The role of nonlinear effects in the propagation of noise from high-power jet aircraft

Abstract

To address the question of the role of nonlinear effects in the propagation of noise radiated by high-power jet aircraft, extensive measurements were made of the F-22A Raptor during static engine run-ups. Data were acquired at low-, intermediate-, and high-thrust engine settings with microphones located 23-305 m from the aircraft along several angles. Comparisons between the results of a generalized-Burgers-equation-based nonlinear propagation model and the measurements yield favorable agreement, whereas application of a linear propagation model results in spectral predictions that are much too low at high frequencies. The results and analysis show that significant nonlinear propagation effects occur for even intermediate-thrust engine conditions and at angles well away from the peak radiation angle. This suggests that these effects are likely to be common in the propagation of noise radiated by high-power aircraft.

Acoustic waveforms produced by a laboratory scale supersonic jet

“…Because these Mach waves are generated by turbulence, they are classified as a component of turbulent mixing noise, which is the most significant source of noise for jets operating at supersonic acoustic Mach numbers. If the amplitude of the Mach wave is large enough to overcome viscous relaxation effects [7,15], the waveform will steepen with distance from its source, which is more easily observed under full-scale conditions where the characteristic frequencies, and hence viscous relaxation effects, are low [12].…”

Toward Active Control of Noise from Hot Supersonic Jets

“…However, only weak observations of cumulative nonlinear effects have been made using a laboratory-scale setup, all the while being observed under full-scale conditions. Examples of full-scale jet and rocket tests can be found in the literature (Morfey & Howell 1981;Mclnerny 1996;Mclnerny & Olgmen 2005;Gee et al 2008;Saxena et al 2009). In particular, significant nonlinear effects from full-scale engine tests were found in the spectra presented by Morfey & Howell (1981) and Gee et al (2008).…”

“…The work of Papamoschou et al (2010 and Baars et al (2011) comprised supersonic jets in terms of the acoustic Mach number (M a = Uj/aao > 1); this definition of the jet Mach number is most relevant to the formation of Mach waves. Aside from conventional spectral analysis, Laufer et al (1976), Gallagher (1982), Petitjean et al (2006) and Veitin et al (2011) studied the temporal characteristics of the acoustic pressure waveform in a laboratory (rangerestricted) environment while Gee et al (2008) focused on the nonlinear propagation effects of a full-scale static jet engine and compared the experimental data successfully to a numerical model based on the generalized Burgers equation. Some of the more relevant numerical studies include the large-eddy simulation of an overexpanded Mach 3.3 jet by de Cacqueray et al (20116) as well as the frequency-domain algorithm for simulating nonlinear noise propagation by Saxena et al (2009).…”

“…Beginning with the pioneering work of Ffowcs Williams et al (1975), the lack of cumulative waveform steepening in the pressure waveform was attributed to low amplitude levels at the source (based on private communication between Blackstock and Ffowcs Williams). Only in recent years, has a successful execution of this algorithm been performed on high speed jet flows and can be found in the work of Gee et al (2008). In response to earlier failed attempts at using the generalized Burgers equation to study nonlinear distortions in the acoustic waveform from high speed jet flows, alternative methods where developed.…”

Development of a Near-field Intensity Measurement Capability for Static Rocket Firings

“…Although terrain and other complicating factors associated with difficult outdoor measurements must also be considered, one possible explanation for the discrepancy between the near-field and far-field directionality is the presence of nonlinear acoustic propagation. The acoustic shock formation and propagation associated with nonlinear propagation of noise around the overall radiation direction 30,31) causes the parametric generation of high frequencies as distance increases. This high-frequency energy transfer may result in relatively larger levels for that angular range.…”