Research On The Flow Field And Bristles Tip Contact Heat Transfer Characteristics Of Brush Seals

Due to the superior sealing characteristic, the brush seal brush seal technology is an important way to improve the performance of aircraft engines, ground and marine gas turbines and other rotating machineries. The friction & wear between the bristle tips and rotor and the corresponding heat problem is the major limitations of brush seals application. Establishes the numerical model more appropriate to practical applications, investigations on the flow field, bristle tip forces and heat transfer characteristics have important significance to improve the brush seal performance.Because of the complexity of the brush seal structure and research, establishment of the theoretical model conformed to the brush seal structure and the work characteristic is the key to the study. The thesis establishes a type of two-dimensional closed staggered tube bundle model of the bristle pack cross section and further develops a three-dimensional slice model of the bristle pack.Based on the two-dimensional closed staggered tube bundle model of the bristle pack cross section, the flow characteristics within the inter-bristle clearance and the sealing principle are studied. The calculated flow results by the models with single-row and multi-row bristles in circumferential direction are compared, also the calculated pressure results compare with the rotor surface pressure test results by Beyley & Long. The impacts of pressure differential, bristle axial rows and inter-tube spacing on the leakage characteristics are researched.Bases on the three-dimensional slice model combines a bristles pack cross section arrangement model, the flow characteristics within the inter-bristle clearance and the sealing principle are further researched. Coupled with the calculated aerodynamic forces derived from CFD results, presents a theory on calculating the bristle tip forces using the torque balance principle and linear superposition method, also an iterative algorithm of the tip forces is proposed by ANSYS. Takes the bristle tip forces, frictional heat and the heat transfer process into consideration, a three-dimensional slice temperature analysis model is established. The results obtain distribution characteristics of the flow pressures, velocities, aerodynamic forces, tip forces & heats and temperatures, reveal the uneven distributions of aerodynamic forces, tip frictional forces & heats and temperatures along the axis direction for idealized contacting brush seals. The simulation results by ANSYS basically agree with the calculated bristle tip forces. The effect of bristle axial row on the leakage rate is studied, and the impacts of pressure differential and rotary speed on the bristle tip temperature are also investigated.Based on the theories above, the orthogonal numerical analysis is used to study the effects of some geometrical parameters on leakages, aerodynamic forces, tip frictional forces and torques of single-stage brush seals. Characteristics of the leakages, aerodynamic forces and tip frictional forces in the two-stage brush seals(TSBS) are studied. The results reveal the inter-stage imbalance of pressures drops, aerodynamic forces and tip frictional forces between the upstream and downstream bristle packs in the TSBS, studies the methods to optimize inter-stage imbalance.A multi-function test system of brush seals is designed and built in order to verify the calculated leakage, torque and temperature results and the corresponding models and theories. A temperature test method of the bristle-rotor contacting zone based on a type of fiber thermocouple is presented. The method is more sensitive to the conditions of bristles-rotor interference and eccentricity, and no obvious disturbances to the original temperature field.