Prediction of nonlinear propagation of noise from a solid rocket motor

Proceedings of Meetings on Acoustics

Kenny

Neilsen

et al. 2013

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As part of investigations into the design of next-generation launch vehicles, near and far-field data were collected during horizontal static firings of reusable solid rocket motors. In addition to spectral analysis at individual microphone locations, the spatial and temporal variation of overall and one-third octave band pressure levels at sideline and polar arc arrays is considered. Analysis of the probability density functions reveals positively skewed pressure waveforms, but extreme skewness in the first-order estimate of the time derivative because of the presence of significant acoustic shocks. However, plume impingement is the likely cause of reduced high-frequency levels and skewness at far-downstream positions.

Section: Discussionmentioning

confidence: 99%

Spectral and statistical analysis of noise from reusable solid rocket motors

Proceedings of Meetings on Acoustics

Kenny

Neilsen

et al. 2013

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“…Other assumptions that come into play are that outdoor measurements are not significantly impacted by wind or terrain or that the propagation of the noise is linear. This last assumption is particularly onerous, as the noise propagation from military jets [10][11][12][13][14] and large rockets [15][16][17][18][19] is known to be nonlinear. Because the nonlinearity is frequency and level dependent, the severity of the nonlinear effects are not uniform as a function of angle for a directional source, causing an ill-defined effect on DI , .…”

Section: Directivity Indices: Measurement Considerationsmentioning

confidence: 99%

Modification of directivity curves for a rocket noise model

James

Salton

Proceedings of Meetings on Acoustics

et al. 2014

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The spatial extent and downstream origin of rocket noise sources can significantly impact the physical interpretation of directivity index measurements. Valuable updates to historical rocket noise directivity indices, based on recent measurements of Space Shuttle reusable solid rocket motor (RSRM) boosters have been published by Haynes and Kenny (AIAA paper 2009-3160). However, measurements at a radial distance of 80 nozzle diameters from the RSRM nozzle exit plane are insufficient to be called the far field at low frequencies and thus require modification to the apparent source origin prior to their use in the empirical sound pressure level prediction methodologies, such as described in NASA SP-8072 (1971). In this analysis, estimates of plume source sound power level as a function of distance along the plume axis are combined with frequency-dependent, far field directivity indices to predict sound pressure level as a function of angle and range. With geometric modifications in place, the predicted overall sound directivity more closely matches that estimated by convective Mach number alone. These improved, more physically-based directivity indices will aid in the accurate prediction of full-scale launch vehicle noise, which is a key factor in estimating both vibroacoustic loading and environmental noise concerns.

“…Noise measurements 12,13) were made during a static firing of an ATK GEM-60 SRM, which is used with a Delta IV orbital launch vehicle and has 879 kN (197,500 lbf) average thrust (see Fig. 5).…”

Section: Application To Measurementsmentioning

confidence: 99%

Analysis of the Effects of Finite Impedance Ground and Atmospheric Turbulence on Launch Vehicle Noise Measurements

Neilsen

AEROSPACE TECHNOLOGY JAPAN

James

2016

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A theoretical model for the ground reflection from a correlated, extended source and including atmospheric turbulence [K. L. Gee et al., Proc. Mtgs. Acoust. 22, 040001 (2014)] is used to correct spectra measured over snow-covered terrain during a horizontal solid rocket motor firing. A sensitivity analysis reveals that at moderate distances, the relative sound pressure level changes are more sensitive to ground effective flow resistivity and microphone height, whereas at long range, the turbulence parameters and ground impedance have greater impact.