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OCR for page 53
53
2
1 Flow
1.5
0.5
Y/B
Y/B
1
0 1.34
1.00 1.68
0.33
2.35
0.5 5.10 0.33
= 0.67
-0.5 0.33
0.33 0.33
0.33
-1 0
-1 -0.5 0 0.5 1 1.5
-1 -0.5 0 0.5 1 1.5 X/B
X/B
Figure 6.18. Bed shear stress contours (N/m2) around a
Figure 6.16. Velocity field around a rectangular pier with rectangular pier (L/B = 0.25).
L/B = 0.25.
2
1 Flow
Flow
1.5
0.5
Y/B
Y/B
0 1 1.15
0.88
1.34
= 0.74
0.47 1.56 0.33
-0.5 0.5 0.33
0.33
0.33
0.33
-1 0.33
0
-1 -0.5 0 0.5 1 1.5 -1 -0.5 0 0.5 1 1.5
X/B X/B
Figure 6.17. Velocity field around a rectangular pier with Figure 6.19. Bed shear stress contours (N/m2) around a
L/B = 4. rectangular pier (L/B = 1).
stress tends to increase with the attack angle. They also show 2
that the location of the maximum shear stress moves back-
ward along the side of the pier as the attack angle increases.
1.5
Flow
6.12 ATTACK ANGLE EFFECT ON MAXIMUM
SHEAR STRESS 0.59
Y/B
0.68
1 0.95
1.12
The maximum shear stress max is the maximum shear = 0.77
1.30
0.51 0.33
stress that exists on the riverbed just before the scour hole 1.56
0.33
0.5
starts to develop. One way to present the data is to plot 0.42
max/max(0 degree) as a function of (Figure 6.26). The param- 0.33
eter max(0 degree) is the value of max for the case of a pier in line
0
with the flow in deep water and is given by Equation 6.1. The -1 -0.5 0 0.5 1 1.5
X/B
attack angle correction factor, ksh, is the ratio max/max(0 degree).
The data points on Figure 6.21 correspond to the results of Figure 6.20. Bed shear stress contours (N/m2) around a
the five numerical simulations. By regression, the equation rectangular pier (L/B = 4).
