Enhancing large-scale motions and turbulent transport in rotating plane Poiseuille flow

TL;DR

This study introduces an injection/suction control strategy on the unstable side of rotating plane Poiseuille flow to significantly enhance large-scale plume currents and turbulent scalar transport, with optimal slot spacing and minimal injection strength.

Contribution

It proposes a novel control method on the unstable side to amplify plume currents and improve turbulent transport efficiency in rotating flow.

Findings

Weak injection/suction can significantly enhance plume currents.

Increasing the distance between plume currents improves transport efficiency.

Control on the unstable side is more effective than on the stable side.

Abstract

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.