWA results from
the present PIV investigation can be observed in the semilogarithmic representation. This
effect is caused by the fact that the boundary layers thickness at HFI is only half of the thickness
obtained at LML. However, this is not relevant for the present investigation, because here
only the near-wall phenomena :à¿Ü ¾¥Á2ÆÏÈ below will be considered and not the outer-flow
effects caused by intermittency. Remarkable is the average dynamic which could be reached
with the PIV-system and the spatial resolution in wall-normal direction. The location of the
, is comparable with the nearest wall location
Û¥ÁÃÂ
first measurement point, located at : T
ØiÛ¥ÁÃ˿ˉˆ
\JŠ
ÈOÁ2ÆŒˆ
Û‹
⎺U / U ∞
⎺U / U ∞
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
Re θ
= 7800 (PIV)
Re θ
= 7140 (HWA)
Ž
0 0.1 0.2
y / δ
Re θ
= 15000 (PIV)
Re θ
= 16080 (HWA)
Ž
0 0.1 0.2
y / δ
⎺U / u τ
⎺U / u τ
30
25
20
15
10
Re θ
= 7800 (PIV)
⎺U + = 2.44 ln(y + ) +5.1
5
⎺U + = y +
Re θ
= 7140 (HWA)
0
10 0 10 1 10 2 10 3 10 4
30
25
20
15
10
Re θ
= 15000 (PIV)
⎺U + = 2.44 ln(y + ) +5.1
5
⎺U + = y +
Re θ
= 16080 (HWA)
0
10 0 10 1 10 2 10 3 10 4
y +
y +
FIGURE 5.2: Comparison of the measured mean velocity profiles in outer- (left) and inner-law scaling
(right) with the hot-wire results by Bruns et al [11, 21] for two Reynolds numbers.
76