Inner–outer interactions in a forced plane wall jet

Abstract

A plane wall jet (PWJ) is used as the model flow field to study the interactions within complex wall-bounded flows. The PWJ is subject to large-scale, large-amplitude forcing, and the subsequent scale interactions, in the forced flow, are characterized using time-resolved particle image velocimetry. These interactions are contrasted with those of the unforced flow. It is observed that the energy of the large-scale structures in the wall region is significantly increased by the forcing. It is unambiguously shown that the PWJ encapsulates an inner–outer interaction in the form of an amplitude and frequency modulation of the finer scales, by the outer representative large scale. In addition, this amplitude and frequency modulation effect is enhanced by the forcing over most of the wall-normal extent of the flow. This is particularly true in the near-wall region. Considering a structural perspective of the flow suggests that the flow scales responsible for the increased modulating effect are the forward-leaning boundary-layer-like structures of the flow.