Inverse Identification of In-duct Source Parameters

for the Quiet Design of Fluid Machinery

                                        

Abstract:
Prediction of the radiated noise from the engine intake or exhaust system is important for the effective noise control and the virtual prototyping of vehicle interior and exterior noise. For the prediction of the radiated sound, the in-duct source parameters, viz., source strength and source impedance, should be precisely defined as a function of frequency. Usually, linear and time-invariant assumption is used for the source model, which often results in an acceptable accuracy and small time effort in computation. The source measurement technique of a linear and time-invariant acoustic one-port source can be classified into two types. Direct method employs a high-intensity external acoustic source in the measurement and the impedance tube technique is used. Multiple microphone method including two-microphone method is usually used for the wave separation. In-direct method adopts multiple acoustic loads in the measurement, for which a simple least square method is used for the data extraction. Measurement should be performed in the engine operation condition, which would be involved in a transient engine run-up and run-down, a noisy condition with flow generated sound, a problem of external source having insufficient magnitude of sound signal, a limited condition for the number of external loads, and a hostile environment due to acid gas and high temperature. In the present talk, the up-to-date technical features, methods, and applications of the measurement of in-duct source parameters for an internal combustion engine will be delivered with a discussion of remaining problems.