Study On Turbulent Effect Of Liquid Film Lubricated Mechanical Seals

In the fields of aerospace,nuclear power and other fields,fluid machinery is developing towards high parameters.Mechanical seals face severe operating conditions of high pressure or high speed.The lubricating liquid film between the seal end faces is often in a turbulent state,which has an important impact on the performance of mechanical seals.This paper aims at the liquid film lubrication mechanical seal under high pressure and high speed conditions.Based on the turbulent lubrication theory of the lubricating liquid film,a finite element mathematical model is established.The influence of turbulence on the sealing performance under different parameters is studied.Firstly,based on the improved turbulent viscosity model of Brunetière,the finite element method combined with relaxation iteration technology was used to realize the numerical solution of the lubrication equation and the liquid film turbulent model.For a typical two-dimensional infinitely large flat plate,under the two basic flow conditions of shear flow and pressure differential flow,a comparative analysis of the laminar,transitional,and turbulent pressures in the classic laminar lubrication model and the turbulent lubrication model under three different flow conditions is performed.Distribution,the influence of different grooves on the plate was studied.Based on this model,the turbulent effect of a hydrostatic pressure mechanical seal with a taper applied to high pressure working conditions was studied.The results show that under different geometric parameters,the opening force,stiffness and leakage rate in the laminar flow model are larger than those in the turbulent model,and the friction coefficient is small.Under different working conditions,the influence of rotating speed on the leakage rate and friction coefficient is significant considering the turbulence effect.As the sealing pressure increases,the liquid film opening force increases.As the sealing pressure increases,the opening force of the liquid film increases and the friction coefficient decreases.The friction coefficient of the turbulence model in the study range increases with the increase of film thickness,while the friction coefficient in the laminar flow model decreases with the increase of film thickness.Aiming at the liquid film lubricated spiral groove end face mechanical seal applied at high speed,the influence of turbulence on seal performance under different spiral groove geometry parameters and operating conditions parameters was compared and analyzed.When the speed n ? 20,000 rpm,the lubricating liquid film is in a completely turbulent state.The turbulent effect of the liquid film significantly enhances the dynamic pressure effect of the liquid film on the end face of the spiral groove mechanical seal.The opening force,leakage rate and stiffness of the lubricating liquid film are significantly greater than predictions of laminar model.Compared with the non-slotted liquid film,the turbulent effect is more obvious in the spiral groove,and the liquid film flow behavior is far different from the laminar model.With the opening force as the optimization target,the optimized spiral groove geometric parameters obtained by the turbulent model differ significantly from the laminar model in terms of helix angle and groove depth.Based on the turbulence effect and the viscous shearing action of the lubricating liquid film,a thermo-hydrodynamic lubrication model of the mechanical seal was established.The finite element method was used to perform the generalized Reynolds equation,the quasi-three-dimensional liquid film average energy equation,and the dynamic and static ring heat conduction equation coupled solutions were used to compare and analyze the effects of geometric parameters and operating parameters on sealing performance under the laminar and turbulent thermal models.The results show that the turbulent effect is very significant for the temperature distribution of the static pressure mechanical seal.Under different parameters,the temperature value of the turbulent thermal model is much greater than the laminar thermal model.For high-speed spiral groove seals,due to the thermal effect of the fluid,the viscosity of the liquid film is significantly reduced,and the dynamic pressure effect of the fluid is weakened,so that the pressure peaks under he two models are not much different.The temperature distribution in the turbulent thermal model is greater than the value of the laminar thermal model.The temperature distribution gradually increases from the outer diameter side to the inner diameter side of the seal ring.For the average temperature of the liquid film and the end temperature of the static ring,more cold fluid Flow into the tank area,the temperature of the non-tank area is significantly higher than the temperature value of the tank area.Under different parameters,the values of the turbulent heat model are larger than the values of the laminar heat model,which is attributed to the effect of turbulence on increasing the viscosity of the lubricated liquid film.