Experimental study on the aeroacoustic characterization of exhaust mufflers in the presence of mean flow

For the aeroacoustic design of mufflers, commonly installed in HVAC ducts, automotive exhaust systems or other confined flow applications, both the convective noise propagation and the aerodynamic noise generation mechanisms should be taken into account. An experimental procedure, based on an active two-port formulation, allows a straightforward characterization of both phenomena and gives further insight in the aeroacoustic performance of acoustic filters. This paper describes the development of such an experimental procedure which is validated for a simple rectangular expansion chamber, using an analytical reference solution. Afterwards, flow effects on the noise attenuation behavior and aerodynamic noise generation mechanisms are investigated for various muffler configurations which are of engineering relevance. The results show that the experimental approach allows to obtain a good estimation for both the attenuation and the noise generation characteristics in a frequency range from 60 to 2000 Hz and in presence of flow with a Mach number up to 0.3. As such the measurement technique offers a valuable tool for the evaluation of the filter performance and allows to generate a benchmark database which can be used for the validation of computational aeroacoustics prediction techniques.