Flow pattern evolution analysis and reduction order modeling for the two-phase flow in a hydrodynamic retarder

As a noncontact auxiliary brake system used in heavy-duty vehicles or buses, hydrodynamic retarders dissipate kinetic energy to heat energy with adjustable braking levels by mixing given different ratios of hydraulic oil and air, or liquid-filled ratio, into the flow passages in its flow passages in rotors and stators. During the transient braking process, flow separations and secondary flows are common to promote the energy conversion and cause significant flow blockage. Therefore, understanding the two-phase flow patterns inside flow passages contributes better prediction for the brake performance. This study proposes a reduced order model (ROM) to describe the flow pattern evolution by numerical simulation of an emergency brake operating condition. The oil velocity fields were decomposed and reconstructed by proper orthogonal decomposition (POD) method and snapshots techniques. At different liquid-filled ratio, the extracted dominant modes of the transient flow containing the majority of energy varied with their numbers, flow patterns and energy percentages. Exact three dimensional flow structures on the interface between rotor and stator by these modes were recreated with enough accuracy, and some basic highly organized flow patterns were recognized from the energy composition standpoint.