Impact of Azimuthally Controlled Fluidic Chevrons on Jet Noise

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The jet flow from a complex engine nozzle system with multiple jet streams is computed using large eddy simulations. The effects of the fan flow, the impact of installation effects created by the addition of a pylon, and the influence of the core-fluidic injection on the resulting flow field and the acoustic radiation are studied. The potential core length reduces slightly with the introduction of the fan flow and further reduces with the introduction of the fluidic injection nozzle geometry. Computations of fluidic-injection nozzle configurations are validated with experimental data. The agreement in the farfield spectra along the sideline and in the peak propagation directions is good for both the baseline nozzle and the fluidic-injection nozzle configurations. The centerline velocity and the turbulent kinetic energy distribution along the nozzle symmetry plane are in good agreement with the experiments. The parametric study varying the pressure ratio shows that as the injection pressure ratio is increased the jet core moves towards the pylon. For a fluidic injection pressure ratio of 4.0, a reduction of 2.0dB-2.5dB is observed with respect to the baseline nozzle with a pylon. Fluidic injection is found to produce two sets of counter rotating vortices, one along the nozzle lip line and the second penetrating the nozzle core flow. The potential reason for the noise reduction is investigated from the changes in the turbulence intensity and the convective velocity in the shear layer. It is shown that the turbulence intensity is reduced and the convective velocity at the end of the potential core remains nearly constant for all injection pressure ratios studied.

Section: Figuresupporting

confidence: 77%

Jet Noise Simulations for Complex Nozzle Geometries

Ramamurti

Corrigan

Liu

et al. 2015

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“…The influence of microjet injection on the near-nozzle shear layer is quite similar to that achieved by an intrusive tab: the generation of streamwise vorticity thickens the near-nozzle shear layer and disrupts the downstream shock structure. Microjets used to generate streamwise vorticity just upstream of the lip are often referred to as "fluidic chevrons", [154][155][156] due to the similarity in the resultant perturbations of the underlying flow structure. More recently, there have been a number of studies where the microjets are placed inside the nozzle itself; the injection of fluid upstream of the nozzle exit is referred to as a "fluidic insert".…”

Section: Active Flow Controlmentioning

confidence: 99%

Aeroacoustic resonance and self-excitation in screeching and impinging supersonic jets – A review

Edgington-Mitchell

2019

172

104

Supersonic jets, particularly shock-containing jets, often exhibit high-intensity, discrete-frequency acoustic tones. These tones are the signature of an aeroacoustic resonance loop established by the flow. This paper considers two of the classical forms of supersonic jet resonance: screech in shock-containing free jets and tones generated by the impingement of a jet against a surface. The first half of the paper provides a historical perspective on research into both forms of resonance, ranging from the seminal works of Alan Powell to recent contributions from high-fidelity numerical simulation, experiment, and stability theory. The second half of the paper provides a critical assessment of current understanding around the four processes that characterize jet resonance: a downstream propagation of energy, an acoustic generation mechanism, an upstream propagation of energy, and a receptivity mechanism.

“…For supersonic jets, air injection has been found to reduce screech tones, broadband shock noise, and mixing noise in hot and cold main jets. Both slotted and circular injectors are very effective at eliminating screech with roughly a 1% mass flow ratio [64,65]. For slotted injection [65,66], increasing injection pressure decreases broadband shock noise possibly due to modifications of the jet shock cell structure resulting from the injection process.…”

Section: The Acoustic Fieldmentioning

confidence: 99%

“…Both slotted and circular injectors are very effective at eliminating screech with roughly a 1% mass flow ratio [64,65]. For slotted injection [65,66], increasing injection pressure decreases broadband shock noise possibly due to modifications of the jet shock cell structure resulting from the injection process. Reductions of 8 dB in broadband shock noise levels have been achieved in a cold main jet with an injection pressure equal to four times the ambient pressure and an injection mass flow ratio equal to 1.2% [65].…”

Section: The Acoustic Fieldmentioning

confidence: 99%

Fifty Years of Fluidic Injection for Jet Noise Reduction

Henderson

2010

Self Cite

112

The paper reviews 50 years of research investigating jet noise reduction through fluidic injection. Both aqueous and gaseous injection concepts for supersonic and subsonic jet exhausts are discussed. Aqueous injection reduces jet noise by reducing main jet temperature through evaporation and main jet velocity through momentum transfer between water droplets and the main jet. In the launch vehicle environment where large quantities of fluid do not have to be carried with the vehicle, water injection is very effective at reducing excess overpressures. For in-flight use, aqueous injection is problematic as most studies show that either large quantities of water or high injection pressures are required to achieve noise reduction. The most effective noise reduction injection systems require water pressures above 2000 kPa (290 psi) and water-to-mainjet mass flow rates above 10% to achieve overall sound pressure level reductions of roughly 6 dB in the peak jet noise direction. Injection at lower pressure (roughly 1034 kPa or 150 psi) has resulted in a 1.6 EPNdb reduction in effective perceived noise level. Gaseous injection reduces noise through jet plume modifications resulting from the introduction of streamwise vorticity in the main jet. In subsonic single-stream jets, air injection usually produces the largest overall sound pressure level reductions (roughly 2 dB) in the peak jet noise direction. In dual-stream jets, properly designed injection systems can reduce overall sound pressure levels and effective perceived noise levels but care must be taken to choose injector designs that limit sound pressure level increases at high frequencies. A reduction of 1.0 EPNdB has been achieved with injection into the fan and core streams. However, air injection into dual-stream subsonic jets has received little attention and the potential for noise reduction is uncertain at this time. For dual-stream supersonic jets, additional research needs to be conducted to determine if reductions can be achieved with injection pressures available from current aircraft engines.