Location
Utah Valley University Sorensen Center
Start Date
5-9-2016 9:15 AM
End Date
5-9-2016 9:27 AM
Description
The effects of nonlinearity on the power spectrum of jet noise can be directly compared with those of atmospheric absorption and geometric spreading through an ensemble-averaged, frequency-domain version of the generalized Burgers equation (GBE) [B. O. Reichman et al., J. Acoust. Soc. Am. 136, 2102 (2014)]. The rate of change in the sound pressure level due to the nonlinearity, in decibels per jet nozzle diameter, is calculated using a dimensionless form of the quadspectrum of the pressure and the squared-pressure waveforms. In this paper, this formulation is applied in detail to atmospheric propagation of a spherically spreading, initial sinusoid and unheated model-scale supersonic (Mach 2.0) jet data. The rate of change in level due to nonlinearity is calculated and compared with estimated effects due to absorption and geometric spreading. Comparing these losses with the change predicted due to nonlinearity shows that absorption and nonlinearity are of similar magnitude in the geometric far field, where shocks are present, which causes the high-frequency spectral shape to remain unchanged. Nonlinear effects are compared for engine conditions of Mach 0.85 and Mach 1.8 as well. Both the Mach-1.8 and Mach-2.0 data exhibit nonlinear trends that slow the decay of the waveform compared to absorption and spreading alone.
Theoretical and Experimental Investigation of a Quadspectral Nonlinearity Indicator
Utah Valley University Sorensen Center
The effects of nonlinearity on the power spectrum of jet noise can be directly compared with those of atmospheric absorption and geometric spreading through an ensemble-averaged, frequency-domain version of the generalized Burgers equation (GBE) [B. O. Reichman et al., J. Acoust. Soc. Am. 136, 2102 (2014)]. The rate of change in the sound pressure level due to the nonlinearity, in decibels per jet nozzle diameter, is calculated using a dimensionless form of the quadspectrum of the pressure and the squared-pressure waveforms. In this paper, this formulation is applied in detail to atmospheric propagation of a spherically spreading, initial sinusoid and unheated model-scale supersonic (Mach 2.0) jet data. The rate of change in level due to nonlinearity is calculated and compared with estimated effects due to absorption and geometric spreading. Comparing these losses with the change predicted due to nonlinearity shows that absorption and nonlinearity are of similar magnitude in the geometric far field, where shocks are present, which causes the high-frequency spectral shape to remain unchanged. Nonlinear effects are compared for engine conditions of Mach 0.85 and Mach 1.8 as well. Both the Mach-1.8 and Mach-2.0 data exhibit nonlinear trends that slow the decay of the waveform compared to absorption and spreading alone.