In-duct flow computation and acoustic propagation using the admittance multimodal formulation

Area of Science:

• Acoustics
• Computational Fluid Dynamics
• Numerical Methods

Background:

• Acoustic perturbations and base flow analysis in ducts are crucial for understanding noise generation and propagation.
• Existing methods often face high computational costs or limitations in handling complex duct geometries.
• The development of efficient and accurate numerical techniques is essential for aerodynamic and acoustic simulations.

Purpose of the Study:

• To present a novel multimodal method for computing base flow and acoustic wave propagation in axisymmetric ducts.
• To investigate the use of a polynomial radial basis to reduce computational expense.
• To address the challenges posed by non-physical high-order modes and improve matrix conditioning for acoustic computations.

Main Methods:

• Utilized a multimodal approach with a polynomial radial basis instead of the standard modal basis.
• Examined the stability impact of introduced non-physical high-order modes.
• Modified axial integration for improved matrix conditioning in acoustic computations.
• Adapted the method for flow computation by setting frequency to zero and modifying exit admittance and density induction.

Main Results:

• The proposed multimodal method demonstrates high efficiency in computing mean flow within axisymmetric ducts.
• The method accurately propagates sound disturbances, validated against finite element methods for various duct wall types.
• The use of a polynomial basis, despite introducing non-physical modes, was managed effectively.

Conclusions:

• The developed multimodal method offers an efficient and accurate solution for analyzing base flow and acoustic perturbations in axisymmetric ducts.
• The modifications to the integration and basis functions enhance the stability and conditioning of the numerical scheme.
• This method provides a valuable tool for researchers and engineers in acoustics and fluid dynamics.