Conference_programme: 19.1 - Duct Acoustics

Lecture: In-duct fan acoustic analysis : from a RTD project to a productive software tool

Author(s): Picard Christophe, Finez Arthur , Paillasseur Sébastien

Summary:
This contribution is intended to give an overview of some results obtained in framework of the SEMAFOR project conducted from 2013 to 2016 and aiming at building advanced methods for noise source discrimination in a ducted turbomachinery context by means of wall-mounted microphone arrays. The originality of this work is to define a complete procedure combining analytical, numerical and experimental approaches to identify physical contributions to noise generation.\nThe focus is set on a ventilation ducted rotor-stator test bench designed so that the first two blade passing frequency (BPF) harmonics should be cut-off according to the Tyler & Sofrin rule. This is not observed experimentally since strong tonal noise can be identified at all BPF harmonics. The question then arises whether this is due to the rotor/stator wake interaction.\nThe strategy adopted in the project to tackle this problem is threefold: first surface microphone array measurements have been carried out in the downstream part of the test bench. A radial & azimuthal acoustic duct mode decomposition is achieved to fully describe the acoustic field in a downstream duct section. Second a numerical back-propagation procedure is applied on the mode set to estimate the modal content a few centimeters downstream of the OGV trailing edge (i. e. before the hub termination). Third and last an analytical model has been built to predict the modal content produced by the rotor/stator wake interaction including a heterogeneous stator. This model is based on the mode matching technique and accounts for the cascade scattering effect in a 2D framework. The paper will comment sample results of each step described here above.\nFinally, MicrodB has develop an industrial software tool including most of the advanced techniques from SEMAFOR project.

Corresponding author

Name: Dr Christophe Picard

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Country: France