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

Abstract

Flow patterns of a supersonic air flow and the related noise characteristics are studied by experiment 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 atmosphere. The pressure ratio is up to thirty. Various types of the flow patterns are shown by shlieren pictures. It is found that, as the pressure ratio increases, the flow along the plug surface is abruptly separated to attach 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 attached-to-plug flow is recovered is lower than the ratio where the attached-to-seat flow 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.