Numerical Simulation of Flow Resistance due to the Limnoperna fortunei
Attachment
Abstract
High-density attachment of Limnoperna fortunei (LF) would lead to the
increase of flow resistance, which has posed big challenges to the
normal operation of water conveyance projects. It is very necessary to
quantify the flow resistance caused by the attachment of LF. In this
study, a 3D geometric model of LF was generated based on real images.
Attachment models of LF were generated with different densities and
mussel size distributions, whose geometric characteristics were
evaluated by some fundamental physical quantities, including attachment
thickness, bed coverage, surface vertical roughness, and roughness
concentration. Furtherly, a 3D numerical model with specific boundary
conditions was established in OpenFOAM to simulate the flow over the LF
attachment. Body-fitted mesh was generated using snappyHexMesh based on
the LF attachment model. The results show that in high-density
scenarios, a big wake zone formed inside LF attachment by the combined
effects of each individual LF. Turbulence kinetic energy distribution
indicated that LF attachment would cause viscous dissipation thus
leading to more energy loss. The flow structure inside LF attachment was
controlled by the size and spacing between each individual LF. Manning’s
n values were calculated based on the CFD results at different
densities. The results show that the flow resistance of LF attachment
also followed the classic flow regimes, where in the skimming flow
regime, the mussel size distribution played a non-negligible role.
Higher flow speed resulted in larger flow resistance, and n could
increase more than 90% compared to the scenario without LF attachment.