FLOW AROUND A CYLINDER - istiarto

– 6.1 –
6 Summary and Conclusions
6.1 The work
The work is about an investigation on flow around a vertical cylinder installed on a
mobile channel bed. When passing around a cylinder, a uni-directional flow undergoes
different processes as it interacts with the cylinder and the mobile bed. The flow becomes
three-dimensional and highly turbulent. At the same time, it erodes the mobile bed
around the cylinder base and a local scouring takes place. These two particular physical
processes, the flow and the scouring, are the main interests in the study of flow around a
cylinder. The present work deals only with the first aspect, in which the flow takes place
in an equilibrium scour-depth condition (the scouring has ceased), under a clear-water
regime (the transport capacity in and out the scour hole is not exceeded). The objective of
the investigation is to get a better understanding on the flow as it is altered by the
cylinder and the scour hole.
Two approaches were adopted in the investigation, namely laboratory measurements and
numerical simulations. This is a continuation of the work conducted previously at the
LRH EPFL by Yulistiyanto (1997) 1 , in which a scoured channel bed replaces the flat
channel bed one of the previous work and a 3D hydrodynamic model substitutes the 2D
depth-averaged one.
6.2 Results
6.2.1 Laboratory measurements
Detailed measured velocities were obtained using a non-intrusive acoustic Doppler
velocity profiler (ADVP), conceived and developed at the LRH EPFL. The instrument
measures instantaneously the vertical distribution of the velocity vectors in the far-field
approach flow and scour hole. Two ADVP configurations were used; each one was suited
for different flow-depths. The focalized ADVP having a cylindrical measuring volume of
diameter �� = 6 [mm] and height �d = 3 [mm] was employed for flow depths
h ≤ 18 [cm]. For deeper flow depths, h > 18 [cm], the non-focalized ADVP having a
measuring volume of diameter 9 ≤ �� [mm] ≤ 26 and height �d = 4.5 [mm] was used.
1 Yulistiyanto, B. (1997). ―Flow around a cylinder installed in a fixed-bed open channel.‖
Doctoral Dissertation, No. 1631, EPFL, Lausanne, Switzerland.