Characterization of Supersonic Laboratory-Scale Jet Noise with Vector Acoustic Intensity

Abstract

A new method for the calculation of vector acoustic intensity from pressure microphone measurements has been applied to the aeroacoustic source characterization of an unheated, Mach 1.8 laboratory-scale jet. Because of the ability to unwrap the phase of the transfer functions between microphone pairs in the measurement of a radiating, broadband source, physically meaningful near-field intensity vectors are calculated up to the maximum analysis frequency of 32 kHz. The new intensity method is used to obtain a detailed description of the sound energy flow near the jet. The resulting intensity vectors have been used with a raytracing technique to identify the dominant source region over a broad range of frequencies. Additional aeroacoustics analyses provide insight into the frequency-dependent characteristics of jet noise radiation, including the nature of the hydrodynamic field and the transition between the principal lobe and sideline radiation. Nomenclature d = spacing between two microphones = nozzle exit diameter , = transfer function between microphones a and b I = time-averaged vector intensity p = acoustic pressure = acoustic pressure magnitude = acoustic pressure phase , ( ) = quadspectrum between microphones a and b 1 Associate Professor, Dept. of Physics and Astronomy, N283 ESC, AIAA Senior Member.

Source characterization of full-scale tactical jet noise from phased-array measurements

“…In addition, the unwrapped-phase array interpolation (UPAINT) method-recently developed for interpolating levels and phase information along the measurement array-is applied to suppress adverse grating lobe effects and extend the usable frequency bandwidth beyond the spatial Nyquist frequency. 36,37 The HM-based source is used to compare the predicted sound pressure levels with those measured at various points in the mid field of the jet.…”

“…49, which was implemented previously on lab-scale rocket measurements for intensitybased measurements. 37 The resultant unwrapped phase matrix, Uðf Þ, contains the unwrapped phase of each array microphone pair. Together, the magnitude matrix, jCðf Þj, andŨðf Þ form the two components of the UPAINT cross-spectral matrix.…”

Bandwidth extension of narrowband-signal intensity calculation using additive, low-level broadband noise

“…In this manner, the correct overall phase gradient can be obtained. [25][26][27][28][29] Phase unwrapping works well for broadband signals with sufficient coherence between microphones, most especially for signals with a linear phase relationship. 31 For narrowband signals, or signals composed of discrete frequencies, however, the sparsity of frequency-dependent phase information can cause problems with phase unwrapping.…”

A proper framework for studying noise from jets with non-compact sources

“…Because jet turbulence manifests an infinite number of scales that contribute differently to the far-field noise, numerous efforts have been undertaken to quantify the location, strength, frequency or directivity of the sound associated with the turbulence source terms. Notable efforts include the development of a polar correlation technique (Fisher, Harper-Bourne & Glegg 1977), the use of acoustic mirrors (Glegg 1975), extrapolation methods based on the inverse square law (Ahuja, Tester & Tanna 1987) or acoustic imaging (Murray & Lyons 2016), beam forming using small-aperture arrays (Papamoschou & Dadvar 2006), optical deflectometry (Veltin, Day & McLaughlin 2011) and acoustic vector intensity methods (Gee et al 2017). The unanimous conclusions from these studies are that the sources of jet noise reside between the nozzle exit and the region following the collapse of the potential core (Fisher et al 1977;Ukeiley & Ponton 2004) and that higher frequencies dominate regions close to the nozzle (where the turbulent large scales of the flow are locally small) while lower frequencies reside downstream (where the turbulent large scales are locally large).…”