Research On Numerical Simulation Method For Flow And Heat Transfer Problems In Internal Combustion Engine Lubrication

At present,Reynolds equation based methods are the mainstream to solve lubrication design problems in China and overseas.However,recent researches indicate that the traditional Reynolds equation based methods couldn't fully reflect the actual thermal effects coupling and cavitational process in the lubricant film due to the existence of complex flow and heat transfer coupling effects existing between the lubrication oil film in ICE(Internal Combustion Engine)applications.As a result,the accuracy of calculation results by the Reynolds equation based methods cannot satisfy higher requirements of energy saving,low friction and wear,and precious lubrication which are requested by the lubrication design technology in the future.This situation has created a urgent need to establish a new numerical lubrication simulation method which can better reflect the physical reality between the frictional pairs in ICE applications.In this paper,the friction pairs in ICE applications were taken as the research object.Based on the existing CFD method,the phase-changing cavitation model and thermal coupling effects were introduced in to establish a new numerical simulation method.The new method took the influences of phase-changing,heat and mass transfer and multi-physical field coupling into consideration when solving flow and heat transfer problems in hydrodynamic lubrication.Using the new established method,the influences of operating condition,physical properties,boundary conditions on frictional performances and flow-heat transfer process of different kind of frictional pairs were studied.Finally,new models and approaches were summarized by applying dimensionless treatment,which could be used to modify and improve the accuracy of current simulation results of friction pairs in ICE.The main research contents and major conclusions are as follows:1.Establishment of the numerical simulation method for flow and heat transfer problem in hydrodynamic lubrication.Based on the existing CFD method,the phase-changing cavitation model and thermal coupling effects were introduced in to establish a new numerical simulation method of flow and heat-transfer process in hydrodynamic lubrication which could take the influences of phase-changing,heat and mass transfer and multi-physical field coupling into consideration.The new established method improved the ability of simulating heat transfer and cavitation process in hydrodynamic lubrication.The results showed that:1)The pressure and temperature distributions showed an evident deviation between the new method and the original Reynolds equation based method.2)The original CFD based method was not able to simulate the phenomenon of flow and heat transfer in cavitation zones,while the results of the new method showed better agreement with the actual process.3)The new method established in this thesis has advantages compared with either the Reynolds equation based or the current CFD based methods in simulating and analyzing the cavitation phenomenon within the lubricant film.2.Experimental validations of the simulation results.Most of the frictional pairs in ICE can be abstracted and divided into two kind of typical lubrication problems:the line contact lubrication problem and the journal bearing lubrication problem.For the line contact lubrication problem,a Block-Flywheel mechanism test instrument was built to verify the new method.For the journal bearing lubrication problem,the experimental data in highly cited references were used to verify the simulation results of journal bearing.The results indicated that the accuracy of newly established method was ideal.3.Study of the influences of various factors on thermal effects and lubrication performance of hydrodynamic lubrication.For different typical lubrication problems,the lubrication performance parameters and thermal effects were calculated under different design parameters,operating conditions,boundary conditions.Then the dimensionless treatment was used to process the results making the result more flexible and easy to generalize.4.Modification study of the current simulation approach and model in ICE and its application.Based on the above research results,the modified heat transfer model for piston ring-liner frictional pair was obtained,and the modified approach for main bearing oil film thickness calculation was studied.The new model and approach were more accurate compared with the original one,which could provide more reliable guidance for engineering design.