Tailored Green's Functions for the Prediction of the Noise Generated by Single and Tandem Diaphragms in a Circular Duct

Noise produced by single and tandem diaphragms in a duct is studied on the basis of compressible Large Eddy Simulation. The applicability and accuracy of a hybrid approach that combines Lighthill's analogy [1] data and Green's function for sound generation and radiation is investigated for broadband noise prediction in low Mach number flows, respectively. A tailored Green's function is proposed using the classical mode-matching technique to account for the scattering of single and tandem diaphragms in cylindrical ducts. To understand the specific contribution of the diaphragm surfaces to noise generation, a noise prediction approach based on Curle's analogy [2] is implemented. The resolution of the acoustic field in the compressible flow data is also investigated through a Direct Noise Computation method based on the characteristic waves. The results of the hybrid and direct approaches are validated against in-duct aeroacoustic measurements.