Data assimilation for turbulence-merged channel branches with the simultaneous enhancement of hydrodynamics and aeroacoustics

Abstract

This study explored the dynamic interplay between turbulent flow and transverse duct acoustic modes within intersecting channel branches containing two inlet branches and one outlet channel, motivated by the experimental findings of Ziada et al., 2009, entitled “Flow-acoustic coupling in T-junctions: effect of T-junction geometry” in J. Press. Vessel Technol. 131(4) and the work of Salt et al. 2014, entitled “Aeroacoustic sources generated by flow–sound interaction in a T-junction” in J. Fluid. Struct. 51, 116–131. We specifically examined how this interaction led to the simultaneous enhancement of both hydrodynamic and aeroacoustic characteristics. Compressible large eddy simulation (LES) was implemented to solve the compressible Navier–Stokes equations, and a data-assimilated momentum loss model with physical constraints was incorporated to enhance the LES accuracy and obtain the self-sustained flow–acoustic resonance fields. We further focused on the influences of upstream flow separation on the excited resonance behaviors. The numerical results with a data-assimilation strategy agreed well with the literature and acoustic modal analysis in terms of frequency, amplitude, and fundamental waveform. Three types of unsteady flow events, characterized by shear layers, recirculation zones, and separation bubbles, were identified in close response to the excited acoustic eigenmodes. The dynamics, including the acoustic-phase-resolved spatiotemporal evolution, kinematics, such as the convection trajectory and speed, and energetics, such as the aeroacoustic power sources, were further elucidated. The vertical Coriolis force, which was influenced by the secondary separation bubbles, along with the horizontal acoustic particle velocity, played a significant role in the generation of aeroacoustic power.