Wave cancellation in jets with laminar and turbulent boundary layers: the effect of nonlinearity

TL;DR

This study investigates how nonlinearity and upstream conditions affect wave cancellation in jets with different boundary layer states, revealing that turbulence enhances linear response and control effectiveness.

Contribution

It provides new insights into the influence of boundary layer conditions and nonlinearity on wave cancellation performance in forced jets.

Findings

Turbulent boundary layers improve linear response regimes.

Nonlinear effects emerge at higher bandwidths in laminar jets.

Reactive control is more effective in turbulent jets.

Abstract

This paper presents a study on wave cancellation in forced jets. Building on recent work on real-time control of forced turbulent jets [1,2], we here assess the effect of jet upstream conditions and nonlinearity on wave-cancellation performance. The experiments are performed in jets with laminar and turbulent boundary layers inside the nozzle. An open-loop campaign is first conducted, in which the goal is to analyse the jet response to stochastic forcing with variable bandwidth. The upstream conditions of the jet are found to have a strong influence on the jet response. For narrow forcing bandwidths, both jets present a clear response regime. However, in the initially-laminar jet, as bandwidth is increased, high growth rates and transition to turbulence in the initial region underpin the onset of nonlinear effects in jet response. In the initially-turbulent jet, on the other hand, lower growth rates allow a linear response regime to be maintained for a broader range of forcing parameters. As the wave cancellation strategy is linear, reactive control is found to be more effective in the initially turbulent jet, consistent with the results of the open-loop analysis.