A study on mufflers with air flow. 3rd report Correlation between fluctuating velocity in muffler and air flow noise.

This paper describes an experimental study on the relationship between fluctuating velocity in a muffler and flow induced noise for an expansion cavity type muffler and a perforated straight-through pipe type muffler. The visualization of internal flow and the measurement of fluctuating velocity in a muffler were performed using the smoke-wire method and hot-wire velocimeter. From these experiments. the flow pattern and the distribution of fluctuating velocity were able to be clearly shown for each type of muffler. The correlation between fluctuating velocity on each point in a muffler and flow induced noise radiated from the open end was also studied by calculating the coherence function between them. It was seen that the flow induced noise was closely correlated with fluctuating velocity of internal flow especially in the ranges of tail pipe and/or cavity resonance frequencies.