Identification of Spinning Acoustic Modes in Aeroengine Inlet Duct With Circular Microphone Array

Abstract

Information on the modal content of the sound field in an aeroengine inlet duct is a prerequisite for development of efficient acoustic liners that ensure maximum attenuation of sound during its propagation along the duct. This paper describes the developed test rig for generation of spinning acoustic modes in the duct and validation of mode measurement techniques in the absence of flow. The test rig consists of the full-scale intake of an aircraft engine and 34 acoustic drivers JBL 2451H. To measure the generated modes, an optimized circular microphone array comprising 100 microphones Bruel & Kjaer 4944 was installed in the duct and the modal content of the sound field was measured. The experiments were carried out in the new anechoic chamber of Perm National Research Polytechnic University. It is shown that the circular microphone array allows correct identification of the azimuthal acoustic modes and their combinations. An analysis of the working region (frequencies and mode number range), where the developed test rig can be applied, is provided As a result, this microphone array has been recommended for installation on the aeroengine intake at the open test bench for full-scale tests.