High performance control valves may be subjected to noise problems especially when gas is the operating fluid. Depending on some geometric characteristics, the noise production can be characterized by broad band noise or tonal noise. When the latter condition occurs, the generated noise could overcome the limit of acceptance and the device does not respect the standard of usability. In a previous work, a dependency between the tonal noise and the main geometrical characteristics of a control rotary valve has been settled by experimental tests. Starting from these fluid dynamic observations in this work we coupled the modal analysis of the structure with experimental data to deeply understand this phenomenon. The natural frequencies of different perforated plates placed in a circular duct (configuration which mimics the full open control valve condition) are therefore considered to verify which of them are responsible of the tonal noise, generated by the interaction between the flow field and the acoustic one, observed in the experimental tests. To do this, the frequency modes consistent with the tonal noise generation, are numerically investigated by changing the geometrical characteristic of the device. By considering the rotary valve fully open, we especially investigated the effects of the plate thickness, the hole diameter and distribution.

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