Investigation of wall effects on combustion noise from a lean-premixed H₂/air low-swirl flame using a hybrid LES/APE-RF approach

A hybrid Computational Fluid Dynamics (CFD)/Computational Aero-Acoustics (CAA) approach, in which Large-Eddy Simulation (LES) and the Acoustic Perturbation Equations for Reacting Flows (APE-RF) are employed for the CFD and CAA, respectively, and hence named the hybrid LES/APE-RF approach, is used to analyze the influence of a wall on the combustion noise from a lean-premixed gaseous H₂/air low-swirl turbulent jet flame. The wall boundary conditions pertaining to the APE-RF system are formulated to account for acoustic reflections from the wall surface. Results show that the Sound Pressure Level (SPL) spectrum obtained from the hybrid LES/APE-RF simulation is in good agreement with that measured in the experiment. In the LES/APE-RF simulation, the SPL spectrum of combustion noise with a wall plate explicitly changes compared with that without the wall plate. Specifically, the presence of the wall plate tends to ease the peak in the SPL spectrum that existed in the case without the wall plate, and creates a nearly constant SPL within a specific frequency band. Analysis of the heat release rate fluctuations reveals that these phenomena are caused by the absence of a single periodic oscillation of heat release rate. The presence of the wall plate creates an asymmetric flow around the flame and distorts the flame structure, thereby altering the flame fluctuation phenomena.