Steam Turbine Control Valve Noise

Abstract

Although noise problems with steam turbine control valves have existed before, they have become more prominent with nuclear turbines, whose valves range to 20 in. in diameter. Our first-generation nuclear control valves were unacceptably noisy when operating under chocked conditions. These noise levels have been ameliorated by incorporation of a valve cage with numerous small holes. Rational design rules for this “dispersive muffler” have been developed from published multiple-jet noise data, and improved through our own tests. However, we are also evaluating other low-noise valve configurations which are consistent with turbine requirements. The approach we are developing is to investigate the internal aerodynamic noise generation in small air model tests, and to combine this with measurements of pipe-wall transmission characteristics (being reported separately) to predict externally radiated noise. These predictions will be checked in a new steam test facility for complete scale-model valves. The small air tests show that acoustic efficiencies of throttling valve flows tend to vary with third power of Mach number when exhausting into space, and with a lesser power when enclosed in a downstream pipe. At some pressure ratios, narrow-band spikes appear in the spectrum, and for some configurations, step changes in sound power are associated with transitions in flow regimes.