Studies on trailing edge and impinging jet noise
Time: Fri 2025-11-07 10.00
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Video link: https://kth-se.zoom.us/j/69716163259
Language: English
Subject area: Engineering Mechanics
Doctoral student: Zhenyang Yuan , Strömningsmekanik
Opponent: Professor Jean-christophe Robinet, Arts et Métiers Sciences and Technologies, Frankrike
Supervisor: Ardeshir Hanifi, SeRC - Swedish e-Science Research Centre, Strömningsmekanik; André V. G. Cavalieri, Divisao de Engenharia Aeronáutica, Instituto Tecnológico de Aeronáutica, São José dos Campos, Brazil; Dan S. Henningson, SeRC - Swedish e-Science Research Centre, Strömningsmekanik
QC 251009
Abstract
Aeroacoustics is a long-standing and active research field of critical importance to a wide range of engineering applications. Typical examples include noise generated by jet engines, airfoils on aircraft, and blades of wind turbines, all of which contribute significantly to environmental noise pollution and pose design constraints in the development of quieter and more efficient vehicles. Among various aeroacoustic problems, trailing edge noise and impinging jet noise problems are concerned in this thesis. Though two topics have been actively investigated for over 80 years, significant challenges remain. The present thesis aims to contribute to the fundamental understanding of these noise mechanisms, and ultimately to predict, model and control the noise generation.
For the trailing edge tonal noise problem at the low to moderate Reynolds numbers, a resolvent based framework is proposed to model the coherent structures that correlated to the farfield acoustics. Then by placing the cylindrical roughness elements to the mid-chord of airfoils, streaks are generated to control the growth of the Kelvin-Helmholtz instabilities, which weakens one leg of the feedback loop and leads to tonal noise reduction.
With increasing turbulence intensity in the flow passing over the trailing edge, broadband noise becomes a dominant acoustic concern. To model the underlying wavepacket structures responsible for this broadband radiation, a reduced-order model based on Spectral Proper Orthogonal Decomposition (SPOD) is employed. The resulting wavepacket source model captures the dominant coherent structures in the turbulent boundary layer and is shown to satisfy the Amiet scattering condition, which provides a framework for predicting farfield sound.
In the impinging jet problem, the tonal-noise generation mechanism and the role of the turbulent boundary layer in noise radiation are investigated. Using both local and global linear stability frameworks, we identify the dominant waves involved in the feedback mechanism and elucidate the frequency selection process. This framework provides an accurate tool for predicting tonal-noise frequencies directly from a meanflow field. Furthermore, we demonstrate that the turbulent boundary layer provides essential conditions for sustaining the resonance, with the reflection coefficient between upstream- and downstream-propagating waves playing a central role in establishing the global instabilities.
Throughout this thesis, a combination of experimental measurements, high-fidelity simulations, stability analysis, and various spectral analysis techniques are employed to obtain, compare, and analysis data. This multifaceted approach ensures a comprehensive understanding of the underlying physics, and enables cross-validation between different methods.