Author:

Keywords:

Beurs_Herve, IDEALVENT, TUMULT, ENLIGHT

Abstract:

Flow duct systems, such as automotive exhausts and ventilation systems, are an important source of noise disturbance. These systems not only contain significant sources of sound, but also act as an efficient transfer path for the noise generated upstream. Because of the growing customer expectations and the restrictive legal requirements regarding the noise emission to the environment, the need for efficient characterization and prediction tools for the aeroacoustic behavior of flow duct systems emerges. The acoustic design of flow duct systems is often based on network modeling approaches, where models for the individual components are connected to predict the behavior of the entire system. In this framework, the components are typically described using acoustic two-port or multi-port models. Such model can be derived analytically for simple geometries, but more complex components require numerical simulations or a dedicated experimental campaign. The first part of this dissertation therefore investigates efficient numerical and experimental techniques for the characterization of flow duct components using two-port or multi-port models. An important aspect of the experimental characterization of a component is the decomposition of the acoustic pressure field into downstream and upstream propagating waves. Therefore, robust iterative techniques are presented in this dissertation which optimize the parameters of the underlying model to improve the accuracy of the decomposition. The numerical part of this dissertation focuses on time-domain models for the flow-acoustic behavior of perforates in a flow duct. These models include a hybrid method, based on the linearized Navier-Stokes equations, and a recursive formulation for a transfer-admittance. In the second part of this dissertation, the developed two-port and multi-port characterization techniques are applied to three components, selected for their industrial relevance. First, a multi-port model is used to describe the acoustic effect of a butterfly valve, which acts at the same time as a shield for noise propagating through the system and as an efficient source of sound. Secondly, an indirect measurement technique is presented for the acoustic impedance of locally reacting wall treatments. Finally, the characterization techniques are applied to investigate the potential of modal filters, a novel silencer topology using micro-perforated panels.