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Öğe Effect of shear heat on hydrodynamic lift of brush seals in oil sealing(2006) Duran E.T.; Aksit M.F.; Dogu Y.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.Öğe Investigation of flow behavior and porous medium resistance coefficients for metallic-cloth fibers(MDPI AG, 2020) Gorgun E.; Dogu Y.; Aksit M.F.The flow through porous metallic-cloth fibers influences the cloth seal leakage performance. Measuring the actual seal leakage proves difficult with challenging turbine operating conditions. A non-Darcian porous medium Computational Fluid Dynamics (CFD) model was employed for the flow within porous metallic-cloth fibers. CFD analyses need leakage data depending on the pressure load to calibrate flow resistance coefficients. A test rig was built to measure leakage with respect to the pressure load and weave orientation in four directions. The Sutherland-ideal gas approach was utilized to determine the flow resistance coefficients for Dutch twill metallic-cloth fibers as a function of pressure load. The results show that metallic-cloth fiber leakage is a linear function of pressure load. The best–worst order for leakage performance was the warp, diagonal, shute, and cross directions. For the best sealing performance, the flow direction in metallic-cloth fibers would be the warp direction. The flow resistance coefficients depend on the evaluation of the pressure level, which changes over the weave flow thickness. This is represented with the pressure constant (Cdown). The best match between the test and CFD leakages was obtained for the weave directions of warp (0.9), shute (0.9), diagonal (0.7), and cross (0.0). Calibrating the resistance coefficients with respect to the pressure and temperature enables performing CFD analyses in turbine conditions. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.Öğe An investigation of pressure stiffness coupling in brush seals(2006) Aksit M.F.; Dogu Y.; Kandemir I.; Kizil H.In recent years, brush seals found common use in turbomachinery applications. There are a number of seal locations on gas turbines that have significant performance derivatives. These include the compressor discharge, bearing seals, turbine interstage packings, and the bucket tips. While brush seal applications keep expanding towards more challenging locations, the need for better understanding of seal dynamic behavior also increases. Inherent flexibility of brush seals allows fibers to compact under pressure load. Due to the frictional interaction between the fibers and the backing plate as well as within the fibers themselves, brush seals are known to exhibit pressure stiffening and hysteresis behavior. While hysteresis affects seal performance after a rotor excursion, pressure stiffening is critical in determining heat generation and seal wear during hard rubs. It is necessary to understand the physical behavior of a brush seal under the operating conditions, and to be capable of quantifying seal life and performance as functions of both operating parameters and seal design parameters. In this paper, a 3-D finite element model is used in order to explore pressure-stiffness coupling behavior. The analysis includes all the frictional effects to better calculate resulting seal stiffness and tip forces. The results indicate that rotor interference has some effect on seal tip forces in the absence of any pressure loading. However, upon application of small pressure loads, seal stiffness is generally dominated by pressure-stiffness coupling. Results also indicate presence of hysteresis when rotor excursion is removed under pressure load. Copyright © 2006 by ISROMAC-11.Öğe A simple FEM model for foil bearings under differential pressure(2010) Aksoy S.; Aksit M.F.; Dogu Y.A bump-type foil bearing consists of a compliant corrugated sheet metal supporting structure that is covered by a thin top foil surface. Bumps serve as stiffener and damping elements to increase the stability of the system while top foil creates necessary wedge surface for aerodynamic film formation. Foil bearings are hard to analyze as flexible foil surface deforms and changes shape while aerodynamic film pressure forms. Iterative solutions required typical of EHL analysis. This work utilizes Reynolds Equation to solve aerodynamic film pressure by coupling structural deformation and the fluid film pressure formation. Bearing performance under various operating conditions and the effect of differential pressure boundary condition on sealing capacity is discussed. Copyright © 2010 by ASME.
