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

Importance of hydrodynamic lift clearance has been stated in previous studies [1, 2, 3]. At those studies, derivation of closed form function for oil temperature has been performed and the shear heat dissipation effect has been successfully integrated into the lift force formulation. Oil pressure is successfully derived by tracking three different ways, all of which give very similar results to each other. All these analyses are advanced fluid mechanics and heat transfer analyses, which give consistent results with real-life applications. In this study, function of shear heating effect included in hydrodynamic lift clearance formulation. For a different pressure loads (which is a design parameter and known), change of hydrodynamic lift clearance with rotor surface speed can be found without requiring any experimental leakage data. Furthermore, theoretic lift clearance has consistency with the experimental lift data

Analysis of shear heating and effect of temperature dependant viscosity on hydrodynamic lift of oil brush seals /

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 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 obtained by using Reynolds formulation. Following a short bearing approximation, a closed form solution of the lifting force has been previously presented. However. solution to hydrodynamic lift force suggests a strong dependence on oil temperature and viscosity, This work presents an analytical solution to oil temperature rise due to shear healing. Stalling with continuity and Navier Stokes equations, temperature distribution is derived by solving thermal energy equation. The hydrodynamic lift force relation has been expanded to include oil temperature and viscosity variability due to rotor speed and lift clearance. Results are also compared with the experimental data obtained from the dynamic oil seal test rig. In addition to temperature analysis, pressure distribution for the brush seal is also derived by tracking three different ways, all of which gives consistent results with each other and real life applications. Derivation of shear heat effect included lift clearance, which is the most important parameter for leakage performance of brush seals, is also done and compared with experimental lift clearance data

A study of brush seal oil pressure profile including temperature-viscosity effects

After proven performance in air applications, brush seals are being considered for oil and oil mist sealing in aero-engines, turbines and generators. The viscous medium between the high speed rotor surface and bearing surfaces formed by brush seal bristle tips generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. Hydrodynamic lift force and seal clearance have strong dependence on oil temperature and viscosity. In a previous study, short bearing theory has been applied to a single bristle to obtain a solution for hydrodynamic lift force developing at a bristle tip. Rather than individual bristles, this work evaluates pressure for the bristle rows. Applying the Reynolds bearing theory to the control volume between bristle tips and the rotor surface fluid pressure distribution is obtained under each bristle row. Effective temperature and effective viscosity approach has been adopted. Pressure distribution for each bristle row in the rotor axial direction is evaluated. Then, pressure profiles for each bristle row are combined to yield the axial pressure profile under the entire brush pack

Stiffness and friction characterization of brush seals

Improvements in steam and gas turbine technologies constantly drive harsher conditions, which result in thermodynamic cycles having higher pressure ratios and inlet temperature levels as well as increased leakage flows. Necessity of reducing the internal leakage flows and thermodynamic cycle losses while increasing the turbine overall efficiency puts greater importance on improvements in sealing technologies. Labyrinth seals have been used almost since the invention of gas turbines and their technology is very well developed over the years. However, leakage rates are still not satisfactory and cannot meet the performance requirements of new generation turbines. Brush seals are fulfilling the leakage performance requirements and they can successfully compensate rotor interference at turbine transient conditions. Due to their superior and stable leakage performance and compact size, brush seals are replacing traditional labyrinth seals at critical sections of turbines. A brush seal consists of a series of bristles which rub on the shaft surface. Since the bristles slide against the high-speed rotating shaft, friction and wear at the bristle tip contact becomes a major concern as it determines the life and efficiency of the seal and also rotor stability. Evaluating bristle tip contact forces and resulting stress levels at operating conditions is critical to optimize the seal performance and safety. A brief literature survey reveals the lack of test data and analysis methods for evaluating seal stiffness and stress levels at operating conditions. In an attempt to meet this need, custom test rig design and methodology has been developed to perform stiffness tests at turbine operating conditions. Analytical studies and finite element simulations have been performed for test seals and results have been correlated with the test data of this study. Furthermore, stiffness and friction characterization of brush seals has been conducted through correlated FE models, and MATLAB based code has been developed for automatic brush seal FE model generation for ABAQUS simulations

Brush seal performance measurement system

Brush seals are rapidly replacing conventional labyrinth seals in turbomachinery applications. Upon pressure application, seal stiffness increases drastically due to frictional bristle interlocking. Operating stiffness is critical to determine seal wear life. Typically, seal stiffness is measured by pressing a curved shoe to brush bore. The static-unpressurized measurement is extrapolated to pressurized and high speed operating conditions. This work presents a seal stiffness measurement system that is capable of measuring brush seal stiffness under engine operating pressure and speed condition which is not available in open literature. Stiffness measurement system design, testing methodology and calibration procedure are discussed

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

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 has 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