This thesis presents the results for measured and predicted rotordynamic
coefficients and leakage for a convergent-tapered honeycomb seal (CTHC). The test
seals had a diameter of 114.968 mm (4.5263 in) at the entrance, and a diameter of
114.709 mm (4.5161 in) at the exit. The honeycomb cell depth was 3.175 mm (0.125
in), and the cell width was 0.79 mm (0.0311 in). Measurements are reported with air as
the test fluid at three different speeds: 10,200, 15,200, and 20,200 rpm; with a supply
pressure of 69 bar (1,000 psi), with exit-to-inlet pressure ratios from 20% to 50%, and
using two rotors that are 114.3 mm (4.500 in) and 114.5 mm (4.508 in) respectively; this
enables the same seals to be tested under two different conditions.
The q factor, which is just a simple way to quantify taper is defined as the taperangle
seal parameter and is calculated using the inlet and exit radial clearance. Two
taper-angles parameters were calculated; q = 0.24 for the 114.3 mm (4.500 in) rotor,
and q = 0.386 for the 114.5 mm (4.508 in) rotor. The q = 0.24 condition was compared
to a constant clearance honeycomb seal (CCHC q = 0) because both sets of data were
taken with the same rotor diameter.
The direct stiffness, effective stiffness, and direct damping coefficients were
larger for q = 0.24. The CTHC q = 0.24 eliminates the direct negative static stiffness
obtained with CCHC ( q = 0). The cross-coupled stiffness and damping also were larger
for q = 0.24, especially at low frequencies.
Effective damping is one of the best indicators in determining the stability of a
roughened stator annular gas seal. The frequency at which it changes sign is called the cross-over frequency. In applications, this frequency needs to be lower than the rotorsystem’s
first natural frequency. Otherwise, the seal will be highly destabilizing instead
of highly stabilizing. The magnitude of effective damping and the cross-over frequency
also increases with q for all frequencies.
Constant clearance honeycomb seals have less leakage than convergenttapered
honeycomb seals. CTHC ( q = 0.24), has approximately 20 percent more
leakage than CCHC ( q = 0).
The experimental results for rotordynamic characteristics and leakage were
compared to theoretical predictions by the two-control-volume developed by Kleynhans
and Childs. All rotordynamic coefficients were reasonably predicted for all cases. The
model does a better job predicting the cross-coupled stiffness and damping coefficients
rather than the direct stiffness and damping coefficients. Also, the two-control-volume
model predicts the dynamic characteristics of CCHC ( q = 0) better, and does not predict
well the effective stiffness and damping for CTHC q = 0.386.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1156 |
| Date | 15 May 2009 |
| Creators | Van Der Velde Alvarez, Daniel Eduardo |
| Contributors | Childs, Dara W. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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