A self-sustained sound, more usually known as a whistle, refers to a distinct tonal noise created due to the interaction between the sound and flow field. When a positive feedback loop is formed between the two fields, the energy in the mean flow will be transferred into the sound wave, thus giving rise to a whistle. In engineering practice, whistles are destructive as they can produce high sound and vibration levels and may result in risk for mechanical failures. In this work, a flow-related high level tonal noise was found during a measurement on a particle agglomeration pipe, which is a quasi-periodic corrugated structure designed for the exhaust system of heavy-duty trucks. The purpose of the pipe is to enhance particle agglomeration to increase the size of exhaust gas particles. To investigate the origin of the detected tonal noise additional measurements were carried out. Based on the measurement result, the aero-acoustic coupling in the agglomeration pipe was analyzed, revealing that the pipe has a large potentiality to amplify the incident sound power in the presence of a mean flow. Furthermore, the Nyquist stability criterion was applied to confirm the existence of exponentially growing modes in the system at certain conditions.

It is well known that the performance of open field acoustic sensors is affected by complex sound propagation phenomena occurring in outdoor settings, such as ground effects, noise from atmospheric turbulence, refraction by wind and temperature gradients, diffraction over buildings and hills, and acoustic sensors on moving platforms. In addition, the behavior of sound propagation changes at the interface of different media. We have developed a time-domain simulation that enables the numerical simulation of all the mentioned factors. This capability provides information on the effect of sound waves once they reach a sensor or a target. We are implementing this algorithm for 3D, long-distance propagations. The challenge is three-fold: a) efficient parallelization; b) moving frame capability in 3D for long-distance propagation simulation; c) accurately implementing the perfectly match layer (PML) methods to represent the free boundaries. In this paper, we have selected cylinders as the objects for sound wave to propagate through. Both 2D and 3D simulations were conducted. The results are compared with available measurement data in the literature. The phenomena are discussed in the context of 2D and 3D propagation behaviors.

During the last couple of years, there has been an increasing focus on the vibro-acoustic performance of built environments due to increasing requirements in building codes regarding impact and airborne sound transmission. Hence, development of efficient and accurate methods for prediction of sound in such buildings is important. In the low-frequency range, prediction of sound and vibration in building structures may be achieved by finite-element analysis (FEA). The aim of this paper is to compare the two commercial codes ABAQUS and ANSYS for FEA of an acoustic-structural coupling in a timber, lightweight panel structure. For this purpose, modal analyses are carried out employing a fully coupled model of sound waves within an acoustic medium and vibrations in the structural part. The study concerns the frequency range 50–250 Hz.