Here we are with our first preview on new features in TwinMesh™ 2019: CFX Berlin implemented non-reflective boundary condition (NRBC) in ANSYS CFX via User Fortran in a stable and robust way so that they can be used for positive displacement compressors instead of the standard openings which are reflective (RBC). The above video compares the periodic state for 6000 (top row) and 12000 rpm for a SRM screw compressor; boundary conditions are 1 bar at suction side to 3 bar at pressure side; left column models inlet and outlet as standard reflective openings (RBC), right column with new NRBC formulation. Each case shows pressure on casing and rotors (left) and in mid-section plane (mid), and velocity as normalized vectors on mid-section plane. While RBC lead to standing waves, especially at pressure side with mass flow strongly pulsating and even flow reversal, NRBC allow pressure fluctuations from pressure port to travel to the outlet and leave there without any artificial reflections so that mass flow is more uniform and realistic.
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