Study On Dynamic Lubrication Characteristics Of A New Floating Cylindrical Groove Gas Film Seal

The rotating machinery equipment is used for the compression and transmission of fluid,which is the"heart"of the petroleum and chemical industry equipment.On the one hand,the rotating machinery is progressing towards to the extreme operating conditions including high speed,high temperature and so on,on the other hand,severe requirements are made for the non-contact gas film seal,such as zero-overflow,environmental-friendliness and enough stability,in the petroche mical industry.However,the end face gas film seal has not been qualified for the ultimate parameters.Because the end face gas film seal is vulnerable to being wear,deformation,instability and so on and it seriously affects the safe operation of the ch emical equipment industry.Therefore,it is very important to develop the non-contact gas film sealing with high parameters.Meanwhile,it is urgently required to explore a new type of sealing with better stability.In this paper,a new floating cylindrical micro-groove gas film seal is proposed,and the lubrication characteristics of the gas film of the micro-gap is deeply researched.A single column spiral groove,a single column parallel groove,spiral groove of double column herringbone and parallel groove of double column herringbone are designed as the structure of groove.The characteristics of steady state and dynamic state,the slip flow effects,optimization of groove and prototype design are become the points of entry.The characteristics of lubrication of the new floating cylindrical micro-groove gas film seal are explored in terms of theoretical calculation and experimental testing in order to verify the feasibility and effectiveness of the new type seal.The central difference method of the high er accuracy and the Newton-Raphson iteration method are used to solve the Reynolds equation and gas film thickness equation,considering the different groove shapes,eccentricity and discontinuous mutation of groove and platform would affect the changes of gas film thickness.The distributions of gas film pressures and gas film thickness are obtained.The effect of different operating conditions,structure parameters and groove structures on the static characteristics of the new floating cylindrical micro-groove gas film seal.The results show that the new seal is adapted to being stable operated in the environment of small film thickness,large eccentricity,high speed and low pressure.The single column parallel groove has the largest gas bearing capacity.And the gas film thickness and eccentricity are the key parameters play a determining role of the groove structure,and the single column spiral groove and single column parallel groove are selected from the four different groove structures and shapes.In view of the two groove types—the single column spiral groove and single column parallel groove,the dynamic Reynolds equation is established by the small disturbance method,making the pressure and film thickness on the displacement and velocity perturbation trace by the Taylor series expansion,establishing perturbations relational expressions between pressure and gas film thickness.The dynamic Reynolds differential equations on perturbation is solved.The eight dynamic characteristic coefficients of the new floating cylindrical micro-groove gas film seal are obtained by using finite difference method and iterative method,and the influence of operation conditions and structural parameters on the dynamic characteristic coefficients is discussed.The results show that the curves of the cross stiffness of gas film(k_xy and k_yx),and the curves of the cross damping of gas film(c_xy and c_yx)presents nearly symmetrical characteristics respectively,the change rules of the main stiffness of gas film(k_xx and k_yy)is same,as well as the change rule of the main damping of gas film(c_xx and c_yy).Differential pressure plays an important role in the new seal axial pressure flow and circumferential shear flow,single column parallel groove is more suitable for the interface structure of the new seal than the single spiral groove.The multi-objective multi-parameter optimization is proposed for the new floating cylindrical micro-groove gas film seal with the single column parallel groove.According to the multi-objective optimization method.The objective function of the ratio of the gas film bearing capacity to the gas film leakage rate is built.The number of grooves,groove depth,and groove length are used as multi-parameter coordinated optimization variables.The logical relationship between bearing leakage ratio and multi-parameters is determined,combining the three-axis global search and multi-round optimal three-parameter interactive verification optimization model to carry out the numerical calculation.The re sults show that the gas film pressure obtained by the optimized groove structure is greater,with more obvious gas film pressure peaks and throttling effect,and the gas film pressure is more stable in the groove zone.The second round of optimized groove structure parameters can be achieved a larger the bearing leakage ratio than the first-round optimization.It can illustrate that the groove structure has important influence on the new seal,and it can be proved that the multi-round optimal three-parameter interactive verification is very necessary.According to the microscale feature dimension of the new floating cylindrical micro-groove gas film seal and the air flow lubrication mechanism,the three-different types of velocity slip models are introduced,the first order velocity slip model,the second order velocity slip model and the F-K model,to modify the gas lubrication Reynolds equation,considering the numerical solution to the problem of deviation caused by extremely thin films.The lubrication pe rformances of the new floating cylindrical micro-groove gas film seal are calculated and analyzed.The results show that the difference of gas film pressure and bearing capacity between the first order slip model,the second order slip model and the F-K model is bigger and bigger,when air flow is transited from the continuous flow state to the slip flow state.The hydrodynamic effect is poor so that the gas film thickness is thinner,so the gas film shear rate is high and the strong characteristics of nonl inear is presented under low pressure and low rotating speed.Thus,the second order velocity slip model is suggested to use in operation conditions of low pressure and rotating speed.However,based on the operation condition of high speed,the F-K model has better stability and it is suggested that use F-K model to calculate gas film lubrication performance under the slip flow effects.To verify the numerical results in this paper,the experimental testing system about the new floating cylindrical micro-groove gas film seal is established,and the high-speed test bench and gas supply system is remolded,the new floating cylindrical micro-groove gas film seal system is designed and processed,and a new process for groove carving on the sleeve surface is pro posed;in addition,the test program is written,the sensors and other equipment that meet high operating conditions are selected and take measures to suppress interference.Then,the experimental value and theoretical calculation are analyzed.The experim ental results show that the gas film bearing capacity of the single column parallel groove is the largest,grooves that is arranged in a single column have greater film bearing capacity and smaller leakage under the same groove shapes.Moreover,the perfor mance of the optimized the single column parallel groove cylinder gas film seal is greatly improved.The F-K model’s film bearing capacity is closer to the test value and the error between the F-K model and the test value is the smallest.The F-K model is used to calculate the stable and dynamic characteristics of the new floating cylindrical micro-groove gas film seal when slip flow effect is occurred.The theoretical model is highly consistent with the experimental results,which indicates that the theore tical model has enough reliability.The research results of the paper systematically expound the static characteristics,the change of the dynamic characteristic coefficient,the optimization of the groove structure and the lubrication characteristics with the slip flow mechanism at the new floating cylinder micro-groove gas film seal.The groove carving technology of sleeve cylindrical surface is solved.Meanwhile,it is found that the spiral groove structure which is suitable for the end face is not the b est choice for the new sealing.The single column parallel groove is more suitable for the new seal.The above research lays a solid foundation for groove structure design,lubrication performance analysis,and engineering application of the new floating c ylindrical micro-groove gas film seal in the future.