Acoustic Measurements of Co-annular Jets at High Subsonic-Low Supersonic Jet Velocities

2020 ◽  
Author(s):  
Richard Auhl ◽  
Stephen Willoughby ◽  
Dennis K. McLaughlin ◽  
Philip J. Morris
Keyword(s):  
Supersonic Jet ◽  
Acoustic Measurements ◽  
Annular Jets ◽  
Jet Velocities

Near- and Far-Field Acoustic Measurements for Stepped Nozzles at Over- and Perfectly-Expanded Supersonic Jet Flow Conditions

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
X. F. Wei ◽  
L. P. Chua ◽  
Z. B. Lu ◽  
H. D. Lim ◽  
R. Mariani ◽  
...  
Keyword(s):  
Near Field ◽  
Source Region ◽  
Supersonic Jet ◽  
Jet Flow ◽  
Far Field ◽  
Acoustic Measurements ◽  
Flow Conditions ◽  
Spectra Analysis ◽  
Highly Sensitive ◽  
Nozzle Configuration

Abstract Detailed near- and far-field acoustic measurements were conducted for two circular stepped nozzles with 30 deg and 60 deg design inclinations at over- and perfectly-expanded supersonic jet flow conditions and compared to those for a circular nonstepped nozzle. Far-field acoustic results show that stepped nozzles play an insignificant role in altering noise emissions at perfectly expanded condition. At an over-expanded condition, however, the longer stepped nozzle produces significant noise reductions at the sideline and upstream quadrants, while the shorter stepped nozzle does not. Noise spectra analysis and Schlieren visualizations show that noise reduction can be primarily attributed to mitigations in the broadband shock-associated noise (BSAN), due to the ability of the longer stepped nozzle in suppressing shock strengths at downstream region. Near-field acoustic measurements reveal that the source region, as well as the intensity of turbulent and shock noises, are highly sensitive to the stepped nozzle configuration. Furthermore, BSAN seems to be eliminated by the longer stepped nozzle in near-field region due to the shock structure modifications.

Flow field and noise characteristics of a supersonic impinging jet

1999 ◽  
Vol 392 ◽  
pp. 155-181 ◽  
Author(s):  
A. KROTHAPALLI ◽  
E. RAJKUPERAN ◽  
F. ALVI ◽  
L. LOURENCO
Keyword(s):  
Large Scale ◽  
Ground Plane ◽  
Large Diameter ◽  
Supersonic Jet ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Acoustic Measurements ◽  
Sonic Nozzle ◽  
Underexpanded Jets ◽  
Noise Characteristics

This paper describes the results of a study examining the flow and acoustic characteristics of an axisymmetric supersonic jet issuing from a sonic and a Mach 1.5 converging–diverging (C–D) nozzle and impinging on a ground plane. Emphasis is placed on the Mach 1.5 nozzle with the sonic nozzle used mainly for comparison. A large-diameter circular plate was attached at the nozzle exit to measure the forces generated on the plate owing to jet impingement. The experimental results described in this paper include lift loss, particle image velocimetry (PIV) and acoustic measurements. Suckdown forces as high as 60% of the primary jet thrust were measured when the ground plane was very close to the jet exit. The PIV measurements were used to explain the increase in suckdown forces due to high entrainment velocities. The self-sustained oscillatory frequencies of the impinging jet were predicted using a feedback loop that uses the measured convection velocities of the large-scale coherent vortical structures in the jet shear layer. Nearfield acoustic measurements indicate that the presence of the ground plane increases the overall sound pressure levels (OASPL) by approximately 8 dB relative to a corresponding free jet. For moderately underexpanded jets, the influence of the shock cells on the important flow features was found to be negligible except for close proximity of the ground plane.

Influence of Microjet Injection on Supersonic Jet Noise and Flow Field

2011 ◽  
Author(s):  
Ryuichi Okada ◽  
Toshinori Watanabe ◽  
Seiji Uzawa ◽  
Takehiro Himeno ◽  
Tsutomu Oishi
Keyword(s):  
Flow Field ◽  
Noise Reduction ◽  
Sound Pressure ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Cfd Analysis ◽  
Jet Engines ◽  
Acoustic Measurements ◽  
Pressure Data ◽  
Supersonic Jet Noise

Jet noise reduction is essential for realization of environmentally-friendly and highly-efficient supersonic jet engines for future civil transport. In the present study, experimental and numerical investigations were conducted to clarify the effect of microjet injection on supersonic jet noise. The experiments were focused on supersonic jet with Mach number up to 1.49 that was generated from a rectangular nozzle with high aspect ratio. Far field acoustic measurements were executed and the spectra and sound pressure data of jet noise were obtained. In order to understand the mechanism of noise reduction, flow field visualization was performed with shadowgraph technique. CFD analysis was conducted as well to observe the flow field and to estimate thrust loss due to the microjet injection.

Influence of Microjet Condition on Characteristics of Supersonic Jet Noise and Flow Field

2012 ◽  
Author(s):  
Ryuichi Okada ◽  
Toshinori Watanabe ◽  
Seiji Uzawa ◽  
Takehiro Himeno ◽  
Tsutomu Oishi
Keyword(s):  
Flow Field ◽  
Noise Reduction ◽  
High Speed ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Experimental Investigations ◽  
Acoustic Measurements ◽  
Supersonic Transport ◽  
Supersonic Jet Noise ◽  
Supersonic Aircraft

Jet noise reduction is essential for environmentally-friendly civil transport. Since jet noise becomes very intense in the case of supersonic aircraft, noise reduction is crucial topic for the realization of next-generation supersonic transport. In the present study, experimental investigations were performed to clarify the effect of microjet injection on supersonic jet noise and flow field. The experiments were focused on supersonic jet with Mach number up to 1.47, which was generated from a rectangular nozzle with high aspect ratio. Far-field acoustic measurements were conducted for widely ranged microjet conditions to understand the influence of the condition on characteristics of supersonic jet noise and flow field. For understanding the unsteady behavior of the flow field and the relation with noise reduction, flow field visualization was performed with schlieren technique using a high-speed camera.

Numerical simulation of supersonic jet instability modes of plane and notched rectangular nozzles

2011 ◽  
Vol 226 (1) ◽  
pp. 104-122 ◽  
Author(s):  
S Y Han ◽  
R R Taghavi ◽  
S Farokhi
Keyword(s):  
Supersonic Jet ◽  
Three Dimensional ◽  
Oscillation Mode ◽  
Instability Mode ◽  
Acoustic Measurements ◽  
Jet Instability ◽  
Rectangular Nozzle ◽  
Instability Modes ◽  
Mass Flowrate ◽  
Shock Simulation

The effect of exit geometry of a rectangular nozzle on the instability modes and mixing characteristics of under-expanded supersonic jets is computationally investigated. The unsteady three-dimensional viscous simulation is based on the Proteus code developed at NASA Glenn Research Center. A shock adaptive grid generator was developed to enhance the shock simulation. The nozzle aspect ratio for both plane and notched rectangular nozzles in this study is 5.0 and the fully expanded jet Mach number is 1.526. For the case of a plane rectangular nozzle, the ‘flapping’ oscillations, which are extensively observed in schlieren flow visualization and reported in acoustic measurements, are also captured in the presented computations. The flapping frequency in experimental measurements (7400 Hz) is closely predicted in the presented computations (7500 Hz). The symmetrical instability mode is also observed as viewed from the nozzle’s small and large dimensions at twice the flapping frequency. For the notched rectangular nozzle, the flapping oscillations ceased and instead a spanwise oscillation mode was observed as viewed from the nozzle’s large dimension. The instantaneous mass flowrate at nine jet widths downstream of the nozzle exit showed an increase of 8.5 per cent in mass flowrate in the jet emerging from the notched as compared to the plane rectangular nozzle.

On the convection velocity of source events related to supersonic jet crackle

2016 ◽  
Vol 793 ◽  
pp. 477-503 ◽  
Author(s):  
Nathan E. Murray ◽  
Gregory W. Lyons
Keyword(s):  
Shock Front ◽  
Shear Layer ◽  
Supersonic Jet ◽  
Extreme Value Distribution ◽  
Front Propagation ◽  
Convection Velocity ◽  
Analysis Method ◽  
Acoustic Measurements ◽  
Shock Fronts ◽  
Field Event

An image analysis method is developed and applied to shadowgraph images of supersonic jet flow to measure shock front propagation angles at numerous interrogation points distributed throughout the quiescent region outside of the jet shear layer. These shock fronts manifest in acoustic measurements of jet noise as steepened temporal waveforms that have been linked to the perception of crackle. The analysis method uses the Radon transform to quantitatively determine a local shock front propagation angle at each point. The dataset of angles is subsequently used to determine the locations and convection velocities of the sources inside the jet shear layer. The results indicate that the shock-like waves emerge immediately from the jet shear layer and are created by the supersonic convection of coherent structures. The statistical distribution of convection velocities follows an extreme value distribution, indicating that the shock front emitting sources are maxima of the underlying turbulence. A noise reduction method known to reduce the convection velocities in the jet shear layer is applied to the jet to investigate the effect on the shock front emission. The shock front angles change in concert with the reduction in convection velocity giving further evidence that the source of crackle is a flow field event.

Evaluation of Acoustic Analyses of Voice in Nonoptimized Conditions

2020 ◽  
Vol 63 (12) ◽  
pp. 3991-3999
Author(s):  
Benjamin van der Woerd ◽  
Min Wu ◽  
Vijay Parsa ◽  
Philip C. Doyle ◽  
Kevin Fung
Keyword(s):  
Repeated Measures ◽  
Voice Quality ◽  
Data Sets ◽  
Acoustic Measurements ◽  
Sample Collection ◽  
Experimental Conditions ◽  
Environment Analysis ◽  
Acoustic Measures ◽  
Recording Conditions ◽  
Cepstral Peak Prominence

Objectives This study aimed to evaluate the fidelity and accuracy of a smartphone microphone and recording environment on acoustic measurements of voice. Method A prospective cohort proof-of-concept study. Two sets of prerecorded samples (a) sustained vowels (/a/) and (b) Rainbow Passage sentence were played for recording via the internal iPhone microphone and the Blue Yeti USB microphone in two recording environments: a sound-treated booth and quiet office setting. Recordings were presented using a calibrated mannequin speaker with a fixed signal intensity (69 dBA), at a fixed distance (15 in.). Each set of recordings (iPhone—audio booth, Blue Yeti—audio booth, iPhone—office, and Blue Yeti—office), was time-windowed to ensure the same signal was evaluated for each condition. Acoustic measures of voice including fundamental frequency ( f o ), jitter, shimmer, harmonic-to-noise ratio (HNR), and cepstral peak prominence (CPP), were generated using a widely used analysis program (Praat Version 6.0.50). The data gathered were compared using a repeated measures analysis of variance. Two separate data sets were used. The set of vowel samples included both pathologic ( n = 10) and normal ( n = 10), male ( n = 5) and female ( n = 15) speakers. The set of sentence stimuli ranged in perceived voice quality from normal to severely disordered with an equal number of male ( n = 12) and female ( n = 12) speakers evaluated. Results The vowel analyses indicated that the jitter, shimmer, HNR, and CPP were significantly different based on microphone choice and shimmer, HNR, and CPP were significantly different based on the recording environment. Analysis of sentences revealed a statistically significant impact of recording environment and microphone type on HNR and CPP. While statistically significant, the differences across the experimental conditions for a subset of the acoustic measures (viz., jitter and CPP) have shown differences that fell within their respective normative ranges. Conclusions Both microphone and recording setting resulted in significant differences across several acoustic measurements. However, a subset of the acoustic measures that were statistically significant across the recording conditions showed small overall differences that are unlikely to have clinical significance in interpretation. For these acoustic measures, the present data suggest that, although a sound-treated setting is ideal for voice sample collection, a smartphone microphone can capture acceptable recordings for acoustic signal analysis.

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