Numerical Investigation On The Flow Field And The Hysteresis Characteristics Of Brush Seal

Brush seal is widely used in the field of aeroengines,gas turbine,etc.It is a contact dynamic seal that can effectively replace the labyrinth seal.Using experimental methods to study the brush seal,the cost of manufacturing is high and the service life is short.In contrast,it is important to study the flow field characteristics and hysteresis characteristics of brush seal by numerical analysis method to improve the brush seal performance.The numerical model was established using two-dimensional cross section of staggered tube bundle of bristles,and the flow field was numerically solved by using Fluent under steady state and transient state,respectively.The simulation results have been proved consistent with the experimental results of Bayley&Long,which proved the accuracy of the calculation model.The effects of different inlet and outlet pressure difference and brush spacing on pressure and velocity distribution were analyzed.This work presents velocity of flow and the variation range under transient state at the-last brush gap are much higher than that of the front row in the axial direction and lead to severe wear of the last row of brush wear.The influence of different pressures and number of bristle bundle on the leakage were analyzed.The effects of different pressure,brush spacing and the axial number of bristles on the drag force under steady state,and the relationship between drag force and bristles deformation were studied.Through the variation of the amplitude of drag force under transient conditions,it is found that the last row of brush is greatly affected by the fluid wake,and the brush welding fatigue easily.A nonlinear contact model of brush seal with rotatable rotor was established.The study analyzed the hysteresis characteristics of single row of five bristles considering the rotation of the rotor.Firstly,the cantilever beam theory was used to establish the mechanical model of the bristle during the rotor rotation.The reason for hysteresis was analyzed by work energy principle,and the concept of hysteresis energy was obtained.On this basis,the model was numerically simulated by the finite element method(FEM)using abaqus.The hysteresis characteristics of the rotor under rotation and static were analyzed,and the effects of different fluid pressures and different friction coefficients between the bristles and rotor on the hysteresis curve were analyzed.The numerical results illustrates that the rotation of the rotor can improve the hysteresis characteristics of the brush seal.When the rotor rotates,the change of friction coefficient between the bristles and rotor has little effect on the hysteresis characteristics.When the rotor is in static condition,the hysteresis energy increases linearly with increase of the friction coefficient.As the differential pressure increases,the hysteresis energy of brush seal become larger.Based on the research conclusions of the flow field and hysteresis characteristics of brush seal,in order to improve the axial pressure bearing property and reduce the friction and wear between the bristles and the rotor,two new brush seals structures were proposed and designed,respectively.The first one is a new brush seals with low wear and high pressure bearing.The second one is composite seal of labyrinth seal and brush seal with low wear.