Numerical Investigations of Generation and Propagation of Sound Waves in Low Mach Number Internal Flows

Abstract: Tra?c is a ma jor source of environmental noise in modern day society. Subsequently, development of new vehicles are sub ject to heavy governmental legislations. The ma jor noise sources on common road vehicles are engine noise, transmission noise, tire noise and, at high speeds, wind noise. At low speeds (< 30-50 km/h), intake and exhaust noise are particularly important during acceleration. One way to reduce intake and exhaust noise is to attach mu?ers to the exhaust pipes. However, to develop prototypes of mu?ers for evaluation is a costly and time-consuming process. As a consequence, in recent years so-called virtual prototyping has emerged as an alternative. Current industrial simulation  methodologies are often rather simple, either neglecting mean ?ow or including only one-dimensional mean ?ows. Also, ?ow generated noise is rudimentary modeled or not included at all. Hence, improved methods are needed to fully bene?t from the possibilities of virtual prototyping.This thesis is divided in two main parts. The ?rst topic is related to the development and evaluation of methods to simulate sound propagation and generation in two-dimensional con?ned geometries with arbitrary internal mean ?ows present. The performance of a new DNS code is evaluated for aeroacoustical purposes and a frequency domain linearized Navier-Stokes equations methodology is developed for acoustic wave propagation applications. Both methods are validated on a case of an in-duct ori?ce plate.In the second part, a so-called global mode decomposition technique is evaluated for aeroacoustical purposes. The ?ow ?eld is described as a sum of the non-orthogonal solutions to its corresponding eigenvalue problem. This enables the acoustic analysis of source terms from each individual global mode, and thus reveals new insight into the sound generating mechanisms.