12th International Symposium on Applications of Laser Techniques
to Fluid Mechanics – July 2004, Lisbon, Portugal
Turbulent Flow Over a Sphere – An Approach to Erosion
R. F. Aleixo
R. Maia
Departamento de Engenharia Civil, Faculdade de Engenharia da Universidade do Porto
Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal
Abstract
The study here presented is devoted to the study of the shear
flow over a sphere for high Reynolds numbers as a way of
analyzing the erosion process.
Theoretically it can be shown that the Shields criteria
(Shields, 1936) can be expressed as a function of the
velocity fluctuation (Durst, 2002):
τc = f(u+).
Fig. 1: Detail of the model
The experimental model used was a loose particle placed over a bed of fixed particles, as shown
in Figure 1. Measurements were made for 4 Reynolds numbers (10000, 20000, 30000, 40000),
and LDA, mounted in a forward-scatter configuration was used to characterize the flow over the
sphere (Figure 1). Some of the results obtained for the u component for the Reynolds numbers
10000 and 40000,
along the centerline of
the channel are shown
Re = 10000
Re = 40000
u (m/s)
in Figure 2.
0,0 0,2 0,4
0,0 0,2 0,4
-0,20,00,2 -0,20,00,20,4 0,0 0,2 0,4
0,0 0,2 0,4
55
50
45
40
50
55
50
45
50
45
40
35
35
30
30
45
40
40
35
35
y (mm)
The obtained data
allowed the analysis
of the flow around the
sphere
and
its
influence
in
the
downstream
flow.
These data was also
used to verify if the
onset of particle lift
out of the sediment
bed occurs when the
turbulent fluctuations
reach a limiting value
proportional to the
weight of the particle.
30
30
25
25
25
25
20
20
15
15
10
10
10
10
5
5
5
5
0
-0,50
0
-0,25
0
0,00
0
0,25
20
20
15
15
0,50
x (cm)
Fig. 2: Detail of the u component at the sphere vicinity
References
Durst, F., Contribution for an Annex of a FCT Research Project Proposal, 2002.
Shields, A., Anwendung der Aenlichkeitsmechanik und der Turbulezforschung auf die
Geschiebbewegung, Mitteilungen der Preussischen Versuchsanstal fur Wasserbau und Schiffbau, Berlin,
1936.