Airflow-generated noise inside dual-chamber mufflers: Experimental and computational studies

The airflow-generated noise inside the dual-chamber mufflers is measured using the coherent power function method and predicted by combining Large Eddy Simulation and Möhring acoustic analogy. The predicted and measured results of sound pressure level for the four configurations of dual-chamber muffler agree reasonably well. The lock-on flow tones are identified for the coaxial configuration of the dual-chamber muffler, while the four mufflers exhibited the longitudinal resonances of the tailpipe and antiresonances of the expansion chamber. The airflow-generated noise can be attributed to the vortices generated by the abrupt change of flow passage in the muffler. The peaks of the airflow-generated noise are mainly composed of locked-on flow tones and longitudinal resonance of the tailpipe, while the valleys are observed at the longitudinal antiresonance frequencies of the expansion chamber. For the four configurations of dual-chamber mufflers, the arrangement of the interconnecting pipes plays a significant role for the airflow-generated noise. The power spectrum densities of the side-inlet mufflers are generally higher than the end-inlet mufflers.