Perturbation-based active flow control in overexpanded to underexpanded supersonic rectangular twin jets

Journal of Fluid Mechanics · 2023 · 37 citations

• Physics
• Mechanics
• Acoustics

The effects of perturbation-based active flow control on supersonic rectangular twin jets (SRTJ) over a wide range of nozzle pressure ratios (NPR = 2.77 to 6.7, corresponding to fully expanded Mach numbers M j = 1.3 to 1.9) were investigated. The aspect ratio and design Mach number for the bi-conic, converging-diverging nozzles were 2 and 1.5, respectively. The flow and acoustic fields of SRTJ are known to couple, often generating high near-field (NF) pressure fluctuations and elevated far-field (FF) noise levels. Large-scale structures (LSS), or equivalently instability waves or wave packets, are responsible for mixing noise, broadband shock-associated noise, screech and coupling. The primary objective of this research was to manipulate the development of LSS in this complex flow to better understand and mitigate their effects. The organization and passage frequency of the LSS were altered by excitation of instabilities over a wide range of frequencies and modes. Key findings include: (1) the screech mode of each jet was flapping along its minor axis; (2) the jets coupled, out-of-phase primarily in overexpanded cases and in-phase primarily in underexpanded cases, along the minor axis of the SRTJ; (3) coupling has significant effects on the NF pressure fluctuations, but only minor effect on the FF noise; (4) standing waves were observed only on the minor axis plane of the SRTJ; (5) altering or suppressing coupling can significantly reduce NF pressure fluctuations; (6) two high-frequency excitation methods proved effective in reducing the FF noise; and (7) nonlinear interactions between the screech tones and excitation input were observed in controlled cases in which screech was only partially suppressed.

An experimental investigation of deep dynamic stall control using plasma actuators

Experiments in Fluids · 2022 · 17 citations

• Mechanics
• Physics
• Aerospace engineering

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

AIAA SCITECH 2022 Forum · 2022 · 8 citations

• Physics
• Acoustics
• Mechanics

View Video Presentation: https://doi.org/10.2514/6.2022-2401.vid 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.