  The discharge of elongated particles from a silo with rotating bottom is
investigated numerically. The introduction of a slight transverse shear reduces
the flow rate $Q$ by up to 70% compared to stationary bottom, but the flow rate
shows a modest increase by further increasing the external shear. Focusing on
the dependency of flow rate $Q$ on orifice diameter $D$, the spheres and rods
show two distinct trends. For rods, in the small aperture limit $Q$ seems to
follow an exponential trend, deviating from the classical power-law dependence.
These macroscopic observations are in good agreement with our earlier
experimental findings [Phys. Rev. E $\textbf{103}$, 062905 (2021)]. With the
help of the coarse-graining methodology we obtain the spatial distribution of
the macroscopic density, velocity, kinetic pressure, and orientation fields.
This allows us detecting a transition from funnel to mass flow pattern, caused
by the external shear. Additionally, averaging these fields in the region of
the orifice reveals that the strong initial decrease in $Q$ is mostly
attributed to changes in the flow velocity, while the weakly increasing trend
at higher rotation rates is related to increasing packing fraction. Similar
analysis of the grain orientation at the orifice suggests a correlation of the
flow rate magnitude with the vertical orientation and the packing fraction at
the orifice with the order of the grains. Lastly, the vertical profile of mean
acceleration at the center of the silo denotes that the region where the
acceleration is not negligible shrinks significantly due to the strong
perturbation induced by the moving wall.
