Aero–acoustics in constricted pipe flow at low mach number

Abstract

In this study, the sound generation in a constricted pipe at low Mach number (M=0.003, Re=1170 at the inlet) flow is investigated using a hybrid modeling approach of computational aero-acoustics (CAA). Large Eddy Simulation (LES) model is used simulate the flow and accurately capture the flow instabilities associated with the constriction. The Acoustic Perturbation Equation (APE) method is used to model the acoustic field where the source terms are derived from the incompressible flow simulation results. The acoustic spectra from the APE simulation results showed good agreement (within 9%) with measured values on the pipe wall downstream of the constriction. The strongest APE acoustic sources were found to occur in the jet core breakdown region that contained the highest pressure fluctuations in the flow field. Proper Orthogonal Decomposition (POD) was used to study the Coherent flow structures in the jet core breakdown region in order to further understand the characteristics of acoustic sources. The strongest structure corresponds to the peak frequency of the measured sound pressure spectra. The study results improve our understanding of the sound generation mechanisms in biomedical applications involving the airways such as phonation and partial airway obstruction.