Study On Gas-liquid Two-phase Flow Mechanism And Blade Bionic Optimization Of Hydrodynamic Retarder

With the rapid development of the national economy,China ’s total highway mileage has developed to the first in the world.However,the terrain in China is complex and diverse,and the safety of vehicles is very important.Therefore,there are higher requirements for the braking system of vehicles.The traditional friction brake has been unable to meet the driving requirements of high speed,heavy load and long downhill of the vehicle,and the auxiliary braking device will become the development trend.Compared with the traditional braking method,hydrodynamic braking has outstanding advantages in braking effect,reliability,safety and cost,and has broad application prospects.Therefore,it is imperative to deeply study the gas-liquid two-phase flow mechanism of hydrodynamic retarder,vigorously innovate,and master the ability of independent research and development of high-performance hydrodynamic retarder.The bionic non-smooth surface has the function of drag reduction.The non-smooth structure is combined with the hydrodynamic retarder blade to improve the braking performance of the hydrodynamic retarder by changing the internal flow state.Therefore,this paper combines the project of Jilin Provincial Science and Technology Department project ’Bionic Super-hydrophobic/super-oleophobic,Drag Reduction Multi-functional Coupling Design and Preparation of Key Technologies’ and Zhejiang Provincial Science and Technology Department Project ’Research and Application of Key Technologies of Water Retarder Brake for Key Components of Commercial Vehicles’.The gas-liquid two-phase flow mechanism and bionic optimization of hydrodynamic retarder are studied.The main research work and related conclusions are as follows:(1)Based on the in-depth analysis of the research status of hydrodynamic retarders at home and abroad,the internal gas-liquid two-phase flow state was qualitatively analyzed,and a three-dimensional model of hydrodynamic retarder was established.The full-flow channel model was selected as the calculation area,and the full-flow channel model was meshed and verified for grid independence.The numerical simulation of the full filling and gas-liquid two-phase transient flow field of the hydrodynamic retarder was carried out.The numerical solutions of the gas-liquid twophase flow of the hydrodynamic retarder under different rotational speeds and different filling rates were obtained,and the braking characteristic surface was obtained.The distribution characteristics of the gas-liquid two-phase flow field under full filling and partial filling conditions were studied,and the causes and flow mechanisms were analyzed in depth.(2)In order to deeply understand the mechanism of gas-liquid two-phase flow in the hydrodynamic retarder and verify the accuracy of CFD numerical simulation,the PIV test of the flow field in the hydrodynamic retarder was carried out.The transparent prototype of the hydrodynamic retarder was made according to the ratio of 1:1,and the flow field test bench of the hydrodynamic retarder was designed and built.The particle images of the radial section of the stator of the hydrodynamic retarder were collected by PIV test under the condition that the rotor speed was 300 rpm and the filling rate was 0.1~1.The cross-correlation algorithm is used to process the particle image,and the velocity field and vorticity field of the hydrodynamic retarder under various working conditions are obtained.(3)In order to solve the problem that the traditional flow field test is difficult to capture the gas-liquid two-phase distribution,the stator radial section image without tracer particles under partial liquid-filled conditions was collected,and the gas-liquid two-phase boundary of the hydrodynamic retarder was extracted by Canny edge detection operator.It is found that when the filling rate of the hydrodynamic retarder is below 0.2,there is less oil in the working chamber.Under the action of centrifugal force,the oil is mainly distributed in the outer ring of the circulating circle,forming laminar flow.When the filling rate is 0.2~0.4,the flow pattern of gas-liquid two-phase changes from laminar flow to slug flow.With the further increase of the filling rate,it eventually becomes dispersed bubble flow.The comparison between the experimental results and the CFD calculation results shows that the velocity field,vorticity field and two-phase distribution are basically consistent under various working conditions,and the parameter values are relatively close,which verifies the accuracy of CFD numerical simulation.(4)Considering the working principle and structural characteristics of the hydrodynamic retarder,the bionic design of the impeller blade is carried out.The axial or radial bionic non-smooth structure is constructed on the surface of the stator and rotor blades,and the bionic non-smooth blade hydrodynamic retarder model is established.The braking torque of the rotor speed of 1700 rpm and full filling condition is obtained by CFD calculation.The results show that the braking torque of the axial strip rotor and smooth stator combined hydrodynamic retarder is up to 2535.51 N·m,which is 14.36 % higher than that of the smooth blade hydrodynamic retarder(2217.14N·m).The multi-objective optimization of bionic non-smooth structural parameters was carried out.The stripe depth,stripe length and stripe spacing were taken as design variables,and the braking torque and volume of the hydrodynamic retarder were taken as optimization objectives.NSGA-II was selected as the multi-objective optimization algorithm to obtain the optimal solution.The optimized bionic non-smooth blade hydrodynamic retarder has a volume reduction of 1.92% and a braking torque increase of 4.35%.The optimized bionic non-smooth blade is made by 3D printing technology,and it is combined with the rotor shell of the transparent prototype.The PIV flow field test of the optimized hydrodynamic retarder transparent prototype is carried out to verify the rationality of the design.