Numerical Simulation Of The Cooling Water Jacket Cavitation Considering Piston Tribo-dynamics Characteristics

The diesel engine has unique advantages in efficiency,reliability and economy,and is widely used in transportation,energy exploitation,national defense equipment and other fields.Due to the continuous improvement of its strengthening index,cavitation has become one of the main failure forms of diesel engine cylinder liner.During diesel engine operation,the vibration of the cylinder liner caused by the knock of the piston causes cavitation in the cooling water jacket,and finally causes the material on the surface of the cylinder liner to fatigue and fall off,which is the main inducing factor of cylinder liner cavitation.Therefore,it is of great theoretical and engineering significance for preventing cylinder liner cavitation.Based on the two-phase mixed model of water and vapor and Singhal-et-al full cavitation model,the cylinder liner is simplified to a simply-supported beam,and the vibration of the cylinder liner is simulated by using a dynamic mesh with sinusoidal law,and the fluid-solid coupling model of cylinder liner vibration-cooling water jacket cavitation with sinusoidal vibration boundary is established and verified with the literature.The influence of different vibration frequencies on cavitation is studied,and the research shows the simulation method that only uses a specific frequency due to the inaccuracy of the cylinder liner vibration boundary resulted in poor model authenticity.In order to correct the vibration boundary,the in-cylinder excitation is solved.Taking into account the secondary motion of piston,corner contact,thermal deformation and surface roughness of the piston-cylinder interface,a piston tribo-dynamics model is established,and the difference in excitation under different calculation methods is compared.On this basis,a vibration model of the cylinder liner considering the tribo-dynamics characteristics of the piston is established,and the displacement response of the cylinder liner in the entire diesel engine working cycle is calculated.Furthermore,the influence of the number of cylinder liner vibration boundary divisions on the flow field pressure and volume fraction is discussed,and the cavitation flow characteristics of the cooling water jacket after the vibration boundary is corrected are analyzed.Studies have shown that the pressure and volume fraction in the cooling water jacket are more likely to fluctuate at the power stroke and the beginning of the exhaust stroke,and the locations that are prone to cavitation would continue to migrate over time.In order to investigate the influence of operating conditions and structural parameters on cavitation flow in cooling water jacket,the parameters of cooling water temperature,inlet velocity,diesel engine speed and piston pin offset are selected to analyze the cavitation flow characteristics.The study shows that when the temperature of cooling water is less than 80℃,affected by the physical parameters of cooling water,the fluctuations of pressure and volume fraction are relatively large.When the temperature of cooling water continues to increase,the fluctuations of the results remain basically unchanged.With the increase of the inlet velocity,the pressure and volume fraction change alternately due to the increase of the average velocity of flow field and the stagnation effect at the narrow channel.Affected by the excitation changes caused by cylinder pressure,when the diesel engine speed is less than 1800r/min,the fluctuations of the pressure and volume fraction in the power stroke stage gradually become larger,and as the diesel engine speed continues to increase,the resulting fluctuations are basically stable.With the change of the piston offset and the influence of the excitation change caused by the change of the piston secondary motion,the changes of the pressure and the volume fraction of the gas phase are basically the same,but the amplitudes are slightly different.With the change of piston pin offset,the changes of pressure and volume fraction are basically the same,and the amplitudes are slightly different.The reason is that the excitation change is affected by the change of piston second-order motion.