-
Hydraulics Prof. B.S. Thandaveswara
Indian Institute of Technology Madras
32.6 Slotted Bucket Stilling Basin Bradley and peterka in 1959
developed the slotted bucket stilling basin (Fig. 32.10) with
an 8D sloping apron on which teeth of 45D are installed. The
teeth introduces stable flow
and little boiling action.
Three types of flow may be distinguished
Sweep out with a too low tailwater level
Minimum tailwater level below which excessive surface waves and
scour occur and
Maximum tailwater above which dividing flow results and the
maximum tailwater
level above which dividing results.
A slotted bucket basin has a lower and an upper limit of
operation. These depends on
the approach Froude number ( )1
1 1 21
= /VF gy and the relative bucket radius
2br 1
1
R 1 0 5 = +
bR . Fy
in which 1V is the approach velocity, is the flow depth measured
perpendicular to the
bed slope, and bR is the radius of the bucket.
The minimum bucket radius should be 11
2 2=bmR . Fy
and the extreme tail water levels ty
are given as a function of brR and 1F . Care should be taken
against material entering
the bucket that may cause damage by abrasion.
-
Hydraulics Prof. B.S. Thandaveswara
Indian Institute of Technology Madras
yt min/F1 = 3
4
5
6
7
8
9
10
111213141516
F1 = V1gy1
______
0 0.1 0.2 0.3 0.4 0.5 0.60
2
4
6
8
10
0 0.1 0.2 0.3 0.4 0.5 0.60
2
4
6
8
10
0.7
yt max/F1 = 3
456781012151820
3040507090
R
bed approx 0.05Rbelow apron lip
Bed slopes up
R
y V12
2g____
________
1 +R
y V12
2g____
________
1 +
Bed approximately 0.05R below lip
(a) Minimum limit (b) Maximum limitMinimum and maximum tailwater
limits (After Peterka, (1958)
H
h
Tail Water Elevation
y
Apron lip
Ry1
Figure-32.7 Definition sketch for Slotted Bucket Stilling
Basin
t yts
yt max
yt minSweep out condition levelSafe minimum tail water level
Upper limit of tail water
-
Hydraulics Prof. B.S. Thandaveswara
Indian Institute of Technology Madras
0 0.2 0.4 0.6 0.80
2
4
6
8
10
12
0 0.1 0.2 0.3 0.4 0.5 0.60
1
2
3
4
5
6
7
8
9
10
Minimum allowable
Minimum bucket radius(after Peterka, 1958)
Tailwater sweepout depth(after Peterka, 1958)
141312131098
7
6
5
4
3
Figure 32.8
Frl = V1____gy1 Frl =
V1____gy1
R
y1V1
2______
+___2g
R
y1V1
2______
+___2g
Tsy1___=15
Following are important characteristics
Tailwater level : Stage discharge relationship should be
known.
Cavitation control : Turbulent (fluctuations in the front part
of basin and rear portion of appurtenances).
Scour control Tailwater waves Based on the Field Experience
following are listed:
The tailwater depth should atleast be equal to the sequent depth
of the classical jump,
Adequate tailwater submergence can reduce the basin length,
Dividing walls help in improving the stilling action and reduce
concentration of flow,
-
Hydraulics Prof. B.S. Thandaveswara
Indian Institute of Technology Madras
Cavitation damage is likely to be increased by high velocity
approach flow and low tailwater levels, and
End sills reduce scour significantly.
Stilling basins are popular and the designers favorite choice
for energy dissipation,
certainly because of the knowledge and experience acquired over
the years. They have
proved to be a reliable hydraulic structure if the approach
conditions and the tailwater
elevation are within certain limits. Abrasion may become a
concern for stilling basins
connected to a bottom outlets.
0.05Rb
0.125Rb
0.5Rb
0.05Rb
168
45
Rb
a)
-
Hydraulics Prof. B.S. Thandaveswara
Indian Institute of Technology Madras
0.05Rb
45
8
Rb
0.125Rb
d)
c)
b)
Figure - 32.9 Geometry of the Slotted bucket stilling basin
}0 4 8 12 16 20 24 28
0.2
0.3
0.4
0.6
0.37
0.24
0.16
0.12
R
yt/y1
F1
A slotted bucket basin has a lower and an upper limit of
operation
Figure 32.10 - Extreme tailwater levels
as function of initial Froude number and
0
4
8
12
16
2
1
for slotted stilling basin yt/y1
[1+0.5 F1 ]Rbr= (Rb/y1 2
br
Minimum tailwater depths
Maximum tailwater depths
