Research on flow and pressure drop characteristics of high-flow combined valves under wide operating conditions

Abstract

High-flow combined valves are critical regulating components in steam turbine systems; their flow capacity, pressure loss characteristics and flow stability across a wide range of operating conditions directly affect the economic efficiency and reliability of the unit. However, the integrated structure of combined valves complicates the throttling jet, separation recirculation and local secondary flow between the upper and lower valves, and the underlying flow mechanisms still require further elucidation. This paper employs a combined approach of numerical simulation and experimental testing to investigate high-flow combined valves under various valve opening and pressure ratio conditions. Given the complex nature of the actual filter screen structure and the difficulty of performing high-precision discretisation directly, a porous medium equivalent model is used to simulate the filter screen. The numerical model was validated using scaled experimental data and total pressure loss characteristics. On this basis, a systematic analysis was conducted of the internal flow patterns, flow regulation characteristics, vortex structure evolution, and energy dissipation patterns within the combined valve. The results indicate that, over a wide range of operating conditions, the Realizable k-ε turbulence model combined with the porous media model can predict the total pressure loss characteristics of the filter screen more accurately than the SST k-ω model. Furthermore, although the filter screen increases the total pressure loss to some extent, it improves the uniformity of the incoming flow, attenuates downstream unsteady fluctuations, and reduces flow entropy generation. This study provides a basis for optimising flow control and designing filter mesh structures in high-flow combined valves.