Erosion and Deposition of Particles in a Periodic Forced Flow - Selected Topics of Computational and Experimental Fluid Mechanics - page 430

3.2 Channel Width of 3 Centimeters

Another experiment was made under the following conditions: the channel width is
H 3 cm and the driving frequency is 0.05Hz. Then, the maximal flow rate and

the representative velocity are: Q 0 =

=

10 − 5 m 3 /s and U 6 . 77 × = 0 . 056m/s. The

Reynolds and Strouhal numbers are respectively Re 0.035.

In Fig. 3 we show the final distribution of particles in the channel and in a section
of the larger domain. This distribution has a similar shape to those obtained in numer-
ical simulations reported by López-Sánchez and Ruiz-Chavarría ( 2013b ). The sand
accumulates into the channel, near to its mouth and again a trough is formed in front
of it. The trough extends about four times the channel width. However, there are
some differences. That is, the length of the zone without particles in the numerical
simulation is twice the corresponding region in this experiment.

= 1,400 and S =

3.3 Channel Width of 5 Centimeters

We made a third experiment with a 5 cm channel width and a driving frequency
of 0.08Hz. The experiment lasted for 18h. The values of maximal flow rate and
representative velocity are: Q 0 = 10 − 4 m 3 /s and U 3 . 47 × = 0 . 173m/s. So the

= =

flow has a Reynolds number Re 0.023. The

experiment extends over 5,200 periods. In a tidal induced flow this corresponds to a
seven year. The final particle distribution is shown in Fig. 4 . The particle distribution
is not similar to the previous cases, since the white spots indicating the absence
of particles are not symmetrical. The size of the trough is approximately twice the
channel width. On the other hand, it is important to remark the appearance of two
regions where particles (see Fig. 5 ) deposit. This regions are outside the area where
particles were initially collocated. Such regions are situated to both sides of the
symmetry axis and extend until the position where the dipole dissipates. In this sense
we can state that the presence of the vortices enhances the particle transport.

8,700 and a Strouhal number S

Fig. 3 Final distribution of
particles in a experiment
with the following
conditions: H = 3 cm, f =
0.05, Re = 1,400, S = 0.035