An analysis is developed for a compressible bulk-flow model of the leakage path
between a centrifugal compressor's impeller shroud and housing along the front and back
side of the impeller. This is an extension of analysis performed first by Childs (1989) for
a shrouded pump impeller and its housing considering an incompressible fluid, and then
later by Cao (1993) using a compressible bulk flow model for the shroud of a cryogenic
fluid pump. The bulk-flow model is used to develop a reaction force and moment model
for the shroud of a centrifugal compressor by solving the derived governing equations
and integrating the pressure and shear stress distribution. Validation is done by
comparing the results to published measured moment coefficients by Yoshida et al.
(1996). The comparison shows that the shroud casing clearance flow and the fluid force
moment can be simulated by the bulk flow model fairly well. An Iwatsubo-based
labyrinth seal code developed by Childs and Scharrer (1986) is used to calculate the
rotordynamic coefficients developed by the labyrinth seals in the compressor. Tangential
force and transverse moment components acting on the rotor are found to have a
destabilizing influence on the rotor for a range of precession frequencies. Rotordynamic
coefficients are derived for a single stage of a multistage centrifugal compressor, and a
comparison is made to stability predictions using Wachel's coefficient using the XLTRC
(rotordynamic FEA code). For the model employed, Wachel's model predicts a slightly
lower onset speed of instability. The results also show that leakage that flows radially
inwards on the back shroud has a greater destabilizing influence than leakage flow that is
radially outwards. Seal rub conditions are simulated by increasing the clearance and
simultaneously decreasing the tooth height, which increased the leakage and the swirl tothe eye seal inlet; and therefore reduced stability. Calculated results are provided for
different seal clearances and tooth height, for seal and shroud forces and moments.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/2470 |
| Date | 29 August 2005 |
| Creators | Gupta, Manoj Kumar |
| Contributors | Childs, Dara W. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 1171847 bytes, electronic, application/pdf, born digital |
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