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.

Experimental and Internal Flow Investigation on the Performance of a Hydraulic Retarder with Different Liquid-Filled Amount and Blade Inclination Angles

In order to study the variation of brake torque,vibration,pressure fluctuation,exterior noise and internal flow for a hydraulic retarder with different inclination angles and liquid-filled amount,a bench-scale hydraulic retarder was built.The INV3020 data collection system was used for the synchronous acquisition of brake torque,vibration,pressure fluctuation and exterior noise signals.Experiments were performed with different inclination angles(90°and 75°)and six liquid-filled amount(50 vol%,60 vol%,70 vol%,80 vol%,90vol%and 100 vol%).The torque-volume ratio was proposed to accurately analyze the influence of inclination angle on the liquid volume in stator and rotor and the brake performance.Mixture multiphase flow model was employed to capture the volume and velocity distribution.The research shows that the brake performance improves and the vibration increases with the decrease of inclination angle and the increase of liquid-filled amount.The pressure fluctuation increases as the liquid-filled amount increases,while the lower inclination angle effectively lowers the pressure fluctuation amplitude.The sound pressure level trends upward with increasing liquid-filled amount,and the lower inclination angle can effectively reduce the noise.The volume distribution of the liquid phase under different liquid-filled amount is basically consistent.The lower inclination angle can induce more vortexes.

Design of Constant-Speed Control Method for Water Medium Hydraulic Retarders Based on Neural Network PID

The water medium hydraulic retarder is the latest type of auxiliary braking device and has the characteristics of high power density,large braking torque,and compact structure.During traveling,this device can convert the kinetic energy of a vehicle to the heat energy of the cooling liquid and replace the service brake under non-emergency braking conditions.With regard to the constant-speed function of the water medium hydraulic retarder,this study designs a controller based on the neural network proportional-integral-derivative(PID)algorithm to achieve the steady traveling of the vehicle at constant velocity during a downhill course by controlling the filling ratio of the water medium hydraulic retarder.To validate the algorithm’s effectiveness,the dynamic model of the heavy-duty vehicle in the downhill process and the physical model of the water medium hydraulic retarder are developed.Three operating conditions,including a fixed slope,step-changing slope,and continuous changing slope,are set,and a simulation test is carried out in the MATLAB/Simulink environment.The neural network PID algorithm has better adaptability in controlling than the traditional PID algorithm.Thus,it controls the water medium hydraulic retarder such that the braking requirements of heavy-duty vehicles under a changing slope working condi-tion are satisfied,and it performs constant-speed control when the vehicle travels downhill.Therefore,the proposed control method can significantly improve the safety of road traffic.