| Gas face seals rely on the hydrodynamic opening force generated by the groove to achieve face separation.The elliptical groove shows an obvious bi-directional fluid hydrodynamic effect.To further study the hydrodynamic characteristics of elliptical grooves under high-parameter operating conditions,the theoretical and experimental studies on thermo-hydrodynamic lubrication properties of elliptical groove gas face seals were conducted.Firstly,the theoretical model of elliptical groove face seals was built.Based on the isothermal lubrication theory analysis method,the pressure and flow field distribution of the elliptical groove and the traditional spiral groove under forward and reverse rotation were numerically calculated.The results showed that the convergence characteristics of the elliptic line caused the airflow to converge with the rising edge of the line under the action of shear,so that a significant hydrodynamic pressure was formed by seal rings in bi-directional rotation.The opening structure of the elliptical line made the resistance of the gas flowing into the groove smaller and the pumping effect stronger.Due to the convergent characteristics of the line,the airflow was reversed outward under shear action,resulting in lower leakage.By rationallly designing the parameters,the elliptical groove could produce a stronger hydrodynamic effect than spiral groove.Besides,the elliptical groove had the ability to rotate in both directions.Secondly,an experiment research on the gas flow characteristics of surface oil immersion was carried out.The influence of surface oil immersion on gas flow was studied by measuring the changes of capillary's inlet and outlet pressure and gas flow with and without oil immersion.The test results showed that,when oil was immersed in the gas,the viscosity of the oil slowed down the sudden variation in pressure and flow.When the pressure before the valve is 0.1 MPa,compared with the air flow condition,the outlet pressure and gas flow only decreased by 7.6% and 3.5% respectively.It showed that the liquid dropout in the gas face seals could delay the separation of the faces,but it will return to the previous lubrication state after a period of continuous gas supply.Therefore,the effect of the liquid precipitation in the faces could be ignored.Thirdly,based on the isothermal gas lubrication theory with consideration of choked effect,the pressure distribution of the elliptical line under forward and reverse rotation conditions was analyzed.Compared with the condition without consideration of choked effect,the influence of choked effect on the gas pressure distribution in the faces was studied.In addition,the investigations of structure parameters including the lone axis inclination angle of the ellipse and the integrity rate of the line,were used to analyze the influence on the hydrodynamic effect.The results showed that,the choked effect contributed to the pressure at the outlet to be significantly higher than the ambient pressure.The gas pressure distribution across the entire surface tended to be flatter,but maintained the same trend taking no account of choked effect.To obtain the optimal hydrodynamic effect,it was recommended that the integrity rate of the elliptical line was 0.8 to 0.9,and the number of grooves was 6 to 10.Besides,the inclination angle of the open elliptical groove suitable for bidirectional rotation was 38 to 90 °.Fourthly,in view of the thermo-hydrodynamic lubrication theory with consideration of gas choked effect and thermal effect,the gas temperature and pressure distribution as well as thermal deformation of the elliptical line under forward and reverse operating conditions were analyzed.Then compared with the spiral groove structure,the deformation mechanism of the elliptical line was further analyzed.It was found that,the effect of thermal deformation weakened the gas compression effect of the elliptical line caused by the shearing effect,and the hydrodynamic effect was significantly reduced.As the medium pressure rised,the gas expanded and cooled along the flow direction under the pressure difference between the inner and outer diameters of the face.The pressure gradient at the seal outlet was greater,so the temperature drop was more obvious.Significant divergent deformation was formed between the two seal rings.Finally,an experimental study on the elliptical groove gas face seals under hightemperature and high-speed operating conditions based on theoretical research was conducted.The influence of parameters such as inlet medium temperature,rotational speed and groove depth on the face temperature distribution as well as leakage was mainly analyzed.The test results showed that,under normal temperature conditions,the shear heat generated at high speed improved the face divergence clearance which caused by the pressure difference.At the same time,under high temperature conditions,temperature enhanced the effect of shear heat,meanwhile the high rotational speed caused the outlet temperature to rise sharply,which eventually resulted in a convergent clearance between the faces.According to the above studies,the study on the thermo-hydrodynamic lubrication properties of elliptical groove gas face seals was carried out.The influence of elliptical groove on the gas pressure field,flow field,temperature field and thermal deformation as well as working mechanism was discussed.The results could provide a theoretical basis for the design and engineering application of elliptical groove gas face seals. |
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