Flow-Acoustic Coupling in Quarter-Wave Resonators Using Computational Fluid Dynamics

Quarter-wave resonators are commonly used as acoustic silencers in automotive air induction systems. Similar closed side branches can also be formed in the idle air bypass, exhaust gas recirculation, and positive crankcase ventilation systems of engines. The presence of a mean flow across these side branches can lead to an interaction between the mean flow and the acoustic resonances of the side branch. At discrete flow conditions, this coupling between the flow and acoustic fields may produce high amplitude acoustic pressure pulsations. For the quarter-wave resonator, this interaction can turn the silencer into a noise generator, while for systems where a valve is located at the closed end of the side branch the large pressure pulsations can cause the valve to fail. This phenomenon is not limited to automotive applications, and also occurs in natural gas pipelines, aircraft, and numerous other internal and external flows. The present approach solves the interaction between the mean flow and the acoustic field by employing the unsteady, turbulent, and compressible Navier-Stokes equations computationally. Experimental comparisons reveal that this method is capable of determining when flow-acoustic coupling occurs and how variations in the geometry and flow conditions influence the acoustic pressure amplitudes.