Transient performance of twin-screw expander based on CFD analysis
WANG Xinwei1, JIANG Xiaoping1,2*, WANG Xingyuan3, WANG Li1, WU Guoqiao1
1. National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China; 2. National Engineering and Technology Center for Information Agriculture, Nanjing, Jiangsu 21009, China; 3. Kunming Branch of Xi′an Precision Machinery Research Institute, Kunming, Yunnan 650110
Abstract：In order to study the transient characteristics of twin-screw expander, a twin-screw air expander model of 4/6 lobe configuration was used as the research object. The SCORG was applied to generate the moving grids in screw fluid field while the stationary grids for the ports were derived by the Pumplinx. Simulation of the whole flow field in the expander was carried out by using computational fluid dynamics(CFD). The internal pressure and velocity field inside the twin-screw expander were obtained while the mass flow rate, torque and the force on the rotors under different rotation angles were calculated. The results show that the screw flow field is divided into four pressure grades from high-pressure end to low-pressure end and the pressure decreases gradually, while the contact line between rotors divides the screw flow field into two parts: upper high-pressure zone and lower low-pressure zone. The internal leakage path mainly includes leakage through the contact line, leakage through rotor tip and leakage through blow hole, in which the leakage velocity through contact line is the fastest, the maximum velocity and minimum pressure in the whole flow field occur near the contact line. The pressure drop loss caused by throttling loss and pre-expansion in the suction stage reduces the work of male rotor, simultaneously decreases the efficiency of twin-screw expander. The mass flow rate, the torque, the radial force and the axial force change periodically, and the radial force on the male rotor has a great influence on the performance of the expander.
