Acoustic source characterization of simulated subsonic jet noise using spherical harmonics

Area of Science:

• Acoustics and Aerodynamics
• Computational Fluid Dynamics

Background:

• Aircraft noise, particularly from subsonic jets, is a significant environmental concern.
• Early integration of near-field flow simulations with quantitative sound data is vital for aircraft design.
• A key challenge is efficiently linking near-field noise data to far-field acoustic radiation, including reflections.

Purpose of the Study:

• To develop a computationally efficient spherical equivalent source model for jet noise.
• To simplify the interface between near-field flow data and far-field acoustic predictions.
• To provide a usable format for large-scale computational fluid dynamics (CFD) simulations.

Main Methods:

• Computation of a spherical equivalent source model using spherical harmonic (SH) coefficients.
• Spherical Hankel extrapolation of sound pressure data from virtual microphone arrays.
• Determination of the acoustic source region radius within the flow field.

Main Results:

• The acoustic source region is confined to a radius approximately five times the nozzle diameter, near the end of the potential core.
• The spherical harmonic transform identified nine elementary sources as the dominant contributors to jet noise energy.
• A simplified, low-complexity spherical equivalent source model was successfully computed.

Conclusions:

• The developed spherical equivalent source model offers a computationally efficient method for jet noise analysis.
• This model facilitates the integration of acoustic predictions into early aircraft design stages.
• The findings provide a convenient format for incorporating jet noise modeling into advanced CFD simulations.