Unsteady Behaviors of Steam Flow in a Control Valve With T-Junction Discharge Under the Choked Condition: Detached Eddy Simulation and Proper Orthogonal Decomposition

Due to the practical space limitation, the control valve in industrial utilities is usually immediately followed by a short flow passage, which would introduce considerable complexity into highly unsteady flow behaviors, along with the flow noise and structure vibration. In the present study, the unsteady behaviors of the steam flow inside a control valve with a T-junction discharge, when the valve operates under the choked condition, are numerically simulated. Toward this end, the detached eddy simulation (DES) is used to capture the spatiotemporally varying flow field in the serpentine flow passage. The results show periodic fluctuations of the aerodynamic forces on the valve spindle and periodic fluctuations of the pressure and flow rate at the two discharge outlets. Subsequently, proper orthogonal decomposition (POD) analysis is conducted using the velocity field and pressure field, identifying, respectively, the dominant coherent structures and energetic pressure fluctuation modes. Finally, the extended-POD method is used to delineate the coupling between the pressure fluctuations with the dominant flow structures superimposed in the highly unsteady flow field. The fourth velocity mode at St = 0.1, which corresponds to the alternating oscillations of the annular wall-attached jet, is determined to cause the periodic flow imbalance at the two discharge outlets, whereas signatures of the first three modes are found to be dissipated in the spherical chamber. Such findings could serve as facts for vibration prediction and optimization design. Particularly, the POD and extended-POD techniques were demonstrated to be effective methodologies for analyzing the highly turbulent flows in engineering fluid mechanics.