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Sound radiation from an open pipe with a mean flow

Authors Masovic, D.
Year 2017
Thesis Type Doctoral thesis
Topic Audio Signal Processing
Keywords radiation pattern
Abstract This work considers analytical and numerical approaches for estimation of sound radiation from an open pipe with a mean flow of fluid. It deals with the identification, characterisation, and assessment of the main flow and acoustic phenomena which influence sound propagation and the resulting far acoustic field outside the pipe. The analysis is focused on the case of low frequency (Helmholtz number) of the emitted sound and low Mach number of a subsonic jet, issued from a straight circular pipe with a sharp trailing edge at the opening. This allows a simpler theoretical treatment of the vortex-sound interaction at the edge of the pipe and the assessment of refraction of the sound wave inside the moving inhomogeneous medium introduced by the jet. The described procedures are aimed to be used primarily for automotive and musical applications, in which sound radiation can be appreciably affected by the mean flow of gas inside pipes. From the theoretical aspect, different sets of acoustic propagation equations and single - unknown wave equations are discussed in connection with more general equations of fluid dynamics. As a step towards more complex geometries and flows which are expected to occur in practice, several possible approaches for a numerical solution of the problem are investigated, based on the combination of acoustic solvers and computational fluid dynamics. Both theoretical and numerical results are validated through the comparison with the results obtained from the laboratory measurements. Ultimately, the thesis should provide an interpretation of the main physical phenomena which affect the far - field sound radiation from a pipe with a hot mean flow and point to the possible methods with which the sound field can be calculated in practice.
Supervisors Höldrich, R., Eckel, G.