Abstract: The valve noise in a lower fluid duct was studied on the bases of fundamental principles and Lighthill's quadrupole theory and regarding the valve steam as a jet with a solid boundary. Some formulae, which can be used to estimate the distribution of velocity and sound source intensity in the valve steam, were derived.
Analyses show that the sound source intensity will increase gradually with the increase of r in the radius direction, and fall down quickly behind maximum. The peak locates near mixing layer. The sound source intensity will decline gradually along the axis. The larger the ratio of areas (S_p/S_v) is, the more slowly the intensity declines.
The experiments not only verify the theoretical result, but also indicate that a group of small holes instead of a valve hole is an efficient way to control valve noise.