Active Control of a Mach 0.9 Jet for Noise Mitigation Using Plasma Actuators

Abstract

Localized arc filament plasma actuators were used to control an axisymmetric Mach 0.9 jet with a Reynolds number based on the nozzle exit diameter of 7:6 10 5. Eight actuators, distributed azimuthally inside the nozzle, near the nozzle exit, were used to excite various instabilities and azimuthal modes of the jet over a large Strouhal number range (St DF of 0.1 to 5.0). Time-resolved pressure measurements were used to investigate the development of actuation perturbations in the jet, particle image velocimetry measurements were used to evaluate the control effects on the turbulence field, and far-field sound was measured to evaluate the control effects on the radiated acoustic field. The jet responded to the forcing over a large range of excitation Strouhal numbers with varying degrees. As expected, the low Strouhal number seeded disturbances grew slowly, saturated farther downstream, and stayed saturated for a longer time before decaying gradually. The saturation and decay of the seeded perturbations moved farther upstream as their Strouhal number was increased. Seeded perturbations with higher azimuthal modes exhibited faster decay. Particle image velocimetry results showed that when exciting the jet's preferred-mode instability at lower azimuthal modes, the jet potential core was shortened and the turbulent kinetic energy was increased significantly. At higher Strouhal numbers and higher azimuthal modes, forcing had less of an impact on the mean velocity and turbulent kinetic energy. Far-field acoustic results showed a significant noise increase (2 to 4 dB) when the jet is excited around the jet's preferred-mode instability Strouhal number (St DF 0:2-0:5), in agreement with the results in the literature. Noise reduction of 0.5 to over 1.0 dB is observed over a large excitation Strouhal number range; this reduction seems to peak around St DF 1:5 to 2.0 at a 30-deg angle, but around St DF 3:0 to 3.5 at a 90deg angle. Although forcing the jet with higher azimuthal modes is advantageous for noise mitigation at a 30-deg angle and lower Strouhal numbers, the effect is not as clear at higher forcing Strouhal numbers and at a 90-deg angle.

On least-order flow representations for aerodynamics and aeroacoustics

“…The need for such a physical understanding is motivated by ongoing efforts from the beginning of civil air traffic with jet engines to suppress jet noise from engine exhausts leading to larger bypass ratios of the jet engine, geometrical modifications of the nozzle trailing edge and active control devices like plasma actuators, microjets, fluidic chevrons and for acoustic forcing (see e.g. reviews in Tam 1998;Samimy et al 2007;Jordan & Gervais 2008;Laurendeau et al 2008). Yet an intuitive understanding of the noiseproducing structures is still in its infancy after more than five decades of jet noise research (see e.g.…”

Supersonic Inlet Flow Control Using Localized Arc Filament Plasma Actuators

“…Originally these actuators were developed to control high-speed, high-Reynolds number jets for mixing enhancement and noise mitigation. [19][20][21] LAFPAs assert their control in the jet by using natural instabilities in the flow to amplify the generated perturbations. This report details the investigation of the LAFPA's control authority in a SWBLI.…”

Simulation of Flow Control with Microjets for Subsonic Jet Noise Reduction

“…Samimy (Samimy et al, 2007a) for instance experimentally observed similar spectral peaks using localized arc filament plasma actuators. Broadband noise modification with the two different forcing frequencies Fig.…”

“…The two forcing frequencies f F = 3 kHz and 9 kHz are considered for the simulations. They are chosen following the experimental results of Samimy (Samimy et al, 2007a) using localized arc filament plasma actuators and who observed a broadband noise increase for the low frequency excitation and a reduction for the high one.…”

“…Noise reduction through energy injection using plasma actuators is also being investigated for subsonic (Kastner et al, 2008;Kearney-Fischer et al, 2009a;Kim et al, 2009;Samimy et al, 2007a) and supersonic (Kearney-Fischer et al, 2011;Samimy et al, 2007b) jets. Control is made with localized arc filament plasma actuators, each actuator consisting in a pair of pin electrodes and generating electric discharge plasmas at a driven frequency varying from 0 to 200 kHz.…”