Effect of shear heat on hydrodynamic lift of brush seals in oil sealing

Abstract

Due to their superior performance and stable leakage characteristics, brush seals are one of the dynamic seals used in oil and oil mist applications in aero-engines and turbines. The viscous medium between the high speed rotor surface and bearing surfaces formed by brush seal bristles generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. The analytical solution to bristle lifting force can be found by using Reynolds formulation. Following a short bearing approximation, a closed form solution of the lifting force has been previously presented. However, the solution suggests a strong dependence of hydrodynamic lift force and seal clearance on oil temperature and viscosity. This work presents an analytical solution to oil temperature rise due to shear heating. The hydrodynamic lift force relation lias been expanded to include oil temperature variability due to rotor speed and lift clearance. Results are also compared with the experimental data obtained from the dynamic oil seal test rig.