16
6 th International Conference on Scour and Erosion 27-31 August 2012 Local Scour by Offset and Propeller Jets Yee-Meng Chiew, Jian-Hao Hong, Indra Susanto, Nian-Sheng Cheng
6th International Conference on Scour and Erosion
27-31 August 2012
Local Scour by Offset and Propeller Jets
Yee-Meng Chiew, Jian-Hao Hong,
Indra Susanto, Nian-Sheng Cheng
2
Outline Introduction
Dimensional analysis
Effect of densimetric Froude
number on jet scour
Effect of offset height on scour
Initiation of scour
Conclusions
3
Sewage outfall
Sewage plant
(a)
Dam
sluiceway
(b)
Introduction
Submerged horizontal jet
Ship-propeller jet
Propeller wash induced erosion
4
One Week Vessel Track at PPT (25 -31 May, 2011)
Source: Maritime Port
Authority of
Singapore, MPA
5
0y
0d
ch
offLsemL
0U
semd
0y
pd
ch
th
(a)
(b)
semd
offL semL
Velocity profileTrack of max. velocity
Velocity profileTrack of max. velocity
thsemW
semW
Symmetric ?
Transverse direction
Centreline
Transverse direction
Scour by (a) offset jet; and (b) propeller jet
6
Objective
To investigate the characteristics
of a 3-D scour hole in non-cohesive
sediment beds due to a submerged
horizontal 3-dimensional offset and
propeller jet
7
Dimensional Analysis
8
Investigators y/do Fo dsem/do Lsem/do Wsem/do Remark
Hamill (1987) 1.14 5.55 -
7.73
0.91 –
1.00 －
6.89 –
20.98
propeller
jet
Chiew and
Lim (1996)
0.50 –
15.75
13.14 –
60.74
0.47 –
12.76
9.88 –
42.20
27.07 –
95.12
circular
jet
Karki (2007) 1.00 –
2.00 10.00
2.03 –
2.87
11.28 –
12.85
28.02 –
29.65 square jet
Hong et al.
(2012)
0.50 –
1.50
6.08 –
10.69
0.50 –
1.50
2.57 –
6.65
5.62 –
11.26
propeller
jet
Range of data collected on scour
cause by submerged 3D jets
9
Effect of Fo on jet scour
1 10 100Fo
0.1
1
10
100
dse
m/d
o
Circular jet Propeller jet y/d0 y/d0
0.50 - 0.81 0.50 1.83 - 1.97
3.94 1.00
1.50
Submerged jets
dsem
d0 = 0.21Fo
Chiew and Lim (1996)water wall jet formula
1 10 100Fo
0.1
1
10
100
Lse
m/d
o
Circular jet Propeller jet y/d0 y/d0
0.50 0.50 0.81 - 0.97
1.83 - 1.97 1.00
1.50
Submerged jets
3.68 - 3.94
Lsem
d0 = 4.41F o
0.75
Chiew and Lim (1996)water wall jet formula
1 10 100Fo
0.1
1
10
100
Wsem/d
o
Circular jet Propeller jet y/d0 y/d0
0.50 0.50 0.81 - 0.97
1.83 - 1.97 1.00
1.50
Submerged jets
3.68 - 3.94
Wsem
d0 = 1.90F o
0.75
Chiew and Lim (1996)water wall jet formular
Circular wall and propeller jets
Chiew and Lim’s (1996)’s circular wall jet formulas form the upper limit The offset height ratio also plays an important role
10
Effect of y/do on scour depth
0.1 1 10 100y/do
0
5
10
15
dse
m/d
o
Circular jet Square jet Propeller jet F0 F0 F0
12.6 - 13.9 10 8.9 - 9.2 24.4 - 25.8
57.3 - 60.7
Submerged offset jets
(a)
0.1 1 10 100y/do
0
5
10
15
dse
m/d
o
dsem
d0
= 0.265[Fo-4.114(y/do)]0.955(y/do)
-0.022
F0 = 60
F0 = 25
y/d0 < 0.5
no avalible data
F0 = 30
F0 = 40
F0 = 50
F0 = 20
F0 = 10
(b)
11
Effect of y/do on scour length
0.1 1 10 100y/do
0
20
40
60
80
100
Lsem/d
o
Circular jet Square jet Propeller jet F0 F0 F0
13.1 - 13.9 10 6.08 - 6.11 24.4 - 25.0
57.3 - 60.7 8.94 - 9.19
Submerged offset jets
(a)
0.1 1 10 100y/do
0
20
40
60
80
100
Lse
m/d
o
Lsem
d0 = 8.824[Fo-4.114(y/do)]
0.535(y/do)0.286
F0 = 60
F0 = 25
F0 = 6
y/d0 < 0.5
no avalible data
F0 = 50
F0 = 40
F0 = 30
F0 = 10
(b)
12
Effect of y/do on scour width
0.1 1 10 100y/do
0
10
20
30
40
50
60
70
Wse
m/d
o
Circular jet Square jet Propeller jet F0 F0 F0
13.1 - 13.9 10 6.08 - 6.11 24.4 - 25.0
57.3 - 60.7
Submerged offset jets
(a)
0.1 1 10 100y/do
0
10
20
30
40
50
60
70
Wsem/d
o
W sem
d0
= 3.834[Fo-4.114(y/do)]0.585(y/do)
0.202
F0 = 60
F0 = 25
F0 = 6
y/d0 < 0.5
no avalible data
F0 = 50
F0 = 40
F0 = 30
F0 = 10
(b)
13
Initiation of 3-D jet scour
0.1 1 10 100Fo
1
10y/d
o
Critical curve
Fo = 4.114 y/do, y/do
No scour depth
Scour
Submerged offset jets Chiew and Lim (1996) Karki et al. (2007) Hamill (1987)Hong et al. (2012)
Circular jetSquare jetpropeller jetpropeller jet
0.5
20
14
1. The offset height ratio, y/do and densimetric Froude number, Fo affects both offset and propeller jets
2. The 3-D wall jet equations proposed by Chiew and Lim (1996) form the upper limits for scour induced by both types of jets
Conclusions
15
3. The variation between the scour length, width and offset height is non-linear
4. Eq. 11 (Fig. 9) in the paper may be used to determine the critical condition for the initiation of scour
Conclusions
