Vendredi 23 octobre 2026 à 11h00 ; salle des séminaires IRPHE
Abstract: Azimuthal acoustic waves can emerge spontaneously in cylindrical and annular cavities, thus causing operational challenges, intense vibrations and accelerated mechanical fatigue in pipe lines and turbomachines. These self-excited instabilities arise from a feedback loop: the acoustic noise generated by an unsteady flow feeds and couples with the cavity eigenmodes, until a limit cycle is reached. In aeroacoustics, the noise originates from the turbulent vortices of a low-Mach air jet; in thermoacoustics, the instability is triggered by unsteady gas expansion induced by intense heat transfers. Despite their different nature, both cases share a similar phenomenology regarding selectivity of the polarization (standing or spinning waves) and saturation of the amplitude.
In this seminar, I will present experimental, numerical and modeling aspects on two systems: a cylindrical whistle featuring mirror symmetry breaking, and an annular hydrogen-fuelled combustion chamber. The perspective of a unified model for designing innovative acoustic metamaterials and hydrogen-fuelled turbines will be discussed.
Francis Pagaud - post-doctorant ; Combustion, Acoustics & Flow Physics (CAPS-ETH Zürich)