Effects of Active Control on Flow and Near- and Far-Field Acoustics of Twin Rectangular Supersonic Jets

Abstract

Rectangular twin jets are quite promising for tactical aircraft. However, the associated screech and coupling phenomena which can produce elevated far-field noise and strong near-field pressure fluctuations (with the potential to damage nearby aircraft components) must be mitigated. The objective of this work is to examine the control authority of localized arc-filament plasma actuators (LAFPAs) over supersonic rectangular twin jets from closely spaced converging-diverging nozzles over a wide range of flow regimes, and to explore the underlying physics of this control technique using perturbations. LAFPAs exert control authority by leveraging flow physics via manipulating the Kelvin-Helmholtz instability to produce significant effects with minimal power input. LAFPAs have previously demonstrated excellent control authority in subsonic and supersonic jets. Spectral proper-orthogonal decomposition of time-resolved schlieren images demonstrate that the twin jets readily respond to excitation by the LAFPAs over a wide range of frequencies, allowing the LAFPAs to control the generation and development of the large-scale structures in the jet’s shear layer and thus their interactions with the shock cells. Time-averaged wavelet coherence magnitude and phase from near-field acoustic data were used to assess the twin jets’ screech and coupling states. The effects of various actuation parameters on the twin jets’ screech and coupling are consistent with empirical predictions based on the classical screech closure model. The LAFPAs’ capabilities include altering the coupling and the screech modes, changing the screech and coupling frequency, and suppressing screech and coupling.