19/09/17 - Antoine Mathieu
Scour around structures is a major engineering issue
that requires a detailed description of the flow field as
well as sediment transport processes. Due to
enhanced suspended load associated with vortices
generated around structures, sediment transport cannot
be solely related to bed shear stress, such as Shields
parameter based formula. In order to address this
issue, we used a multi-dimensional two-phase flow
solver, sedFoam-2.0 (Chauchat et al., GMD 2017)
implemented under the open-source CFD toolbox
OpenFOAM. Two configurations of an
horizontal cylinder lying on a sediment bed (Mao,
1986 ; Sumer et al., 2001) are studied and
compared with experimental and numerical data from
the literature.
The process of scour under a pipeline is usually
decomposed into three stages (Sumer et al., 2001) :
the onset, corresponding to the formation of small gap
underneath the pipe ; the tunneling stage during which
the channel formed below the pipe is enlarged and
sediment is transported downstream under the
accelerated flow ; the lee-wake erosion in which the
vortices triggered by the cylinder contribute to further
transport sediment in the downstream direction. We
demonstrate that the two-phase flow model is able to
reproduce qualitatively the onset of scour. The results also show that
the tunneling
stage is well reproduced by the two-phase flow model.