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

2018 AIAA Aerospace Sciences Meeting

Phong

2018

Self Cite

We assess the potential of three-stream nozzle concepts to reduce the takeoff perceived noise level from future supersonic aircraft. The study encompasses the effects of nonaxisymmetric exhaust configurations as well as the effect of an enlarged plug. Asymmetry in the plume was created via eccentric tertiary and secondary ducts, in combination with a wedge-shaped deflector in the tertiary duct; and by reshaping the primary plug from circular to elliptical cross-section. The eccentricities were directed to increase the thickness of the lower-speed tertiary and secondary flows underneath the fast primary stream, thereby reducing noise in the general downward direction. The plug ellipticity was designed to flatten the primary stream along the major axis of the ellipse, thereby improving its coverage by the lower-speed streams with the goal of improving sideline noise reduction. The enlarged plug design was motivated by sonic-boom signature considerations. Acoustic measurements using helium-air mixture jets from small-scale, rapid-prototyped nozzles generated sound pressure level spectra at a number of polar and azimuthal angles for each configuration. These were converted to estimates of flyover perceived noise level and effective perceived noise level (EPNL) assuming a typical takeoff profile. The effect of the enlarged plug is to reduce the takeoff (downward) and sideline EPNLs, each by about 1.7 dB. Configurations with eccentricity in the tertiary flow only, all other components being axisymmetric, reduced the downward EPNL by as much as 5.1 dB but did not reduce the sideline EPNL. Adding eccentricity to the secondary ducts results in sideline noise reduction of about 2 EPNdB while providing downward reduction of around 5.6 EPNdB. The effect of the elliptical plug is to add another 1.0 dB to the sideline reduction. The best configuration involves the combination of eccentricity in the secondary and tertiary ducts with ellipticity of the primary plug; it yields noise reductions of 5.8 EPNdB and 2.9 EPNdB in downward and sideline directions, respectively. Including the effect of the enlarged plug, a cumulative (takeoff plus sideline) noise reduction of 12 EPNdB is estimated.

Section: Axisymmetric Designsmentioning

confidence: 99%

“…2,3 The focus is on jets with three streams as they relate to the development of advanced variable-cycle engines for supersonic propulsion. We build on past efforts at UC Irvine [4][5][6] as well as research at NASA Glenn Research Center [7][8][9] to study the acoustics of such jets.…”

Section: Introductionmentioning

confidence: 99%

Perceived Noise Assessment of Offset Three-Stream Nozzles for Low Noise Supersonic Aircraft

2018 AIAA Aerospace Sciences Meeting

Phong

2018

Self Cite

“…Past reports have provided details on this nozzle design, called AXI04U, and its evolution from earlier axisymmetric designs. 5,13 The subscripts p, s, and t will refer to the primary (inner), secondary (middle), and tertiary (outer) streams, respectively. Nozzle AXI04U has secondary-to-primary area ratio A s /A p = 1.44, and tertiary-to-primary area ratio A t /A p = 1.06.…”

Section: Jet Flowmentioning

confidence: 99%

The Very Near Pressure Field of Three-Stream Jets

Adam

2018 AIAA Aerospace Sciences Meeting

Xiong

et al. 2018

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Using large eddy simulation (LES) of a hot coaxial three-stream jet we assess key assumptions of a recent volumetric model of the jet noise source based on the Reynolds-Averaged Navier Stokes (RANS) flow field and explore the proper definition of a linear surface-based model. Direct evaluation of the Reynolds stress and convective velocity shows that the RANS-based outer surface of peak stress (OSPS) and convective velocity on this surface are in good agreement with the LES results. In addition, examination of the instantaneous LES pressure field indicates that the most energetic pressure events occur on the OSPS. These results lend credence to the use of the RANS-based OSPS to simulate the convective Mach number distribution in a multi-stream jet, one of the most critical decisions in the volumetric modeling. The effort on the surface-based model focuses on the proper location of the "radiator surface", at the boundary between the rotational and irrotational fields, on which linear partial fields would represent the imprint of turbulent structures in the jet flow. Definitions of the radiator surface based on thresholds of the gradient of the mean axial velocity place the surface outside of the hydrodynamic/acoustic boundary as determined by space-time correlations of the pressure field, thus fail to produce a surface with the desired property. A surface on which the convective velocity is identical to that on the OSPS falls exactly on hydrodynamic/acoustic boundary. This surface also appears to follow the outer band of a layer of negative pressure skewness.

“…airframe surfaces) using well known linear propagation techniques such as the boundary element method [4][5][6]. In addition, surface-based models could simplify the treatment of complex multi-stream asymmetric jets that have shown promising noise reductions [7,8]. To be able to inform the surface-based noise source model from the RANS flow field one needs to establish physical connections between the dominant turbulent events in the vortical region of the jet and the linear pressure statistics near the edge of the jet where the surface-based model is defined.…”

Section: Introductionmentioning

confidence: 99%

The Imprint of Vortical Structures on the Pressure Field at the Edge of a Turbulent High-Speed Jet

Adam

AIAA Scitech 2021 Forum

Bogey

2021

Self Cite

We investigate the distributions of length and velocity scales in a Mach 0.9 isothermal round jet for the purpose of developing a linear surface-based model for the noise source that can be informed by the time-averaged flow field. Large eddy simulation of the flow enables the computation of two-point space-time correlations throughout the jet and its near acoustic field. The resulting time, length, and convective-velocity scales are examined on the surface of peak Reynolds stress (SPS), representing the location of the most energetic eddies, and on a "radiator surface" at the boundary between the rotational and irrotational fields. The radiator surface is defined such that the convective velocity distribution on it matches that on the surface of peak Reynolds stress. The location of the radiator surface, and distributions of flow scales on it, are critical elements of the noise source model and are examined in detail. The nature of the space-time correlations, and resulting scales, differ significantly for axial velocity fluctuations and pressure fluctuations. Velocity-based correlations appear to capture localized turbulent events, while pressure-based correlations appear dominated by the interaction of large eddies with the surrounding potential flow. Consequently the axial and radial distributions of the corresponding length scales exhibit different trends. Correlation scales on the radiator surface are larger than on the SPS thus indicating that fine-scale vortical motions do not make a significant imprint on the radiator surface. Scales associated with the Reynolds-averaged flow field, relevant to low-cost modeling, are emulated from LES data and compared to the LES-based scales. Simple relationships are established that may aid the development of rapid predictive models.