Abstract
Compared with a straight pipe, the sound pressure level of flow noise in abrupt-expansion pipes was larger for certain expansion length. The flow noise level hit maximum when the reattachment region coincided with the location of the open end of the expansion pipe. It is considered that the noise source was generated by the eddy collision on the edge of the open end of the expansion pipe. The expansion length for the maximum noise level was generalized using the ratio of the expansion length L to the expansion diameter D, irrespective of the expansion diameter and the flow velocity.
