Aeroacoustical coupling and its structural effects on a PWR steam line. Part 1. Numerical investigations of flow acoustic coupling in a subsonic flow past a shallow cavity

A pure tone phenomenon has been observed at 460 Hz in a PWR steam line. The acoustical energy has been identified to be generated in an open gate valve and to be of cavity noise type. The objective here is to understand the flow acoustic coupling in the cavity and in the duct. Both experimental and numerical investigation ways are used. The flow acoustic phenomena are modeled by computing the Euler equations. Two different computations are carried out: in the first one, a pure Euler modeling is used, in the second one, a boundary layer obtained from experimental data is introduced in the computation in order to have a realistic flow profile upstream the cavity. In the first computation, the acoustic excitation due to the cavity is qualitatively retrieved but the frequency is too high compared to the experimental one and no cavity duct coupling is detected. In the second computation, the frequency of the cavity oscillation is very close both the theoretical one and the experimental one. As it is also very close the frequency of the first transverse mode of the duct, the two modes of oscillation (the cavity one and the duct one) are coupled.