Aeroelasticity analysis of air-riding seals for aero-engine applications

Sayma, A I, Breard, C, Vahdati, M and Imregun, M (2002) Aeroelasticity analysis of air-riding seals for aero-engine applications. Journal of Tribology, 124 (3). pp. 607-616. ISSN 0742-4787

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This paper presents the results of a feasibility study on air-riding seal aeroelasticity for large-diameter aero-engines. A literature survey of previous seal studies revealed a significant amount of experimental work but numerical modeling using CFD techniques was relatively scarce. Indeed, most existing theoretical studies either deal with the structural behavior, or use simplified flow modeling. The aeroelasticity stability of a simplified air-riding seal geometry, devised for this particular feasibility study, was analyzed in three dimensions for typical engine operating conditions. Both the unsteady flow and structural vibration aspects were considered in the investigation. The boundary conditions and the seal gap were varied to explore the capabilities and limitations of a state-of-the-art unsteady flow and aeroelasticity code. The methodology was based on integrating the fluid and structural domains in a time-accurate fashion by exchanging boundary condition information at each time step. The predicted characteristics, namely lift and flow leakage as a function of pressure and seal gap, were found to be in agreement with the expected behavior. Operating seal gaps were determined from the actual time histories of the seal motion under the effect of the aerodynamic and the restoring spring forces. Both stable and unstable cases were considered. It was concluded that, in principle, the existing numerical tools could be used for the flow and aeroelasticity analyses of hydrostatic seals. However, due to large Mach number variations, the solution convergence rate was relatively slow and it was recognized that a preconditioner was needed to handle seal flows. For small gaps of about 10 microns, typical of spiral groved seals, the flow has a high Knudsen number, indicating that the Navier-Stokes formulations may no longer be valid. Such cases require a totally different treatment for the modeling of steady and unsteady aerodynamics, either by modifying the transport parameters of the Navier-Stokes equations or by considering rarefied gas dynamics.

Item Type: Article
Additional Information: This paper investigates the use of aeroelasticity models developed for turbomachinery aeroelasticity in the stability of air riding seals. These are devices under investigation for use in aircraft engines to cut weight, improve performance and increase reliability. The challenge encountered is the ability to analyse flows with speeds ranging from near stationary to transonic. The geometric scales also vary from the order of meters to order of microns within the seal. This represents a challenge to the most sophisticated numerical models. The paper addressed the modelling issues involved and produced guidelines for future work in the evolving research area.
Schools and Departments: School of Engineering and Informatics > Engineering and Design
Depositing User: Naser Sayma
Date Deposited: 06 Feb 2012 20:47
Last Modified: 07 Jun 2012 09:58
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