Investigation On Flow Dynamic,heat Transfer,friction And Wear Characteristics Of Finger Seal

With the improvement of the comprehensive performance of the aero engine,the thermal parameters are increasing,resulting in severe working conditions of the seals.The traditional sealing techniques such as labyrinth and carbon seals have failed to meet these requirements.Finger seal is a new type of compliant seal configuration,which is used to control leakage throughout the blade tip,compressor and turbine stage,bearing and disk cavities of an aero-engine or its accessory systems.It has superior sealing performance compared with labyrinth seals and a lower manufacturing cost than brush seals.However,the high-temperature,high-pressure difference and high-speed working conditions coupled with the structure characteristics lead to complex wear,friction heat,leakage flow,heat transfer and thermal deformation characteristics of finger seals,especially for contacting type.Thus,the above characteristics of basic finger seal are studied in this paper by using theoretical analysis,numerical simulation and experimental research.In terms of model establishment,firstly,a bilateral wear model and a friction heat model were established on the basis of energy conservation theory,respectively.In these models,the effect of structural parameters,working conditions and material properties are considered.Then,the experimental methods for determining the friction coefficient,wear coefficient,correction coefficient of contact force and ratio of wear energy to friction power were proposed.Secondly,an anisotropic porous media model for leakage flow and heat transfer analysis of finger seals was established,while the friction and wear effect were considered.The model considers the spatially anisotropic distribution of the flow resistance coefficient and thermal conductivity tensor,and the variation of the above parameters with time caused by deformation and wear of fingers.Finally,the numerical analysis methods of fluid flow,heat transfer and thermal deformation wre developed and the experimental data of typical finger seals were used to verify the calculation accuracy of the calculation models,test results prove that the accuracy of the modified models are mostly within 10%.In terms of experimental research,firstly,a high-temperature,high-speed seal test system was established which can be used to test the leakage,heat transfer,friction resistance and wear performance of various seals.The advangtages of this test system are as follow: it can test the sealing performance of a variety of sizes,especially for large-scale seal structure;upstream and downstream air flow is stable;it is easy to disassemble and assemble with high accuracy;many kinds of parameters including torque of shaft and surface temperature of seal can be measured.Secondly,the author proposed the processing technology of finger seal include the sheet material flattening,the whole ring tardily wireelectrode cutting and high precision dowel assembly.The results show that the finger seal designed in this paper has superior sealing performance compared with the same type of seal structures.Finally,designing and manufacturing eight kinds of finger seals and test their friction,wear,leakage and heat transfer performance.The results show that the leakage increases with the increase of pressure difference,but decreases with the increase of fluid temperature;the leakage initial decreases and then increases with the surface velocity in the rising stage,but there is obvious hysteresis effect in the descending stage,and the higher the maximum value of surface velocity,the more serious the hysteresis effect;the highest temperature of the seal increases with the surface velocity in the rising stage but also shows hysteresis in the descending stage;the temperature of the contact surface decreases but the leakage increases with the wear time,and the drastic changes of wear,temperature rise and leakage all occurred in the initial wear stage;the friction torque caused by the seal is proportional to the surface velocity of the rotor and increases with the increase of pressure difference.In terms of numerical simulation of performance of finger seal,the example scheme was designed based on the orthogonal test design method and the pressure,velocity and temperature distribution of typically finger seal were numerically simulated,and the influence of structural parameters and wear effect on leakage and heat transfer characteristics were analyzed respectively.The results show that the larger the rotor surface velocity and initial installation interference,the larger the final radial wear length,the wear rate,the initial friction heat flux and its decay rate;the numerical results of the effect of wear on leakage and heat transfer are consistent with the experimental data;most of the fluid leaks through the finger foot while the pressure drops mainly in this field;the highest temperature occurs at the downstream side of the contact surface between the finger foot and the rotor,and then the temperature decreases in the radial and axial direction,but more significant in the radial direction;In addition,by using the orthogonal test design method,it is suggested a large value of the diameter of finger foot upper and finger beam arcs’ centres,while synthetically considering the effect of structural parameters on wear,friction heat,leakage flow and heat transfer characteristics;it is found that the circumferential thermal deformation is the largest.