Aeroacoustic sound generation in simple expansion chambers (original) (raw)

Experimental acoustic identification of flow noise sources in expansion chambers

2000

For the aeroacoustic design of expansion chambers, commonly installed in e.g. HVAC ducts or automotive exhaust systems, the aerodynamic noise generation mechanisms as well as the transmission characteristics of acoustic waves propagating in a non-quiescent medium have to be taken into account. The attenuation of downstream propagating acoustic waves should be maximized with a minimum of additional flow noise generation

Lecture 1: Introduction to experimental aeroacoustics

hal-04437042v1, 2017

This introductory lecture gives an overview of the challenges and pitfalls of wind tunnel experiments in aeroacoustics. Most concepts introduced here will be developed in following lectures. 1.0 EXPERIMENTAL AEROACOUSTICS: WHAT FOR? 1.1 The Origin of Experimental Aeroacoustics Strouhal [1] was probably the first to relate sound generation to fluid motion in 1878 in his experimental investigation of Aeolian tones generated by a stretched wire, but he incriminated fluid friction as the origin of the radiated sound. It was only in 1915 that Lord Rayleigh [2] related the sound radiation to the periodic vortex shedding after discovering that even rigid cylinders produce Aeolian tones when placed in a flow, which really was the beginning of aeroacoustics as a branch of flow physics. The next jump of aeroacoustics also came along with experimental evidence of the extreme acoustic nuisance caused by the first jet engines that led to the pioneering work of Sir J. Lighthill [4], [5] about the physics of jet noise, followed by many others who investigated the role of solid surfaces in turbulent flows. This advance also revealed a need for aeroacoustic investigations in wind-tunnel experiments, which provided information that could not be measured on real flying aircrafts. The latest step of aeroacoustics came along with the progress of unsteady high-order Computational Fluid Dynamics (CFD) and CFD in general, that became applicable to aeroacoustic problems [6], [7], [8], [9] giving birth to a new branch of aeroacoustics, Computational AeroAcoustics (CAA). This progress also fostered a new type of aeroacoustic experiments, so-called benchmark experiments, whose role it is to provide verification, validation and calibration data for CFD codes. Today a new age is dawning with the upcoming of highly efficient and versatile CFD methods (such as LBM) on one hand and the rise of high-resolution experimental tools on the other hand. These tools (such as time resolved PIV or multi-sensor pressure arrays based on MEMS technologies) become increasingly accurate, reliable and applicable to aeroacoustic investigations. These developments will certainly deeply modify our approach to aeroacoustics in the next decade: the process has already begun. 1.2 Motivation for Experimental Aeroacoustics This brief introductory history of aeroacoustics highlights the three types of experimental approaches that are still encountered in our community's wind tunnels as well as the purposes they are designed for. 1.2.1 Fundamental Aeroacoustics Experiments for fundamental studies in aeroacoustics are meant to characterise basic mechanisms of sound

0 EXPERIMENTAL AEROACOUSTICS : WHAT FOR ? 1 . 1 The Origin of Experimental Aeroacoustics

2017

This introductory lecture gives an overview of the challenges and pitfalls of wind tunnel experiments in aeroacoustics. Most concepts introduced here will be developed in following lectures. 1.0 EXPERIMENTAL AEROACOUSTICS: WHAT FOR? 1.1 The Origin of Experimental Aeroacoustics Strouhal [1] was probably the first to relate sound generation to fluid motion in 1878 in his experimental investigation of Aeolian tones generated by a stretched wire, but he incriminated fluid friction as the origin of the radiated sound. It was only in 1915 that Lord Rayleigh [2] related the sound radiation to the periodic vortex shedding after discovering that even rigid cylinders produce Aeolian tones when placed in a flow, which really was the beginning of aeroacoustics as a branch of flow physics. The next jump of aeroacoustics also came along with experimental evidence of the extreme acoustic nuisance caused by the first jet engines that led to the pioneering work of Sir J. Lighthill [4], [5] about the...