Large eddy simulation of acoustic propagation in turbulent flow through ducts and mufflers

This research involves study of acoustic propagation of pulse in a simple expansion muffler, which is very often used in HVAC or automotive exhausts. A hybrid pressure-based compressible solver is developed and validated for a low Mach number flow simulation of acoustic pulse. This new solver is developed using C++ based OpenFOAM toolkit and further tested for low Mach number flow test case. The analysis of simple expansion muffler for various structures, frequency ranges and numerical schemes is performed and results are summarized. RANS simulation of duct and muffler with mean flow is conducted and results are presented with inherent limitations associated with the method. Further, a mixed synthetic inflow boundary condition is also developed and validated for LES of channel flow. The mixed synthetic boundary is then used for LES of a simple expansion muffler to analyse the flow-acoustic and acoustic-pulse interactions inside the expansion muffler. The improvement in the prediction of tonal noise and vortex shedding inside the chamber is highlighted in comparison to the RANS method. Further, the effect of forced pulsation on flow-acoustic is observed in regard to the shift in Strouhal number inside the simple expansion muffler. Finally, a set of benchmark results for experimental analysis of the simple expansion muffler both, with and without flow is obtained to compare attenuation in forced pulsation for various mean-flow velocities. These experimental results are then used for validation of the proposed pressure-based compressible solver.