Acoustic Pressure Waveforms Measured in High Speed Jet Noise Experiencing Nonlinear Propagation

2005 ◽  
Author(s):  
Benoit Petitjean ◽  
K. Viswanathan ◽  
Dennis McLaughlin
Keyword(s):  
High Speed ◽  
Acoustic Pressure ◽  
Jet Noise ◽  
Nonlinear Propagation

Acoustic Pressure Waveforms Measured in High Speed Jet Noise Experiencing Nonlinear Propagation

2006 ◽  
Vol 5 (2) ◽  
pp. 193-215 ◽  
Author(s):  
Benoît P. Petitjean ◽  
K. Viswanathan ◽  
Dennis K. McLaughlin
Keyword(s):  
High Speed ◽  
Acoustic Pressure ◽  
Jet Noise ◽  
Nonlinear Propagation

‘Crackle’: an annoying component of jet noise

1975 ◽  
Vol 71 (2) ◽  
pp. 251-271 ◽  
Author(s):  
J. E. Ffowcs Williams ◽  
J. Simson ◽  
V. J. Virchis
Keyword(s):  
High Speed ◽  
Angular Position ◽  
Jet Noise ◽  
Wide Frequency Range ◽  
Nonlinear Propagation ◽  
Wave Form ◽  
Long Term Effects ◽  
Recorded Sound ◽  
Recording Process

The paper describes an investigation of a subjectively distinguishable element of high speed jet noise known as ‘crackle’. ‘Crackle’ cannot be characterized by the normal spectral description of noise. It is shown to be due to intense spasmodic short-duration compressive elements of the wave form. These elements have low energy spread over a wide frequency range. The crackling of a large jet engine is caused by groups of sharp compressions in association with gradual expansions. The groups occur at random and persist for some 10−1s, each group containing about 10 compressions, typically of strength 5 × 10−3 atmos at a distance of 50 m. The skewness of the amplitude probability distribution of the recorded sound quantifies crackle, though the recording process probably changes the skewness level. Skewness values in excess of unity have been measured; noises with skewness less than 0·3 seem to be crackle free. Crackle is uninfluenced by the jet scale, but varies strongly with jet velocity and angular position. The jet temperature does not affect crackle, neither does combustion. Supersonic jets crackle strongly whether or not they are ideally expanded through convergent-divergent nozzles. Crackle is formed (we think) because of local shock formation due to nonlinear wave steepening at the source and not from long-term nonlinear propagation. Such long-term effects are important in flight, where they are additive. Some jet noise suppressors inhibit crackle.

scholarly journals Jet-Surface Interaction Test: Far-Field Noise Results

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Clifford A. Brown
Keyword(s):  
High Speed ◽  
Radial Distance ◽  
Jet Noise ◽  
Surface Interaction ◽  
Shielding Effect ◽  
Noise Prediction ◽  
Far Field ◽  
Wide Range ◽  
Field Noise ◽  
Surface Length

Many configurations proposed for the next generation of aircraft rely on the wing or other aircraft surfaces to shield the engine noise from the observers on the ground. However, the ability to predict the shielding effect and any new noise sources that arise from the high-speed jet flow interacting with a hard surface is currently limited. Furthermore, quality experimental data from jets with surfaces nearby suitable for developing and validating noise prediction methods are usually tied to a particular vehicle concept and, therefore, very complicated. The Jet-Surface Interaction Tests are intended to supply a high quality set of data covering a wide range of surface geometries and positions and jet flows to researchers developing aircraft noise prediction tools. The initial goal is to measure the noise of a jet near a simple planar surface while varying the surface length and location in order to: (1) validate noise prediction schemes when the surface is acting only as a jet noise shield and when the jet-surface interaction is creating additional noise, and (2) determine regions of interest for future, more detailed, tests. To meet these objectives, a flat plate was mounted on a two-axis traverse in two distinct configurations: (1) as a shield between the jet and the observer and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface length was varied between 2 and 20 jet diameters downstream of the nozzle exit. Similarly, the radial distance from the jet centerline to the surface face was varied between 1 and 16 jet diameters. Far-field and phased array noise data were acquired at each combination of surface length and radial location using two nozzles operating at jet exit conditions across several flow regimes: subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic. The far-field noise results, discussed here, show where the jet noise is partially shielded by the surface and where jet-surface interaction noise dominates the low frequency spectrum as a surface extends downstream and approaches the jet plume.

Adaptation of the Beveled Nozzle for High-Speed Jet Noise Reduction

AIAA Journal ◽  
2011 ◽  
Vol 49 (5) ◽  
pp. 932-944 ◽  
Author(s):  
K. Viswanathan ◽  
M. J. Czech
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Jet Noise

High-speed jet noise simulations for noncircular nozzles

2001 ◽  
Author(s):  
Said Boluriaan ◽  
Philip Morris ◽  
Lyle Long ◽  
Thomas Scheidegger
Keyword(s):  
High Speed ◽  
Jet Noise

Predicting Bubble Migration due to Bjerknes Force in a Complex 3D Geometry: Numerical and Experimental Results

2012 ◽  
Author(s):  
Francisco I. Valentin ◽  
Silvina Cancelos
Keyword(s):  
Acoustic Field ◽  
High Speed ◽  
Acoustic Pressure ◽  
Pressure Field ◽  
Piezoelectric Materials ◽  
Bubble Diameter ◽  
Absolute Pressure ◽  
Flowing Fluid ◽  
3D Geometry ◽  
Bjerknes Force

While the Bjerknes force is not the only force experienced by a bubble subjected to an acoustic field; studies of bubble translation in non-flowing fluid have identified Bjerknes force as being the most influential. Therefore, Bjerknes force can be used to trap bubbles in predefined locations of maximum and minimum absolute pressure. Specifically challenging is to determine these locations in complex geometries because direct measurement of the acoustic pressure for the whole system is generally not possible. The objective of this research is to numerically predict Bjerknes force effect on bubble migration and accumulation in a complex 3D geometry that includes piezoelectric materials, elastic materials and a fluid media. A numerical solution of the acoustic pressure field was obtained for this geometry, valid in the range of small pressure oscillations. Additionally, using the linearized Rayleigh-Plesset equation, which gives the volumetric oscillations of a bubble subjected to an acoustic field, the Bjerknes force was numerically computed. By knowing the Bjerknes force, a bubble migration pattern upon entering the system was predicted. A CMOS high speed camera was used to experimentally monitor bubble multimode excitation and bubble response to a stationary pressure field validating our numerical results. Results are presented for experiments conducted for a 1mm bubble diameter with acoustic fields ranging from 7 to 10 kHz which correspond to values of the structure and/or the bubble’s resonant frequency.

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