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Abstract
The basic structure and working mechanism of the shallow-slot split floating ring were introduced. Parameters optimization, including the variables optimization of structure and operation, were conducted by using the general engineering method-nonlinear, single objective and one-parameter optimization. The results indicate that the structure and operation parameters have strong influence on the sealing performance. The leakage rate is decreased and the static stiffness is increased as the slot-depth increased. When the number of slot, pressure difference of sealing and the velocity of bearing are increased, the leakage rate is increased and the stiffness is decreased. In order to get the lowest leakage rate and improve the sealing performance, the structure parameters should be synthesized according to the working condition.
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Conventional bearing shaft seal systems used in gas turbine engines are often limited to a sliding velocity of about 100 m/s, differential pressure of 3 bar, gas temperature of 300°C and a seal life less than 8000 h. Advanced engines will require bearing shaft seal systems to operate up to sliding velocity of 200 m/s, differential pressure of 6 bar, gas temperature of 500°C and seal life in excess of 30 000 hours. For seals operating in these advanced conditions, a design with no rubbing contact will be required to achieve long life and reliability. A good validated approach is the use of a gas lift augmentation seal. The design objective for a seal of this type is to have the faces of the seal seek an equilibrium position to avoid any contact. The gap must be small enough to ensure a minimal air leakage, but it must be large enough to limit power dissipation, due to shear in the gas film, and face deformation by shaft displacement, misalignment and vibration. Dynamic seals for a bearing compartment have the following main functions: provide static and dynamic sealing in order to prevent oil leakage from the bearing oil compartment to the air compartment and consequently no oil smell pollution by the use of bleed air; control air leakage to the bearing oil compartment in order to improve performance of the engine and to reduce oil consumption; reduce volume of the oil tank and lubrication system and hence provide weight reduction; to operate in extreme conditions of temperature and with normal and reverse pressure; and reduce the mean time between overhaul (MTBO) and have a very long life. Techspace Aero and Burgmann have carried out design, development and testing of lift augmentation carbon seals and demonstrated that high life and performance levels of these seals are possible in a gas turbine engine environment.
The static and dynamic characteristics of a hybrid gas-lubricated journal bearing with surface-restriction compensation through multiple sawtooth grooves are analyzed by applying FEM. The design criteria of this bearing are discussed using the theoretical results of the fundamental bearing characteristics calculated under the variations of several bearing parameters. In particular, the optimum groove depths for the maximum static stiffness and for the maximum dynamic stiffness are clarified.
The experimental research on this bearing is also presented in this paper. The theoretical and experimental results show that this bearing has a higher bearing performance and more applications in engineering compared with the traditional gas-lubricated bearing.
This paper describes a finite-element solution of the nonlinear and coupled hydrodynamic and thermal equations for pressure and temperature profiles in an oil seal including the influence of circumferential grooves. Different models of grooves, considering and neglecting the entrance loss as the fluid passes over the groove, are analyzed. Perturbation analysis is used to determine the static and dynamic characteristics. The hydrodynamic forces are calculated by integrating the pressure distribution along and around the seal. This analysis shows that the smooth and rounded edge grooves tend to increase the leakage, and the size of the grooves significantly influences the axial and circumferential pressure variation in the groove. The results of grooved and ungrooved seals are compared and discussed. Presented at the 49th Annual Meeting in Pittsburgh, Pennsylvania May 1–5, 1994
A three-lobe journal bearing is analytically investigated to determine its dynamic performance when three main parameters, i.e. turbulence, load orientation, and rotor flexibility are varied. Reynolds numbers up to 12000, rotor dimensionless flexibilities up to 4, and load orientations up to 30 degrees on either side of the vertical load line are considered. Thus, almost all cases of practical interest are studied. The stability of a three-lobe bearing improves due to turbulence at high Sommerfeld numbers (more than 0.6) for a rigid rotor, while it is virtually the same for flexible rotors. Conversely, the load orientation has a pronounced effect on stability for both rigid and flexible rotors.
The floating ring seal is often used in an oxidizer and a fuel pump of the turbo pump unit in the liquid rocket engine because the floating ring seal has the ability to minimize clearance without rubbing phenomenon. For the analysis of performance and vibration characteristics of the turbo pump unit with floating ring seals, the exact prediction of the lock-up position of the floating ring is essential to evaluate the leakage and rotordynamic coefficients from the floating ring seal. The governing equations, which are based on the ‘bulk-flow model’, are derived from extending the eccentric annular plain seal analysis. The solution procedure is developed by using the Fast Fourier Transform Method of Nelson and Nguyen. The results of lock-up position, attitude angle of the floating ring, leakage flow rate, and rotordynamic coefficients are presented with operating conditions and geometric parameters of the floating ring seal for an example case.