Study on the vortex flow field and flow-induced noise characteristics of a submarine steam regulating valve

Abstract

Steam regulating valve is an important device of regulating steam flow rate and pressure in a submarine steam turbine equipment, and the flow-induced noise caused in regulating process is a dominant factor affecting its regulation performance and even submarine concealment. In this paper, the steam vortex flow field in a submarine steam regulating valve, and the flow-induced noise characteristics affected by the unstable vortex flow were studied. An experimental setup for testing the far-field sound pressure level (SPL) and frequency spectrum of the steam regulating valve under different lifting degrees was built. The RNG k-ε turbulence model was adopted to obtain the steady flow field information, and the large eddy simulation (LES) turbulence method and Ffowcs-Williams and Hawking (FW-H) acoustic model were coupled to simulate the unsteady flow field and flow-induced acoustic characteristics of the steam regulating valve. The coupled numerical method was verified by the noise testing experiment. Correlation between the turbulent kinetic energy and the acoustic power level (APL) in steady state was discussed, and cross-sectional velocity and vorticity distribution characteristics in unsteady state were analyzed under different lifting degrees. Due to the throttling effect at the throat region, a high-velocity steam jetting flow accompanied with shearing vortices was found around the valve spool, especially under a smaller lifting degree. The dynamic evolution of unstable vortex flow on the monitoring cross sections in the conical channel was revealed. The Q criterion was employed to identify the vortex generation and distribution in the steam regulating valve, and the correlation of the peak Q with the pressure variation in the vortex flow field was discussed. The development of the maximum SPL with the maximum cross-sectional vorticity for various lifting degrees was determined by linear fitting. The far-field SPL directivity and 1/3 octave frequency spectrum characteristics for various lifting degrees were analyzed. Results showed that the SPL presented more asymmetrical distribution at a smaller noise monitoring circle around the steam regulating valve even under a greater lifting degree. And a higher SPL was often accompanied with a greater decay rate in frequency spectrum.