  Based on the properties of large-scale plume currents, an injection/suction
control strategy is introduced to enhance the strength of plume currents and
the turbulent transport of passive scalar in rotating plane Poiseuille flow.
The control keeps the classical non-penetrative condition on the stable side,
and prescribes spanwise varying wall-normal velocity on the unstable side.
Direct numerical simulations show that at medium rotation numbers, very weak
injection/suction (the root-mean-square velocity on the controlled side is
below $1\%$ of the bulk mean velocity) with properly distributed slots could
significantly enhance the large-scale plume currents which have the same
spatial distribution as the injection slots. In addition, if the distance
between plume currents are increased, the turbulent transport efficiency can be
promoted. Therefore, taking the strength and transport efficiency into account,
the distance between injection slots should be slightly larger than the
intrinsic distance between plume currents to achieve maximum enhancement of
turbulent transport. For comparison, the control with non-penetrative condition
on the unstable side and injection/suction on the stable side is also examined
with simulations. It is found that the injection/suction on the stable side has
much weaker influence compared with that on the unstable side. This is because
that plumes are generated on the unstable side, and that controlling the origin
of plumes is more effective.
