Sound intensity measurements of transient noise in presence of extraneous noise

摘要

The objectives of this study are to visualise the sound energy flow from a transient mechanical source, and to investigate possible errors in the visualised sound field caused by the presence of other extraneous transient mechanical sources. The partial source under investigation is the unit fuel injector of a diesel engine. Three types of FFT-based intensity measurements were performed: (i) Free run measurements; (ii) Triggered measurement using uniform time windows of different length; (iii) Reference measurement with no extraneous noise sources, using a triggered uniform time window that capture the complete transient. The most accurate estimates of the intensity vector field in comparison to the reference test were obtained using a short time window. The window length was adjusted to capture the single transient and to avoid interference of transients caused by other cylinders. The truncation of the transient only caused a minor increase of random error in the mean intensity vector field.