Aerodynamic study on noise and vibration generated in high pressure gas valves. Part 1: Flow patterns and noise of supersonic air flow discharged through conical valve plugs into atmosphere.

Flow patterns of a supersonic air flow and the related noise characteristics are studied experimentally for simplified geometries of the valve. The valve consists of a conical plug and a plane seat, and high pressure air is discharged through it into the atmosphere. The pressure ratio is up to thirty. Various types of flow patterns are shown by Schlieren pictures. It is found that, as the pressure ratio increases, the flow along the plug surface abruptly separates and attaches to the seat, and that, at the same time, the noise is reduced by more than 10 dB(O.A.). The pressure ratio where the flow attached to the plug is recovered is lower than the ratio where the flow attached to the seat occurs. This change of pattern, which may cause a significant variation of force on the valve trim, is closely related to shock / boundary layer interaction. (from authors' abstract)