Bicoherence analysis of model-scale jet noise

Area of Science:

• Acoustics
• Fluid Dynamics
• Nonlinear Wave Phenomena

Background:

• Noise propagation from jets exhibits complex nonlinear effects.
• Understanding these nonlinearities is crucial for accurate acoustic modeling.
• Previous methods for identifying nonlinear propagation have limitations.

Purpose of the Study:

• To characterize nonlinear effects in Mach 2.0 jet noise propagation using bicoherence analysis.
• To evaluate the validity of spectral comparison methods for identifying nonlinearity.
• To determine the spatial extent of nonlinear propagation effects.

Main Methods:

• Bicoherence analysis applied to noise propagation data from a model-scale jet.
• Comparison of spectral data measured at different propagation distances.
• Analysis of nonlinear propagation in the context of geometric near-field effects.

Main Results:

• Nonlinear propagation effects were primarily observed near the peak directivity angle.
• The spatial extent of nonlinearity was limited for the studied jet source and propagation range.
• Spectral comparison methods can yield misleading conclusions about nonlinearity in the geometric near field.

Conclusions:

• Bicoherence analysis effectively characterizes localized nonlinear propagation in jet noise.
• The geometric near field of directional sources like jets complicates the interpretation of spectral comparisons.
• Careful consideration of measurement location is essential when assessing jet noise nonlinearity.