An improved multimodal method for sound propagation in nonuniform lined ducts

Area of Science:

• Acoustics
• Fluid Dynamics
• Mechanical Engineering

Background:

• Modeling acoustic propagation in ducts is crucial for noise control.
• Nonuniform linings and circumferential variations present significant modeling challenges.
• Existing methods may lack efficiency or accuracy for complex geometries.

Purpose of the Study:

• To develop an efficient and accurate method for modeling time-harmonic acoustic propagation in nonuniform lined ducts without flow.
• To improve upon existing multimodal propagation methods by enhancing radial convergence rates.
• To enable practical computation of acoustic propagation in aeroengine intakes.

Main Methods:

• The sound pressure is expanded using rigid duct modes and an additional impedance boundary function.
• Rigid duct modes and the additional function are known a priori, avoiding complex true liner mode calculations.
• Scattering matrices are computed for axially segmented uniform lining sections and combined for global analysis.

Main Results:

• The radial rate of convergence is improved from O(n(-2)) to O(n(-4)).
• The method allows computation of acoustic propagation in nonuniform lined aeroengine intakes on a personal computer.
• Accurate calculations are possible for dimensionless frequencies (K) up to 80, relevant for turbofan noise.

Conclusions:

• The proposed method offers an efficient and accurate approach for modeling acoustic propagation in complex lined ducts.
• This advancement facilitates better prediction and control of noise in applications like aeroengine intakes.
• The improved convergence and computational feasibility make the method suitable for practical engineering applications.