The experimental assessment of flow-generated noise emissions from intake and exhaust systems

Recent progress in the technology for rapid acoustic design or refinement of piston engine intake or exhaust systems is described, with particular reference to flow noise. The new developments include the application of selective averaging, order tracking and optimised sampling rate methods to clearly identify and quantify the small fraction of the total fluctuating wave energy that is propagating across each discontinuity along the flow path through reverberant or acoustically reactive intakes and exhausts. Illustrative examples include measurements of the installed acoustic performance of each element, or sequence of elements, both on the flow bench or during controlled acceleration on a test bed. The procedures have been validated with wave component spectral levels approaching 170 dB. The measurements are sufficiently precise to clearly identify the location, strength and spectral characteristics of any flow generated noise sources from the small gains in acoustic power flux at the relevant sites.