Study On Static And Dynamic Characteristics Of Lubricant Film For Spiral-Grooved Mechanical Seals

Spiral-grooved end face mechanical seals are widely used in the fluid machinery.They are often affected by the viscous shearing heat of lubricating fluid film in the course of use,which has important influence on the static and dynamic characteristics of seals.In this dissertation,the theoretical analysis was carried out to study the effect of this factor.The static and dynamic mathematical models of the lubricant film for the spiral-grooved mechanical seals was solved by the finite element method.The static and dynamic characteristics of lubricant film at the different sealing conditions and different geometrical parameters of spiral grooves were obtained considering the film heat dissipation.Firstly,based on the finite element method（FEM）and hydrodynamic lubrication（HD）theory,a JFO cavitation lubrication model with mass conservation was established.The steady-state Reynolds equation was solved by the streamline upwind finite element method,and the cavitation region and pressure distribution of the liquid film were obtained.Meanwhile,the pressure perturbation equation was derived based on the small perturbation method,and the dynamic coefficients of the lubricant film were numerically solved.The results show that when the groove depth is about 10?m,the groove dam ratio is about 0.75,groove width ratio is about 0.4 and the spiral angle is about 9?,the film gives the maximum axial and angular stiffness coefficients.When the groove depth is about 5?m,groove width ratio is about 0.6 and the spiral angle is about 20?,the film yields the maximum absolute value of the angular cross damping coefficients.The fluid film pressure is unsymmetrical when the seal rings is misaligned and the cross-angular dynamic coefficients is not equal to each other in the absolute value.The magnitude of the axial stiffness k_zzz was far greater than the other stiffness values.The axial dampness d_zzz and angular dampness d_??d_??are far greater than the other dampness values and decrease with the increase of the rotational speed and clearance.Secondly,a quasi three-dimensional thermohydrodynamic model（THD）of the spiral-grooved mechanical face seals considering the mass and energy conservation was established.The finite element method was applied to simultaneously solve the average energy equation of the cross film and the heat conduction equations of the rotor and stator.The generalized Reynolds equation and the temperature equations were iteratively solved to obtain the liquid film pressure and the temperature distribution of seal ring and liquid film.The static and dynamic sealing performance was compared between the THD and HD results at the different spiral groove parameters and working conditions.The results show that the thermal effect can’t be neglected for the medium with high viscosity.Compared with the THD model,HD model overestimates the opening force and friction coefficient but underestimates the leakage rate.When taking the opening force as the objective,the optimal value of the groove depth from THD is smaller than one from HD model.The increase in the groove-dam ratio and the groove number leads to the rise in the leakage rate of the seal.The influence of the spiral-grooved parameters on the friction coefficient is opposite to the opening force.The increase in the groove depth and the groove-dam ratio is help for reducing the temperature rise of the liquid film and the seal rings.For the two models,the dynamic coefficients of liquid film in THD model are less than those in HD lubrication,and the variation trend is similar.There exit optimum values in the groove depth,groove dam ratio,groove width ratio and spiral angle,which give the maximum axial and angular stiffness coefficients.The damping coefficients d_zzz d_??and d_??decrease with the increase of structural parameters.The increase of rotational speed not only increases the leakage rate,but also is not conducive to the dynamic stability of the seal.The misalignment of the mechanical seals can enhance the dynamic pressure effect,so as to increase the opening force and dynamic coefficient.The temperature rise can be reduced by properly increasing the seal rings clearance,but the hydrodynamic effect may reduce and the dynamic performance deteriorates sharply.The optimum range of spiral groove structure parameters were obtained,for example,the groove depth is 5¹5?m,the groove dam ratio is0.60⁰.85,the groove width ratio is 0.5⁰.8 and the spiral angle is 20?.Finally,based on the simulation annealing method,the multi-parameter optimization on the groove parameters was carried out to obtain the optimal opening force and dynamic coefficients k_zz,k_??and k_??.Compared with the single-parameter optimization,the optimal opening force is increased by 39%,the optimal axial stiffness is increased by 18%,the optimal angular stiffness is increased by 15%,and the optimal angular cross stiffness is increased by 21%.In the high-speed conditions,further researches should be carried out to study the effects of fluid inertia,cavitation,turbulence and viscous shear heat on the static and dynamic effect of the mechanical seals,which are significant in these situations.