Geoscience Reference
In-Depth Information
Fig. 1 Cylinder setup in the measurement section (
top view
). Left side staggered; right side in-
line. Lateral and horizontal spacing 20 cm. Cylinders in
gray scale
were attached to drag force
measurement systems
Table 1 Experimental boundary conditions, measured drag forces, coefficient of variation and
measured and computed drag coefficients
Setup
C
D
i
a
C
D
i
b
u
0
h
S
Re
d
<F
D
>
c
v
(m/s)
(m)
(%)
(1)
(N)
(1)
(1)
(1)
In-line (L)
0.20
0.247
0.06
2,043
0.04
0.17
0.80
0.72
0.30
0.251
0.13
3,001
0.09
0.10
0.86
0.72
0.40
0.250
0.24
4,011
0.18
0.14
0.92
0.72
0.50
0.251
0.36
5,002
0.27
0.06
0.87
0.72
0.60
0.251
0.54
6,012
0.39
0.07
0.88
0.73
0.69
0.252
0.72
6,944
0.51
0.06
0.87
0.73
Staggered (S)
0.20
0.246
0.07
2,032
0.05
0.12
0.98
1.12
0.30
0.250
0.14
2,998
0.12
0.10
1.06
1.12
0.40
0.252
0.26
3,973
0.21
0.06
1.08
1.12
0.50
0.251
0.41
4,972
0.33
0.07
1.09
1.12
0.59
0.253
0.62
5,938
0.47
0.09
1.09
1.12
0.70
0.251
0.92
6,975
0.65
0.06
1.10
1.12
a
Calculated on the basis of the measurements.
b
Computed with Lindner (
1982
) approach.
ensured that the DFS did not disturb the flow and that they could be easily rear-
ranged to match the corresponding cylinder arrangement. The cylinders attached to
the DFS are highlighted in Fig.
1
(light gray elements).
The experiments were carried out with steady uniform and just submerged flow
conditions with a constant water depth
h
0.25 m. In order to achieve uniform
flow conditions, discharge and flume slope were adjusted so that the average water
surface slope was identical to bed slope in the test section. In total, six different flow
conditions were investigated for each arrangement. The experimental boundary
conditions are summarized in Table
1
.
The drag forces were measured with a sampling frequency of 200 Hz and a
sampling interval of 60 s. Each measurement was repeated two times showing a
high degree of reproducibility. A more detailed analysis of the time series showed
that the mean value of the drag forces became, in general, stable after a sampling
time of 30 s indicating that the sampling interval of 60 s was sufficient to obtain a
stable mean value.
ΒΌ
