摘要 :
The acoustic near-field of a supersonic underexpanded jet at M_j=1.34 was studied experimentally. A near-field azimuthal microphone array was utilized to study the jet oscillation dynamics and infer the geometrical pattern of the ...
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The acoustic near-field of a supersonic underexpanded jet at M_j=1.34 was studied experimentally. A near-field azimuthal microphone array was utilized to study the jet oscillation dynamics and infer the geometrical pattern of the upstream-traveling acoustic waves involved in the jet screech mechanism. Operation of the jet in isolation resulted in a lateral oscillation (mode B) with an acoustic field containing strong screech tones. Addition of a conical reflector of 60° cone half-angle changed the oscillation dynamics, with new mode E appearing prominently and coexisting with mode B. The cross-spectral densities at the distinct tone frequencies are utilized to discern the jet oscillation dynamics and screech frequency and wavelength prediction formulas are utilized to assess if mode E is an extension of previously observed screech modes.
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摘要 :
The effect of a conical reflector upstream of the nozzle exit of a supersonic underexpanded jet was studied experimentally. The jet had a fully-expanded Mach number M_j = 1.34 and the reflector half-angle was 60°. Experiments wer...
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The effect of a conical reflector upstream of the nozzle exit of a supersonic underexpanded jet was studied experimentally. The jet had a fully-expanded Mach number M_j = 1.34 and the reflector half-angle was 60°. Experiments were performed using a near-field linear microphone array that included one continuously-scanning sensor enabling high spatial resolution. The isolated jet emitted well-known screech mode B (lateral oscillation), with the fundamental tone and its harmonics appearing prominently in the sound pressure level spectrum. Addition of the reflector caused significant changes in the modal emission pattern, with new oscillation mode E appearing prominently, in conjunction with mode B. The near-field data obtained from the continuous-scan experiments were processed using a partial fields decomposition approach, in which the fixed sensors were utilized as the phase references. The technique allowed the construction of a global cross-spectral matrix based on the finely-spaced locations of the scanning sensor. Beamforming maps and deconvolved noise source distributions were computed using the global cross-spectral matrix and provided information on the structure of the noise source for the two jets. Cross-beamforming indicated significant coherence between shock cells at the screech frequencies. The partial fields were decomposed into radiating and non-radiating components, including separation in upstream- and downstream-propagating events. This information was used to assess the location of the screech sources for modes B and E with a high degree of spatial resolution. Finally, the tonal partial fields were propagated to the acoustic far-field using the boundary element method. The resulting directivity of the sound pressure level spectrum is in fair agreement with experimental results for the same jets.
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We present a computational study of three-stream jets simulating the exit conditions of future commercial supersonic aircraft engines. The study is conducted for coaxial and asymmetric configurations at a realistic cycle condition...
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We present a computational study of three-stream jets simulating the exit conditions of future commercial supersonic aircraft engines. The study is conducted for coaxial and asymmetric configurations at a realistic cycle condition. The asymmetric arrangement involved offsetting the tertiary duct and applying an internal wedge-shape deflector. Computations using Large Eddy Simulation (LES) provide detailed time-resolved information on the flow field. The resulting statistics are compared with the output of a Reynolds-Averaged Navier-Stokes (RANS) solver, a low-cost method that can be used as a design tool. The statistics are in overall agreement, with both methods predicting the thickening of the low-speed layer and reduction in turbulent kinetic energy on the underside of the asymmetric jet. There are quantitative differences in the initial region of the jet, with RANS predicting a longer potential core than does LES. The far field noise is calculated by-applying the Ffowcs Williams-Hawkings (FWH) equation to the LES results. The results show similar trends of far field noise spectra as measured by experiments.
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摘要 :
We present a computational study of three-stream jets simulating the exit conditions of future commercial supersonic aircraft engines. The study is conducted for coaxial and asymmetric configurations at a realistic cycle condition...
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We present a computational study of three-stream jets simulating the exit conditions of future commercial supersonic aircraft engines. The study is conducted for coaxial and asymmetric configurations at a realistic cycle condition. The asymmetric arrangement involved offsetting the tertiary duct and applying an internal wedge-shape deflector. Computations using Large Eddy Simulation (LES) provide detailed time-resolved information on the flow field. The resulting statistics are compared with the output of a Reynolds-Averaged Navier-Stokes (RANS) solver, a low-cost method that can be used as a design tool. The statistics are in overall agreement, with both methods predicting the thickening of the low-speed layer and reduction in turbulent kinetic energy on the underside of the asymmetric jet. There are quantitative differences in the initial region of the jet, with RANS predicting a longer potential core than does LES. The far field noise is calculated by-applying the Ffowcs Williams-Hawkings (FWH) equation to the LES results. The results show similar trends of far field noise spectra as measured by experiments.
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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 explo...
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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 full-scale frequency around 300 Hz, the combined effects of the enlarged plug and dual asymmetry yield reductions of IS 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.
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摘要 :
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 explo...
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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 full-scale frequency around 300 Hz, the combined effects of the enlarged plug and dual asymmetry yield reductions of IS 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.
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摘要 :
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. Computat...
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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.
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摘要 :
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. Computat...
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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.
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The acoustic near field of a subscale ducted fan was measured experimentally for the purpose of understanding the physics of sound generation and refining low-order models for aft-emitted tonal fan noise. The experimental rig simu...
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The acoustic near field of a subscale ducted fan was measured experimentally for the purpose of understanding the physics of sound generation and refining low-order models for aft-emitted tonal fan noise. The experimental rig simulates the fan conditions of an ultra-high-bypass turbofan. Acoustic measurements were performed with a phased array of microphones comprising fixed and scanning sensors, the combination of which offers spatial resolution sufficient to resolve detailed features of the pressure field. Partial-fields decomposition of the signals of axially-scanning sensors shows the potential of recovering the complete harmonic pressure field along the scan line. Axial space-time correlations and azimuthal correlations show trends that are in line with the predictions of a recently proposed source model that is partially informed by internal duct acoustics.
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Reconfigurable drones were developed, tested, and flown in multiple configurations in order to model flight characteristics for missions with varying requirements of employed drones. This resulted in the successful production of a...
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Reconfigurable drones were developed, tested, and flown in multiple configurations in order to model flight characteristics for missions with varying requirements of employed drones. This resulted in the successful production of an evaluation function that identifies optimal drones for missions. Missions include tasks such as hovering in a desired position for a set amount of time, designated stationary flight, and flying a distance greater than one hundred meters and returning, designated long range flight. The ranking function considers a particular drone configuration's maximum payload, hover time, maximum speed, maximum range, and steadiness in relation to other drones and weighs each according to the requirements of the mission.
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