GLTRS--Glenn
TITLE AND SUBTITLE:
Numerical and Analytical Study of Fluid Dynamic Forces in Seals and Bearings

AUTHOR(S):
L.T. Tam, A.J. Przekwas, A. Muszynska, R.C. Hendricks, M.J. Braun, and R.L. Mullen

REPORT DATE:
September 1987

FUNDING NUMBERS:
WU-505-62-21

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191

PERFORMING ORGANIZATION REPORT NUMBER:
E-3903

SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Washington, DC 20546-0001

REPORT TYPE AND DATES COVERED:
Technical Memorandum

SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA TM-100268

SUPPLEMENTARY NOTES:
Prepared for the 11th Biennial Design Engineering Conference on Vibration and Noise sponsored by the American Society of Mechanical Engineers, Boston, Massachusetts, September 27-30, 1987. L.T. Tam and A.J. Przekwas, CHAM of North America, Inc., Huntsville, Alabama 35816; A. Muszynska, Bentley Rotor Dynamics Research Corporation, Minden, Nevada 89423; R.C. Hendricks, NASA Lewis Research Center; M.J. Braun, University of Akron, Akron, Ohio 44325; and R.L. Mullen, Case Western Reserve University, Cleveland, Ohio 44106. Responsible person, R.C. Hendricks, organization code 5000, 216-977-7507.

ABSTRACT:
A numerical model based on a transformed, conservative form of the three-dimensional Navier-Stokes equation and an analytical model based on "lumped" fluid parameters are presented and compared with studies of modeled rotor bearing/seal systems. The rotor destabilizing factors are related to the rotative character of the flow field. It is shown that these destabilizing factors can be reduced through a decrease in the fluid average circumferential velocity. However, the rotative character of the flow field is a complex three-dimensional system with bifurcated secondary flow patterns that significantly alter the fluid circumferential velocity. By transforming the Navier-Stokes equations to those for a rotating observer and using the numerical code PHOENICS-84 with a nonorthogonal body-fitted grid, several numerical experiments were carried out to demonstrate the character of this complex flow field. In general, fluid injection and/or preswirl of the flow field opposing the shaft rotation significantly intensified these secondary recirculation zones and thus reduced the average circumferential velocity; injection or preswirl in the direction of rotation significantly weakened these zones. A decrease in average circumferential velocity was related to an increase in the strength of the recirculation zones and thereby promoted stability. The influence of the axial flow was analyzed. The lumped model of fluid dynamic force based on the average circumferential velocity ratio (as opposed to the bearing/seal coefficient model) well described the obtained results for relatively large but limited ranges of parameters. This lumped model is extremely useful in rotor bearing/seal system dynamic analysis and should be widely recommended. Fluid dynamic forces and leakage rates were calculated and compared with seal data where the working fluid was bromotrifluoromethane (CBrF3). The radial and tangential force predictions were in reasonable agreement with selected experimental data. Nonsynchronous perturbation provided meaningful information for system lumped-parameter identification from numerical experiment data.

SUBJECT TERMS:
Seals; Numerical; Fluid dynamics; Forces; Bearings; Stability

NUMBER OF PAGES:
38

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