DefinePK

Abstract

With the aero-engine manufacturers aiming for Operating Power Ratios (OPRs) higher than 50:1 and improved engine efficiency, the capabilities of the present sealing systems are bound to be severely tested. Air riding seals have emerged as potential candidates to deal effectively with the high pressure discharge air from the compressor. The simplest types of air-riding seals are those with an axial gap. Radial gap seals can provide another level of advantage in terms of their applicability and the total axial travel that needs to be accommodated. This paper provides an overview on a preliminary design effort in modeling and designing a radial gap air riding seal having a continuous ring structure. It investigates a key issue regarding these seals: developing a positive radial stiffness in the air-film to drive the sealing ring to accommodate for any radial shaft movement while maintaining a minimum clearance from the shaft to avoid any contact (in effect, having sort of a bearing-like action). The paper discusses the results from 1D and 2D analyses of the flow through a small sector of the seal, and demonstrates a methodology to calculate the stiffness and damping coefficients of the fluid-film. This is followed by steady state and transient CFD simulations to further analyze the characteristics of this fluid film and understand the time-constants associated with perturbations of the film.