Study On Thermo-hydrodynamic Lubrication Properties Of Inclined-ellipse Dimpled Gas Face Seals At High Speed

The hydrodynamic effect of inclined-ellipse dimples is introduced to keep the mating sealing faces separate quickly during starting operating in non-contacting gas face seals.With the expanding application of operating working toward the high-speed condition,the gas film temperature gradient caused by the circumferential shear effect and radial pressure flow induces the thermal distortion to affect the geometrical morphology of sealing face.To control the gas film temperature distribution and face distortion,the study on thermo-hydrodynamic lubrication properties of inclined-ellipse dimpled gas face seals at high speed was conducted.Firstly,to the microscopic surface roughness,a hydrodynamic lubrication theoretical model considering roughess effect was built.Rough surface with a Gaussian distribution of asperity heights was mathematically described by typical topographical characteristic parameters of surface roughness,including the standard deviation of surface roughness?,asperity radius of curvature?_r,asperity density?,elliptical slender ratio?_r and inclination angle of asperity?_r.The load capacity was derived with consideration of random hydrodynamic effect.Then a theoretical analysis was compared with the results by Patir-Cheng's model on the load capacity of a rough slider surface.The difference between them can be controlled into 10%,which verifies the accuracy of present model.Secondly,a hydrostatic flat-plate experiment on the throttling effect of deep-grooved surfaces at low pressure was conducted.And a theoretical model on the inlet pressure loss was built and compared with test datas.Then a parametrical investigation,including the supply pressure,lubrication clearance and groove depth,was used to analyze the influences on the flow characteristic and pressure distribution.The experimental results showed that the throttling effect firstly increases,then decreases with the increase of groove depth,and reaches the largest value of R_Q=65%near h_d=0.5 mm,finally keeps steady.The deep-grooved surfaces present significant throttling effect in a range of h_d=0.5~2 mm.Besides,the inlet pressure loss was enhanced with the increases of lubrication clearance and supply pressure.Thirdly,based on the hydrodynamic lubrication theoretical model of rough surface with consideration of the inlet pressure loss and outlet chocked flow,the influence of surface roughness on seal performances were analyzed at isothermal condition.Results show that the surface asperities increase the opening force and decrease the leakage rate.When the film thickness ratio?is less than 3,the hydrodynamic effect of surface roughness should not be ignored.The inlet pressure loss decreases the inlet pressure of gas film,and meanwhile the chocked flow elevates the outlet pressure boundary,which can decrease the surface opening force and leakage rate.Fourthly,the transient thermal hydrodynamic gas lubrication model for inclined-ellipse dimpled face seal was established based on the gas thermal hydrodynamic lubrication theory.The steady-state and dynamic characteristics were presented under different operating conditions.It was found that the gas expansion causes the temperature decrease along gas flow,which generates a divergent distortion due to the complex interplay between temperature field and pressure field.The surface distortion weakens the hydrodynamic effect of inclined-ellipse dimples as a result of that the opening force makes a 50%reduction.The axial movement and angular swing of seal rotor generates additional pressure and temperature distributions.The dynamic characteristics such as the damping and stiffness have no obvious changes at low perturbation frequencies,but change rapidly with perturbation frequency increasing to a critical value.Finally,an experiment was carried out to test temperature distribution and wear morphology on seal surfaces as well as the leakage rate of gas face seal at high speed.The test results showed that,with the increase of running time,the temperature of seal stator increases especially in the beginning of 10 mins where the temperature increases rapidly,then tends to keep steady,and meanwhile the leakage rate presents a decreasing tendency.Beside,the wear is observed near the high-pressure side of seal stator and rotor,which illustrates that the temperature of gas film decreases gradually from high-pressure side to low-pressure side to induce a divergency clearance distribution.According to the above research,the studies of thermo-hydrodynamic lubrication properties of inclined-ellipse dimpled gas face seals at high speed were carried out.The lubrication mechanism on gas thermal effect and face distortion was discussed.Influences of surface morphology on sealing performance were studied.The results can provide a theoretical guidance for surface design and enginnnering application on non-contact mechanical seals.