A Unique Ducted Fan Test Bed for Active Noise Control and Aeroacoustics Research

摘要

This paper describes a unique, large diameter, low speed, axial fan test bed with an externally supported duct. This fan can be used both to investigate active noise control and for more general fan aeroacoustics research. Several of the features and the design philosophies are presented. The most important feature is the installation of two mode measuring systems that enable the complete modal structure (all circumferential and radial orders) of both the inlet and exhaust ducts to be determined. A sample of data for two configurations, rotor alone and rod/rotor interaction are presented. In-duct modal data for rotor alone reveals minimal extraneous modes that might interfere with any interaction modes being investigated. The rod data shows strong interactions for the expected modes. High resolution spectral and spacial far-field data reveal a directivity pattern consistent with the modal structure. The unique ability to view both far-field and in-duct modal structure makes this test bed well suited for the test and development of fan active noise control systems. The rod modal data was projected to the far-field using a finite element code and compared to the actual far-field data showing an excellent agreement. This not only validates the code but contributes to confidence in the in-duct and far-field data quality.