Artificial noise systems for parametric studies of turbo-machinery aero-acoustics

Abstract

The study of turbo-machinery aero-acoustics encompasses source generation, duct propagation, and radiation to the far field for the purposes of physical understanding, evaluation, and noise reduction. Further, the acoustics subset can be divided into overall, broadband, or tone emphasis. Ultimately, assessments on full-scale turbofans are required. However, for isolating specific effects, or for costs reasons, it is useful to test models. These models may be scaled versions of turbofan components depending on the physical process of interest. The advantage of using models is the lower cost allows for a wider range of conditions to be studied. Even so, the cost of manufacturing and testing scale model fans in mid-technology readiness level can be limiting. A potentially useful supplement to turbo-machinery aero-acoustics studies is the use of artificial sources to generate acoustic signatures. The advantage is that a wide range of signatures can be quickly and efficiently studied, particularly useful for noise reduction concepts, or validating prediction methodologies that are sensitive to variations in geometry or acoustic signature. A disadvantage is the lack of the ability to study source generation. This trade-off must be considered carefully when deciding on the usefulness of utilizing fan artificial noise sources for the study of turbo-machinery aero-acoustics. This paper presents two test articles that have contributed to turbo-machinery aero-acoustics studies. One is a 48 in. diameter duct (nominally full-scale) generating acoustic signatures in the audible range; the second is a 6 in. diameter duct (nominally scaled) generating acoustic signatures in the ultrasonic range.

Supersonic Engine Inlet Tone Noise Radiation

“…The device was previously used to study noise shielding due to airframe or wing configurations [4] [5], and the use for supersonic inlet acoustics is a new application. Fan noise simulators can be a very useful alternative to rotating machinery for detailed noise studies [6]. Compared to computational methods, experiments may lend themselves to larger domain sizes or higher frequencies that may take a large amount of finite element grid nodes, such as shielding studies.…”

Liner development at low technology readiness level utilizing the advanced noise control fan

“…A Configurable Fan Artificial Noise System (CFANS) 19 integrated into the ANCF was developed and utilized to generate and control circumferential modes (m) and to generate radial modes (n) for the purpose of providing an even wider distribution of acoustic sources to evaluate modal propagation and for assessing the efficacy of noise reduction technologies. The system consists of four axially distributed rows, each with 16 circumferentially distributed sets of electromagnetic drivers flush mounted on the inner wall.…”

Multi-degree-of-freedom liner development: Concept to flight test

“…The Configurable Fan Artificial Noise Source (CFANS) 39 -a unique ANCF featurewas utilized to generate and control circumferential modes and to generate radial modes to provide an even wider distribution of acoustic sources for the assessment of the efficacy of liner concepts.…”