Several acoustic elements are used in internal combustion engine to tune engine intake/exhaust manifold systems. Components in intake and exhaust systems that create flow separation can for certain conditions and frequencies amplify incident sound waves. This vortex-sound phenomena is the origin for whistling, i.e., the production of tonal sound at frequencies close to the resonances of a duct system. One way of predicting whistling potential is to compute the acoustic power balance, i.e., the difference between incident and scattered sound power. This can readily obtained if the scattering matrix is known for the object. For the low frequency plane wave case this implies knowledge of the two-port data, which can be obtained by numerical and experimental methods. In this paper the development of multi-port models to describe linear acoustic problems in ducts with flow is presented. From an engineering point of view this field covers many important applications ranging from ventilation ducts in vehicles or buildings to intake/exhaust ducts on IC engines and power plants.In this paper the procedure to experimentally determine whistling potential will be presented and applied to side-branch resonators and orifices.

experimental method, noise generation, resonators, engine noise, power balance, system instability, whistling