Methodology for Measuring Higher-Order Acoustic Modes in Uniform Heated Flows
Shane V. Lympany, K. K. Ahuja
Abstract
In this paper, the complete methodology for measuring the acoustic properties of a test article under uniform heated flow and higher-order mode propagation conditions is developed from the theory of higher-order mode propagation in circular ducts. The major steps in the methodology include modal decomposition based on multiple acoustic pressure measurements; determination of the acoustic scattering matrix using a multiple-source method; and calculation of the sound power reflection, transmission, dissipation, and absorption coefficients from the scattering matrix. These steps are based on contributions by a number of authors spanning several decades, but the purpose of this paper is to unify the various techniques and nomenclature used by these authors into a single, cohesive methodology. Thus, this paper is intended to provide a comprehensive reference on the methodology for measuring the acoustic scattering coefficients under the conditions of uniform heated flows and higher-order mode propagation.