Self-sustained azimuthal aeroacoustic modes. Part 2. Effect of a swirling mean flow on the modal dynamics

The whistling induced by a low-Mach turbulent flow through deep axisymmetric cavity in duct is investigated theoretically and experimentally. experiments include acoustic measurements stereoscopic particle image velocimetry (PIV). paper focuses on the effect of mean swirl dynamics azimuthal aeroacoustic modes. has two origins: one component imposed controlled tangential air injection upstream cavity, other spontaneously arises under action self-sustained mode, as explained companion paper, Part 1 (Faure-Beaulieu, Xiong, Pedergnana & Noiray, J. Fluid Mech. , vol. 971, 2023, A21). Experiments show that wave influenced swirl. In particular, spinning propagating against promoted. To explain this, linear perturbation analysis performed around an incompressible swirling obtained from RANS simulations. It reveals dominant shear layer modes order −1 involved phenomenon are helical winding respectively with swirl, counterswirl co-swirl directions. hydrodynamic mode least damped two, which agreement experimental observations. Finally, low-order model based equation derived. With only few parameters, it fully reproduces observations for wide range intensity flow, allows us to disentangle mechanisms responsible this complex instability.