Yazar "Akşit, Mahmut F." seçeneğine göre listele

Listeleniyor 1 - 3 / 3
  • [ X ]
    Öğe
    Effect of shear heat on hydrodynamic lift of brush seals in oil sealing
    (2006) Duran, E. Tolga; Akşit, Mahmut F.; Doğu, Yahya
    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.
  • [ X ]
    Öğe
    Effects of geometry on brush seal pressure and flow fields - Part I: Front plate configurations
    (Asme-Amer Soc Mechanical Eng, 2006) Doğu, Yahya; Akşit, Mahmut F.
    Pressure and flow fields lay at the basis of such common phenomena affecting brush seal performance as bristle flutter, blow-down, hang-up, hysteresis, pressure stiffening, wear and leakage. Over the past two decades of brush seal evolution, manufacturers and researchers have applied many geometric configurations to the front and backing plates of a standard brush seal in order to control the flow field and consequent seal performance. The number of studies evaluating the effect of geometric configitrations on the brush seal flow field remains limited in spite of the high number of filed patent disclosures. This study presents a numerical analysis of brush seal pressure and flow fields with regard to common conceptual front plate configurations. A CFD model has been employed to calculate pressure and flow fields in the seal domain. The model incorporates a bulk porous medium approach for the bristle pack.. The effectiveness of various conceptual geometries has been outlined in terms of flow field formation. Results disclose unique effects of geometry on pressure and floss, fields such that a longer front plate drives outward radial flow while playing a protective role against upstream cavity disturbances. Findings also indicate that variations in from plate geometry do not directly affect leakage performance. A long front plate or damper shim considerably changes the flow field while at the same time having limited effect on the pressure field. Moreover; a strong suction towards the clearance enhances inward radial flow in clearance operation.
  • Küçük Resim
    Öğe
    An investigation of pressure stiffness coupling in brush seals
    (2006) Akşit, Mahmut F.; Doğu, Yahya; Kandemir, İlyas; Kızıl, Hüseyin
    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.