  The discharge of polydisperse grains in a two-dimensional silo, operating in
a continuous-discharge mode, is studied with the help of soft-particle discrete
element simulations. We find that the mass flow rate displays similar variation
with vertical normal stress at the base and the transition-point in the bulk,
signifying that the base normal stress can be considered as a representative of
its bulk counterpart. The variation of the base and transition-point normal
stresses with fill height follows the Janssen's model, with the former being
larger than the latter. The transition-point ($y_t$) is defined as the vertical
extent of Region of Orifice Influence (ROOI), which is situated directly above
the orifice in its neighbourhood. The transition-point occurs largely at the
same location irrespective of the fill height. It shifts, however, upon
changing the orifice size, indicating its occurrence to be a localized
phenomenon. Finally, the scaling of the vertical velocities at the
transition-point and outlet uncovers $y_t$ to be a more relevant length scale
than the orifice size $D$. This scaling provides a new insight into the
dynamics of the silo discharge in the case where the flow rate varies but the
normal stress stays largely invariant to change in the orifice size.
