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Chapter 4 - Experimental setup and test procedure
Ultrasonic probe (US)
100 117
US ∅30
7
40
100
20
UVP ∅13
27
32
10
140
10..15
30..35
Difference of 5 mm
due to inclined
UVP probe
Flow direction
US 7
8 9
3
6
UVP
2
1
5
4
8
90 270
9
7
95
50
145
y
x
c
b
a
Cotations in mm
c
b
a
UVP probes inclined by
20° to vertical axes
Figure 4.21: Geometry of the probe support
In the present study, the main interest was the average flow field. Therefore a rather short measurement
was performed. For each 1D-velocity profile, 64 data points (in time) were recorded
with a resolution of 128 points (in space) over the flow depth. The multiplexer switched to the
next probe after 64 measured profiles. Consequently the measured flow field is not an instantaneous
3D-field. But for average values, it can be assumed to be constant considering the short
record time. The acquisition frequency was of 77 Hz for most tests, which would even allow an
analysis of turbulence characteristics for longer samples. Therefore longer recordings were performed
with 2048 data points (in time) for some selected cases. A set of nine 1D-profiles performed
at a given frame location was stored in a specific binary file for later treatment and analysis
(§ 4.6.2).
The velocity measurement is quite short with 64 time averaged data points (about 1 second).
Therefore longer recordings (more than 2000 measurements) were analyzed by averaging the measured
velocities over different time spans (Fig. 4.22), showing that a sampling time of about 1 second
(64 measurements) gives satisfactory results.
page 88 / November 9, 2002
Wall roughness effects on flow and scouring