Simulations of coupled acoustic multi-layer systems for particle velocity measurements in the presence of airflow

This dissertation focuses on the mathematical modeling and numerical simulation of thermo-acoustic coupled systems, specifically addressing the challenges posed by Microflown PU probes in measuring particle velocity and acoustic pressure fields under wind influence. The research is a part of the ROMSOC project, specifically within the work package 2 “Coupled problems,” and contributes significantly to the development of novel windscreen designs to mitigate airflow effects on acoustic probe measurements.

Microflown Technologies' state-of-the-art sound intensity PU probe is central to this study. This probe, notable for its compact size and lightweight, is unique in its ability to directly measure acoustic particle velocity, making it highly applicable in industrial settings. However, its sensitivity to airflow presents significant challenges. This research identifies three main effects of wind on the Microflown transducer: cooling of sensor wires, pre-amplifier overload, and self-noise induction. To address these, the project explores various windscreen strategies.

The core of the thesis is the mathematical modeling and numerical simulation of a coupled system comprising the probe, the compressible fluid in the presence of flow, and the multilayer windscreen. The project leverages multiscale techniques to achieve accurate numerical results, which are vital in optimizing windscreen design parameters.

The dissertation is structured into five chapters

• Introduction to the ROMSOC project, Microflown sensor, and the challenges in measurements in the presence of flow.
• Exploration of pressure projection field computation methods on unstructured grids.
• Modeling and simulation of package gain and insertion loss in acoustic probes due to porous and steel meshes in airflow.
• Development of a mathematical model for acoustic propagation in porous materials in the presence of flow.
• Numerical simulations based on the proposed models, including validation tests and results with the PU probe.