Localization of Acoustic Sources in Shock-Containing Jet Flows Using Phased Array Measurements

Abstract

In this paper, we shall examine the feasibility of using time-resolved hybrid RANS-LES (HRLES) simulation data to perform noise source localization studies on a hot jet from a conic nozzle operating at pressure matched conditions. The source localization will be performed using a traditional delay-and-sum beamforming technique. This technique requires time-resolved data on a phased array of microphones located in the acoustic farfield of the jet; this data will be obtained by coupling the HRLES simulation with a Ffowcs Williams and Hawkings equation noise prediction code. Using insights gained from experimental beamforming, we shall show that beamforming using CFD data is a feasible, and potentially less expensive and time-saving, alternative to constructing complicated phased array systems for performing these calculations on experimental data. I. Background and MotivationNoise from supersonic jets falls primarily into two categories, either turbulent mixing noise or shock noise. Of these two, turbulent mixing noise is comprised of two sources, both of which are broadband in nature: (a) the eddy Mach wave radiation which propagates downstream relative to the jet flow direction, and (b) fine scale turbulence which is omni-directional. On the other hand, shock noise can be either narrowband (also called jet screech) or broadband (called broadband shock associated noise, or BSAN), and propagates towards the sideline or upstream direction relative to the jet flow. Shock noise most commonly occurs when a convergent-divergent nozzle is operated at off-design conditions. However, jets exhausting from military nozzles typically contain shocks even when operated at design conditions; this is primarily because the internal contour of these nozzles are not shaped in order to ensure a smooth expansion of the gas.Jet noise contributes significantly to noise-induced hearing loss, structural degradation of airframes, and restrictions to maintenance, testing, and training schedules due to noise pollution of communities surrounding military installations. To this end, it is imperative to gain a better understanding of jet noise generation mechanisms in a turbulent flow. Such an understanding is essential if one is to construct predictive models for jet noise. One approach that has been considered is the beamforming technique using a phased array of microphones. 1 This technique has been shown to provide an estimate of the distribution of noise sources in a

Advances in Experimental Aeroacoustics

“…A brief description of the CLEAN-SC beamforming algorithm as explained by Sijtsma [11] is presented here. Source-cross powers are used here, which are defined by (21) Where C is the CSM with its diagonal elements removed. The degraded source powers P j (0) are calculated for the points on the scan grid using conventional beamforming.…”

“…The Orthogonal Beamforming method, shown at the bottom of the plot, indicates a number of noise production peaks within the jet. Panickar et al [21] performed a detailed study on the feasibility and accuracy of applying beamforming to computational results. One of the major concerns when obtaining time-resolved HRLES simulation data is the amount of computational time required.…”

“…A MAGMA express box handles the task of interfacing Beamforming maps for the jet from the conic nozzle with the centerbody operated at pressure matched condition using, (a) the concentric circular microphone array, (b) the log spiral microphone array and (c) the large aperture log spiral microphone array. (reprinted from Panickar et al [21], 2013 by the authors, used with permission).…”

Identification and Localization of Airfoil Noise Sources at Low Angles of Attack

“…Thus the restriction on the microphone number and resolution encountered while working in an experimental facility no longer exists. To date, such methodology has been examined in the investigation of jet noise [17][18][19] .…”

Analysis of Converging-Diverging Beveled Nozzle Jets Using Large Eddy Simulation with a Wall Model

“…[13][14][15] Other techniques have also been employed. To reduce simulation costs, it is common for researchers to utilize thin laminar BLs, [16][17][18][19][20] slip wall boundary conditions, [21][22][23][24] and mean flow conditions in the near-wall region (i.e., RANS/LES hybrid methods) 25,26 The method used in ref. 27 is unclear.…”