Valve noise at high pressure ratios

Abstract

When high pressure air expands through an orifice it can be an intense noise source, which may be hazardous for nearby personnel if it occurs in an unexpected or uncontrolled way. This paper describes a set of measurements that were carried out to validate and calibrate the well-known Beranek semi-empirical prediction method. A number of valve mockups were tested over a range of mass flow rates with pressure ratios up to 11 Bar, so that the model could be used with confidence to extrapolate up to much higher pressures and larger valve sizes. Interpretation of the measured noise data is carried out using an isentropic analysis of the flow, assuming choked conditions in the orifice to infer a jet Mach number and mass flow rate for each test condition. Based on this inferred flow data the sound power scaled as expected with 8th power of jet Mach number, although there were some deviations at high frequencies and for particular valve configurations. It is also shown that for all valves the sound power varied as 1.5th power of mass flow rate, which is in reasonable agreement with the law that is implicit in the Beranek model, and provided a good basis for extrapolating to larger devices.