Research On Hysteresis Effect Of Brush Seal And Optimal Design Of Low Hysteresis Bush Seal

Brush seal is an excellent flexible sealing technology that has been widely used in aviation engines,gas turbines and steam turbines.However,the conventional brush seal will cause a hysteresis effect during the work due to the friction between the bristles and the bristles,the brush pack and the back plate,resulting in an increase of leakage.In order to reduce the hysteresis effect,a low hysteresis structure with a pressure relief chamber between the brush pack and the back plate was designed abroad in 1996.At present,there is no calculation model for analyzing the hysteresis effect of brush seal leakage at home and abroad,and few studies focus on the optimization design of low-leakage and low-hysteresis brush seal structures,which are critical to its engineering design.This paper will carry out experimental research on the hysteresis effect of the leakage of the brush seal,thereby establishing a calculation model of the leakage hysteresis effect,and optimizing the design of the low hysteresis brush seal structure.Firstly,a three-dimensional finite element model of multi-row staggered brush wires was established in this paper.The hysteresis effect of bristles deformation under the instantaneous radial reciprocating offset of the rotor was numerically studied.The results show that the structural parameters that have the greatest effect on the hysteresis effect of the bristles deformation are the bristle diameter,bristle lay angle,and axial width of the pressure relief chamber.Therefore,the structure of the brush seal test piece is designed.Secondly,this paper designed and processed 6 brush seal test pieces with different bristle diameters d,bristle lay angle β,and axial width of the pressure relief chamber w.Leakage and hysteresis tests of pressure difference increasing and decreasing cycles,rotor increasing and decreasing cycles and rotor diameter increasing and decreasing cycles were carried out.The test results show that the hysteresis effect under dynamic conditions is weaker than that under static conditions;the larger d,the greater the leakage,but the weaker hysteresis effect under high pressure difference;the larger β,the larger the leakage,and the stronger the hysteresis effect;The leakage of the conventional structure is higher than that of the low hysteresis structure,and its dynamic hysteresis effect is also stronger than that of the hysteresis structure.Too large or too small of w will cause the leakage to increase,and the hysteresis effect will also stronger.Thirdly,based on the leakage hysteresis effect test data,a calculation model for leakage hysteresis effect was established in this paper.The brush pack was treated as a porous medium,and a threedimensional CFD model of the brush seal leakage flow was established.According to the requirement that the calculation result of leakage amount matches the test data under the same conditions(the error is less than 2%),the porosity of the brush pack in the pressure rise and drop cycle,and rotor diameter increase and decrease cycles are respectively modified,and thus established the relationship between the porosity of the process of pressure difference increasing and decreasing and the process of rotor diameter increasing and decreasing with the parameters such as pressure difference,speed,bristle diameter,bristle lay angle,and axial width of the pressure relief chamber.This is the calculation model of the leakage hysteresis effect.Finally,this paper optimized the design of the low hysteresis brush seal structure.With the optimization goals of low leakage and low hysteresis,the design parameters of bristle diameter,bristle lay angle,and axial width of the pressure relief chamber were taken as design variables,and a limited range of leakage coefficients were used as constraints to establish the mathematical design of the optimal design of the brush seal structure model.Then,the structural optimization design of the brush seal was carried out by combining the agent model and particle swarm optimization algorithm.The results show that within the limited range of design variables,the structure with bristle dimmer of0.09 mm,bristle lay angel of 40°,and axial width of pressure relief chamber of 0.6mm meets the requirements of low leakage and low hysteresis.