Numerical investigation of wall effects on combustion noise from a lean-premixed hydrogen/air low-swirl flame

A hybrid computational fluid dynamics (CFD)/computational aero-acoustics (CAA) approach, in which large-eddy simulation (LES) and APE-RF (solution of the acoustic perturbation equations for reacting flows) are employed for the CFD and CAA, respectively, calling it the hybrid LES/APE-RF approach, is used to analyze the influence of a wall on the combustion noise from a lean-premixed gaseous hydrogen/air low-swirl turbulent jet flame. The wall boundary conditions pertaining to the APE-RF system are formulated to account for acoustic reflection from the wall. The results show that the sound pressure level (SPL) spectrum obtained from the LES/APE-RF is in good agreement with that measured in the experiment. In the LES/APE-RF, the SPL spectrum of combustion noise with the wall plate explicitly changes compared to that without the wall plate. Specifically, the presence of the wall plate tends to ease the peaks that appeared in the case without the wall plate and create a nearly constant SPL within a specific frequency band. The analysis of the heat release rate fluctuation 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.