Computational Analyses of Offset-Stream Nozzles for Noise Reduction

55th AIAA Aerospace Sciences Meeting

2017

An experimental aeroacoustic investigation of three-stream nozzle concepts with potential to reduce takeoff noise from future supersonic aircraft is presented. We use guidance from previous three-stream nozzle experiments to explore asymmetric designs where both secondary and tertiary streams are concentrated in the downward direction. The impact of increasing the plug size on noise is examined. Enlarging the plug provides moderate noise reduction for axisymmetric and asymmetric nozzle configurations. Nozzle configurations that combine asymmetry in both secondary and tertiary streams provide a distinct noise benefit in the sideline azimuthal direction. Considering the sound pressure level at a fullscale frequency around 300 Hz, the combined effects of the enlarged plug and dual asymmetry yield reductions of 15 dB and 6 dB in the downward and sideline azimuthal directions, respectively, and at angles close to the angle of peak emission. Installation effects with an aft deck indicate minimal impacts on radiated noise, except in the case of a long deck at a scrubbing position. In that case, the ability of the asymmetric nozzles to reduce noise is disrupted. Marginal shielding at high frequency is noted at forward observer angles.

Section: Introductionmentioning

confidence: 99%

“…The enlarged secondary core reduces the convective Mach number of the primary eddies that radiate sound in the directions of the thickened coannular flow 14 . The addition of a third (tertiary) stream opens a parameter space to explore noise reduction technologies using the aforementioned methods [13][14][15][16][17] .…”

Section: Introductionmentioning

confidence: 99%

Investigation of Isolated and Installed Three-Stream Jets from Offset Nozzles

Phong

55th AIAA Aerospace Sciences Meeting

2017

“…Asymmetry in the nozzle entails offsetting the primary and secondary ducts, while asymmetry in the jet plume (issuing from a coaxial arrangement) can be induced by placing deflectors in the secondary stream. These "offset stream" approaches have been investigated for supersonic [13][14][15][16][17] and subsonic [16][17][18][19] jets. The acoustic benefit at supersonic speed can be substantial, while it is more moderate at subsonic speed.…”

Section: Introductionmentioning

confidence: 99%

Quiet Nozzle Concepts for Three-Stream Jets

54th AIAA Aerospace Sciences Meeting

Phong

Xiong

et al. 2016

We present a study of three-stream nozzle concepts with potential to reduce takeoff noise of future commercial supersonic aircraft. The concepts were evaluated at realistic cycle conditions in a subscale acoustic facility. Computations solving the Reynolds-Averaged Navier-Stokes equations provided insight into the changes in the flow field that can impact noise generation. The investigation encompassed long-and short-cowl nozzles in coaxial and asymmetric arrangements where the third stream was concentrated in the downward azimuthal direction. In coaxial configurations, addition of the third stream makes a modest impact on the noise emission, with a small benefit at high frequencies in the aft arc. This benefit is more evident in short-cowl nozzles. Asymmetric arrangements involved offsetting the tertiary duct and/or application of an internal wedge-shaped deflector. The asymmetry produces significant noise reduction in the direction of the thickened tertiary flow, and is more effective at cycle conditions with high specific thrust. Reduction of the skewness of the far-field pressure fluctuations suggests suppression of Mach wave radiation by the asymmetric tertiary flow.

“…1,2 Experiments and computations have revealed that the deflectors reduce the downward turbulent kinetic energy (TKE) but can also introduce a localized increase in the upward TKE. [3][4][5][6] Recent work has shown a correlation between the reduction in downward TKE and the reduction in downward peak overall sound pressure level. 7 The wedge-shaped deflector is an intriguing device with strong potential benefits but requiring great care in its design.…”

Section: Introductionmentioning

confidence: 99%

Computation of the Flow of a Dual-Stream Jet with External Solid and Perforated Wedge Deflectors for Noise Reduction

Xiong

Liu

40th Fluid Dynamics Conference and Exhibit

2010

We present a methodology for the computation of flow fields involving complex perforated surfaces in propulsion applications. Of particular interest is the treatment of perforated flaps used as wedge-shaped fan flow deflectors for reducing jet noise of a supersonic turbofan engine. A three-dimensional Reynolds-Averaged Navier-Stokes solver is used to compute the flow field of the external jet plume with solid and perforated deflector flaps, the latter with 50% porosity. Flow computation for perforated flaps presents a particular challenge and is handled by use of a localized body force model in the momentum equation. The study is conducted at two operating conditions: a cold condition at which mean velocity surveys were conducted and against which the computational code is validated; and a hot condition that corresponds to the takeoff engine cycle. The code predictions replicate adequately the mean velocity fields of the cold experimental flows. The code is then extended to the conditions of the actual engine cycle to study the impacts of the deflectors on the turbulent kinetic energy (TKE) distributions in the jet plume and on the aerodynamic performance of the nozzle. Consistent with findings of past studies, the solid flaps decrease the TKE on the underside of the jet and increase it at the top of the jet. The perforated flaps mitigate the TKE increase on the top of the jet, thus reducing the potential of excess noise from that region. The thrust loss of the perforated flaps is approximately one half that of the solid flaps.