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.

Issue Section:
Technical Papers
Keywords:
aerodynamics, gas turbines, seals (stoppers), compressors, modelling, stability, mechanical engineering, Navier-Stokes equations
Topics:
Aeroelasticity, Flow (Dynamics), Modeling, Pressure, Aircraft engines, Unsteady flow, Stability
1.
Munson
,
J.
, and
Pecht
,
G.
,
1992
, “
Development of Film-Riding Face Seals for a Gas Turbine Engine
,”
Tribol. Trans.
,
65
(
1
), pp.
65
–
70
.
2.
Hwang, M. F., and Pope, A., 1995, “Advanced Seals for Engine Secondary Flow Path,” 31st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, San Diego, CA, AIAA-95-2618.
3.
Wolfe, C. E., et al., 1996, “Full Scale Testing and Analytical Validation of an Aspirating Face Seal,” 32nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Lake Buena Vista, FL, AIAA-96-2802.
4.
Turnquist, N. A., Tseng, T. W., McNickle, A. D., and Dierkes, T. J., 1998, “Analysis and Full Scale Testing of an Aspirating Face Seal with Improved Flow Isolation,” 34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit.
5.
Gardner, J. F., 1999, “Development of a High Speed, High Temperature Compressor Discharge Seal,” 35th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit.
6.
Shapiro, W., and Nikayuna, N. Y., 1997, “Stiffness Enhancements of a 36 Inch Aspirating Seal,” AIAA Paper 97-2875.
7.
Turnquist, N. A., Tseng, T. W., McNickle, A. D., Steinetz, and B. M., 1999, “Full Scale Testing of an Aspiring Face Seal with Angular Misalignment,” 35th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit.
8.
Begepalli, B., et al., 1996, “Dynamic Analysis of an Aspirating Face Seal for Aircraft-Engine Applications,” 32nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Lake Buena Vista, FL, AIAA-96-2803.
9.
Leefe, S., 1994, “Modelling of Plain-Face Gas Seal Dynamics,” 14th Int Conference on Fluid Sealing, 397-424, BHR Group Conference Series No 9, Firenze, Italy.
10.
Sayma
,
A. I.
,
Vahdati
,
M.
,
Sbardella
,
L.
, and
Imregun
,
M.
,
2000
, “
Modelling of 3D Viscous Compressible Turbomachinery Flows Using Unstructured Hybrid Grids
,”
AIAA J.
,
38
(
6
), pp.
945
–
954
.
11.
Sayma
,
A. I.
,
Vahdati
,
M.
, and
Imregun
,
M.
,
2000
, “
An Integrated Non-Linear Approach for Turbomachinery Forced Response Predictions: Part I—Formulation
,”
J. Fluids Struct.
,
14
, pp.
87
–
101
.
12.
Vahdati
,
M.
,
Sayma
,
A. I.
, and
Imregun
,
M.
,
2000
, “
An Integrated Non-linear Approach for Turbomachinery Forced Response Predictions: Part II—Case Studies
,”
J. Fluids Struct.
,
14
, pp.
103
–
125
.
13.
Baldwin, B. S., and Barth, T. J., 1991, “A One-Equation Turbulence Transport Model for High Reynolds Number Wall-bounded Flows,” AIAA Paper 91-0610.
14.
Essers
,
J. A.
,
Delanaye
,
M.
, and
Rogiest
,
P.
,
1995
, “
Upwind-Biased Finite-Volume Technique Solving Navier-Stokes Equations on Irregular Meshes
,”
AIAA J.
,
33
, pp.
833
–
842
.
15.
Swanson
,
R. C.
, and
Turkel
,
E.
,
1992
, “
On Central-Difference and Upwind Schemes
,”
J. Comput. Phys.
,
101
, pp.
292
–
306
.
16.
Jorgenson
,
P. C.
, and
Turkel
,
E.
,
1993
, “
Central Difference TVD Schemes for Time Dependent and Steady State Problems
,”
J. Comput. Phys.
,
107
, pp.
297
–
308
.
17.
Roe
,
P.
,
1981
, “
Approximate Riemann Solvers, Parameter Vectors and Difference Schemes
,”
J. Comput. Phys.
,
43
, pp.
357
–
372
.
18.
Melson, N. D., Sanetrik, M. D., and Atkins, H. L., 1993, “Time-Accurate Navier-Stokes Calculations with Multigrid Acceleration,” Proceedings of the Sixth Copper Mountain Conference on Multigrid Methods.
19.
Newmark
,
N. M.
,
1959
, “
A Method of Computation for Structural Dynamics
,”
ASCE Journal of Engineering Mechanics Division
,
85
, pp.
67
–
94
.
20.
Vincenti, W. G., and Kruger, C. H., 1965, Introduction to Physical Gas Dynamics, J. Wiley and Sons, NY.
Copyright © 2002
 by ASME
You do not currently have access to this content.