Considerations for the Measurement of Very-High-Amplitude Noise Fields

This chapter discusses a research focused on the measurement of very-high-amplitude acoustic noise, primarily jet noise. This research addresses long-range issues in measurement technology in the anticipation of advances in the computational predictions of radiation from full-scale jets. An accurate measurement of acoustic noise very near to the jet plume provides critical data, which are required to validate computational jet-noise models. Different specific sources of jet-engine noise are linked to unsteady flows associated with the mean flow of the engine exhaust. The research intends to develop well-controlled and repeatable sound fields and to measure the perturbation of these fields and the distortion introduced by a number of sensor types and configurations. A technical approach focused to investigate the performance of standard measurement microphones in very-high-amplitude sound fields-with emphasis on the potential degradation of performance because of nonlinear mechanical and acoustical processes-and to develop alternate sensors and sensing techniques against which to compare the performance of standard microphones is also discussed in the chapter.