Teoretical And Experimental Study On Surface Textured Finger Seal

Finger seal,as a new type of flexible seal developed after brush seal,has the same sealing performance as brush seal.It has the potential of low leakage rate,long service life and high-cost performance,and its compact axial structure is conducive to lightweight design of equipment.Because of these advantages,it has broad application prospects in the field of gas and oil circuit sealing parts of high-speed rotating equipment such as aeroengines,gas turbines,vehicle engines,high-speed gear boxes,turbochargers,etc.In recent years,it has become a research hotspot in the field of dynamic seals.However,with the continuous increase of the linear speed of high-speed rotating equipment,although the flexible design of the finger seal makes it have excellent low wear potential,but also due to the lack of basic research on the friction pair design and lubrication and wear reduction under harsh working conditions,when it is used in high-speed railway,automobile,commercial aeroengine,gas turbine and other equipment,the friction and wear control under the requirement of high reliability and adaptability is facing new challenges.Recently,surface texturing wear reduction technology has been deeply studied and has been successfully applied to a variety of occasions with high speed and heavy loads,such as heavy load sliding bearings,mechanical seals,piston ring seals,and other important components.Given this,this study proposes a method to improve the tribological characteristics of the finger seal by surface texturing and carries out relevant work by combining numerical simulation,theoretical analysis,and experimental verification.The theory and method of wear reduction design of surface textured finger seal are established through systematic research such as optimization simulation analysis of texture configuration,numerical analysis of surface textured finger seal performance,friction mechanism test,and bench test.The specific research contents and conclusions are as follows:(1)Based on friction simulation and fluid-structure interaction simulation,five types of common surface texture(triangle,circle,diamond,hexagon,and rectangle)are optimized and analyzed.The analysis results show that the surface texture can change the stress distribution of the contact interface,effectively improve the fluid film-bearing capacity of the finger seal,and thus reduce the leakage rate.The diamond texture has better contact and hydrodynamic characteristics,followed by hexagonal and circular textures,and the triangular and rectangular groove textures have the worst performance.In addition,the surface texture changes the fluid streamline direction,and an obvious eddy phenomenon occurs in the texture area.The flow velocities in different directions cancel each other,reducing the axial flow velocity and axial leakage;The surface texture changes the fluid pressure distribution,and the micro-texture unit forms a local high-pressure area along the direction of pressure difference and rotor speed.(2)Given the characteristics of finger seal applied to high-speed oil sealing,a hydrodynamic lubrication numerical model of surface textured finger seal based on the Reynolds equation is constructed,and the finite difference method and successive overrelaxation method(SOR)are used for numerical solution.The mechanism of the hydrodynamic effect generated by surface texture is revealed,and the influence of texture parameters and operating conditions on finger seal performance is analyzed.The analysis results show that the surface texture provides a regular convergence gap,which makes the hydrodynamic pressure effect between the interfaces of the friction pairs and improves the bearing capacity of the fluid film.To obtain a better hydrodynamic effect,the surface texture profile should be consistent with the rotor motion direction;The appropriate range of texture density is 10%～25%,and the range of texture depth is 5～25μm;When the seal clearance exceeds 10μm and the working temperature exceeds 120℃,the hydrodynamic pressure effect of textured finger seal becomes worse;Compared with other texture types,circular and hexagonal textures have better antifriction and wear resistance(with larger average dimensionless pressure and smaller friction coefficient).(3)Given the characteristics of finger seal applied to gas path sealing under variable working conditions,a mixed lubrication numerical model of surface textured finger seal based on the unified Reynolds equation is constructed.The influence of texture parameters and working conditions on the interface pressure distribution is studied,which provides a theoretical basis for revealing the friction and wear mechanism of the textured finger seal.The results show that air can be regarded as a low viscosity,low density,and compressible lubricant under the dry friction condition.The existence of surface texture makes the Hertz contact zone also have air,resulting in the gas dynamic pressure effect.The normal load is shared by the micro convex contact and the gas dynamic pressure effect.The gas bearing capacity increases with the increase of texture density and depth diameter ratio,which is conducive to reducing the actual contact pressure and improving the wear phenomenon;The suitable range of texture density is 5%～25%,and the depth diameter ratio is 0.1～0.7;The higher the rotor speed and the ambient pressure,the greater the gas bearing rate,while the greater the external load,the lower the gas bearing rate.(4)The friction and wear test of the disc pin based on P·V value equivalence is carried out,and the friction mechanism of the surface textured finger seal is revealed.The results show that surface texturing can effectively improve the wear characteristics of the GH605-GH4169 friction pair,and reduce the friction coefficient and wear.When the texture diameter is 200μm and the texture density is 10%,the tribological properties are the best;Under the dry friction condition,the surface texture can effectively collect the wear debris and reduce the abrasive wear caused by the second cutting of the wear debris.(5)The physical bench test of the surface textured finger seal is carried out to verify that surface texturing can improve the leakage and friction characteristics of the finger seal.The bench test results show that the leakage rate of textured finger seal can be reduced by about 15%compared with the non-textured side.