Engineering Analyses for Gas Pocket
Damper Seals and Combined Labyrinth-Brush Seals
MAJOR APPLICATION:
Pocket damper seals are used as balance drum, interstage and impeller eye seals to restrict leakage flow
rate from a high-pressure region to a low-pressure region in compressors and
turbines. [1]
Combined labyrinth-brush seals are common in aircraft engines
and steam turbines to increase plant efficiency and reduce leakage in a similar
size labyrinth seal.
SPONSOR: Turbomachinery Research
Consortium (TRC)
OBJECTIVE: To develop computational models
for prediction of leakage, drag power loss and force coefficients of fully
portioned PDS and combined labyrinth-brush seals. In the first year, leakage
models will be developed and verified, and in the second year the computational
models will advance to predict rotordynamic force coefficients.
SIGNIFICANCE:
Pocket damper seals (PDS), adding baffles in (alternating) circumferential cavities of
labyrinth seals have demonstrated enormous benefits in seal stability by
providing physically large damping coefficients [2].
A Fully-partitioned pocket
damper seal (FPDS) has axial baffles covering the whole seal extent and the
pockets are separated by thick small clearance regions (not sharp teeth) which
can amount to 20% of the whole sealing area.
These
seals, as shown in Fig. 1, when properly designed, can act as damper bearings
by offering also large stiffness coefficients. In experimental comparisons [3]
with a labyrinth seal and a honeycomb seal, the FPDS showed the largest
destabilizing cross-coupled stiffnesses, strong functions of inlet pre-swirl
and rotor speed.
Fig. 1. Schematic view of
a conventional pocket damper seal (PDS) and a fully-partitioned pocket damper
seal (FPDS).
Ertas, B.H., Vance, J.M., 2007, “Rotordynamic
Force Coefficients for a New Damper Seal Design,” ASME J. Trib. 129, pp.
365-374
Fig. 2 shows a combined
labyrinth-brush seal. Combined labyrinth-brush seal may increase plant
efficiency and reduce the leakage in a similar size labyrinth seal. In
addition, some steam turbines presently incorporate a hybrid seal composed of a
BS installed mid-way of a multiple-teeth labyrinth seal. The hybrid BS-LS [4]
affords significant sealing improvements over conventional labyrinth seals.
“Additionally, when retrofit into labyrinth seals with radial movement, the
individual labyrinth seal segments are free to move radially
independently of one another during transients.” [4]
Fig. 2. Schematic view of a
combined labyrinth-brush seal.
Patent
Number: WO 2004/023008, Inventors: R.P. Menendez and H. King, Publication date:
18 March 2004
REFERENCES
[1] Li, J., 1999, “A
Bulk-flow Model of Multiple-Blade, Multiple-Pocket Gas Damper Seals,” Ph. D
Dissertation,
[2] Childs, D. W.,
Vance, J. M., 1997, “Annular Gas Seals and Rotordynamics of Compressors and
Turbines”, Proc.26th Turbomachinery Symposium,
[3] Ertas, B.H., Delgado, A., and Vannini,
G., 2011, “Rotordynamic Force Coefficients for Three Types of Annular Gas Seals
with Inlet Preswirl and High Pressure Differential
Ratio,” ASME GT2011-45556.
[4] Skinner, D.R.,
et al., 2001, “Combined Brush Seal and Labyrinth Seal Segment for Rotary
Machines,” US Patent 6,257,586 B1 (see also http://www.turbocare.com/retractable_brush_seals.html