Scale-resolving simulations and investigations of the flow in a hydraulic retarder considering cavitation

Cavitation has a significant influence on the accurate control of the liquid filling rate and braking performance of a hydraulic retarder; however, previous studies of the flow field in hydraulic retarders have provided insufficient information in terms of considering cavitation. Here, the volume of fluid (VOF) method and a scale-resolving simulation (SRS) were employed to numerically and more comprehensively calculate and analyze the flow field in a retarder considering the cavitation phenomenon. The numerical models included the improved delayed detached eddy simulation (IDDES) model, stress-blended eddy simulation (SBES) model, dynamic large eddy simulation (DLES) model, and shear stress transport (SST) model in the Reynolds-averaged Navier-Stokes (RANS) model. All the calculations were typically validated by the brake torque in the impeller rather than the internal flow. The unsteady flow field indicated that the SBES and DLES models could better capture unsteady flow phenomena, such as the chord vortex. The SBES and DLES models could also better capture bubbles than the SST and IDDES models. Since the braking torque error of the SBES model was the smallest, the transient variation of the bubble volume fraction over time on a typical flow surface was analyzed in detail with the SBES model. It was found that bubbles mainly appeared in the center area of the blade suction surface, which coincided with the experiments. The accumulation of bubbles resulted in a larger bubble volume fraction in the center of the blade over time. In addition, the temperature variations of the pressure blade caused by heat transfer were further analyzed. More bubbles precipitated in the center of the blade, leading to a lower temperature in this area.