Study On Thermohydrodynamic Lubrication Performance Of High Speed Deep Spiral Groove Mechanical Seals

As a key basic component of high-end equipment,mechanical seal is widely used in high-speed pumps in aerospace and other fields to prevent high-pressure side fluid leakage along the rotating shaft.In high-speed operation,the lubrication fluid in the face gap creates a great deal of viscous heat due to the strong shearing action of the moving ring.The traditional hydrodynamic mechanical seal is generally a micron shallow groove,and the viscous heat is very serious in high-speed operation,especially in high-viscosity fluid.The fluid in the gap is easy to vaporize,which leads to the instability of the sealing device.The submillimeter deep groove can increase the average film thickness of the liquid film,reduce the viscous shear heat generation,and improve the sealing stability.In addition,the submillimeter deep groove retains part of the performance of the shallow groove,effectively avoiding the excessive dynamic water pressure effect of the shallow groove caused by a large amount of leakage.The viscous heat produced by the cross-scale liquid film in the gap of seal is greatly affected by the high speed shear of the moving ring.The hydrodynamic lubrication(HD)model and thermohydrodynamic lubrication(THD)model of classical spiral groove mechanical seal(SG)under turbulent condition are established by using ANSYS Fluent,and the liquid film flow characteristics and pressure distribution under the two models are compared.The differences of sealing characteristics between HD and THD models are analyzed under different spiral groove geometric parameters and working condition parameters,so as to reveal the action mechanism and influence law of liquid film viscous thermal effect on mechanical seal performance.The results show that the liquid film pressure distribution of the HD model is similar to that of the THD model,and the maximum pressure appears at the convergence of the groove root,but after taking into account the thermal effect,the hydrodynamic viscosity decreases and the dynamic pressure effect is weakened,and the peak pressure of the THD model is smaller than that of the HD model.Under different spiral groove geometric parameters and working condition parameters,the predicted values of liquid film opening force and friction coefficient of THD model are lower than those of HD model.When viscous heat effect is taken into account,the seal leakage rate increases obviously,and rotational speed is the key factor affecting temperature rise.The high viscosity heat and the high temperature rise of the end surface are the most common problems in the high-speed mechanical seal.Thus,a composite end face configuration with a deep annular groove and deep spiral groove(ASG)is proposed,and its thermohydrodynamic lubrication(THD)model is developed by ANSYS Fluent.In the turbulent state,the heat transfer process of annular groove is compared and analyzed,its cooling mechanism is revealed,and the influence law of its geometric parameters on the sealing performance and cooling effect is discussed in mechanical seals.The results indicate that the viscous shear heat of the fluid in the annular groove area on the inner diameter side of sealing face decreases significantly because the film thickness is large and the shear effect is small,which effectively reduces the temperature of the lubricating liquid film and the seal face.The cooling effect of annular groove can be increased to 15 K by appropriately increasing the groove depth and width,that is,the temperature rise can be reduced by about 33%.Besides,the cooling effect of annular groove reduces the fluid viscosity loss,then the bearing capacity and the tribological performance of seal are improved.The annular groove increases the radial pressure gradient on the inner diameter side of sealing face and the leakage rate increases.The viscous heat generation of the fluid in the sealing clearance is serious and the flow behavior is complex under high speed.The fluid flow state is one of the key factors affecting the fluid-solid heat transfer process and temperature distribution in the cross-scale clearance.A 3D thermohydrodynamic lubrication(THD)model of annular groove and spiral groove compound end configuration(ASG)is established by using ANSYS Fluent under turbulence and laminar flow computational models.The cooling performance difference of the spiral groove and the cooling effect of the annular groove under the two models are compared,thus the influence mechanism of the fluid flow state on the cooling effect of the end groove is revealed.The effects of groove geometric parameters on temperature field and sealing performance under the two models are analyzed.The results show that the large dead fluid zone in the deep spiral groove under the turbulence model hinders the cold fluid from entering the root of the groove,resulting in the attenuation of the cooling effect of the spiral groove on the high temperature fluid in the sealing clearance.Under the laminar flow model,the deep spiral groove is filled with more cold fluid,and the cooling effect is stronger.The annular groove has a significant cooling effect under the two models,and the cooling effect is enhanced with the appropriate increase of groove depth and width.The continuous increase of spiral groove depth can’t achieve the purpose of continuous cooling,and the predicted value of the peak temperature of liquid film under the turbulence model is about 29K～40K higher than that of the laminar flow model.