Performance Research And Optimization Design Of Axial Electrically Assisted Turbocharger Rotor

For savings shipping operating costs,commercial merchant ships often run at economical speeds.In this case,the matching point between the exhaust gas turbocharger and the engine keep at a non-design operating point.Therefore it requires much time to keep the low-efficiency auxiliary blower supplied air to the engine running,which caused the increased grid load and energy wastage.The driving conditions faced by land vehicles are changeable.It is frequent for land vehicles to start and stop on urban roads,and the instability of the exhaust temperature and volume of the engine results in the instability of the volume of the supercharged air provided by the exhaust gas turbocharger,which lead to turbo lag,increased pollutant emissions,and decreased vehicle maneuverability.As an effective technical to solve above problems,Electrically Assisted Turbocharger(EAT)is one of the development directions of engine supercharging technology.However,the non-coaxial EAT equipments has been used now,and most compressor rotor of them directly adopts the existing exhaust gas turbine compressor rotor,which is not specifically designed and optimized based on the working characteristics of the EAT equipment.The axial flow compressor rotor has high flow rate and efficiency and moderate pressure ratio,and these advantages are more suitable for EAT equipment directly driven by a motor.First,based on the self-designed axial flow EAT compressor rotor(prototype EAT rotor),this thesis systematically studies the properties at the designed speed and different speeds and the changeable rule of the internal flow field structure of the rotor,and analyzes the aerodynamic load of prototype EAT rotor at design speed and the reason why secondary leakage leads to flow instability caused by outlet flow blockage under the near stall conditionFurthermore,in order to tap the potential of the prototype EAT rotor,modern compressor design technologies,including compressor tip wing technology,swept blade technology and axisymmetric endwall modeling technology,are used to improve the flow field structure and improve its working performance.Aiming at the characteristic that the outlet back pressure of EAT rotor changes periodically in the working environment of engine intake pipe,the prototype EAT rotor is optimized by using the tip winglet design technique which can effectively control the tip clearance flow.In order to solve the problems of high cost of obtaining the sample value of stable working margin and difficulty in constructing the sample database,an optimization design platform for compressor tip winglets was established,which was based on support vector regression as the agnet model and genetic algorithm as the optimization algorithm.At the same time,the optimization effects of support vector regression and artificial neural network respectively agnet models in the optimization design of tip winglets were compared.The research shows that when the tip winglet is the structural form of partial pressure surface winglet,the stable working margin of EAT rotor increases by 1.69 %.In the optimization design of tip winglet,the optimization effect of support vector regression agnet model is better than that of artificial neural network.In order to adjust the blade surface pressure gradient and control the boundary layer flow,the meridional stacking line and tangential stacking line of the prototype EAT rotor were optimized by using the curved swept blade technology.The research shows that the design of blade forward swept can improve the tangential velocity of blade tip at the inlet and reduce the inflow angle at the blade tip.The design of positive curved blade can reduce the aerodynamic load of blade tip and root and improve the flow efficiency of the end wall region.After using the multi-objective optimization algorithm with elitism strategy to optimize the performance of the designed flow rate point,the optimized blade stacking line has the geometric characteristics of positive curved of the blade body,forward-swept blade tip and blade root.After optimization design,the total pressure ratio of the EAT rotor is increased by 0.14 %,and the isentropic efficiency is increased by 1.2 %.For adjusting the flow in the endwall region of the EAT rotor,the hub profile and casing profile of the prototype EAT rotor were optimized by axisymmetric endwall modeling technology.The research shows that the change of hub profile will affect the blade surface load distribution in the hub area and the airflow velocity in the hub section.The change of casing profile will affect the axial velocity of tip leakage flow and trailing edge separation.The geometric characteristics of the end wall profile with convex hub and concave casing are obtained by using the optimization algorithm,which significantly improves the performance of the EAT rotor.Finally,the best optimization scheme obtained by using axisymmetric endwall modeling,compressor tip wing and swept-curved blade is studied in the EAT rotor,and the compound EAT rotor is obtained.The characteristics and flow field structure of the compound EAT rotor are studied.The effects of different modeling techniques on the distribution of aerodynamic parameters are analyzed.The sensitivity of the compound EAT rotor to the change of gap size is given.The results show that the effect of different modeling techniques on the distribution of aerodynamic parameters is superposition.Compared with the prototype EAT rotor,the maximum efficiency point flow of the compound EAT rotor is increased by 11.5% and the maximum efficiency is increased by 0.3%.The conpound modeling EAT rotor reduces the ratio of tip leakage flow to total flow,stabilizes the momentum relationship between tip leakage flow and separation of trailing edge corner,and reduces the sensitivity to clearance change.