Numerical investigation on cavitation erosion and evolution of choked flow in a tri-eccentric butterfly valve

Abstract

The tri-eccentric butterfly valve is widely utilized in the petrochemical, nuclear, and metallurgy industries due to its robust sealing performance and great pressure resistance. When the local static pressure is lower than the saturation vapor pressure, the fluid phase is transformed into vapor, and cavitation occurs. Cavitation intensifies and the bubbles generated by cavitation severely hinder the flow when the inlet pressure remains constant and the outlet pressure further decreases. This phenomenon is known as choked flow. Choked flow is a derivative phenomenon of cavitation, which seriously threatens the lifetime of valves and the safety of the operation system. In this paper, a multiphase flow of the tri-eccentric butterfly valve is modeled to investigate the choked flow characteristics. The numerical results based on the proposed model are in good agreement with the experiments. The effect of the pressure drop on the mass flow rate and flow coefficient is studied and the liquid pressure recovery factor of the tri-eccentric butterfly is determined at the certain valve opening degree based on the Schnerr and Sauer cavitation model. The relationship between the pressure ratio and choked flow is studied by pressure and velocity contours. The susceptible erosion locations and primary causes of erosion for the tri-eccentric butterfly valve at the certain valve opening degree are investigated. By comparison of the distribution of the vapor volume fraction and vortex structures, the spatial correlation between vortex and choked flow is revealed. Meanwhile, the effect of the pressure ratios on the average vapor volume fraction at 70 % and 100 % valve opening degrees is studied. The evolution of choked flow in the tri-eccentric butterfly is revealed and the cause of choking is pointed out.